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I just added a fixer upper to the Thirdgen fleet. This car is a 92 z28 5.7 hard top.
top.The car has a the vats bypassed some how and the previous owner didn't know how it was done as he bought it this way.
The way the bypass was wired is a hack job and I don't even understand how it even works.
The key tumbler vats wires are cut and the plug on the cars harness was removed ( wires left exposed).
a start button was added with 4 wires going to it to start the car. 2 red wires from an orange wire under dash 1 black ground and 1 wire in main harness under the hood.
A relay under the dash is bypassed ( wires cut from relay and twisted together)
To start the car you turn the key to on then hit the start button. Fires up fine then the security light come on. The car doesn't die or anything and you can turn it off and fire it back up with no problems.
I would like to put this back to factory and get rid of this bypassed crap and use the key tumbler as it originally was.
Where should I start?
I would hate to remove all this crap just to be left with a vats problem car. Junk wires to start button 2 wires from start switch to orange wire in body harness under the dash. Relay bypassed under the dash behind drivers kick panel Red wire from start button to purple wire in engine harness by firewall above brake booster. Gray wire from an under dash relay grounded to the chassis with a yellow wire.
these are the only areas I could find with bypassed or modified wiring for the vats/starting. Any info I can use to put this back to factory is really appreciated.
Somewhere, you've gotta have a resistor pack to trick the VATS module, or a VATS signal generator, OR a chip with VATS bypassed. The computer with the stock chip requires a VATS signal for the car to run.
The photos all add up to bypassing the start enable relay, which normally would be triggered by the key and VATS module, but I'm not seeing anything to let the ECM run the EFI.
I can't see any resistor in the harness anywhere. That's what has me confused as to how this thing works without a resistor or something to trick the computer. If the chip was burned to disabled the vats would the security light still illuminate? None of the wires on the lower column ignition switch are modified. How can I get the key/tumbler to crank the engine instead of this stupid button. Here's the column and harness wired for the vats. It was just hanging exposed.
That's the start enable relay. The yellow wires are from the start position of the ignition switch. The Green wire is what is Wht/Tan on some diagrams, it goes to the Park/Neutral switch. From Park/Neutral it turns into the PPL wire to the CRK fuse and also through C100 into the engine compartment and eventually ends up at the starter solenoid. The BLK/YEL goes to the VATS module.
The Orange wire they spliced into should be a full time 12V battery connection. So if I had to guess, the start button is jumping 12V battery power directly to the starter solenoid. So it's bypassing the ignition switch, and start enable relay, but not VATS. Assuming the original wiring is still connected, the green to yellow splice is bypassing the relay.
If you correct any messed up wiring between the ignition switch and the starter, it should use the ignition switch and you can dump the retarded boy-racer push button start.
Now your VATS bypass that's letting the engine run, is somewhere else and unrelated. The security light could be coming on because the relay is bypassed.
If there is not a resistor installed or a reprogrammed memcal.There might be a hz modulator installed. F10 at the ecm a blue wire would have 2.5v or 30-50hz at 50-60%. https://m.ebay.com/itm/GM-VATS-or-PA...%257Ciid%253A6
I'll drop the computer down tomorrow and check
This brown wire comes from the headlight switch plug and goes no where. Ran out of time today to find it. I have everything ready to solder back up to the factory. I have a new ignition switch on the way with the vats wiring.I pulled a plug off another harness I have to replace the missing vats plug.
. I found 1 more wire cut and shoved up into the dash. It's Brown and coming from the headlight switch plug.
Update:
pulled computer and its not modified and no module connected to it. So In assuming vats is deleted in the chip.
I worked today to solder all the wires back to it's factory state. My trunk button now works and I have interior lights.
Where I'm at now is I have no crank with turning the key. I have power everywhere and the fuel pump primes, security light is off. When I turn the key nothing happens. No drop in volts no cut off of the gauges nothing.
I can do just about anything to a Thirdgen but wiring is not my thing. It started before with the button every time. When I use to turn the key with the button installed you would get the normal voltage drop but now I get nothing. What could I be missing?
Trace the circuit from the fusible link to the starter.... Or cut to the chase and check the 2 red wires going into the ignition switch have 12V+. If you have 12V in, check to see if you have 12v out. If you have power into the switch, but nothing coming out when you turn the key to start, might be a switch problem.
Was just looking at this wiring diagram. Do I need to bypass the starter enable relay since the vats module reader controls it? I confirmed with the previous owner the vats was programed out of the chip. I'll start at the fusable link and work to the ignition switch. Taking my time through this process so I can better understand the wiring aspects of the thirdgen.
If the green and yellow are still spliced it's bypassed already. If it's wired back in, you can just jumper the black/yellow to ground to switch the relay. But it'd be easier to check that the ignition switch is being supplied power, and that it's switching, then move on to the relay after testing the switch.
Thanks for the help Drew
I have power from the starter all the way into the ignition switch through the red wire. With the switched clicked to the on position I have power coming out of the switch for accessories. I held the switch for starting and I have no power going through the yellow wire for the start enable relay. So It looks like my ignition switch needs to be replaced. I'll drop the column and replace it and update once done.
Update. Pulled the ignition switch out of my 91 parts car, dropped my column and plugged in the 91 ignition switch and boom she starts. Now time to put it back together. Thanks to all.
I have a 1990 camaro convert 305 the vats are frying my brain , i have spark I have fuel, all of the relays are new and every thing in the motor is new but can't get the car to fire up at all, i need some help
I have a 1990 camaro convert 305 the vats are frying my brain , i have spark I have fuel, all of the relays are new and every thing in the motor is new but can't get the car to fire up at all, i need some help
You need to start your own thread. Pin b6 of your ecm will have 2.5-5v Koeo if the passkey is working.
The common failure is the key reader. You can bypass it with the correct resistor under the dash there are two white wires that can. be disconnected and a resistor installed. Or a hz modulator or prom bypass. Removing the prom if it's a vats issue the engine will start.
Update. Pulled the ignition switch out of my 91 parts car, dropped my column and plugged in the 91 ignition switch and boom she starts. Now time to put it back together. Thanks to all.
Good stuff! Now that wasn't that hard was it? Wiring is kind of fun next to some things.
Your diagrams and the one my friend Shawn sent me helped me understand the paths alot better. When You drop the kick panel and see spaghetti it's very intimidating. Definitely satisfying being able to figure it all out
I am new to Third Gen, so I am not sure where to post questions, lol. I purchased a 1992 shortbed Chevy with a Third Gen L98 TPI motor.
I spray starter fluid and it runs till it burns out. I am pretty sure it is electrical because with my test light on the fuel pump wiring i have a very dim light. Also with test light under the dash (steering column) what i believe should be hot is not. It has passkey, so if anyone could please guide on the right path. I would greatly appreciate y'all. Oh and one more thing I am picture kinda guy. This is my first baby and its got to be RIGHT!!
09-12-2017, 07:55 PM
Good stuff! Now that wasn't that hard was it? 
Wiring is kind of fun next to some things. 
