94LT4Corvette

Anyway... everytime I fix something... something else seems to start rearing it's ugly head. The new problem is backfiring. The car runs fine when cold and stays that way for a good say 15 to 20 mins. After it heats up and has been sitting at lights here and there... it starts running rough... and then starts backfiring... more than 4 to 8 times a minute... ranging from mild to loud backfires. I'd diagnose the problem... but I have no idea how read the readouts from my PC connected to the OBD port running the LT1edit / pccomm programs let alone I don't know if I have the software for reading codes or anything like that. Anyway... if anybody has experienced the running good cold to running like a POS warm and hot symptoms... give me the rundown... thx. Also if anybody is in the Houston area... give me a tuner that can actually tune an LT1 engine... no one wants to touch the damn thing it seems even if I have the computer to do it with.

For those who have not seen what I replaced before this... here is the list of new stuff: MSD opti, Hi-flow water pump, stock injectors, O2 sensors, ICM, Ignition coil, knock sensors, spark plugs, 8.5mm spark plug wires, FPR. I think I got it all... lol.

antfarmer2

All you need s a paper clip to read the codes look on youtube to see how. You have a ob2 connector and a ob1 puter. Just a wild guess would be new coil and icm and thermal paste.


Just reread and saw the msd have heard bad things.


When you replaced the icm did you use the right thermal paste? If not that might do it.

94LT4Corvette

Thermal paste... I have no idea on... I hope MSD Opti isn't just a bad thing catching on... lol... that damn thing isn't cheap to buy nor is the labor to change that out. Yeah I have the cable for the laptop... OBDII connector for OBDI computer they used in 94 / 95. I do know after replacing the ICM it seemed to run... worse.... can you link me the thermal paste I should be using? Just in case that is the problem... it'd be a quicker fix and cheaper for sure.

antfarmer2

You did it yourself? Yes must use thermal paste six buck fix. Radio shack has it if yours is not closed yet maybe a computer store. Not sure if the icm would be damage if paste is not used but why risk it.

94LT4Corvette

No had a local mechanic do the work... I assume he used some kind of paste... but as of the type... I have no idea... he works right across from an Auto-Zone and O'Reily.... lol

94LT4Corvette

Okay I called him and he said he used the Dielectric grease that came with the ICM in the package. I don't know if that is the same thing as the thermal paste that you are talking about. If not... let me know... I can fix that fast... lol. If so... I need the next thing to look at... btw do you know if there is an aftermarket harness I can get for the ECM to the ignition stuff... the stock old wires after 20 years of being in that car are more than likely an issue as well.

antfarmer2

No not the same thing!!!!! I would look at the o2 sensor wires make sure they installed right easy to touch the exuast and short out.


Use the paper clip trick and cheak for codes

94LT4Corvette

Okay... so needs thermal paste... I hope the damn ICM isn't already screwed... lol... at least it's a cheaper part. O2 sensors... I can find the upstreams but not the downstreams on sites... would it matter if I used the LT1 Camaros sensors instead for that? is it bascially universal for the LT engines? Thx... I'll do the thermal paste this weekend and see if the thing runs better and stays that way... hopefully a new ICM isn't needed.

antfarmer2

Try rockauto they have them at a good price on the 94 they were just setting up for ob2 but is still ob1. I just did the front two on my 94. I hope you did not get a bad opti have seen some in here get three bad msd in a row I would call them.

Hot Rod Roy

If the stuff he used came with the ICM, it's the right stuff. He just called it by the wrong name. He may not have realized the true purpose of the grease, but it sounds to me like he did the job right.

94LT4Corvette

I hope not... though the mechanic said an Opti would definitely fit the symptoms... yeah going to do the sensors and paste for the hell of it though first.

94LT4Corvette

Eh... might as well get the thermal paste anyway... not like that stuff is expensive... the Opti on the other hand... is something I'd hate to mess with again... it's only been a couple months... yet it hasn't exactly run like it should for a while... I had so many problems back to back... it's hard to tell if something else didn't just go bad in a domino effect from something else being bad before. I hope it's something as simple as paste and sensors.

antfarmer2

I would sure ask where he put it and how. might have just used it on the connectors.

94LT4Corvette

Okay so my question is if he did use it like that... does that need to be done... or should he have just covered everything else but the connectors? My lack of mechanic knowledge shows... lol

1993C4LT1

On my previous C4 LT1, I changed the ICM and put the thermal grease it came with. I was chasing a stalling issue when warm. Problem was my opti. Anyways, just trying to say that if he put the thermal grease the ICM came with, it's fine. I know how you feel about fixing one thing after another

Good lookin car If you were in Dallas, or I was in Houston for whatever reason, I'd try and troubleshoot it for you.

antfarmer2

A thin layer under the icm when mounted.

94LT4Corvette

Roger that!

94LT4Corvette

THX... I've been thinking about dropping an LS1 in it sometime next year... get rid of all the heartaches of the LT1 like the Opti... lol... but you know... takes money and time.

94LT4Corvette

****UPDATE**** 8/27/2015

Replaced O2s, coil, and got an ACDELCO Optispark put into the vette. Ran great... ran really great... up till it reached 185/190 temps on gauges and then it starts to stumble a lot... no backfiring at least. When temp goes back below 185/190, it runs fine again. There has to be some sensor or temp issue somewhere that the computer is picking up as bad... maybe it thinks it is overheating even though it isn't?! Also the check engine light has decided to come on constantly even though the old MSD optispark never caused it to come on when it was crapping out on me... it is the code 43 of course. It flicked a bit on/off after temps when back down below 185. Anyone have any idea what could be causing this now? and tell me it isn't the computer now... LOL! I'm about ready just to sell the damn thing....

antfarmer2

If your going by the digital sensor it would be the temp sensor on top of the water pump it can play hell.

Make sure you have all the air burped out first.