My 'vette won't stay running!!
 

Iknow I know.. who's does.... but anyway.

So the vette left me stranded and had an intermittant fail to start problem and went from running like crap to not running at all

It was ignition related and so I replaced pretty much everything in the ignition system. still wouldn't start.

I figured it was flooded, so I took out all the plugs and opened the throttle up for half a day.

Put it back together and fired it up. it FINALLY ran for more than one or two revolutions. the PROBLEM is that it won't stay running.

THE SYPMTOMS

it backfires, and won't run unless i keep stabbing the throttle. as soon as I try to hold it at any throttle position, the revs drop and it dies.

it will only start if I turn it over and start blipping the throttle as it's spinning.

it seems to be hitting on all 8, but can't really tell.


WHAT"S THE DEAL!?!?
:willy:

Year
mods
codes?

I would start looking at your injectors. What is your fuel pressure ? Does it hold for very long ?
If it starts better when you depress the gas peddle, there is a good chance that it is getting flooded. Maybe one or more stuck or leaking injectors.
Food for thought :cheers:

it's a '93 with nitrous and transmission
no codes

The fuel pressure is good- 43# and steady, and the injectors click when the engine runs, although they MAY be diry, they are injecting fuel.

this is about the strangest crap a car has ever pulled on me.

to start it, I have to crank it while quickly tapping the throttle. when it starts running, it runs like it's really really cold or somthing...very rough. I keep tapping the gas and the RPMs climb higher, as high as i want to let it go, but i have to keep modulating the pedal to keep it running. If i hold it to the floor, the rpms drop and it cuts out. If i stop modulating the pedal and try to hold at say, 3000 rpm, the revs drop and it quits. it won't idle, it won't rev up if I floor it. it backfires a lot and barely runs, but it sounds pretty smooth, like it's actually hitting on all 8.

Just an opinion, but sounds real lean. Back fire is lean usually. Loosing rpms with open throttle is usually lean. Good pressure eliminates the pump and maybe the filter. I'd look at the tps, or map. Try pulling the codes first. Oh, try flooring it when you get it started. I had a map go out and the only way it would run was wide open. Oops you already tried that. You even got a map? Just my musings.

TPS ? check it.

try resetting the ECM

Have you checked for vacumn leaks?

looked at the TPS, and noticed somthing- THe gray 4-prong connector below the throttle body on the passenger side appears damaged.

question is, WTF is it and what does it do?


I will try resetting the ECM (diconnect battery) and see if it helps.


and it's speed density, so no MAP.

I've only been working on electroniclly controlled cars for 6 since october! (that is how long I've owned the 'vette)

OK just tried it again. same business is happening

I checked all my connections, and they were good

no black (rich) smoke is comming from the exhaust

the car had been sitting overnight with the battery unplugged, so the ECM is reset

and blink......blink blink...........code 12 -all clear

wierd thing though, when I plug in my little code getter, the fans kick on... what's with that?


the only thing i see that's still funky is the plastic part of that one connector.

ALSO how can I troubleshoot the TPS and ECM?? that's the only stuff I can think of that could be wrong


and no vac. leaks either

The TPS (three wires) is not adjustable on your '93. About all you can do is check that the output is smooth and gradual from idle to WOT.

The four wire device is the IAC (Idle Air Control). It is a stepper motor that that allows the proper amount of air to pass for the idle speed the ECM is commanding at the moment. I sounds like the IAC is at least a part of the problem. It also sounds like you NEED a Factory Service Manual.

RACE ON!!!

IAC, huh? sort of makes sense....car won't idle, so maybe IAC....

which wire would I test to see the voltage rise signal from the TPS?

I'll get a new connector from the stealership tomorrow, and attempt to clean and repair mine tonight. It seems that the plastic bit has been cracked in half. perhaps the inner prongs are touching.


could someone test this IAC theory for me? disconnect your IAC and see if it will run?

any other ideas??

Iac
 

I definitely don't have the knowledge a lot of these guys have but ...

The flooring it and dying part I don't get but the other sounds just like an IAC problem I had. It won't idle if you let the foot off the gas.

Disconnect all the various crap and pull the throttle body off. Unscrew the IAC and see if there is all kinds of black crap in there. Clean the whole throttle body.

Do a couple searches here and on google and you can find pretty detailed instructions on cleaning the IAC. Mine (89) cost $50 or so I think so I replaced it. If it looks like the connector is bashed up enough to screw up the connection, I might be tempted to just fix that first.

The IAC stepper motor moves the pintle to vary the amount of air it will pass. It is commanded by the ECM to maintain the idle speed the ECM is programmed for under different conditions. Unplugging it will only stop the pintle from moving. The car will run. If the IAC is unplugged when it is wide open, you will have a very fast idle. If it is unplugged when it is closed, it won't idle at all. Simple?

RACE ON!!!

SO! in theory, what happened is this- The car is turned off and battery disconnected. I'm working on my opti, and somehow whack the IAC connector. it busts the little plugs out and the damage to the plastic prevents the plugs from engaging the IAC when it's "connected"

being that it was unplugged with the car off, and never plugged back in, the pintle remains in the closed throttle position and will not allow the car to idle.


I'm going out and going to mess with this thing a little

AWWWWW CRAP

well I unplugged the connector and pulled on the pins to make sure they were out all the way, but when I went to stick the connector back in, it CURMBLED into a bunch of very very small grey plastic pieces. I can't believe how brittle that thing was...

so now I have 4 little wires hanging out in the breeze with the connector pins on them. I have no idea what order they go in, and they are all green-2 with a whie stripe, 2 with a black stripe.

I'm going to get a new connector plug tomorrow, but what order do they plug in??


ALSO, will i have to reset the ECM after I plug them in the right way?

and why isn't this throwing any codes if the IAC is disconnected?

and why will It fall from higer RPMS? (example, I start it and blip the gas to raise the RPMS to 3500 and then give level throttle...the RPMS drop and it stalls.)

my ignorance of these electrical systems makes me feel a little......stupid

oh, and TTT by the way. I need insights

are you running with cats? Sounds like they are clogged. You need to pull error codes from your ECM to start with....

sounds like you are in "panic Mode" ....., take your time reporting symptoms back to this forum and you will get the right kind of help you need to get rolling again...

You can use a paper clip, and short pins A and B together on your ALDL, and read the error codes from blinking "Check Engine" light:

http://img256.echo.cx/img256/6426/obd1pinout6za.gif

After shorting A and B, and turn ignition to ON, but do not start engine:

"Within a few seconds, your “Check Engine” light (early C4s) or "SYS" light (later C4s) will flash a code of 12. There will be a single flash followed by two flashes and this will repeat three times: Flash (pause) Flash Flash (long pause), Flash (pause) Flash Flash (long pause), Flash (pause) Flash Flash (long pause). Code 12 is a delimiter or marker code to show where the error code string begins and ends.
After the three code 12 flashes, you will either get an error code (or codes) or you will get another string of code 12 flashes if there are no trouble codes stored. All codes are repeated three times with a long pause between each code group so (for instance) you could recover a string like this: 12, 12, 12, 36, 36, 36, 44, 44, 44, 12, 12, 12. In this example, your OBD has stored error codes indicating that the Mass Air Flow burn off circuit has exceed the Hi/Lo limits (Code 36) and that the Exhaust is to lean (Code 44). Whether or not this means that the sensor is bad or that the parameter it measures has truly been exceeded is yet to be determined however, you do know that the PROM based limits for these two sensors have been exceeded."

check out this link for good description of how to read your error codes using the paper clip method..

http://www.obd1.com/

and here is a troubleshooting URL:

http://www.chevythunder.com/fuel%20i...20acceleration

and here is a decent URL describing the function of many of the components like IAC, TPS, MAF, O2 sensors....etc etc.:

http://members.aol.com/InjuneerZZ/Sc....htm#step%2013


:cheers:

did the codes- got a code 41. looks like it is
"EST circuit voltage was above 4.6 volts when engine speed was under 1500 "

so the electronic spark timing is out of whack.... sort of sounds plausable- it kind of acts like a car would if the timing was jacked up
what with the backfiring and easy starting and not running when the throttle opens up...

I called the dealership and asked for a copy the EST troubleshooting guide and I'll be picking it up today, along with that connector.

anyone run into this before?

My engine acting same; just put in a new ECM and it did not solve problem. ($185 down the drain!). Try running the CCM test. Put a paper clip between G (lower left pin) and A (upper right pin) on ADL connector. Then turn ignition on and read CCM codes in speedometer area. I get a C41, H72, etc. which says I have serial link down between CCM (under center of dash) and ECM (under hood). If you get these codes, we got same problem and I don't know what to do next. Mine won't run enough to get to dealer. I have service manuals. I can tell you what CCM codes mean.

Buck in Virginia

Rubydog - do a search on my name for threads I've started. I have the EXACT same symptoms as you and crkemppainen. There are about 4 threads with different symptoms being troublshot so you can read through and get some ideas.

I've done a whole lot of work on this (although it's not fixed) so you can see what I've done and hopefully eliminate some things from your list to try.

My current status is here:

http://forums.corvetteforum.com/show...18&forum_id=48

Although I'm starting to think it's my ECM and you've already done that.

I'll check the injectors next. If you do yours and it fixes the problem please let me know.