red86man

Good stuff, zr1fred - thanks!

zr1fred

I guess if you are getting code 46, you have your answer. I have several of the modules, but my interagator is broken and I don't think I recorded the vats code for them. I could send you one, I don't believe I've ever used one (thought I needed one once, but no, it was a bad ignition switch (dropping the voltage on the ignition fed lines to about 9.5 volts occassionaly when the key was turned on). good luck, let me know if you need one.

red86man

Thanks, again. Unfortunately, the ECM throws no codes for this problem. 12, 12, 12, 12 - forever. Consequently, this problem has been a tough nut to crack. I may be talking to you about those modules, if the VATS turns out to be the culprit.

red86man

I forgot to mention one other symptom that points to VATS, even though I'm not getting any numerical error codes. Turning to the key on position, the Security light goes out along with the other DIC indicators after power on. While cranking, though, the Security light continues to flash on and flash off. From what I understand, this would indicate an issue with VATS, correct?

Aggravated4life

No...when the alarm is armed the light FREEZES or STAYS STILL on the dash info center.

Make sure your key holes in both doors have been turned back and forth as well...they disarm the system as well.

Your timing might be wayy off..have you even checked it?

When the security light flashes when you open the door and sit in the car,its not armed.When the light freezes or stays lit up,it is.

red86man

Thanks. Yes, I've checked, rechecked and re-rechecked the timing. The timing was an issue earlier on in the process - after I rebuilt the distributor (180 degrees out).

I'll try the door lock cycling suggestion. Is it normal for the Security light to flash on and off while cranking, though?

AGENT 86

Is the ECM receiving a reference signal from dizzy during cranking ??

red86man

Yes, I checked reference signal from dizzy to ECM last year and, as I recall, it was OK. Of course, that was last year, so it wouldn't hurt to check it again. I did try cycling the lock cylinders on the doors, but to no avail.

I got a chance to probe my DIPs (Diagnostic Information Panels) that I rigged up yesterday. First of all, let me make a correction on previous references to the 2 VATS modules - I made reference to them 180 out. The gray (VATS Decoder) module is the one behind the breadbox, which recognizes the key's resistor value, initiates ground to the starter enable relay and also initiates ground for the cranking fuel enable part of the VATS. The cranking fuel enable output (circuit grounded) via pin P to the purple wire goes to the blue module, which produces the 30HZ square wave reference signal. The 30Hz ref signal gets output to the ECM to intitiate the pulsing of fuel through the FIs. That's my current understanding of the system.

Before I post my DIP readings, though, I'd like to draw reference to the schematic of the older C4 VATS system as posted on GIJoe's www.vatssucks.com site. This is the schematic that I am using as a reference for my troubleshooting.

Here's the pinout readings I took:
- T to U - Check key resistance - appr. 6 Kohms - well within tolerance of that particular key code. Jiggling the key in the lock causes the resistance to jump up over 7 Kohms. Possible lock cylinder / key replacement issue.
- L (ground) to V - Check starter enable output - .7 - .8 VDC, which is satisfactory since the starter cranks the engine.
- L to P - Check voltage output to the cranking fuel enable circuit (blue module) - cranking voltage of 2.4 - 2.9 VDC; the voltage jumped up and down in the range, as might be indicative of a square wave pulse. Will validate later with O-scope.
- L to S - check VATS line-in / ignition voltage - key on 12.2 VDC, dropping down to 10.1 VDC while cranking. Voltage drop seems excessive to me. Could be related to lock cylinder.
- L to U - check voltage between ignition key lock cylinder and VATS. Cranking voltage of 5.8 VDC. That doesn't seem right at all. Points again at lock cylinder.

My conclusion? The data above would suggest that I replace the ignition key lock cylinder assembly, which I think I'll do. Anyone have a few good DIY replace lock cylinder links that they would like to share?

Any other thoughts, suggestions and advise would be appreciated.

red86man

So, I went out to Advanced Auto and picked up a new ignition lock cylinder for about $65. The pair of keys did not have the resistor chip embedded in them, though. All the Chevy dealers parts dept. were closed, so that was the best that could be had today.

No sense fiddling with the new no-resistor ignition key lock cylinder, because I still had to input a 6.04 Kohm resistance to the VATS circuit to simulate my particular key. So, I went to Radio Shack and bought a 10K PCB trim pot, a small prototype breadboard and a SPST switch and dialed-in 6.04K Kohm for the pin-outs. I soldered two wires off the PCBs pin-outs and plugged them into the yellow and brown wires which go to pins T & U of the gray VATS Decoder module. Verified 6.04K at pins T & U, effectively simulating my key's resistance code. Cranked the engine, but still no start or run. I can now effectively eliminate the key lock cylinder and/or embedded resistor as potential sources of the problem, given the fact that I completely bypassed both.

Here are a few new test observations: 1) Hooked noid light up to #1 FI connector, cranked and noted noid light pulsing on and off as it should. 2) Cycled key lock cylinders to lock and unlock several times, then locked both doors. The Security light on the DIC does not illuminate at all on the DIC with the doors locked. Unlock and open the door(s), the Security light flashes. Key on, the Security light goes out after lamp test. While cranking, the Security light flashes.

I'm going to probe the Pin P (purple wire) output to the cranking fuel enable module with an O-scope tomorrow and see what's up there. I don't have any schematics or pin-out info for the blue VATS module - the 30Hz square wave generator. If anyone has a link to the schematic for the blue module, please post links or any info you might have. Otherwise, I'll trace out the wires to see where they go and try to figure out what should be riding on them. Two of them I know already - purple wire input from VATS Decoder and ground. The other 5 pin-outs I'm not sure about yet.

jfb

If your starter cranks the engine and the injectors pulse during cranking, then you do not have a problem with VATS !!!!!!!! If VATS doesn't measure the correct pellet resistance, then it will not close the start enable relay (no cranking) and it won't supply the 30 Hz signal to the ECM and you won't have any pulses on the injectors during cranking. You have some other problem. During cranking, check for spark and spark at the right time with your timing light. Put a fuel pressure gauge on the shrader valve on the end of the fuel rail and see how much pressure you have and observe if the pressure holds up with the ign off. Rapid pressure drop indicates possible leaky injector/s and too rich a mixture to start. Unplug the MAF and try to start the car. Look at the EGR valve and determine if it is fully closed. Measure intake vacuum during cranking to determine if you have a vacuum leak. Measure the voltage on the throttle position sensor, it should be 0.54 volts +/- .075 volts throttle closed ign on.

red86man

Thanks for the detailed info, jfb. It certainly wouldn't hurt for me to go back and recheck all the things you've mentioned here.

After evaluation of the VATS test readings and the additional test indications (i.e. - noid light blinking while cranking, resistor emulation, etc.), it would seem as if the VATS may not be the problem. There are a few indicators that are still not quite right, though: 1) Security light does not come on when doors are locked. 2) Security light blinks when doors are opened, but goes out when the ignition is in the key-on position. Therefore, the VATS will not allow me to do any sort of "relearning" procedure. 3) The Security light blinks while cranking, which indicates an issue with the VATS.

Yes, the VATS is recognizing my key and is energizing the start enable relay and the starter system. I haven't hooked the O-scope up to pin P of the gray TDM yet, but I did measure a pulsing voltage of 2.4 - 2.9 VDC on my DMM. I'm going to scope it tomorrow to verify the presence / absence of the 30 (or 50) Hz square wave signal on that circuit and the signal input to the ECM.

The only other possibility that I read somewhere during my research is that there could be an issue in Comm 2 (?) circuit signal with the ECM that defines the Security light indications. I didn't find any detailed info about this schematically - just an honorable mention. If the comm circuit which drives the Security light signal indications is faulty, then this might point to the reason why I am getting the discrepant Security indications that I listed above.

I'll know better tomorrow. I'm into it deep now and I won't be satisfied until I hunt this problem down and kill it - once and for all. If nothing else - and most importantly - this technical exploration may help others diagnose and fix similar problems as to what I am experiencing. Certainly, it's been one helluva learning experience for me, as I have gone through and educated myself on almost every system in my Vette. That's always a good thing.

red86man

Had an "ooops" - please refer to my post below.

Aggravated4life

Im not sure if im following everything...so let me try and help what I can think of.

Ok,when you open the doors to the car,the security light will Flash saying its NOT ARMED.SO when you turn the key,its gonna appear to flash because your not getting the car to run.

Try this..sit in your car with the door open...security light is blinking...push the power lock to lock the doors while watching the security light.DOES the light now freeze?
If so,the system is arming itself.Get out of the car and shut the door.

Now use your key to unlock the door then open it.It should open with no horn going off.If it does,turn the key back and forth and disarm the alarm.

If you use the power lock to arm the system and it keeps flashing on the dash,then its not arming the alarm.

Now,back to basics,when you crank the engine over,have you had someone to check for spark?

Did you unplug a spark plug wire and ground a plug tester somewhere and check for spark?If not,DO THAT FIRST and check every plug wire for spark.

If they all spark,then do the Fuel pressure test and be sure youre getting gas into the engine.

Like JFB said,the car will NOT turn over if the vats is armed and not letting you.It wont do anything,not even crank.

I did not go back and read everything but check the basics first.When an engine cranks,its good...then you need to be sure spark and fuel is happening.

staugur

It's an overcomplicated system that's caused so many problems and also a lot of controversy on these forums.After years of intermittent grief(mine I traced to the starter enable relay) i ripped the whole system out.I did however reroute a couple of the wires to the cigarette lighter.If the first thing a prospective thief does is light a ciggie after he's jumped the system it might fire up but I doubt it.

red86man

Since I haven't found a lot of detailed information on the VATS set-up in my '86 coupe, I'm going to try to document it myself while I'm in the middle of it. Perhaps, the info will prove to be of help to myself and others, as well.

Let start with the gray module behind the "breadbox." My Haynes manual referes to it as the Theft Deterrent Decoder Module (TDDM). I traced out the wiring diagram in the manual have referenced the pin-outs below with some of my readings.

The TDDM in my car has a single edge connector with 6 pin-outs, which are as follows from top to bottom:
- Pin L (black) - Ground
- Pin P (purple) - 30 Hz FI enable signal to ECM. Measured swings of 2.4 to 2.9 VDC with my DMM. Measured .5V 30 Hz square wave with O-scope.
- Pin S (pink/black) - +12 VDC. Diagram shows it coming from 10A Gauges fuse.
- Pin T (yellow) - from resistor pellet / ignition connector
- Pin U (brown) - from resistor pellet / ignition connector
- Pin V (green) - to starter enable relay

I listed my readings for the TDDM in a previous post.

The second module of the VATS is blue, has a 2 row connector with a total of 7 pins, 4 in the top row and 3 on the bottom row. The blue module is referenced as the Theft Deterrent Control Module (TDCM).

The wiring diagram in my manual referencing this module doesn't not represent the actually set-up of my TDCM. After some wire diagram tracing, here's a few connections that I gather from the manual (pin-out references are by row and pins from top to bottom):
-Top Row, Pin 1 - Pin N (pink/ black) +12 VDC from VATS 10A fuse.
- Top Row, Pin 2 - Pin B (yellow) - supposedly coming from LH Door harness, Pin H (I believe it's actually going to an indicator light circuit in the DIC)
- Top Row, Pin 3 - Pin A (black) - Ground
- Top Row, Pin 4 - Pin C (black) - going to RR Body wiring, pin R(?)
- Bottom Row, Pin 1 (green) - going to Center Cluster, pin 5(?). Measured 10.3 and 9.1 VDC from On to Crank.
- Bottom Row, Pin 2 (pink/white) - Pin / wire not referenced - measured 12.4 and 10.2 VDC from On to Crank.
- Bottom Row, Pin 3 (brown) - Pin / wire not referenced. Measured -11.5 mv to 41.5 mv from On to Crank. Readings here are suspect - will physically trace wire.

red86man

Guys, thanks for the posts. I'm going to go back through all the basics tomorrow, while I continue to wire trace and validate the mysterious TDCM module. Got to hit the hay now.

AGENT 86

Sounds like your using the Haynes manual. Try this instead.
http://members.shaw.ca/dankai/Vats%20Electrical.pdf
Should help clear some of the fog.

red86man

Great stuff, AGENT 86 - thank you!

red86man

AGENT 86's excellent reference link allowed me to get a better understanding of the 2 module system for the VATS / TDM. Thanks again.

While the pin-outs on the diagram do not exactly represent all the pins and associated wire colors on my blue TDCM, it was close enough for me to understand and track down almost all the wires. As I understand it now, the blue Theft Deterrent Control Module is basically just a built-in car alarm system that serves as the first line of defense against theft.

Apparently, the TDCM cannot cause a no start / no run condition with the vehicle. So, I can nix the TDCM as cause of the current crank but no start problem.

Back to the gray Theft Deterrent Decoder Module, which can and will cause this condition. The documentation on the website tells me that I should be reading battery voltage (>12 VDC) on the dark green wire associated to pin V. Since I only read about .8 to .9 VDC on the last probing, I decided to pull the Starter Enable Relay and see what was up.

To my surprise, the contacts on both the connector and the relay were highly gunked with a thick black grease. Very old, very oxidized dielectric grease I must assume. This could very well be the source of the voltage drop / bad reading on pin V - and perhaps the source of the problem.

Obviously, the starter enable relay was energizing and allow the starter to crank the engine, but may have been dropping excessive voltage on the system. Perhaps enough of a voltage drop across the system to not allow the car to start.

I'm going to the store to pick up a new starter enable relay, clean up the connector and see if this baby starts. Cross fingers.

bill83c4

hoping to hear that solved the problem. waiting here in anticipating of hearing. can't imagine all that time without my vette, and all the troubleshooting you've been through. good luck