Correct. (at least as far as how '87's were set-up. I don't imagine timer function was different for later c4's)


So you DO have 12V into the relay, and the ground (completed circuit, to starter) is also good.

The fault is in the ignition switch harness. Many 90's GM's have a 'rod' which is integral with the ignition lock cylinder, and when you turn the key to 'START', it makes a contact that energizes the relay (instead of manually 'jumping it).

Breakdown of the steering column bezel won't be too tough. Disconnect your battery first, and you should easily find the switch fault when you examine the lock action.

 

Your diagnosis makes sense on some levels, but if the key will cause the motor to crank with the starter relay jumped, can there really be a problem in the column wiring?
I was assuming CCM and have half the dash tore apart.
Is there a test I can try at a connector to see if your analysis is correct? The Service Manual doesn't cover this situation, or at least I have not found it yet!
Thanks SO much for your help and please continue to offer your advice.

 

Anyone?

 

I don't think you have eliminated the vats issue first yey. Read this stuff and then use a terchnique to bypass your vats system and try to start the car. If it doesn't then you'll know for sure and can move on.

VATS measures the resistance of the pellet in your ign key. If it doesn't agree within 5% of the value it will not close the start enable relay and your starter will not crank. It also tells the ECM to not exercise the injectors so the car cannot be push started. The ECM upon determining that the VATS disallowed a crank, will not a crank for 6 minutes.
Most likely your pellet contacts are worn, or the contacts in the ignition switch tumbler are no longer making reliable connection to the pellet. Also, there is a clutch safety switch which forces you to depress the clutch in order for the starter to work (gear selector switch if automatic).

The next time you can't crank, jump the clutch safety switch and measure the voltage on the jumper. The voltage should be 12v with the ign sw in crank position. If not, then VATS isn't closing the start enable relay. You can check the ign tumbler contacts by removing the hush panel above the driver's feet and find the two wires from behind the steering column going to a 2 pin connector. Unplug the connector, insert your ign key and measure the resistance across the wires from the steering column. It should measure the same as your pellet. If over 13k ohms, you need a new ign tumbler or key.
You can temporarily bypass VATS by clipping a fixed resistor across the 2 wires going into the wiring harness (goes to the VATS module) the same value as your pellet. You can use a 1/4 watt 5% resistor from Radio Shack. Don't permanently bypass VATS because 99% of thefts are done by bashing the column and jumping the ignition.

Guys,
I'm going to wire in a bypass and switch to cure my intermittant VATS problems. Before I go cutting things, I want to make sure I'm working with the right wires.I traced out the wiring to a set of VERY skinny black wires under the steering column which connects to another set of larger black and white wires.Are these the ones I need to be working with?
Yes..the vats wires are very skinny, but there is a pair of them, white in colour, housed in an orange outer. They connect, via a small black plug, to a brown and yellow wire that go directly to the vats module.
The other extremely skinny wires, housed in a black outer, are cruise control wires...! These have a blade-like connector at the end..
IMO you are better off cutting the brown and yellow wires to fit a resistor or by-pass, as they are heavier and easier to work with.
As long as your cont test comes out from the lock column, then it's most likely the correct wires. I think mine were yellow and some other color, i don't recall. Its dark under the dash. It's pretty obvious though. Sitting in the drivers seat, the wires came out of the dash, then ran up right-of-center from the bottom of the steering column up to the lock cylinder.

My dad helped me with this project... we clipped the wires after the connector (between the lock and the connector) and then I just unhooked the connector and brought it inside.
We then measure the OHMs of the key, and I had bought a large pack of resistors at RadioTrash and we found 3 that gave it the correct OHM reading. We soldered them together and then soldered them to the clipped wires. Now what I had was a connector with 2 wires, and 3 resistors soldered between them which I covered with heat shrink.
I then just went back out to the car, plugged in the connector and the car fired right up with NO problems!! this was after a year of sitting in the driveway scratching my head as to how to make it start... all it took was 3 resistors costing me $.06 total!!the whole project took roughly 15-20 mins to do.

Vats Q and A


The VATS module closes the start enable relay and tells the ECM to exercise the injectors by comparing the pellet resistance with the stored number. If the resistance isn't correct, then VATS makes you wait 6 minutes to try again. The starter solenoid gets power through the ign sw crank contact, the start enable relay, and then the clutch safety switch (gear selector switch if automatic). First try your spare ign key as its pellet contacts aren't worn like your everyday key. Next, jump the clutch safety switch and try a crank while measuring the voltage on the jumper. If you don't have 12v on the jumper in crank position, then you will have to determine where the circuit is not continuous. You can test the starter by jumping 12v to the clutch safety switch jumper, the starter should run. Most VATS troubles are due to worn contacts in the ign tumbler that make connection to the pellet. You can check this out by removing the hush panel above the drivers feet and finding the 2 wires from behind the steering column that go to a 2 pin connector. Unplug the connector, insert ign key and measure the resistance across the wires from the column. It should measure the same as the pellet. If over 13k ohms, you need a new ign tumbler which has new contacts that touch the pellet. You can temporarily bypass VATS by connecting a fixed resistor the same value as your pellet across the 2 wires that go into the harness (these go to the VATS module). You can use 1/4 watt 5% resistor from Radio Shack. There is no need to spend $30 for a bypass kit.

VATS Bypass how to
The VATS Bypass Modules that you see in the Corvette catalogs cost anywhere from $30 - $50. Add to that shipping and sales tax where applicable and you’re looking at $35 for a resistor that you can pick up at Radio Shack for under $1! Another problem with the bypass modules is that you have to know what code value (1-15) to buy. That means you'll have to go to a dealer that can use their VATS Interrogator. If you take a multi-meter and measure the resistance between the metal contacts on either side of your key, you can buy a resistor of this value at any Radio Shack store. ¼ watt will do. You then need to remove the hush panel under the steering column. Disconnect C281 (two-cavity connector at base of steering column with two black wires in the female end and one yellow and one brown wire in the male end). Your newly purchased resistor goes into the male side of this connector, so you'll need to crimp a couple of female pins to the resistor legs. If you insist on purchasing the VATS bypass from one of the Corvette catalogs, again measure the resistance of your key pellet and compare it to the code chart to find your code. It is also possible to reprogram the PROM to ignore the VATS signal, but that is beyond the scope of this article. The real fix came from GM in July of 1988 as TECHNICAL SERVICE BULLETIN number 88-292. This TSB includes the part number for a new ignition cylinder that has better contacts. Keys have also been updated that are slightly longer and have the better contacts. This virtually eliminates VATS problems caused by connections. You still want to keep your key clean and dry, but with the TSB competed, you should enjoy VATS problem free starting for a good long time.

...at least you now have a manual on vats anyway.

 

Thanks for the VATS info, but I have already tested the key and the cylinder.
I will continue my quest.
Off to do more diagnostics.
If anyone has any more thoughts, please help!!

 

I have 12V at the gear selector switch, 5 volts on the module side of the VATS 2-pin connector. 887 ohms on the key pellet and 887 ohms on the ignition switch side of the VATS 2-pin connector.
Car starts with key in "start" position with the relay removed and big yellow and purple wires jumped. Car only runs a few seconds in this fashion, however.
One more symptom I forgot about until now: recently, the battery would discharge after sitting for only a few days. This happened for 3-5weeks before my no-start problem appeared.
I appreciate all of your help and am learning more about this car than I ever thought I would!!

 

I may be on to something here...
A GM tech friend was convinced today that my problem is the ignition switch. I told him I had checked the resistance on the pellet and the two-pin connector and they match.
HOWEVER, he asked if I had checked the resistamce with the key in "start" position. I went home and checked it and while my readings are fine in the "off" position, as soon as I move the key to "run" or "start", connection fails.
New ignition switch will be ordered today.