VATS bypass not working
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Cruising
Joined: Jul 2025
Posts: 14
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VATS bypass not working
My 1986 4+3 C4 corvette is facing a major problem. It will only run for about 3 seconds then die out. Initially I did the cheap resistor bypass under the steering wheel and that worked for a few months but then failed. Since then I have installed the proper Bypass kit from PCM of NC(which plugs into the ECM) but still the car will only run for 3 seconds then die. I have tried installing the chip in every which way it can possible go but still no difference. I am 18 years old I have had the car for 1 year now and it has been sitting for the past 4 months. I really miss driving the car any help will be appreciated thank you.
Safety Car
Joined: Aug 2009
Posts: 3,750
Likes: 275
From: Melbourne, Victoria, Australia
Just thinking out loud don't have an early c4 shop manual handy, I believe the resistor bypass only bypasses the factory vats system to enable starter. So if you can crank the engine and no security light showing its working as it should, the vats should have no effect once engine is started. If it stalls check the usual stalling issues, your fuel pressure? the fuel pump may be failing? Any error codes in ecm history ?.
Check the usual ignition wires plugs, distributor cap coil.
Sounds unrelated to vats to me, hopefully someone can post an 86 vats operation from their shop manual.
To check that vats should not interfere with a running engine once vats has been bypassed to start the car, should be unrelated.
Cheers
Gerard
Check the usual ignition wires plugs, distributor cap coil.
Sounds unrelated to vats to me, hopefully someone can post an 86 vats operation from their shop manual.
To check that vats should not interfere with a running engine once vats has been bypassed to start the car, should be unrelated.
Cheers
Gerard
Melting Slicks
Joined: Nov 2016
Posts: 2,236
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From: So Cal
2023 C4 of the Year Finalist - Unmodified
In an 86-89 There is no visual indication to the driver that VATS is disabling fuel injection.
The SECURITY light has NOTHING to do with VATS in a 1986-1989. There's no wire to the light, no connection. Nothing! (geardvg has been around long enough that he should have see at least one of the hundred or more times I've written this about the 86-89.)
Jumper the diagnostic connector A&B (Top row, far right two cavities). Turn the key to RUN. Watch the Service Engine Soon light. If it flashes Code 46, you have an active VATS fuel disable.
Unless it is starting on the Cold Start Injector, and the main fuel injectors are disabled. CSI is active when the key is in START, completely separate system from the ECM.
The SECURITY light has NOTHING to do with VATS in a 1986-1989. There's no wire to the light, no connection. Nothing! (geardvg has been around long enough that he should have see at least one of the hundred or more times I've written this about the 86-89.)
Jumper the diagnostic connector A&B (Top row, far right two cavities). Turn the key to RUN. Watch the Service Engine Soon light. If it flashes Code 46, you have an active VATS fuel disable.
To check that vats should not interfere with a running engine once vats has been bypassed to start the car, should be unrelated.
Last edited by IHBD; Today at 01:08 AM.
