Help! 93 exhaust backfirig/afterfiring

[lakeguy72]

Backfiring/Afterfiring?
My Ruby(27000 miles) has been actingweird.
On a cold start(winter or summer), itstarts and runs like it should. After running or driving for 10minutes it starts popping out of the driver side exhaust. It doesn'tstall if you go easy on the throttle. After driving about 5 miles at45 MPH it runs perfect again for the rest of the drive. If you shutit off when popping and then restart it kicks like the advance is toohigh. If you wait about 20 minutes it starts and runs like nothing'shappened.
This seems to happen at around190+(digital) degrees. When the problem clears it's running around205+.


I heard that the maybe the ICM wasgetting hot but packing ice around it didn't help. Would a sticky EGRvalve cause this? I checked at night for arcing of plug wires—noluck. There is no sign of water pump leakage staining and the optiappears to be dry. No bubbles in radiator reservoir or loss ofcoolant. The car is not driven daily and this happens mostly whensitting for 2 days or more. My MPG is 25-27 so I don't think it's aopen loop issue as I've read that in open loop mileage drops.Everything is original. I can't see throwing parts at it if iteventually runs like it should.
If it was the O2 sensor I would thinkthe popping would be heard from both pipes. No codes thrown and no CEL.
Help
Lakeguy

 

[93Rubie]

My car does something similar however it ONLY does it when you start the car and its been sitting in near or below freezing temperatures. I've checked everything and near as I can tell it is the Opti-Spark. Car runs perfect otherwise and since I don't operate the car in those conditions very often I don't worry about.

I also had a buddies 94 that does something VERY similar to yours. I went thru the whole car and can find nothing wrong with it. Again my best guess on his is an Opti-Spark issue. His clears up as soon as it hits closed loop. It ONLY does it when the coolant temps are between 100-140 degrees. I can replicate it like its my job I know the car and the issue that well in his 94. Never found ANYTHING via tests, scan tool data, etc...that indicates anything obvious is wrong. He is going to run it till it stops and/or decides he wants to bite the bullet on the Opti-Spark.

My guess is on both cars its a timing issue which means one thing. That being said, I would check EVERYTHING else with the scan tool, FSM, etc...before I'd condemn the Opti. I've done all that on both these Corvettes.

 

[tmkassin]

Does it have the original spark plug wires? If so I would invest in new ones. Just because you can't see sparks jumping doesn't mean they are ok.

 

[boomdriver]

this is classic Opti symptoms...

moisture in the opti from condensation, storage, extreme temp swings. Early optis were not vented as later yrs are. Many folks opt for the newer vented Opti to solve this problem.

 

[hcbph]

Moisture

I'm going to throw a thought out here, use it if you like at your own risk. Has anyone tried using a water dispersant spray on the optispark when something like this happens?
I've used the brand "LPS" water dispersant spray on a car that had water in the distributor when a relative drove it in deep water and inundated the engine and getting water in the distributor (darn British cars). After spraying it around inside the distributor, I drove it home having done nothing else, including not sucking out the standing water in the distributor. After sucking the water out of the distributor at home, I dried it out using air and a heat gun. Had that car for several years with no problems relating to the distributor and the water incident.

If it was mine and I thought it might be moisture related, I'd pull the cap and blow out the housing then use something like LPS water dispersant on it and see if it made a difference. I'd go so far as to pull as many connections as I could get to and spray them before reassembling.

What sold me on trying it out LPS water dispersant (there's more than one so watch what you get): I was at a Hardware Show and LSP was on display at one of the booths. The presenter had a 100v open relay wired to a porcelain socket with a regular 60 w light bulb. After it was all wired up, he sprayed it all over with the stuff then plugged it in a placed it in a full aquarium. I watched that thing run underwater for over 30 minutes, clicking on and off continually and even dipped a finger in the water and did not get a shock. I bought a can on the spot. Now if I could just find it

 

[lakeguy72]

93 exhaust backfiring/afterfiring

Everything is original except the tires and air cleaner. When in open loop it runs fine. The problem(left side only) is when it goes into closed loop at 190+ degrees then after 10 minutes it's fine again. If you shut down right when it starts and wait 10-20 minutes it's fine. It's like there is moisture that dries up but why does the popping occur when you to closed loop. In closed loop could a sticky EGR be causing the problem? I believe that in open loop the EGR is by-passed.
I will mist some water on the wires and see what if anything happens. The car is in CT and I'm in FL until mid April.

 

[2VettesMike]

this is classic Opti symptoms...

moisture in the opti from condensation, storage, extreme temp swings. Early optis were not vented as later yrs are. Many folks opt for the newer vented Opti to solve this problem.

Unless you are talking about aftermarket vented isn't an option. The earlier 92-93 LT1's have a different drive gear cover setup and the later 95-96 vented will not fit without changing the time cover and a lot of other parts.

Thanks,

Mike

 

[2VettesMike]

Everything is original except the tires and air cleaner. When in open loop it runs fine. The problem(left side only) is when it goes into closed loop at 190+ degrees then after 10 minutes it's fine again. If you shut down right when it starts and wait 10-20 minutes it's fine. It's like there is moisture that dries up but why does the popping occur when you to closed loop. In closed loop could a sticky EGR be causing the problem? I believe that in open loop the EGR is by-passed.
I will mist some water on the wires and see what if anything happens. The car is in CT and I'm in FL until mid April.

Having gone through a confirmed Opti failure several years back I agree with the others to check the obvious first and work backwards. With the age not miles on your car you are definitely ready for the following which could be causing your problem:

Plugs
Wires
Fuel Filter

Now if that doesn't fix it you can move towards the Optispark
If you or your mechanic does replace the Opti change the water pump too.
You don't want it failing later or you get to replace the Opti twice, search the forum for many stories on this experience.

Lastly, when my Opti failed it gave similar symptoms as yours and even sudden, temporary loss of power under load. It never set a code not even when if finally stopped driving down our street home one day.

Good luck,

Mike