Hey everyone, I'm experiencing an issue with my C4 Corvette, and I need help! Here is the pertinent information!



Car Information:

• Year: 1993
  
• Model: Base LT1 Engine - (Stock)
  
• Mileage: 44,000 ~
  

The Problem:

The car has long cranks and on very rare occurrences, won't start when the engine is warm from a cruise.

So let's say I go on a drive and go into a store - when I come back out to start the car, it acts like it won't want to start.

That said, it cold starts fantastic.


- I should also note my engine temperature gauge doesn't work, but I have no reason to believe it's overheating.

What I've Tried So Far / My Findings:

• So far I've had a professional mechanic replace the optispark with a brand new one.
  
• I replaced the ECM (with a USED ONE) I thought maybe the ECM was heating up too much causing issues.
  
• I found out that the fuel injector pulse was not there to fire up when the engine was hot. I did a current waveform reading on all injectors and the waveform showed no sign of shorting out. I did a OHM on each injector and they all read in the 12's. But again, when the engine was hot, the fuel injector pulse wasn't there, which made me believe the ECM was faulty.
  

Conclusion:

I'm not 100% sure to go from here, I would love advise from people who have experienced something similar!

 

Codes. Injector pulse comes from ECM . if it has spark Opti is sending signal.

 

Yes - any stored codes? That would be the biggest help.

very strange... I see you already replaced the ECM...did anything change at all (Less frequent? More frequent?)? What other symptoms if any have you had? Service ASR or security light blinking or SYS messages while engine running once hot?

Used ECM may have same problems (or PROM???)

Are you 100% sure you have spark? Are you sure you have fuel pressure but no pulse from the injectors?

if you have fuel pressure and spark but FI not pulsing that could point at a handshake issue between ECM and CCM...

check grounds, clean batt terminals, make sure batt in good shape etc...

 

The 'NO CRANK' when hot is 'SILENT" (nothing when key is turned to CRANK) or it's a 'CLICK' when turned to 'CRANK'?

 

Sounds like a bad battery! Alternator might not be charging battery if it is new. Do you have it on a battery charger when you park it?

 

Pull codes like others have suggested. Hot start issues can be caused by a failing ICM. If you have code 41/42 I’d look in this direction.

 

I have found codes on my 1993 i bought new mean nothing! I have a Innova and it tells me nothing. Look for the items that work and a process of elimination. Here is a example had bad opti no codes and water pump had a frozen shaft and no codes, no over heating. Inside Opti a shot full off rust that would fill a shot glass. Find a well known Corvette only shop if you hit a dead end, they are best experience on this car.

 

OR it's time for a starter 'tune up' and maybe more substantial starter repairs

 

This.

I didn't see that the OP actually said that he had spark. Inj pulse actually starts with the opti. Opti>ECM>ICM>Ign coil. So if it were me, when the symptom occurs, I'd want to know if I've got spark or not.

 

Where did the OP say that there was a problem with cranking? Why are we talking about starters and batteries?

 

The OP also didn't clarify the comment "it acts like it won't want to start" - OP needs to 'clarify' what actually happens! My original comment was to get the OP to actually do just that!

**If it actually cranks then .....................................

 

Hey guys,

The battery is one month old!!

On hot start it cranks quickly and it takes longer than desired and occasionally it wont start on first try.

It always cranks though!

 

Please please please pull codes with paper clip and post...and when you get a chance please try and answer the other questions if you can...

 

I'm not sure that there are any codes that would be generated by a crank but no start situation.

 

Hi,

• We checked the codes first, there were none!
• There is no security light!
• It cranks, and it cranks strong! So as far as I believe, no reason to think it's the starter.

 

Why wouldn't you after a short park after running at temp just 'pause' at run before CRANK to let maybe the fuel pressure to maximize? I get the ECM attempt for '92 & '93. Does it have a recent pump, filter and sock in the tank?

 

He's saying that he's got no injector pulse. If that's true, pump prime ain't the problem (nor should it be...pump should flood the fuel lines w/volume and pressure nearly instantly).

If it's true that he's got no inj pulse when it won't start, he needs to be confirming a good, consistent, reliable signal from the opti (most easily viewed with a scan tool or scope), then move on to harness/ECM.

 

I've had that happen personally and there were codes about ECM to CCM comm failures among others... on another forum topic just yesterday person had similar situation (although it was dying out and not restarting not just a no restart but running fine) it was throwing ICM related codes and turned out to be ICM. I would also think OPTI signal issues could throw a code in a no start condition, maybe, but a new opti was thrown at this thing?

A bad ICM I've read can present a no code but no start heat related issue...but I would think there would still be some drivability issues while running (i.e. the car would just shut off vs only on restart).

With no codes we are at basics, fuel, spark, air. The OP claims FI not cycling when issue occurs and mentions how this was confirmed...I'd like to know if there is *spark* when there are no FI pulses.

Yes... if that is absolutely true (i.e. the test being done shows definitively when starts there are FI electrical pulses and when no-start there are no FI electrical pulses) then it narrows things downs quite a bit. IF that is true yes harness, maybe recheck grounds, maybe PROM (?) or ECM, opti sensor issue (loses low resolution pulse hot but only on restart? just cannot believe it wouldn't throw a code?)...

 

Yep, it sounds like an odd one, so far. We've seen plenty of DOA brand new opti's on here though....and I proved that an opti can and will DIE FROM HEAT.

 

Hey guys, thank you for helping with this so far,

We have made a video of the issue to hopefully help:

https://imgur.com/a/GklaP5e