Scott Horner

Have a 1994 that will run rough at times, cuts off, won't start but still starts after sitting for a while and runs fine at times but has gotten worse. Rarely messes up when the mechanics have it but have been told it's the ecm(computer). Any ideas, options?

Bfenty

Could we get a little more info? Right now you've narrowed it down to just about everything

Is there a specific RPM range where it runs rough? At idle? At WOT? On a hot day? After it's been running a while? After a cold start?

Won't start after it's been running for a while? Or a cold start?

That will help narrow it down and give people something to work with

Scott Horner

OAT doesn't seem to matter, neither does if the car engine is warm or cool. Have noticed at times when it is going to mess up that the idle will slightly increase. One time I was traveling at about 70mph and it just cut off. Would not start back up, came back to it the next day and it started right up. Has new ignition control module, distributor, plugs and wires.

knikula

Intermittent problems are the toughest to diagnose... that said, the times where it won't start are the sweet spots for diagnosing it... fuel pressure during that time? spark at that time? wet plugs after cranking?

that's an optispark car, no?

good luck...

Bfenty

My first thought is Ignition Control Module. I know you just replaced it, but any chance it could have gone bad again?

Scott Horner

Have 3 ignition control modules and it does the same thing on all 3. Fuel is all good. All that is brand new as well. Has always had fuel pressure in these situations just no fire.

Bfenty

Have you checked voltage to the distributor? Could possibly be a loose wire there that works its way off sometimes? My other thought is the ECM. I'm not terribly familiar with the Optispark cars however-just a few thoughts is all.

aklim

IF it cranks, lets do this. Next time it fails, put a noid light on all injectors and see what happens. Every one should pulse. IF not we go elsewhere. If so, fuel pressure and injectors.

ddahlgren

There are a pile of parts be bad and still get a pulse. I would go with a timing light and 1 noid light at the same time

bac22

Almost sounds like a failing optispark to me...I assume your mechanics looked for codes?

aklim

I'm sure there are. Hopefully it will be simple.

HAD2HAV2

Does a LT engine have a TPS?

1800Wing

Yes, located on the starboard side of the throttle body, just above the IAC or Idle Air Control. If you take out the IAC don't push on the pintle shaped end that goes into the throttle body, it operates off a worm drive and can be stripped if you push too hard.

I'd try giving them both a good cleaning before I did anything else.

later, tiny

aklim

If you push too hard, perhaps you will learn what not to do with the NEW one?

If you are going to clean the IAC, it would be better to take the TB apart so you can get to the passages.

81c3

What the OP described is exactly what my 93 Z28 did when its opti was failing. No rhyme or reason, hot or cold.... sometimes it would run fine for a few days, then Id come out to crank it up and it would only crank... no start.... An hour later... all was well. Sometimes it would start, then stumble for a few miles, then fine. Sometimes it would stall out and start, sometimes it wouldnt... strange stuff. I sent the opti off to MSD (it was an MSD) for an overhaul, and everything was perfect after that.

redcorvettedave

OPTI
been there, done that 5 times...after you replace this one have the drive sleeve coupler that connects to water pump replace.. I believe this is the most often missed replacement part that keep the water pump flowing properly and eliminating leaks on opti...