Pop from exhaust

[94_T/A]

2 days ago I went to pass someone on the highway and when I got about even with the car I was passing I heard a really loud POP from the exhaust, I was going about 80mph-4000rpm. Then the check engine light came on and it ran rough for about 1 minute then seemed to clear up, check engine light was still on though. I got to work and shut it down. After I got off work I fired it up and it ran fine for about 15 minutes, no check engine light (I drive about 130 miles a day round trip.) While cruising down the highway at 65 mph-1650rpm it popped again. This time twice but alot quieter. Then the check engine light came on and it ran rough for about a minute and then cleared out again. I drove it real easy for about 30 miles and pulled over at a gas station. I popped the hood and noticed both of the radiator fans were on which is weird since it was like 17 degrees outside and the temp gauge was only about 1/4 of the way up, maybe 160-170 degrees. When I took off from the gas station it lugged down real bad, ex. 600rpm idle-push the gas-300rpm, then right back up to 600rpm and accelerated smoothly. I got home and shut it off then fired it right back up, no check engine light, the radiator fans weren't on and no lug off of idle. I drove it around today and it ran great . It is a 94 T/A, auto, 176,XXXmiles, completely stock except for the cat being remove a long time before I got it. Thanks in advance for anybody's help on this matter.

[FTA1995]

One word: OPTISPARK

Sounds like trouble, get it checked

[94_T/A]

How would I check the optispark to see if it is going bad?

[sneitzel]

How would I check the optispark to see if it is going bad?

You would look up Shoebox's website of course...
http://shbox.com/1/4th_gen_tech2.html#opti_test

[FTA1995]

Definitely use shbox.com for help,

What was that code it threw?

That will probably give the most information and can save you a crap load of time and effort.

It MIGHT be the cap and or rotor.

I had an interesting experience with a severely damaged cap, it's a bit uncommon as far as OPTI failure goes, but anything can happen thanks to GM for the most practical distributor ever!

[94_T/A]

I finally had a chance to check it with a snap-on scanner and it said the opti-spark was bad. I think it was code 36. I had to drive it for about 30 mins before it popped and then the scanner showed the opti code. Does anyone know if the opti would not work all of a sudden while driving or would it be because of oil or coolant getting in there and messing it up after driving for a while. I looked down there with a flash light and could not see any coolant, but I did see a little oil and dirt/grime. The coolant hose going to the heater core off of the water pump was not spraying but when I ran my finger on the end of the hose there was some coolant there. Mabye after driving for a while it leaks enough to get into the dist cap and messes the opti up???

[Joe 1320]

the optispark is literally a basic distributer using an optical pickup. it is subject to the same wear and tear of any traditional unit. With your mileage, I wouldn't be suprised if it had already been replaced once and you're getting close to where it's time again.

[94_T/A]

New development, or so I hope. While ripping everything out to get to the dist I noticed that the coil was loose. The round part is loose inside of the square part. Could this cause the problems I am having??

[Black97]

How do i get it so that the pics are showing in the message?

You would have to host them on some picture site or personal web page.

[94_T/A]

Bump

Sorry for the early bump, I just need to know if the loose coil would cause the problem i'm having.

[Injuneer]

DTC 36 is for loss of the high resolution pulse from the optical cam position sensor in the Optispark distributor. You could be losing it intermittently because of a problem with the harness connector, or a problem with the electronic module for the sensor. First thing to do would be to check the harness connector at the Opti for corrosion and/or damaged pins. If that one is OK, check the intermediate connector for the Opti harness, which is a gray 4-pin connector on a bracket in the middle of the passenger side of the intake manifold. But the problem could be caused by a failing cap/rotor.... just not the code.

While a loose coils might cause an intermittent problem as you describe, it would not set DTC 36. That code also has nothing to do with the cap & rotor, since the optical module is in the back 1/2 (base) of the Opti. Generally, DTC 36 will not cause the exact problem you are having, since the high resolution pulse is simply to keep track of the rotation rate (precision cam and crank position) between the low resolution pulses that tell the PCM when to fire the injectors and the spark. But is is possible for the PCM to lose track of exactly where the engine is in its rotation when the problem occurs, causing mis-timed spark and injection.

[94_T/A]

Is removing the water pump the easiest way to get to the opti?

[Mark B]

Its not the easiest.... It NECESSARY to remove the opti.

[94_T/A]

Well, I'm getting ready to drop the money for the new opti. Just wondering if anybody else has any ideas before I do. The reason I am asking is because the car runs just fine until it does the pop, then 30 or so seconds later it runs just fine again except for the off idle hesitation. Seems to me that if the opti was bad or going bad it would run like junk all the time or at least after the pop. I really don't want to drop that much money if it wont fix it, but I guess if it doesn't fix it then I have ruled out the opti and I can move on with other diagnostics.
Everyone I have talked to has never had this problem before.

[Injuneer]

Have you cleared the PCM codes, then scanned it after each "pop" to see if DTC 36 is coming back? If it is, it would point to the Opti. If it isn't, it would mean the problem is somewhere else.

Have you checked the wiring harness, as I suggested?