'86 Cranks, But Won't Start - VATS Problem?
 

It's been about a year and a half since I last posted about an ongoing "cranks but won't start issue" with my '86 coupe. Some of you may remember my extensive troubleshooting posts starting back about this time 2 years ago.

Yes, the car has not run in 2 years. I have put literally hundreds of hours into fixing my coupe's no start / no run issue. This problem has baffled myself and a number of savvy mechanics. There were actually numerous problems with the car which have been fixed, only to reveal yet another problem. It's been like peeling and onion.

Here are some of the failed components that have been fixed / replaced so far during this process:
- Fuel pump
- Fuel pump relay
- Fuel pressure regulator
- Clogged EGR
- Vapor cannister check valve
- Ignition module
- Idle Air Control

Other work that has been done in the interim:
- Reconditioned fuel sending unit along with replacing fuel pump.
- Cleaned, ported and polished manifold, tube runners and TB.
- Ultrasonically cleaned FIs
- Cleaned fuel rails, reconditioned & re-ringed, installed new FPR.
- Installed new knock sensor.
- New cap, rotor, wires, coil
- Rebuilt distributor with new components.

Basically, there isn't much that hasn't been done or many systems that I haven't been through several times already. I recently finished the detail painting and put the fuel / air system back together again - praying that it would finally start. Exhaust system is disconnected to eliminate the possibility of clogged cats / exhaust. Still no dice.

Back to the drawing board. So, what do I know for sure? I've got good spark, I've got good fuel rail pressure, I've got good compression on all cylinders, timing is right on, exhaust is unblocked, the car doesn't throw any codes - so what the hell could be wrong?

I was going through some old C4 tech posts on the forum and came across a thread that GIJoe had posted on and talked about the VATS. Given the fact that everything is new and all systems appear to be in order, what else could possibly keep my car from starting up? The freaking VATS, of course! There's not much else left.

So, I went out and did some searching around and came across GIJoes very helpful site at www.vatssucks.com. After some studying and reflection, I am convinced now that I have a problem in the Cranking Fuel Enable part of the VATS. If that part of the system is not working properly, then the car would crank but not start because no enable signal (30Hz square wave) would be sent to the ECM for the ECM to pulse the injectors. Go figure... :crazy:

I spent my day today digging into the DIC and "breadbox'', yanking the 2 VATS modules, cleaning the pins and the PCBs and soldering test point wires off the 7 pins on the gray module and 6 pins on the blue modules. The outputs of each module are hard wired into a Radio Shack 8 phone jack module. The idea is that I now have 2 diagnostic patch panels that I can jack into anytime for troubleshooting purposes - without having to mess with yanking the dash panels. I'm going to mount both phonoplug jack panels to the front of the otherwise useless breadbox bezel and then jack into them tomorrow for some troubleshooting.

I also found and ordered a very cool dual freq (30 / 50 Hz) VATS Bypass module from Baxter Electronics' store on Ebay. Base price is $25for a single freq VATS Bypass module. I opted for the dual freq upgrade ($10) and the quick disconnect option ($10), also. Can't beat that for less than $50 delivered!

Obviously, I'm betting that the Cranking Fuel Enable circuit is bad. I wasn't able to check it conclusively today, but I will be tomorrow. Any bets that this is, in fact, the final answer to my crank-but-no-start problem? I really hope it is.

Thanks, GIJoe, for your excellent website. I'm starting to believe that VATS Sucks, too. :thumbs: I'll let you all know tomorrow.

I'd first look at the FSM and figure out how to completely disable the VATS and try again.

You said you have fuel and spark. So which savvy mechanic decided to replace these parts that can have absolutely nothing to do with the problem?

- Fuel pump
- Fuel pump relay
- Fuel pressure regulator
- Vapor cannister check valve
- Ignition module
- Idle Air Control

That was my thinking, too, before I checked out the www.vatssucks.com site. If you refer to the schematic diagram, if there is an issue in the circuit from the output of the VATS decoder module (pin P, purple wire) to the 30Hz generator module (not referenced) to the ECM, then you would have crank, but no start. Interesting, huh?! Finally, there is a ray of hope for my car.

aaaa, if the car is cranking, you are getting a VATS enable signal! Really, seriously!

As I mentioned, there were multiple problems with the car to begin with. Each one of the above mentioned parts were, in fact, bad and needed to be replaced. Just like peeling an onion.

He was responding to my deleted post. I said the same thing as you, then I read the rest of his post and changed my mind.:lol:

VATS doesn't suck, it prevents opportunist thieves from stealing your Corvette. 99% of thefts are done by bashing the column and jumping the ignition. You bypass VATS and you might find out the hard way how much your insurance company thinks your vette is worth. I vote for keeping your car in good repair, not bypassing circuits. Its like gluing a flashlight onto your hood when one headlight stops working. Anyway, I doubt VATS is your problem, but you can prove its the fuel cutoff by connecting a noid light (available from parts stores), or use a low power 12v lamp like a side marker lamp across the socket of an injector while you crank the engine. The lamp should pulse during cranking. If it doesn't, I would next check both injector fuses and then check for reference pulses during cranking on the purple/wh wire out of the distributor with an oscilloscope.

Yes, I would agree that the starter enable part of the system is working fine, because it's cranking. My contention, though, is that the section of the VATS system that sends the cranking fuel enable pulse (30Hz square wave) to the ECM for the ECM to pulse the injectors to squirt fuel and allow the engine to start is not working.

Sounds like time for either an oscilloscope, or a depowering of the VATS module.

:iagree: I might buy a bad computer not supplying the injector drivers, I could be wrong, it's been pointed out before, but the vats signal goes to the ecm which in turn enables the fuel pump and the starter. Not the injectors.

Thanks for the info. Certainly, the VATS serves a useful purpose. It doesn't allow a thief to steal it easily. What might suck about VATS, though, is when the system might not let the owner drive it either. ;)

Sort of reminds me of Robocop 2.

Here's some a quote from the site: "When VATS has not detected anything wrong and is working properly, it will send a 5v 30Hz signal to the ECM to tell it to enable the fuel injection system during cranking."

When the starter motor doesn't work the owner can't drive their C4, so what do you do, put a hand crank on the vibration damper? My 87 stranded me at church about 6 years ago due to VATS and I bypassed it so I could get it to my mechanic who replaced the worn out lock cylinder and it has started every day since then (its my DD). If the lock cylinder contacts wear out again, once more I will fix it!! If my headlight quits working, I find out why and I fix it, I don't epoxy a flashlight onto the hood. If you take care of your car, your car will take care of you! Keep your car in good repair. The person I bought my 87 from ordered a 90 vette and one day they came out of work and found their driver window and steering column busted out but the vette hadn't budged an inch due to.............VATS!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!

Come on man, lets focus on the problem at hand...

I already did!

I'm not arguing the usefulness of and need for the VATS system. I am merely exploring the possibility that part of the VATS is not funtioning properly. I've posted the information about this very perplexing problem on this forum to get constructive feedback and good advise from the members of the forum, who know alot more than I do, regarding the problem with my car.

I believe that is in the 90 up computers, they enable the injectors rather than the fuel pump. At any rate, wouldn't it be easier to just get a new module?

Well, I was wrong, again, damn this memory! From the 86 FSM ....."If the proper signal does not reach the ecm on CKT963, the ECM will not pulse the injectors "ON" and thus not allow the vehicle to be started. Code 46 will set,if the proper signal is not being recieved at ECM terminal "B6" (CKT963) when the ignition is turned on."

None of the Chevy dealers or salvage yards in my area have a VATS module in stock. A quick search on the internet didn't reveal any sources that had them in stock either. What I did find was this particular aftermarket module that will help to troubleshoot the problem, if nothing else.

The blue VATS decoder module that senses the resistor in the ignition key, grounds the starter enable relay to crank the engine and also supplies circuit ground for the cranking fuel enable circuit is probably not the problem, unless it is not initiating ground on the purple wire. The second module, the gray one, generates the 30HZ square wave signal to the ECM - after the blue VATS Decoder module initiates ground on the purple wire.

If it does turn out to be part of the VATS system, I will certainly replace the culprit with a new part - as I have done many times over already with this car. I don't like to rig flashlights up on my car, either... :)

Good stuff, zr1fred - thanks!

I guess if you are getting code 46, you have your answer. I have several of the modules, but my interagator is broken and I don't think I recorded the vats code for them. I could send you one, I don't believe I've ever used one (thought I needed one once, but no, it was a bad ignition switch (dropping the voltage on the ignition fed lines to about 9.5 volts occassionaly when the key was turned on). good luck, let me know if you need one.

Thanks, again. Unfortunately, the ECM throws no codes for this problem. 12, 12, 12, 12 - forever. Consequently, this problem has been a tough nut to crack. I may be talking to you about those modules, if the VATS turns out to be the culprit.

I forgot to mention one other symptom that points to VATS, even though I'm not getting any numerical error codes. Turning to the key on position, the Security light goes out along with the other DIC indicators after power on. While cranking, though, the Security light continues to flash on and flash off. From what I understand, this would indicate an issue with VATS, correct?

No...when the alarm is armed the light FREEZES or STAYS STILL on the dash info center.

Make sure your key holes in both doors have been turned back and forth as well...they disarm the system as well.

Your timing might be wayy off..have you even checked it?

When the security light flashes when you open the door and sit in the car,its not armed.When the light freezes or stays lit up,it is.

Thanks. Yes, I've checked, rechecked and re-rechecked the timing. The timing was an issue earlier on in the process - after I rebuilt the distributor (180 degrees out).

I'll try the door lock cycling suggestion. Is it normal for the Security light to flash on and off while cranking, though?

Is the ECM receiving a reference signal from dizzy during cranking ??

Yes, I checked reference signal from dizzy to ECM last year and, as I recall, it was OK. Of course, that was last year, so it wouldn't hurt to check it again. I did try cycling the lock cylinders on the doors, but to no avail.

I got a chance to probe my DIPs (Diagnostic Information Panels) that I rigged up yesterday. First of all, let me make a correction on previous references to the 2 VATS modules - I made reference to them 180 out. The gray (VATS Decoder) module is the one behind the breadbox, which recognizes the key's resistor value, initiates ground to the starter enable relay and also initiates ground for the cranking fuel enable part of the VATS. The cranking fuel enable output (circuit grounded) via pin P to the purple wire goes to the blue module, which produces the 30HZ square wave reference signal. The 30Hz ref signal gets output to the ECM to intitiate the pulsing of fuel through the FIs. That's my current understanding of the system.

Before I post my DIP readings, though, I'd like to draw reference to the schematic of the older C4 VATS system as posted on GIJoe's www.vatssucks.com site. This is the schematic that I am using as a reference for my troubleshooting.

Here's the pinout readings I took:
- T to U - Check key resistance - appr. 6 Kohms - well within tolerance of that particular key code. Jiggling the key in the lock causes the resistance to jump up over 7 Kohms. Possible lock cylinder / key replacement issue.
- L (ground) to V - Check starter enable output - .7 - .8 VDC, which is satisfactory since the starter cranks the engine.
- L to P - Check voltage output to the cranking fuel enable circuit (blue module) - cranking voltage of 2.4 - 2.9 VDC; the voltage jumped up and down in the range, as might be indicative of a square wave pulse. Will validate later with O-scope.
- L to S - check VATS line-in / ignition voltage - key on 12.2 VDC, dropping down to 10.1 VDC while cranking. Voltage drop seems excessive to me. Could be related to lock cylinder.
- L to U - check voltage between ignition key lock cylinder and VATS. Cranking voltage of 5.8 VDC. That doesn't seem right at all. Points again at lock cylinder.

My conclusion? The data above would suggest that I replace the ignition key lock cylinder assembly, which I think I'll do. Anyone have a few good DIY replace lock cylinder links that they would like to share?

Any other thoughts, suggestions and advise would be appreciated.

So, I went out to Advanced Auto and picked up a new ignition lock cylinder for about $65. The pair of keys did not have the resistor chip embedded in them, though. All the Chevy dealers parts dept. were closed, so that was the best that could be had today.

No sense fiddling with the new no-resistor ignition key lock cylinder, because I still had to input a 6.04 Kohm resistance to the VATS circuit to simulate my particular key. So, I went to Radio Shack and bought a 10K PCB trim pot, a small prototype breadboard and a SPST switch and dialed-in 6.04K Kohm for the pin-outs. I soldered two wires off the PCBs pin-outs and plugged them into the yellow and brown wires which go to pins T & U of the gray VATS Decoder module. Verified 6.04K at pins T & U, effectively simulating my key's resistance code. Cranked the engine, but still no start or run. I can now effectively eliminate the key lock cylinder and/or embedded resistor as potential sources of the problem, given the fact that I completely bypassed both.

Here are a few new test observations: 1) Hooked noid light up to #1 FI connector, cranked and noted noid light pulsing on and off as it should. 2) Cycled key lock cylinders to lock and unlock several times, then locked both doors. The Security light on the DIC does not illuminate at all on the DIC with the doors locked. Unlock and open the door(s), the Security light flashes. Key on, the Security light goes out after lamp test. While cranking, the Security light flashes.

I'm going to probe the Pin P (purple wire) output to the cranking fuel enable module with an O-scope tomorrow and see what's up there. I don't have any schematics or pin-out info for the blue VATS module - the 30Hz square wave generator. If anyone has a link to the schematic for the blue module, please post links or any info you might have. Otherwise, I'll trace out the wires to see where they go and try to figure out what should be riding on them. Two of them I know already - purple wire input from VATS Decoder and ground. The other 5 pin-outs I'm not sure about yet.

If your starter cranks the engine and the injectors pulse during cranking, then you do not have a problem with VATS !!!!!!!! If VATS doesn't measure the correct pellet resistance, then it will not close the start enable relay (no cranking) and it won't supply the 30 Hz signal to the ECM and you won't have any pulses on the injectors during cranking. You have some other problem. During cranking, check for spark and spark at the right time with your timing light. Put a fuel pressure gauge on the shrader valve on the end of the fuel rail and see how much pressure you have and observe if the pressure holds up with the ign off. Rapid pressure drop indicates possible leaky injector/s and too rich a mixture to start. Unplug the MAF and try to start the car. Look at the EGR valve and determine if it is fully closed. Measure intake vacuum during cranking to determine if you have a vacuum leak. Measure the voltage on the throttle position sensor, it should be 0.54 volts +/- .075 volts throttle closed ign on.

Thanks for the detailed info, jfb. It certainly wouldn't hurt for me to go back and recheck all the things you've mentioned here.

After evaluation of the VATS test readings and the additional test indications (i.e. - noid light blinking while cranking, resistor emulation, etc.), it would seem as if the VATS may not be the problem. There are a few indicators that are still not quite right, though: 1) Security light does not come on when doors are locked. 2) Security light blinks when doors are opened, but goes out when the ignition is in the key-on position. Therefore, the VATS will not allow me to do any sort of "relearning" procedure. 3) The Security light blinks while cranking, which indicates an issue with the VATS.

Yes, the VATS is recognizing my key and is energizing the start enable relay and the starter system. I haven't hooked the O-scope up to pin P of the gray TDM yet, but I did measure a pulsing voltage of 2.4 - 2.9 VDC on my DMM. I'm going to scope it tomorrow to verify the presence / absence of the 30 (or 50) Hz square wave signal on that circuit and the signal input to the ECM.

The only other possibility that I read somewhere during my research is that there could be an issue in Comm 2 (?) circuit signal with the ECM that defines the Security light indications. I didn't find any detailed info about this schematically - just an honorable mention. If the comm circuit which drives the Security light signal indications is faulty, then this might point to the reason why I am getting the discrepant Security indications that I listed above.

I'll know better tomorrow. I'm into it deep now and I won't be satisfied until I hunt this problem down and kill it - once and for all. :smash: If nothing else - and most importantly - this technical exploration may help others diagnose and fix similar problems as to what I am experiencing. Certainly, it's been one helluva learning experience for me, as I have gone through and educated myself on almost every system in my Vette. That's always a good thing. :flag:

Had an "ooops" - please refer to my post below.

Im not sure if im following everything...so let me try and help what I can think of.

Ok,when you open the doors to the car,the security light will Flash saying its NOT ARMED.SO when you turn the key,its gonna appear to flash because your not getting the car to run.

Try this..sit in your car with the door open...security light is blinking...push the power lock to lock the doors while watching the security light.DOES the light now freeze?
If so,the system is arming itself.Get out of the car and shut the door.

Now use your key to unlock the door then open it.It should open with no horn going off.If it does,turn the key back and forth and disarm the alarm.

If you use the power lock to arm the system and it keeps flashing on the dash,then its not arming the alarm.

Now,back to basics,when you crank the engine over,have you had someone to check for spark?

Did you unplug a spark plug wire and ground a plug tester somewhere and check for spark?If not,DO THAT FIRST and check every plug wire for spark.

If they all spark,then do the Fuel pressure test and be sure youre getting gas into the engine.

Like JFB said,the car will NOT turn over if the vats is armed and not letting you.It wont do anything,not even crank.

I did not go back and read everything but check the basics first.When an engine cranks,its good...then you need to be sure spark and fuel is happening.

vats suck
 

It's an overcomplicated system that's caused so many problems and also a lot of controversy on these forums.After years of intermittent grief(mine I traced to the starter enable relay) i ripped the whole system out.I did however reroute a couple of the wires to the cigarette lighter.If the first thing a prospective thief does is light a ciggie after he's jumped the system it might fire up but I doubt it.

Since I haven't found a lot of detailed information on the VATS set-up in my '86 coupe, I'm going to try to document it myself while I'm in the middle of it. Perhaps, the info will prove to be of help to myself and others, as well.

Let start with the gray module behind the "breadbox." My Haynes manual referes to it as the Theft Deterrent Decoder Module (TDDM). I traced out the wiring diagram in the manual have referenced the pin-outs below with some of my readings.

The TDDM in my car has a single edge connector with 6 pin-outs, which are as follows from top to bottom:
- Pin L (black) - Ground
- Pin P (purple) - 30 Hz FI enable signal to ECM. Measured swings of 2.4 to 2.9 VDC with my DMM. Measured .5V 30 Hz square wave with O-scope.
- Pin S (pink/black) - +12 VDC. Diagram shows it coming from 10A Gauges fuse.
- Pin T (yellow) - from resistor pellet / ignition connector
- Pin U (brown) - from resistor pellet / ignition connector
- Pin V (green) - to starter enable relay

I listed my readings for the TDDM in a previous post.

The second module of the VATS is blue, has a 2 row connector with a total of 7 pins, 4 in the top row and 3 on the bottom row. The blue module is referenced as the Theft Deterrent Control Module (TDCM).

The wiring diagram in my manual referencing this module doesn't not represent the actually set-up of my TDCM. After some wire diagram tracing, here's a few connections that I gather from the manual (pin-out references are by row and pins from top to bottom):
-Top Row, Pin 1 - Pin N (pink/ black) +12 VDC from VATS 10A fuse.
- Top Row, Pin 2 - Pin B (yellow) - supposedly coming from LH Door harness, Pin H (I believe it's actually going to an indicator light circuit in the DIC)
- Top Row, Pin 3 - Pin A (black) - Ground
- Top Row, Pin 4 - Pin C (black) - going to RR Body wiring, pin R(?)
- Bottom Row, Pin 1 (green) - going to Center Cluster, pin 5(?). Measured 10.3 and 9.1 VDC from On to Crank.
- Bottom Row, Pin 2 (pink/white) - Pin / wire not referenced - measured 12.4 and 10.2 VDC from On to Crank.
- Bottom Row, Pin 3 (brown) - Pin / wire not referenced. Measured -11.5 mv to 41.5 mv from On to Crank. Readings here are suspect - will physically trace wire.

Guys, thanks for the posts. I'm going to go back through all the basics tomorrow, while I continue to wire trace and validate the mysterious TDCM module. Got to hit the hay now.

Sounds like your using the Haynes manual. Try this instead. :D
http://members.shaw.ca/dankai/Vats%20Electrical.pdf
Should help clear some of the fog. :lol:
:cheers:

Great stuff, AGENT 86 - thank you!

AGENT 86's excellent reference link allowed me to get a better understanding of the 2 module system for the VATS / TDM. Thanks again.

While the pin-outs on the diagram do not exactly represent all the pins and associated wire colors on my blue TDCM, it was close enough for me to understand and track down almost all the wires. As I understand it now, the blue Theft Deterrent Control Module is basically just a built-in car alarm system that serves as the first line of defense against theft.

Apparently, the TDCM cannot cause a no start / no run condition with the vehicle. So, I can nix the TDCM as cause of the current crank but no start problem.

Back to the gray Theft Deterrent Decoder Module, which can and will cause this condition. The documentation on the website tells me that I should be reading battery voltage (>12 VDC) on the dark green wire associated to pin V. Since I only read about .8 to .9 VDC on the last probing, I decided to pull the Starter Enable Relay and see what was up.

To my surprise, the contacts on both the connector and the relay were highly gunked with a thick black grease. Very old, very oxidized dielectric grease I must assume. This could very well be the source of the voltage drop / bad reading on pin V - and perhaps the source of the problem.

Obviously, the starter enable relay was energizing and allow the starter to crank the engine, but may have been dropping excessive voltage on the system. Perhaps enough of a voltage drop across the system to not allow the car to start.

I'm going to the store to pick up a new starter enable relay, clean up the connector and see if this baby starts. Cross fingers.

hoping to hear that solved the problem. waiting here in anticipating of hearing. can't imagine all that time without my vette, and all the troubleshooting you've been through. good luck

Had to order the starter enable relay today - will be in tomorrow. Only $14 w/ tax. I can't wait myself. It would be wonderful to hear the engine roar again. It's been a long time coming.

The start enable relay switches 12v from your ,"crank", contact in the ign sw to the clutch safety switch. From the clutch sw, 12v goes to the starter solenoid on the starter. If the relay contacts are gummed up and won't make a low resistance connection, then your starter solenoid will not close and the starter motor won't crank. Best re -read my last post.

Waiting to see what you find out. I am having the same exactly problem with my 89. Cranks but will not start. after all my checks the only thing I'm not getting is fuel. (double checked with some starting fluid and it'll start when sprayed into intake).

It's alive! For the first time in 2 years, my '86 coupe cranked, coughed, spit and ran for about 10 - 15 secs on 4 occassions. Very loud (exhaust pipes disconnected), lots of smoke - very dramatic. Thank God! :thumbs:

I wish someone had a video of my joyous war cry when it first started. It was almost as loud as the roar of my engine - and ripe with a few choice expletive deletives. :eek:

Unfortunately, I couldn't dial it in tonite, though, since I was already running late for my son's ball game at 8PM. I can savor the joy until tomorrow, I guess.

So, here's the final pieces of the puzzle:
- Replaced the old, gunked up starter enable relay with a new one after cleaning up with connector. Engine cranked, but didn't start - as usual. One thing that did change, though. Key on / run voltage on the system jumped from 12.2 to 13.3 VDC, and cranking voltage on the system jumped from 10.1 to 11.4 VDC. Apparently, the old dielectric grease had become resistive over the years, so there was, in fact, an issue in that part of the circuit.
- So, I went back to basics again and made the same basics checks I made a few days ago: ESC connector disconnected. Fuel pressure in the rail about 45 psi - good. Noid light on #1 injector blinked while cranking - good. Spark on #1 plug - not there. WTF - the spark was there 3 or 4 days ago! The gremlin in my car has once again moved to try and confuse me and keep me from fixing the car.
- Troubleshot the distributor / HEI reference signals from the ECM coming in on the 4 pin connector on the distributor. 0 volts on all of them. Ran down to the junk yard and pulled a 1271665 ECM out of an '87 Camaro. It was a score for only $45. Even better, when I got the ECM home and popped the chip cover on the ECM to check the PROM and Memcal, my eyes noted in bold capitalized letters, "SUPERCHIPS". Turns out to be quite an excellent score for $45!
- Cleaned the connectors and plugged in the new ECM. Cranked the engine and still no start. Unreal! The problem has to be in the distributor, but everything in it was brand new 2 years ago before the no start problem. Nevertheless, I had spark 3 or 4 days ago - and now nothing.
- Pulled the distributor cap and found the latest problem - battery lead (red wire input) to the coil melted in half. That could be a problem! Went down the parts store and picked up a new coil and cap. Brought it home and installed it before my son's 8PM game. Cranked it and the car sputtered to life for the first time in 2 years! I am proud to say that I hunted that gremlin down, trapped it and killed it. History!

The sense of relief and accomplishment I am feeling right now is literally beyond words. Thanks to each and every one of you in the forum who contributed to this very informative thread.

Tomorrow I'm going to work on dialing it in and getting her to stay running. Got to blow some of that old gummy gas out the system. Then it will be time to go out and hunt some ricers, like the old days... :flag:

Im very glad to hear after all that searching you found it.The good news is,you learned about your car,and whats new,old and been checked and it makes future diagnosing problems easier.

Btw,be wary of the ADS Superchips. They work allright but sometimes dont.I had one and threw it away.I bought a new GM prom,IT was UPGRADED by the factory over the years and it ran way better with it.

My ADS Superchip,when I put the car into D,it would stall sometimes...in Reverse,the idle would bounce up and down! Nothing fixed it,so it went a new GM prom and all the idle problems went away and never came back.

Just wanted to share that...anyways good luck and hope the car brings ya alot of fun now!

:cheers:

I just realized,and this is for others with similar problems,did you ever check for spark?I posted the other day about checking for it.

You found a bad wire in the cap...car cranks but wont start.Did it ever have some spark or none?Its important to bring up because while it can be a few items at once,without gas or spark,the car wont start when it turns over and cranks.

No spark or fuels helps to track down a ignition or fuel problem real fast,especially when the car cranks but doesnt start.
The Vats is not a likely problem but is soemtimes the case...so for those tracking down problems,do all the basics until your blue in the face.

Still had to hear ya got the car running.DO check your wires again inside the cap and etc.Make sure it doesnt melt or break again,IF there was a cause the first time.Sometimes when a wire melts or breaks,it does happen again.Be sure theres no shorts or chafed wires anywhere near the ignition system.

:cheers:

Thanks for the additional information. Yes, I did check for and had spark 3 or 4 days ago (maybe 5). Of course, given the numerous problems I have had since I started this troubleshooting journey 2 years ago, there's not much that surprises me anymore about the C4 Vettes. The evil gremlin in my car jumped one last time to avoid me and to keep my car from starting.

As a matter of fact, I think one of my last posts on this thread will include all the problems I've encountered and fixed along this journey. When she went down, she went down hard. Beware, though, it's is scary story and it's enough to curl your hair! :eek:

Grats on fixing your problem.

I've checked the spark on mine also, its generally one of my first checks. Thing I need to do is get the ol test light out and check to see if the injectors are getting a signal. I don't think they are, but just in case. I do have a spare computer to swap in if I can figure out where/how to get it out easily. I've never taken one out of a vette before.

Rico,
The ecm is located behind the passenger side dash area.To get it out,you have to remove the plastic panels under the dash and then remove the 2 10MM screws that hold the bottom of the ecm inside there.

Once you know,learn,where it is,becomes very easy to do and drop down,swap out exchange.What I did when I dropped my ecm I left it on the floor and swapped ecms and did back to back testing,checking voltages and stuff.The ecm wire harness I believe have 3 plugs,white,blue,etc,youll see when you disconnect it.The harness will pull down enough for you to swap ecms for testing without putting it all back.

No need to push the new ecm back inside there,bolt it away,and have no idea if you are fixing the problem.Just more work.Let it hang down there and test away before securing it back inside the dash.

ECM Problem???
 

Are you sure that you don't have an intermittent ECM problem ?:willy:

No, just swapped in another ECM and it's still running rough, BUT it does start and run for 5 - 10 secs. Still not throwing any codes either.

The starter seems to be loading up while cranking and 8 - 10 cranks kicks the charge right out of the battery. At least the damn thing is starting, so I thank God for small miracles. I'm going to drop the starter motor check it and clean it up, replace the starter solenoid, clean up all the connections - including ground.

It was pretty gummy down there and the connections weren't as tight as they should be. We'll see what onion reveals as I continue to peel away the layers.

Might want to load test your battery. :)

Thanks for the help.. I'ma give it a try soon!

Catching up on the last few days. Just to recap, engine starts and runs labored for brief intervals (5 -10 secs.) and then sputters and dies. On first crank, engine turns fast - almost like there is no load on the engine - and doesn't start. Second crank is the same, but seems like there is a little more load. Again, engine doesn't start. By the third crank, the load is almost normal and it seems like the engine is going to catch, but it doesn't. Fourth crank, the engine starts, sputters and dies. Then the cycle starts all over again.

Suspected that there may be some issues with the starter motor and/or solenoid, so I decided to tear the starter motor and solenoid apart and clean them both up. Solenoid cap had broken boss that captures the tang that prevents the battery connector from turning while tightening retaining nut. Also noted heat damage / discoloration on plastic solenoid cap, so I decided to replace the starter solenoid altogether.

Cleaned all the connectors and bolted it back up and starter seemed to turn much more normally. Car now starts on every crank, but still dies after about 5 - 10 secs. Still peeling the onion...

Right now, it just has to be a timing issue or perhaps the ignition module was damaged partially when the coil melted down. Any other thoughts would be appreciated.

'90 C4 runs then quits & no start
 

Anyone had this problem..... car starts, runs 10 minutes then quits. I installed new dist cap, rotor, HEI module, fuel filter. I have spark (during the no start condition) and the fuel pump is running (I can hear it). Is this related to the VATS problem I have been reading about ? This seems a bit different in that it will start after sitting over night.

If the engine starts initially, then VATS isn't a part of your problem. You need to monitor the fuel pressure on the end of the fuel rail and see if it drops out causing the engine to quit after 10 minutes. You could also connect up your timing light and see if it stops after 10 minutes. If ignition is ok, you will see the timing light flash while the engine is coasting to a stop after it quits. Also check for stored error codes.

Haven't posted in a few days as I've been chasing the gremlin. Down the rabbit hole we go...

The gremlin turns out to be a ground. Ground on the pink Circuit 3 wire which starts on the ignition switch and is supposed to supply +12VDC to a variety of important systems in the "On and Crank" positions. Circuit 3 supplies power to the following systems: - VATS - IGN 1 - IGN 2 - GAUGES - CLSTR - ECM - CRUISE - HORN. There's one or two more that slip my memory right now.

Obviously, a ground on Circuit 3 would affect each of the systems listed above. To any loyal followers of this thread so far, a ground on 3 begins to explain a number of the problems I have noted on this thread and have been troubleshooting.

I dug out the ignition switch the other day - what pain in the @ss!! The ignition switch definitely had some fused contacts and was bad. After having just replaced a new coil that blew the BAT+ wire - not to mention the numerous other problems I've seen, I had to ask myself that maybe the ignition switch wasn't the root cause of the problem. Bad ground, perhaps.

Sure enough, I probed the pink wire and it was grounded. So, I've been pulling fuses, probing wires and popping connectors for the past 2 days solid. You gotta love troubleshooting grounds like I do. ;)

Anyway, it turn outs that the ground on Circuit 3 doesn't actually live on on Circuit 3 at all - it does ground circuit 3 very effectively, but the ground actually lives on Circuit 39. Circuit 39 supplies +12VDC "On and Crank" to the other half of the vehicle. Nice!

I found this when I pulled the GAUGES fuse and the ground on the pink Circuit 3 wires disappeared. Circuit 39 sits on the other side of the GAUGES fuse terminal. How about that for a kick in the head!

Now, I know where the ground lives and I'm going to hunt the b@stage down tomorrow and kill it. Once and for all. It's been one elusive SOB, I've got to tell you. Soon to be dead meat! :smash:

I FOUND THE GROUND! You're not going to believe this one. This is one for the record books.

I will reveal the root cause problem of this very elusive ground in a follow-up post. For now, I'll identify the possible culprits that relate to Circuit 39 and let you all take a few guesses:
- GAUGES Fuse terminal circuit
- VATS Fuse terminal circuit
- Module ASM Low Engine Coolant Indicator circuit
- Key, HD Lamp & Seatbelt Warning Chime circuit
- TCC Brake Switch circuit
- Theft Deterrent Decoder Module to Fuse block circuit
- Dome Lamp Delay Timer circuit
- Vanity Mirror circuit
- Map Light Mirror circuit
- Programmer circuit
- Rear Window Defogger circuit
- Export Harness circuit
- Door Ajar lamp indicator circuit
- Illum lamp indicator circuit

Any guesses from the forum?

No wonder you are having so much trouble you don't have a ground problem, you have a 12v power problem!(and worse, you don't know the difference) Wire 39 comes from the gages fuse and goes to S208, a large splice that supplies power to all the places in your long list.

Technically speaking, the problem is +12VDC being shunted to ground. In layman's terms, there was a short to ground on the power circuit. Not a problem with chassis ground, but a "ground problem," nevertheless. And, yes, I do know the difference. Thanks for pointing out your superior knowledge of all things electrical / electronic, though. :thumbs:

For everyone else's information, though, the source of the "ground" on the #39 power circuit came from the map light circuit on my rear view mirror. The ribbon cable got pinched between the mount and frame causing an internal short in the cable between the pink / black wire (relative to pin C, circuit 39) and the black wire (relative to pin B, circuit 150).

I'll be putting the car back together today and we'll see if I've finally got all the bugs worked out.

I'm still peeling the onion. Just to recap, I found and removed the direct short to ground on the rear view mirror map light circuit. This short to ground directly affected the entire +12VDC #39 circuit and also affected the entire +12VDC #3 circuit with the VATS and GAUGES fuses plugged in.

With that ground removed from the equation, I'm now trying to isolate the source of an 80 Ohm ground on the #3 pink wire circuit. I suspect that one of the pink wires in the main wiring bundle (which runs from the fuse box across the dash panel) has a break in the insulation and is semi-grounded to a metal bracket somewhere behind the dash.

The main wiring bundle is not very accessible, unless I pull most of the dash out. I'm going to dig into it today and see what I can find. If anyone knows where I can find the common splice point for all the #3 pink wires, please let me know.

I only had a little time today to chase grounds between family holiday functions. I pulled the DIC panel and the radio out today, as well as the DIC mounting bezel, to gain access to the main wiring bundle. I stripped back the electrical tape around the bundle and only had about 10 minutes to look for a common splice / tie point for the pink #3 wires. Wasn't able to find it, but will dig further tomorrow.

I should take a picture and post a link of my dash opened up like a cadaver. It might be a little too graphic for those who have never or will never dive in there, though, so maybe not. :eek:

While I still had some daylight, I did a number of ground checks on various exposed circuits behind the DIC. I found another major short to ground - a big one - on the two green and white wires (circuit 916) that merge together on one of the starter enable relay terminals.

Several posts back, I had identified a large voltage drop on the starter enable relay - connector and relay terminal were gunked with crusty old, black, oxidized dielectric grease. Cleaned everything up, replaced the starter enable relay with a fresh new one, and, of course, it didn't start.

Now that I've narrowed the problems down to troubleshooting grounds, I pulled the new relay to check for any grounds on the terminals, and sure enough it was sitting right there on green / white, pin A. Tracing circuit 916 in my Haynes manual leads me back from the starter enable relay to the neutral safety switch and the clutch safety switch. Applying a bit of logic, I would assume that, since my car is an automatic, I don't have a clutch safety switch to worry about and that the other green / white goes to my ignition switch.

So, the short to ground on the circuit 916 is either coming from my brand new ignition switch - or more likely from the neutral safety switch, which is one of the few things left on the car that I have not dug into or replaced yet. :willy:

A short to ground on the green / white terminal of the neutral safety switch would definitely cause a significant +12VDC voltage drop and current drain on the whole starter system. It could also cause a large drain on the whole +12VDC system, as a result.

I think I may have finally peeled my way down to the final layer(s) of this onion. What a blessing that would be! Tomorrow, I'll replace the neutral safety switch, button her up a bit and we'll see what happens.

Happy 4th of July to all. Picked up a new neutral safety / back-up switch yesterday. Pulled the old switch and ground-checked the harness. Turns out the ground on green / white, circuit 916, was caused by a short to ground on the purple wire that goes to the starter solenoid. Of course, it showed up on the green / white wire from the starter enable relay harness because the car was in Park and green / white is shorted to purple via the neutral safety switch in that position.

Also noted a ground on the light green wire in the neutral safety switch harness - I'll be checking that out later on. Obviously, a short to ground on purple wire between the neutral safety switch and the solenoid terminal could cause some problems.

So, I'm going to run a new wire from the harness to the solenoid later today or tomorrow, slap in the new switch and see what happens. I hope this is going to be end of it and that I'll finally be able to drive her again. The endless troubleshooting and fixing is getting old.

Recap and update. Chased the ground on green / white, circuit 916 back to neutral safety switch. Pulled switch and probed ground on green / white (#916) and purple (#6) wires. Ground turned out to be on purple, #6. #6 comes from CINJ (Cold Start Injector) fuse, goes through neutral safety switch and on to supply +12VDC to solenoid "S" terminal.

On the flip side of the CINJ fuse is circuit #806, which goes to the cold start injector harness and the thermo timer switch. Pulling the CINJ fuse and probing both circuits for ground revealed ground on the #806 circuit. Obviously, the ground condition was manifested back to the #6 circuit via the CINJ fuse and the #916 circuit through the neutral safety switch.

So, I've now isolated the ground problem to the #806 circuit, which can only be one of three things: 1) ground on the cold start injector circuit 2) ground on the thermo timer switch circuit 3) ground on the wiring between the CSI and TTS or the wiring coming from the CINJ fuse.

Hopefully, this should reveal the root cause issue of my 'No Run' problem.

The source of the ground on circuit #806 turned out to be the cold start injector / thermo timer switch. With everything else connected and functioning properly, this ground also affected circuits #6 and #916 directly. The respective systems and components relative to these circuits have already be described in previous posts.

Drove around town to several parts stores and 2 Chevy dealerships before I found I found a replacement timer switch that I could order and have it overnighted. Part no. for the cold start injector timer switch is 14084318 - just in case anyone else ever has the same problem. I wouldn't wish this problem on my worst enemy, though. What a nightmare this car has been.

Was there ever a resolution on this? :lurk:

Maybe the MAF ???
Try unplugging the MAF and see if it starts.


Just my .002

No resolution yet. Have been working on my '85 Omni GLH N/A to get her tweaked up for daily driving, as I just sold my workhorse '92 Caravan to a buddy. She had 142K on her and was still running like a top. Without a doubt, the most reliable and trouble-free vehicle I have ever owned.

Unfortunately, I can't say the same for my '86 coupe. I love her to death, but she has been nothing but a headache and money pit for over 2 years. I've got to put the dash and console back together after going through all the wiring and fixing all the cracked, split and pulled-back wire insulation. More than I would have anticipated.

I'm sure the plugs are pretty gas fouled by now, so I'm going to replace them. I'm also going to disconnect the exhaust to ensure free flow and eliminate the possibility of plugged cats.

Its all a learning curve ! it sounds like you will eventually conquer your problem , good luck. :cheers: