rcssr

My 93 40th Anniv with 30K stumbled several times while on cruise at 65 MPH. Never died but cut out several times, limped it home. I pulled code 36 (the only code is showed) which is the Mass Air Flow sensor. It is located in the rubber tube from the air cleaner to the throttle body. I pulled it out but no burn off wire, instead it has a metal disc on the end the size of a small pea protected by plastic loops over it. Cleaned it with brake clean and replaced it, so far so good but doesn't put me at ease. I thought I would buy a new one so if it dies on the road I can just plug in a new one. No parts suppliers carry it so I called the dealer. He says there is NO mass air flow sensor in a 93?? What am I holding in my hand then and now what? So far no code and no stumble after 15 miles??

Cliff Harris

You're using the wrong error code list. Try this one:

https://www.corvetteforum.com/forums...post1576116036

Check for a bad connection (loose or corroded pins) in the connector. Also look at the wiring for breaks.

rcssr

Thanks for that info, the list is totally different than mine. Now I have two issues. What is that sensor that is in the air duct tube between the air cleaner and the throttle body? Could it be the air temperature sensor? When I removed it and cleaned it the check engine light went out???
Second (and now prominent) issue is that code 36 says it is the Opti-Spark ignition timing system. Does that mean the distributer cap is bad or is there another sensor down there? This car sits for long periods of time, can it be moisture in the cap and if so is there a good way to dry it? I know this car has the Opti-Spark cap with the three holes in it.

Cliff Harris

....

rcssr

The code 36 means the Opti-spark problem. I have read a lot of stories on the forums and there seems to be a common problem. The coil wire seems to be a culprit. I replaced the cap and rotor about 3K ago but not the wires (my bad). I wonder if I can change that wire without taking the water pump off as I had to do when I changed the cap?? It was a bear and not looking forward to that one. Is there a trick to doing it?

Cliff Harris

Look at the wiring/connectors/pins associated with the ignition module.

rcssr

I have decided not to fool around and play the try this game as the wires and the connections are all clean and good. I have ordered (from Chevrolet) a new Ignition module, new coil and new spark plug wires. I am doing this as all of those parts are the factory stuff even though the car only has 30K miles, but it is 22 years old. I know there is a paste that is recommended for the back of the IM to help with heat from the cylinder head. I do not know what the correct paste to use is if you can help with that. I also wish there was a magic trick to replace the wires WITHOUT removing the water pump (ugh).
Thanks for all the help so far.
Bob Smith

Cliff Harris

The new ignition module should come with thermal grease. If it does not then use heat sink grease made for computer microprocessors.

drk1313

Just my additional 2 cents - I had a '95 Trans Am with a similar problem - it turned out to be a bad connection to the ignition module. If I wiggled the connector with the car running it would actually stumble and even stall. I was able to sort the wires and add new heat sink paste and solve the problem.

As Cliff says - don't downplay the importance of the connections!

Good luck -

rcssr

I only asked because somewhere/sometime ago I remember reading that the factory past should not be used but to buy an aftermarket type (can't remember where though) I have always believed in the factory parts etc. so I questioned why it would not be the right thing to do.

Thank you DRK as well for your help. I did not wiggle wires while it was running and now can not as it is all apart but I did examine that connection closely and it looked fine. I am just confused/upset since this car sits 10 months a year in a heated garage and only has 30K on it. Replaced the opti-spark twice already???

No one told me if there is a way to replace the wires without removing the water pump so I guess I am doomed to that task. I will post when the deed is done to help others down the road.

rcssr

Someone please tell me that what I found was NOT my problem. I bought all new stuff as I previously stated and in the process of replacing the Ignition Module and coil.....The two bolts that hold the module coil assembly (they are attached to each other with an heat dissipating mounting panel) were HAND TIGHT. Is it possible that by being loose the module caused all this?? Is that some kind of ground?

drk1313

I don't believe there is a ground involved - bolting it tightly helps dissipate the heat, so it may be tied into your issue if the ICM was overheating.

rcssr

IF the problem is solved then I may never know what it was as I have replaced everything. I would just hate to think that all this trouble could have been avoided with two loose bolts. However the car is 22 years old and all the parts were factory so I can justify the replacements either way. Thanks everyone
Bob Smith

rcssr

I am at my wits end with this thing. I am cursed with having the dreaded 93 version of Optispark with the three air holes that do NOT function as thought. I have replaced the plugs, wires, coil, ICM, air temp sensor, both water temp sensors (while I was at it) and the air filter. The car si still not right and I am afraid to go long distances. I either have a bad Opti or water in the fuel or both. SO my questions and symptoms are as follows: MOST of the time the car runs fine but every so often it stumbles badly. It will idle fine but every so often it dies at idle. It ALWAYS restarts, albeit sometimes it cranks a tad longer than normal. Occasionally it will have a very rough idle (like 7 cylinders)when cold starting but it goes away quickly. Yesterday at highway speed I jumped on it to pass and it backfired through the intake Most of the time it purrs like a kitten and is very responsive to the throttle.
Is there any way I can spray WD40 into the air holes in the Opti (don't know how or if I can get near it)so that I don't have to remove it? (especially since I don't know if that is the culprit) Can this thing run great most of the time if the Opti is bad?
Can this be water in the fuel? This car sits 95% of the time and I have added dry-gas to it and last year I believe I added StaBul to the tank. How would water affect the way it runs? I am a dinosaur and good with HVI, points/condenser distributors, duel points and even magnetos. I know carbs, Hillborn and Rochester Injection but Opti and sensors and computers are out of my league. I NEED HELP AND DIRECTION PLEASE.
PS the check engine light stays off, comes on, goes out...UGH. The only code it shows is 36

Cliff Harris

Code 36 is telling you that the opti is not connected to the PCM. If the engine runs then it's an intermittent connection. If the connector pins are corroded you can get this error. Contact cleaner is the solution.

You might also have a bad connection where the pin is attached to the wire. The way to find this one is to pull and twist the wires while the engine is running.

Another possibility is a break in the wire inside the insulation. This can happen if the wire is flexed too much, especially at a sharp bend.

The connectors at the PCM are also suspect and contact cleaner might help there.

rcssr

The PCM seems to be fine I unbolted it an twisted it and all the wires around while it was running but not a stumble. It would seem that the optispark is the culprit and I do NOT want to go through all that work of pulling off the whole front of the motor INCLUDING the water pump. Is it possible to squirt WD40 (or similar) up through the three air holes on the bottom to displace any moisture that might be inside causing this ?
I do not know much about the optispark except that twice in 20K miles I had to replace it. The car sits in the garage 11 1/2 months a year or MORE. My knowledge of electrical components (prior to computers) was that it either worked or it did not. This work/not work/stumble/run fine crap is hard to wrap my brain around.

rcssr

Well I may have good news here (98%). I decided to go the water in the fuel route one last time before I pulled the water pump. I added dry gas to the half full tank and ran it to the low fuel light came on. I never, ever do that so that the fuel pump stays cold but for this test I took a chance. When it was that low I added another can of dry gas and filled the tank. I have driven the car about 200 miles so far and there has not been a single stumble. Idles fine, runs great, 23 MPG on cruise, and I wind it up to the shift out point on full throttle flawlessly. I know it did not totally act like water in the fuel but so far it sure seems that way. I am not an electrical maven but I do know that those problems do NOT heal themselves. I will post any changes, good luck to me.