Corvette neophyte here in need of some help! I just bought a used 1992 Corvette with the LT-1 engine, 6 speed manual. It runs good with no hesitation, misses, etc, but has been showing an occasional problem.
When I am driving down the road, occasionally, the dash will show "sys" and the Security light will flash on and off. The car does not always do this, but it does happen with some regularity.
Also, sometimes, when I have been driving it, and I park it for 10 or 20 minutes, when I try to restart it, the engine will turn over but will not start. Usually, within 5 minutes or so, the engine will finally start and everything will be fine. The engine will then run perfectly.
Anyone able to suggest what might be wrong? Is it the computer, Optifire distributor, or what? Additionally, any thoughts as to what it might cost to have it fixed? I am guessing a dealer would be the best place to go? I am in Chester County, PA. I hope I didn't just buy an expensive fix! Thanks!

 

Does anyone have any thoughts on this? I'm afraid to drive the car anywhere for fear it may leave me stranded. Are the Sys and security error messages related to the occasional refusal to start or seperate problems?

 

Start with checking battery them make sure it is charging. If you search under SYS you will get tons of info. My 93 has been flashing SYS on and off since i got it and hasnt left me...yet.

 

To pull the code use a piece of wire. Jump together pins A to pin G on the diagnostic connector located above the drivers right knee.

Turn the ignition On. Don't start the car. The fans will come on.

Look at the Dash Cluster speedometer LCD

Module 1 is the CCM
Module 4 is the ECM
Module 9 is ABS/ASR

Pull the codes and post what they are.

 

Thanks for the reply! Unfortunately, I'm a little too big and stiff to contort myself under the dash to get to the plug. I can see it but there is no slack in the cable, and I don't want to short the wrong pins and cause any damage doing it by feel. I will draft one of the kids to do it for me.
Meanwhile, can I get into the ECM to access the circuit boards or is it sealed shut? Although I'm not much of a mechanic, I do know my way around circuit boards and am confident I can locate and fix any cold solder issues. Also, where is the ECM located, and is it easy to remove to work on on my bench? Thanks again!!

 

Pull the codes first. Then clear any codes by disconnecting the negative battery terminal.

The ECM is the black box located above the battery and has 4 plugs going to it.

The ECM's that i've opened up had a protective coating on the circuit board.

The only removable thing on a 92-93 ECM is the Cal Pak. It contains the
circuitry to keep the engine running if there is a partial ECM failure and the Eprom
that contains the engine calibration program.

You could reseat the ECM connectors and see if that cures the problem.
Also you could start the engine and bang on the ECM and see if you can reproduce the problem.

If it is the ECM some people have sent 92-93 intermittent ECM's out for repair and they
came back not repaired.

 

Finally got #1 son to crawl under there for me! The error codes displayed were:
H41
H54
H62
H72
So, what does all that mean, and what can I do to track down the interrmittant security & sys lights flashing as well as the occasional engine rev but no start when warm. Again, thanks for the help!!

PS Two other things which may affect all this. The previous owner installed a Kenwood stereo in the car. Also, there is some kind of short throw shifter in there. The shifter has a definite click feel when going from gear to gear and seems somewhat heavily spring loaded to help guide the shifter. I asked the mechanic who inspected the car prior to my purchasing it and he said it was some kind of short throw shifter, but he didn't know anything else about it except it seems to work fine.

 

The CCM communicates with the ECM, Electronic Brake and Traction Control Moduleand the HVAC Programmer via a serial bus.

DTC 41 indicates the CCM has lost communication with the ECM.
This DTC points to the ECM because when you pulled the codes Module 9 (EBTC Module) showed no errors.

DTC 54 Fuel Enable Failure.
When you insert the ignition key in the key cylinder and turn the ignition On the CCM reads the resistance of the key pellet and compares it to what the CCM was programmed for. If the resistance is correct, the CCM enables the starter relay and sends a password to the ECM. The ECM responds and the CCM sends a signal to the ECM to allow the injectors to pulse.

If the key pellet resistance is incorrect the CCM will not ground the starter enable relay or allow pulsing of the injectors. A three minute time out period will begin. It should also set a DTC code of an invalid key pellet resistance value was detected. If you try to start the car again and don't wait for the time out period to expire, the 3 minute time out period begins again.

An indication the key pellet is not read properly is the Security light stays On. Normal operation is when you insert the key and turn the ignition On, the Security light should go on then Off.

DTC 62 is a DTC you should never see unless you are replacing the CCM.

This is a error code when a new or remanufactured CCM is being installed. The first time you insert a key and turn the ignition On that key pellet resistance value is programmed into the CCM. This is an indication the prior owner replaced the CCM.

DTC 72 Indicates a problem when the CCM does a diagnostic test on the LCD dimming circuit. This is caused by the aftermarket radio. The fix is to install two 1k pull up resistors.

Because you can crank the engine when you have the no start problem but the engine doesn't start indicates the reading of the key pellet isn't the problem. The problem is the injectors are not being pulsed by the ECM because the ECM never receives the signal to allow the pulsing of the injectors from the CCM because the ECM is off line.

Here's link for the cure for DTC 72
http://www.corvetteforum.net/c4/dave8476/index4.shtml



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Thanks for the detailed response! So, I am assuming the pull up resistor issue can be safely ignored, since I am not crazy about trying to pull the radio out to install the new resistors and it doesn't seem to cause any real problems?
What do I do about the other stuff? Can the codes be ignored or what is mandatory to address? Especially, how do I fix the fuel injector issue since that's the one that might leave me stranded in some parking lot if/when the Vette decides not to start.
Are all these codes indicating a cold solder joint, defective module which needs to be replaced, or what?? Sorry for the newbie questions but I'm trying to learn as fast as I can. Thanks!

 

If it were mine I'd purchase a used computer and hold on to the original one. Your other choice is to shop around and have some one repair yours.

The going price for a used one with no core charge is around $350. Not cheap because they are hard to find.

GM 16159278 used on 92-93 Corvettes and some Camaro's.

You could try your local Autozone . They use Cardone a large re-manufacturer of auto parts in CA for the repair. $170.00.

Read the features and benefits paragraph. They claim 100% resolder of critical components.
They also offer a 1 year warranty. The smaller shops offer 90 days.

http://www.autozone.com/autozone/par...9989_461347_0_



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Is the computer that is giving me the problem the black box which is above the battery with four plugs going into it which you mentioned a few posts back? Is that also referred to as the ECM? If so, I might try to fix it myself. Do you think that is possible? I work on circuit boards frequently since I restore and sell pinball machines and other gameroom equipment as a hobby. Reflowing cold solder joints on circuit boards is a big part of fixing a lot of pinball machine problems. I do quite a bit of that.
Does the computer control the security aspects of the car? Do you think the security system is shutting off the fuel injectors leading to an initial "vroom" followed by a quick engine shut off?

 

Also, on the link you provided for the rebuilt computer, it says "Additional relearns (theft, crankshaft, idle, etc) may be required." WTH does that mean? What would I have to do?

 

The computer/ECM is the Black box above the battery.
If you replace the ECM/computer when you disconnect the battery it wipes out the information stored in some computer memory chips. The temporary information stored in the memory by the computer is used to fine tuning engine parameters. Such as idle quality and fuel mixture.

When you re-connect the battery the computer will re-learn the values. You don't have to do anything but drive the car.

Note: When you swap out a computer you need to remove the small circuit board behind a small metal plate on the bottom of the ECM and transfer it to the replacement computer. This is the module that contains the engine calibration firmware.

If you have the time go ahead and examine the ECM circuit board and see if you see anything wrong.

I have a feeling the prior owner knew about this problem and didn't want to spend money in diagnosing and fixing it.

As for the shifter. I believe there were four aftermarket shifters for the ZF6 speed.

http://www.whiteracingproducts.com offered a modified factory shifter. I don't see it on their web-site anymore.
http://www.zfdoc.com also offers a modified stock shifter.
Hurst offered one that I'm guessing is the shifter that makes a click sound.
B&M offered one that I believe had the shortest throw and is very notchy.

Here's two links about the Hurst, B&M and ZF docs shifter.

http://www.corvetteactioncenter.com/...n-shifter.html

http://www.zfdoc.com/S6-40ShifterOptions.htm




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I pulled the ECM off its mount today, but had some trouble removing the connector plugs. One on the end came out with a minimum of fighting but the other three are much tighter. Is there a special technique or tool to use. Looks like after you press in the two release buttons, the plugs should slide straight off, but some are really tight.

Once on my bench, do you recall how to get into the black box? Looks like there are various screws and/or bolts which may serve to keep it together. Which ones are the ctritical ones holding it together?
Does the box open into two halves, or do the boards slide out the end?

I want to be really careful taking this thing apart since if I screw it up, the car will need to be towed out of my garage, or wait for a replacement ECM.

I don't suppose this security system could just be by-passed with a jumper somewhere so that the ECM does not shut off the fuel when the engine gets hot?

 

The connectors can be very tight. I use one hand to pinch the two release tabs and with the other hand grab all the wires at the same time and carefully wiggle the connector off.

There's a parameter in the Computer Eprom program called Data Stream Fuel Enable that can be set on or off. I believe that could fix the no start problem. This would be a work around and does not fix the actually problem. You would need to pay someone to reprogram the Eprom.
The going rate is around $70.00.

Here's the description for a code 54 read it carefully and you can decide where the problem is. Using the flow chart it says to turn the ignition On. Verify the Service Engine Soon indicator is On. This indicates the ECM is functioning to some extent. No Service Engine Soon light would indicate the bulb is burnt out or the ECM has failed self test.

You also have a DTC 41 which is a communication problem with the ECM which is not covered in the flow chart..





As for removing the ECM circuit board, remove all the screws on the metal case and the board will slide out. Here's a picture of a 90-91 ECM. A lot of the components are surface mount.

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