My '92 6 speed was experiencing a similar no start when hot symptom, even though the car would crank fine when not starting. It would also flash "sys" and "Security" while driving.
I took it to a local "Corvette Expert/dealer" who spent a boat load of money replacing everything under the sun with no luck. I pulled the car from them and sent it to County Corvette in West Chester PA. They diagnosed the problem in about 5 or 6 hours as a bad CCM and sent it out for rebuild.
Two weeks later, it came back, went in, and I have not had a bit of trouble since.
The only physical symptom at the time was that the CCM would get very hot after the car ran for a bit. Putting a fan or bag of ice on the hot CCM to cool it allowed for an immediate start.
Try taking a frozen bag of corn with you next time and try it. Doesn't cost much, unlike my "expert corvette mechanic"!!

 

Hi all,
Sorry bout the absence. Started a new job amongst other things, anyway...

YES,
But it was lengthy overall and I may write a new thread to shorten all this up.
The occasional not wanting to start got more frequent and ultimately became untrustworthy to use the car. My 92 Vette essentially did not provide me ANY fun for MOST of the summer because I had other stuff on my plate.

But I can lay down the basics....

Recap:

The PROBLEM as you know, runs great, even when the system flashing and service ASR light comes on, but IF YOU SHUT IT OFF, usually doesn't start. Turns over, so it is NOT the VATS (pellet key reading) as this disables the starter. So it is FEDS, this is where the CCM and the ECM code back and forth ULTIMATELY enables the fuel injectors ONLY. Fuel pump can be working, starter working, ignition working, everything, but no injector pulse is FEDS not happy.
What the Factory Service Manual says is a type of handshake, yet I read other posts of a square wave frequency sent directly to the ECM imitates this supposed decoded, recoded, deciphered, comes up with an appropriate response little conversation, but the handshake part IS important or the injectors will NOT be enabled.

OK I'm off topic.. Many things can inhibit the handshake, I will stick to what I was dealing with. Serial Data. Circuit 800, tan wires (there ARE other tan wires in the harnesses) that communicate to 3 or 4 modules on the 92, 93 Corvette.
Central Control Module CCM, Engine Control Module ECM, Electronic Brake Traction Control Module EBTCM, and on Vettes that have the Electronic Climate Control (C68 AC Programmer) ARE ALL COMPUTERS SHARING THIS PARTY LINE Circuit 800 Serial Data. A leg also goes to the ALDL.

You can see on the prior posts all the interrogations performed, and the high resistance on some of the circuit 800 legs caused me to find and RE-TERMINTE the major S222 junction that is really in a despicable location, to take the resistance possibility of further problems out of the serial data wiring. Also fixed and repaired bunch of previous wire hacking that had occurred during its prior life to me.


UpDate Findings:

Ultimately, as the FSM states, Serial Data when a leg goes open to a active computer, it simply goes off line and the other computers can still talk enough usually to still run, but when a leg shorts to power or ground, it destroys ALL the conversations on the Circuit 800 Serial Lines scores of codes, failures, and usually a no start occurs.

In this 92-93 Vette computer configuration, the CCM is the MASTER. the other 2 (or 3 if you have electronic HVAC) are SLAVES. The CCM is the "house speaker" when you scan tool the car AND if you use the screen dash button onboard diagnostics. (The others can be entered individually YES but, no matter)

So, I needed to know why the CCM had serial loss codes for itself, ERR for the ECM, and loss communication to EBTCM. The FEDS fuel handshake is not occuring (when it doesn't want to start) and shows as ERR through the CCM scan, EBTCM HAD a CODE set in the CCM, Looks like the EBTCM is communicating and the ECM is at fault.

When jumping the ALDL from ground to the ECM pin it would simply flash 12, NO CODES.

"Hooked on Vettes"
Stated early on this thread to simply disconnect the EBTCM to isolate it from the serial lines. HE WAS RIGHT. Ultimately my EBTCM WAS BAD

With The EBTCM unhooked, now the CCM says ERR for both ECM and EBTCM but at least starts. Ultimately I found another EBTCM and it IS ALL WORKING PERFECT NOW.

Except, after I was enjoying that for a couple weeks, it WOULD NOT START again...AURGH!!!
What the.. so NO codes, I tried "clear flood" (WOT) and while depressing the peddle it fired off and died??? So I discovered something I have read about on other posts.. "If I pump the throttle it will run but when I stop it dies" these posts where asking what this was, I was having a hard time seeing what that would even do on a fuel injection system, yet here, I experienced this.

Found what it was doing to be quite interesting. When you depress the throttle the fuel injectors activate, (kinda like shooting blanks) but somehow the vacuum in the engine during let up to the gas peddle was sucking on the injectors just enough to get minimal fuel flow WITHOUT A FUEL PUMP.


After experiencing this for a few minutes I opened the hood and put a jumper to a pigtail (I installed while servicing all the wires at the ECM) to the fuel pump relay feed wire and found no fuel pressure. Literally I went back and medium gently BANGED on the back of the car area and I heard the pump kick on. Remember I had fuel pump jumped, car started right up, but this no start thing is getting old.

Most GMs have a fuel pump jumper ON THEM from the factory, I couldn't find one on this car so I put one on it. Glad I did.

The only other finding I had was during early wiggle tests I found the Coil driver wire when wiggled right at the ECM connector would KILL the Car, wasn't a symptom (dieing) but somehow seemed like it might become one so I re-terminated that wire/contact and retested OK now.

Then, after I put in the new fuel pump (AND RELAY) I went to go test drive it and noticed a DIM headlight, so before I could actually test drive it (was dark) I had to back DOWN to the Garage and change the light. Geeze, really. YES, if your headlight burns out a warning inside is the blue hi-beam light on and the remaining working filament in that light is on resisted voltage. Looks like you have a bad ground but GM started this stuff early on the Vettes and Cadillacs.

So, am I sorry I took all the wiring apart and re-terminated the dreaded splice S222 to the serial lines, not really because on mine I found some out of range resistances, its worth it to NOT have them in the circuit now.

So like "Hooked on Vettes" said, if you have service ASR flashing, starter works, fuel pressure, and spark, but no start, disconnect the EBTCM. If it starts, the EBTCM is BAD. (Also add a fuel pump jumper for later

OK that's it for now, My little electronic gremlin is happy and running good so... We'll see.

Cheers:

 

Okay so you're saying that the next time my car won't start I should try to disconnect the EBTCM and if it does start then that means that my EBTCM is bad?

By the way thank you very much for the follow up your saving me a hell of a lot of headache

 

I am going to try and disconnt the ebtcm as my'93 is having problems.

 

My Helms is over at my remote garage, so please help me out. ECM located top passenger side. EBTCM is up on the middle drivers side above the exhaust and by the left front wheel and in front of the brake booster.

Where is the CCM?

 

pkincy

The CCM is located behind the radio. It is an unpleasant location to say the least. Basically it is installed and removed from the drivers side just above the gas peddle. You have to pull the underside of the drivers dash out, then remove the console side panel, then remove the big silver bracket plate on the drivers side behind the radio (8 or 10? bolts, 2 nuts), the CCM lives there. the connectors are actually coming out bottom of the CCM, (smashed against the carpet above the transmission tunnel) and you want to treat them as gingerly as you consciously can as you realize the CCM does NOT come out with the 2 separate connectors still attached. Yes you have to reach in with a long flatblade AND your other hand holding both the CCM and assisting the pull while the other hand gets to latch loose with the long flatblade. Once its out you'll say it was easy.
FYI might want measure resistances between the 2 terminals in the CCM connector for the circuit 800 serial data to the tan circuit 800 on the EBTCM connector. If you have low or little resistance between them, then you are OK. But if you do have more than 2 OHMS (especially when cold) It it advised you re-crimp the splice S222 which is even worse located ABOVE where the EBTCM lives Inside that giant 2" harness covered with split conduit plastic and then wraps of GOOEY tape where the sun don't shine. If you have high resistance tip to tip on any of the destinations IT WILL effectively fail communication between the modules.
You will also need a good chiropractor. LOL

 

1stVetteFinally

Um yea pretty much

So if all your symptoms match,

When driving and the service ASR and the system flashes occur, there is no effect except the ASR does not work.

When you go to Start it, and there are "NO" ASR or SYSTEM flashing before or during using the starter (even if they WHERE during last engine run) It will start right up.

But when you go to start it and their "IS" ASR or SYSTEM flashing before or during using the starter (even if they where NOT during last engine run) It will NOT start.

This condition did not exist to the car and then, once or twice to nearly every time just within a short period. this rendered the car basically unreliable for transportation.

Above Recapped for definition clarity.

If you have checked resistance between the tan circuit 800 wire between EBTCM connector and the ALDL and it is UNDER 1 OHM.... Then what is failing???

At first I thought it was the ECM. When using the scan tool or the Onboard dash diagnostics the CCM is the spokesperson for all the modules.

When the lights aren't flashing
It reported a serial data code in the CCM history (and an LED code about the radio lighting)
--- for the ECM meaning - no codes
and history serial data code in the EBTCM

When the lights are flashing and will NOT start
It reported a serial data code in the CCM history AND CURRENT
ERR for the ECM
and serial data loss codes to the EBTCM

So when you turn on the key, there is actual a serial data handshake of state of health and readiness to/between ALL of the modules, not just the ECM and the CCM. While the fault was current, the ECM being reported as ERR and the EBTCM reporting a serial code, it appeared the EBTCM was successfully reporting a problem and the ECM was off line or illegible.

What really happened is - During the initial handshake cycle the EBTCM either miscommunicated, could not respond, or internally shorted to power or ground caused the mutual agreement to all the modules to fail. THE CCM captured this and stored it and ignored the ECM. Basically the CCM is powerful enough to at least store the code that brought the system down - EBTCM serial data.

So

If you unplug the EBTCM and the car still does not start, I would be looking at the ECM or the CCM, (don't think the C68 electronic HVAC can cause a no start) rescan for new configuration of codes.
Also if you jump ALDL ground to ECM diagnostic slot and flashes 12 ( * - **) which indicates NO CODES, then it is likely your CCM.

If you unplug the EBTCM and the Vette STARTS, then its the EBTCM bringing down the FEDS fuel enable.

 

Ok, if I was correct in knowing what the EBTCM was (see 1st pic), I disconnected it and the car still would not start. I'm starting to think my problem is in the ECM. My car is showing all the same symptoms as your's, but I do have one question though.

Did you ever try the quick fix of icing down the ECM to get the car to start? I read about this little trick here on the forums. When the car doesn't start, if you chill the ECM, the car will start everytime. I have done this multiple times, and anywhere between 5 seconds to 5 minutes, the car starts.

This is why I'm thinking my ECM is to blame, but any advise from you, or any forums members with experience with this would be greatly appreciated.







Yes, I know the engine is dirty, I'll worry about that after I get all the little gremlins living in the car taken care of.

 

That is not the EBCM, it is the cable slacker/tensioner for the traction control system. The EBCM is the control module that is located on the right side wall, in the storage cubby behind the driver's seat.



It is HIGHLY unlikely that putting an ice bag on your ECM could have made a difference in 5 seconds. The components that are inside the ECM that could be affected by heat, are just what I said; inside. That black box that houses the ECM is just a tin shell around the thing, to provide protection and a somewhat finished look. An ice bag would cool that tin some in seconds, but the air space between it and the working components inside would mean that "in seconds", they won't change temp at all.

ECM's don't fail often. I'd continue diagnostics before spending money on an ECM. For "temp testing", could you pull the ECM out of it's mount, pull the harness a bit and lay it out on the windshield (where it won't get hot) and drive it? Conversely, you could remove the ECM, put it in your oven at 250*F for ~15 minutes to ensure all components w/in are hot...then plug it in to the cold car and see if the car starts and runs normally.

In fact, you should probably start at step 1, and describe your symptoms more clearly.

 

Thank you for the clarification on the location of the EBTCM. Now that I know exactly where it is at, next time the car won't start, I'll try disconnecting it.

As for the ice pack working in 5 secs, I'm only stating what I have observed. Normally it takes 3-4 minutes, but twice the car has started within seconds of placing the ice pack on the ECM. I may not be very experienced with working on Vettes, trust me when I say I have a pretty good understanding of what heat can do to electronics (I am a computer enthusiasts with several very high-end highlyoverclocked computers that I built/assembled myself).

Ok, you asked, and here it is. This is exactly what my Vette is doing.

Get in, turn ignition on, all lights on system status display light up. Wait for the system to cycle and lights to go out except for check engine and air bag lights to go out. If "service ASR"light does not turn off, the car will not start.

It is sometimes possible to get the engine to start and run extremely rough by pumping the gas pedal when the "service ASR" is lit, but it stop running once the pumping of the gas pedal is stopped.

If the light does go out with the other lights, the car will start and run great until you turn it off.

While driving the car, occasionally the security light in the gauge cluster will blink in unison with the system error where the fuel milage is displayed flashing, and the "service ASR" light will illuminate. The majority of the time, if this is happening, if the car is shut down, it will not restart.

The ECM does get very hot to the touch. Not hot enough to burn you, but it is uncomfortable to hold your hand on it.

 

Ok if you have the pumping the gas thing going on you have a failing fuel pump and or fuel pump relay.

 

Would/could that cause the "service ASR" light and other symptoms I'm experiencing? And if so, how does the icing of the ECM allow it to start?

Not saying this is not what is happening, I've seen stranger. I've seen a ground out power wire for power seats totally disable a Mercury Sable before.

 

No fuel pump won't cause the codes and stuff. But no idea is a dumb idea while diagnosing for a reason. Inversely if you are getting the engine to flutterly run by pumping the gas then it might be your FEDS is allowing the fuel injectors to pulse.
Simple test the Schrader valve is under your R/H plastic cover at the rear of the fuel injector rail. Without damaging the Schrader press in the center and verify that fuel actually squirts out under pressure while cranking or during the first 3 seconds of turning the key on.
If you have fuel pressure then continue with the original path of diagnoses.

 

Not if the no start occurs w/a "Service ASR" I'm thinking.

I understand that is what you observed. I was trying to let you know, that the componentry inside the black box didn't cool much in 5 seconds, so that you didn't replace your ECM for no reason. I was trying to point out that what you saw was more likely likely, coincidence.



It sounds like you have an issue w/the EBCM, which controls the ASR that needs to be diagnosed. When you have an issue that prevents injectors from firing, you can get it to run by pumping the gas pedal wildly -I think it runs on the "accelerator pump shot" from the TPS, and that is the only way that the injectors fire under those circumstances. Anyway, you need to draw codes from the CCM, shown through your DIC (speedometer), and then start the diagnostic process to determine why you're getting an ASR light, and hopefully, a no start.

You can read CCM DTC's by grounding pin G in the ALDL, then turning the key to the on position, the codes will display in the speedometer.



Codes 51, 52, 53 and 54 indicate problems with VATS or FEDS.

.

 

Thank you for the replies. I'll be looking into this today with my mechanic friend

 

OK so here is some pictures to assist locating devices.





This is where the Electronic Brake Traction Control Module lives. a trap door directly behind the drivers seat. It does not lift easily, and when you do it has a black insulation mat that hides all this, you have to lift out the mat to see this.





This is the connector you need to unplug from the EBTCM to see if the car starts. The circled pin location is the serial data line recomended to check resistance between here and the tan serial data wire to the ALDL. this is not a complete test of the serial data lines but if it fails here, then is a sign of the need to actually check the rest of the serial data pins at the other modules.<br/>You want to see low resistance, good continuity, under 2 OHM (MAX).

 

And the CCM which not sure how anyone knows is getting hot unless this is all apart during testing, since it is by the heater, usually gets pretty hot alright.





So WAY DOWN THERE above the GAS PEDDLE. this is where the CCM lives, this is the plate bracket needed to remove to get it out.





So here you see the CCM is removed, and that giant 2" harness opened up and THE tan serial data circuit 800 Splice S222

 

Thank you so much for the help 36volt and Tom400CFI. You guys have giving me a lot of information on my problem that will help out tremendously if fixing my problem.

Question, I have a friend that is a much better mechanic than my roommate and actually has an idea about what is going on with my car. The problem is he lives down around Charlotte NC (6 hour trip one way). I have plans to go down there either next weekend or the weekend after that to work on the car. If I disconnect the EBTCM and the car starts, would it hurt anything to leave to EBTCM disconnected and drive the car like that until I can go to my friend's house down around Charlotte?

 

Well I tried disconnecting the EBTCM, the service ASR light went out,the service ABS light stayed on, and the car would not start.

Something that is dumbfounding me. How is icing the ECM allowing the car to start if the problem is with the EBTCM?

 

I may have not been following this thread closely enough, but are we working with "flashing lights" or have we put a scanner on the ALDL to get any stored or history codes?

That can be done by driving by your local AutoParts store and they will pull the codes for you at no cost generally.