Symech

New to the form, first posting.
I have a 94 base coupe which has had a very hard life before I got it about a year ago. I have replaced the opti, spark plugs and wires but still have a stumble / back fire under hard accelerations. Idles rough and now it looks like I am loosing coolant but see no leaks. When the opti was replaced the water pump was too so I am hoping that it is not bad or lame workmanship on my part. I have rechecked the wires to make sure they are not arching 5&7 and the gaps are correct, NGK’s. Starting to think I have a blown head gasket but not sure at this point.
Was hoping someone might have had similar issues and could point me in the right direction?

1986coupe

Welcome to the forum.

Backfiring means that unburned gas is in the exhaust system and igniting.

This could mean several things based on your car.

Are all of the emissions systems on the car? Are they operational?

Have you tested the injectors?

Have you tested the ICM?

Throttle position sensor?

Also, are you getting any codes? If so please post.

Symech

Sorry for the delay in getting back.
Thanks for the info. Here is what I know so far:
- Replaced all the fuel injectors, fuel pressure regualtor, fuel filter and pump.
- New cat's about 3 months ago with new bosh sensors.
- Replaced plugs and wires.
- Replaced opti about a year ago.
- New coil and control mod.
- Replaced the EGR valve and solenoid.
- Had issues with my routing of the plug wires and will be replacing all the wires as I may have damaged them.

As for codes, I beleive I have a history code 42, coil short and I think it was 62 right O2 lean. Both of these only show up under history nothing new. I hope to get some time tonight to recheck the codes and maybe replace the wires, o'what fun! I did test the injectors before I changes them and found three on the passanger side were not firing or very little as the idle did not change when discconected.

It sounds like you think I may not be getting enough spark to inginite all the fuel and that is causing the backfire? I guess I could get a spark checker to ensure al are firing?

Thanks for your help!

ddahlgren

I think you have answered your own question but don't like the answer... Pull the plugs and put compressed air in each cylinder one at a time with the radiator or expansion tank cap off. You can also get an inexpensive test kit from most auto supply stores. It would make sense to check for water / coolant in the oil as well.

tahoemedic

I would recheck all your plug wires one by one and make sure they are plugged into the correct terminal on the opti. I have built my c-4 several times and even during tune ups if I'm not extra careful I always get one crossed. There just isn't enough room to see what you're doing under the waterpump and between the power steering hoses,etc. Also, if you had a blown head gasket (even between cylinders) these LT-1's will make a bigger leak in short time. You would see some visible smoke at some point, and definitely see foam in your coolant resevoir up by the passenger cowl. Typically though, you don't get backfiring with a blown head gasket as the coolant mixing with the fuel makes it virtually impossible to ignite. The OEM wires have thin insulation on them and if they come in contact with the exhaust manifolds for any length of time, they will wear through. If you're worried about arcing, fire the car up at night without the lights on in the garage and look around where the wires are, you should see a visible spark if the insulation has been torn or worn through.

Symech

Thanks for the suggestion but I think or thought I found the issue.
Finally got some time off and pulled the opti off. When I opened it, I found one of the screws that holds the rotor rolling around inside. I could see arch spots all over the inside, one year old opti!! I ordered a MSD and it came just before Thanksgiving holiday. I went to install it but the key will not allow the opti to go all the way home. Since I do not have alot of time I bought a rebuild kit and replaced all the wires. Ran great, issue gone but one of the heater hoses decided to spilt a spray on to opti, next day same issue came back. I guess when I removed the hose I damaged it and did not notice until it was too late. I am still waiting to hear back from MSD, hopefully I will get a replacment soon and try again. I love working with after market parts!!!

Symech

When I replace the opti again I will double check my routings, I have caused myself a lot of headaches in the past when trying to get them through the slot. I just changed the oil and no signs of a blown gasket. All the plugs looked good, replaced 3 months ago so hopefully your right. I cleared all the history codes the other day and ran the car, no new codes. I ran it today after checking the wires again but still missing so I checked codes and I see H42, shorted or grounded coil circuit?

pcolt94

Just a question on the opti, was it a Delco OEM type or an inexpensive china knock off?

And a suggesting for the code. What kind of ICM are you using. If it is not a quality OEM part, it can set a code. You can go nuts checking everything.
Also check the ground wire for the ICM.

Symech

Thanks for all the help everyone. The opti was a cheap knock off, replaced with MSD and so far so good. I have not driven it much since the replacement but it currently is pulling smoothly in all gears under load. I purchased a chemical head gasket check kit and hope to test this weekend.
Additionally, I replaced the coil and control model with AC Delco and between these items my check engine soon light has gone away at startup. No new codes so I am hoping that these changes have fixed my issues. Now let's hope the head gasket is good to go as well.

Thanks again all!