Den14

I have had so many different codes that I don't have any idea why this car won't start. I think that it may be the ECM with all the weird codes thrown. I thouhgt it was a consistent 41 and now it shows nothing but a c-12. Waiting on the opti harness and I will see if that is it. Can I get some help on the fuses and relays under the passenger dash and behind the battery. What can I look for and what is common?

bogus

could be a bad fuel pump or a bad ignition module.

don hall

Scroll down to RECOVERING TROUBLE CODES. You will read about
C12 as a starting point, not a trouble code.

http://www.corvettephotographs.com/c4vettes/ecm.htm

Cliff Harris

C12 means no reference pulses from the distributor. You get that when the engine is not running. Normal.

Den14

If I need a new ECM or rebuild... is it going to be better to send mine in or find a donor?

Blue95C4

My 95 shows a C12 when doing a diagnostic check.

I was looking for a reason the SERVICE ASR light and Check Engine light was on and I get a C12 and a C22 and H22 and H64. No C12 code after it starts.


Don

Den14

I have had a number of different codes and it just won't start. I am leaning toward the ECM at this point. If I could get it to start I would have a better idea. If anyone knows of a stock ECM for my car I would be interested. Thanks Forum!

Tom400CFI

WHen it won't start, what is missing? SPARK or FUEL?

Den14

Fuel pump is new and filter is new as well. It seems there is a very small amount of spark. It tries to start but won't catch.

1stVetteFinally

I recently had my ECM rebuilt by S.I.A. Electronics ( http://www.siaelec.com/index.aspx ). Cost about $200 total with shipping. No issues with the ECM since getting it back. Not saying this is your problem, it may be, it may not be. But I am happy with the job they did with my '92 LT1 ECM.

EDIT: BTW, the engine in the base model '92 Vette is a LT1, not a LT-1. The LT-1 was an optional 370hp 350cid that was produced for the 1970-72 Vettes.

c4cruiser

What is the fuel pressure at the injector rail? Go to AutoZone and rent (no charge) a fuel pressure gauge. With it installed, turn the ingition to ON and see what the pressure is. Then turn the key off and watch the fuel pressure. what do you see as soon as the key is turned off and what is the pressure after a couple minutes?

Also, why do you think a new or reman ECM is needed?

Tom400CFI

But you didn't answer the question. I don't care how new the pump is. DOES IT HAVE FUEL?

You can confirm spark in a compressed mixture by grounding your spark tester to a spark plug that is screwed into a cylinder. If you get spark at your tester, then you know for sure that you have spark in the cylinder too. The issue then, wouldn't be spark.


IDK why you're all about the ECM when you haven't even confirmed the basics here.

Den14

Because I just don't know... Can you break down the procedure to check the spark for me? If I don't know then maybe I can learn.

Den14

Is there a relay or fuse that I may be missing in the greater scheme?

Tom400CFI

I sure can....
^The gauge will thread on to a schrader valve on the fuel rail.

Den14

Got a pressure gauge and I am not getting pressure at the rails. Checked the fuses at the panel and under the passenger dash and they are good. The pump is running when I turn the ignition on. No change in pressure to the rails. All the fuses are good. Where to go from here? I can't find any leaks. The filter was changed less than a year ago. No codes after trying to start it. Are there any in line fuses to check or the relays and fuses behind the battery? Can I get a spark tester at Advance auto? Seems to be fuel related since I have no pressure at the rails. Stumped at the moment.

Tom400CFI

EXCELLENT! You ran a good test, and got good results. Well done! Much better than WAG'ing and throwing parts at it, right?


If the pump is running at key on and you've got no pressure at the rails, that is your problem; "no fuel". There are only two likely causes for this;
1. a ruptured rubber fuel hose in your tank (connecting the pump to the sending unit hard-piping)
2. A bad fuel pressure regulator.


How to test? Take a tool such as vise grips or a clamp of some type, clamp off the fuel return line where it's rubber. Run your test again w/the gauge. If you have no pressure still, it's in the tank. If you have pressure, it's your regulator. OR, simply pull the fuel pump/sending unit assy and look at it, as that only takes maybe 10 minutes to do.

Post back, and keep going.

Den14

Thanks for the great advice! I did eliminate the pulsator and it did not change the no start. Checked the relays per the FSM and they all seem good. I happen to have another FPR on the shelf and I will swap it out. If a rubber tube was ruptured would it be inside the tank or on the filler neck assembly that the pump is attached to? Could it be a plugged line coming from the tank to the lines going to the rails? Thanks again for the insights and I really appreciate it.

Tom400CFI

If you are SURE, and I mean SURE, that the pump is running when you KEY ON (for ~2 seconds), then there is no need to look at fuses, relays, etc. IF the pump is running, it's getting power, the electrical is good. If you're sure.


If the hose that I'm thinking about had ruptured, it would be here;




...and a close up of that hose, in this pic here (top of pump is just visible on the left in this pic)...






Incredibly unlikely. The pump picks up fuel through a sock (filter). If the sock allowed something through that were large enough to plug a 3/8" line, then the pump itself would grind it up. So, not likely at all.

Den14

I now have 40lbs at prime and it is holding at 35lbs after 1 hour. Per the FSM protocol, it is saying that the ECM is faulty. When I ran the spark test, it seemed rather weak. I am only going on what I am testing and reading, but it seems like there is a lack off real spark to get the motor going. The coil is new and the opti and harness is new. I will test further into the ECM tomorrow. Any ideas between now and then are appreciated.