tcom98

My 88 C4 frequently will not start. It seems the VATS system has to relearn the key chip resistance after which the car will generally start. I have bypassed the chip with resistors which helped for a while. Recently the problem popped back up but seems to be more frequent. I replaced the actual ignition switch and all seemed well until I bolted the steering column back up even after letting it sit for 20 mins to relearn the resistance. I unplugged the harnesses from the ignition switch and plugged them into the old switch (unmounted) let the system relearn the resistance and the car started. Plugged the harnesses back into the new switch and it started. Once I bolted the column back up it would not start again.

Can anyone point me to which wire/wires might be the problem? When I put the key in the run position the dash lights come on as they should. When I try to start it I get nothing. Doesn't even crank.

vetteoz

Nothing to "relearn" the resistance is fixed ;
the VATS module either reads it correctly or not.
If it doesn't then the module takes 5 min to reset before it will attempt a read again.
If you turn the key during that period the delay timer resets

If done correctly bypasses the Ign switch contacts completely

Possible VATS is working fine and the starter enable relay it operates is either faulty or
not being operated by the VATS module resulting in it not passing power to starter
Remove fascia over DIC and confirm correct operation.
Bypass the relay and see if engine cranks over

Dans 85

What is the value of your key and what is the value of the resistor you used?

Cliff Harris

The VATS module can disable the starter relay and the injectors (through the ECM). The best way to tell that VATS has kicked in is that the starter relay doesn't click. Since it's right behind the center cluster it's easy to hear it.

Even if you bypass the starter relay, you still need to get a 30 Hz square wave into the ECM somehow or it won't enable the injectors. The various "tuners" know how to bypass this check in the ECM firmware.

There is a resistor in the VATS module and the resistor in the key must match it for the VATS module to enable the starter and injectors. The magic VATS resistor values you see in the various tables are 1% values. One problem with a resistor bypass is that places like Radio Shack sell mostly 5% tolerance resistors, so it can be a little tricky to get the correct value by mixing and matching resistors.

If the starter relay doesn't click then your resistor bypass didn't work. If it does click but the engine doesn't crank then your problem is elsewhere (starter, solenoid or wiring -- could be bad relay contacts).

trulytex

I had the exact same issue with my 1990. I bypassed the VATS with resistors under the dash, grounded the starter enable relay to the instrument panel frame, etc. All worked for a little while, then more issues. I finally was told about an old school fix that has worked now for about 2 years with no problem. Here is my post from Nov, 2010:


Well, after 4 years of several fixes to my 1990 Vert for No-Start Issues, I am hoping that this is the last. So Far, So Good! I haven't had any issues since adding this Painless 25 Amp Remote Starter Relay. I installed it on the Firewall on the Driver's Side. We cut the Large Purple Wire in the Wiring Harness and spliced the Large Purple Wire from the Remote Relay onto the side that goes to the Starter and the Small Purple wire from the Relay that goes to the Battery. Then we spliced the Red wire from the Relay to the Battery Wire at the Alternator and the Black Ground Wire from the Relay onto a nut near the Intake Manifold.







It would only Not Start after it was warmed up. There was never a problem with the initial start of the day, only after driving for a little while. Then I would have to wait an hour or two before it would start back again. I have driven it several times since adding the Remote Starter Relay a few weeks ago, and so far - No Issue. And it would have happened by now.

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I was told by several people that the Starter Solenoid was probably getting hot. I had the starter rebuilt, but was still having problems. It looks like this may be the solution. I know that several people on the Forum were having this same issue, so I took pics and described the install - after waiting a few weeks to make sure that it worked.

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this is a really neat old school trick from back when, we used to use ford starter solonoids and mount them on the fire wall away from engine heat on chevys that had 'heat soak' problems. It works good and makes the chevy starter last longer. also works on other things. excellent job

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Here is a little more clarity to the Remote Starter Relay issue. I also own a 1987 Cadillac Allante' and receive the "Insider Magazine" published by the Allante' Club of America. An Allante' Specialist that has a regular column in the magazine suggests installing the same thing on an Allante' (made from 1987-93) that has "No-Start issues when Hot". The following is his explanation of why this works:

"This issue can show up in all GM cars up to 1999. [The Remote Starter Relay] reroutes the power so that it goes directly from the battery to the Starter Solenoid. With the cars now 20 years old, resistance can build up in the now older wires and not allow the Starter System to work the way that it was designed."

I hope that helps explain why this works. I have never professed to be a mechanic by any means and even less of an electrical engineer. Just trying to pass on what little bit of knowledge that I have learned playing with these toys to other people who were as frustrated as I was with my Baby leaving me somewhere on the road waiting gor her to decide to start.

tcom98

Many thanks to all who replied to my thread. I do appreciate your input. It looks like I have the problem fixed. Apparently the new ignition switch I installed was faulty (even worse than the original). I exchanged the switch for a new one yesterday afternoon. Once the new switch was in place the car started right up and seems to be back to normal. This is my first Vette and it is great to know there is a place like this forum to go for advice on technical issues.

Thanks again to all for your input.

JT-Monster-

Good info guys. I orderd the Vats bypas from mid america motors and its on its way but after seeing tons of vids of others having vats issues all of there seemed to not cranck at all.

my 86 vette does crank but no spark or fuel. is it something else?

tcom98

You could also have a bad ignition module. From my understanding, the ignition module not only controls spark, it also controls fuel flow to the injectors. The module is fairly easy to remove and can be tested at most auto parts stores at no cost.

JT-Monster-

Thanks for the reply. I actualy repladced both the distributor coils and ingnition module. and still no spark thats what lead me to the VATS. ill have to wait and see what happens after I install my VATS bypass

vetteoz

VATS has no effect on spark ; it takes out the fuel injectors and the starter only
Have you pulled the codes ?

If the engine cranks over , unlikely it is VATS related because VATS takes out the starter ( unless a PO has bypassed that function )

Back to Auto 101 basics
Do you have fuel pressure ( tested with a gauge ) at the fuel rail?
When key on , when cranking over ??????????????/

Do you have 12V at the coil ; key on?
How to test whole spark system here
http://easyautodiagnostics.com/gm_ic...n_module_1.php

cesmachines

I had the same problem on my ’87 at 5 years old. I took it back to a Chevy dealer and they tried to correct the problem. After a couple of “back to the dealer-fixed”, “back to the dealer-fixed” circus routines, they finally admitted their was an update to the design of the VATS module itself. They replaced it with the new design and I haven’t had a problem since. If GM felt they had to redesign the PC board, they should have had a recall. Apparently they decided to only send out a service bulletin to it’s dealers.