Bad Optispark?
 

115K Miles, just had a leaky intake gasket, and valve cover gaskets replaced. I really hope the technician didn't get coolant on the Opti. Engine used to be smooth while accelerating, but after the gasket replacement, it's different above 2K RPMs. I'd describe the sound as a machine gun, or someone rolling their Rs like "Guitar-r-r-r-r-r-r-ra."
I swapped the original plug wires (what a PITA on the diver's side!) and the engine was great for about 5 minutes. Now the noise is back.

Is my Opti toast?

Forgot to mention - It's a 1992, with the non-vented Opti. Yay.

Can't rule out the opti, but if the noise changed when you swapped plug wires, then that leads me to think that isn't the problem. When your car stutters, what does your tach do? Unless it goes berserk, it's probably not the opti. I honestly think the whole coolant-in-opti thing is overblown. It's pretty hard for moisture to get inside the opti if the sensor connection is still plugged in. I think the culprit for most opti failures is corrosion due to condensation and ozone buildup.

ETA: it sounds like you're describing a single (or maybe two) cylinders that are missing regularly. That is also not a likely failure mode for the opti. I'd be looking at plug wires and plugs. It is possible that there is a bad terminal on the opti's cap, though.

Only coolant involved is to throttle body. Wires can stay in.place. As you play with your car the technician loses liability. Who's to say it's not your fault. Take it back tell him what's wrong and let him review repair. A scope test should shop ignition issues.

The noise was there before I swapped plug wires. It started after the shop replaced gaskets. I was told the wires were original, so I was hoping replacing the wires might be an easy fix.
The tach doesn't seem to go berserk. I'm trying to rule out any easy problems before I dive into the waterpump and opti. The plugs are possibly original as well. Maybe one or more be fouled?

I talked to them about the problems it developed after their work, and they said it could be the opti. Got an estimate for opti replacement with waterpump, wires, other minor stuff, labor for $2K. Before I dive into opti replacement, I want to exhaust any easy fixes.

It's not the opti. That's the scapegoat for every LT1 problem, but it rarely actually is the problem. This is something else.

I like the what you're saying!

I drove it today, and it doesn't run rough until the engine is warmed up. I had 5-7 minutes of smooth accelerating. The tach is always smooth.
I guess I'll pull the spark plugs and check them out.

This sounds very much like some sensor is bad. The car is fine while it's warming up in open-loop mode. Then when it hits its target temp and goes into closed-loop mode, it begin paying attention to all the sensors. One of them is dead or dying. On my car this happened with a bad O2 sensor. I hear that the Coolant Temp Sensor is a common culprit too. Anyway, that's what I'd be looking for.

https://cimg8.ibsrv.net/gimg/www.cor...5574b549ab.jpg
old plugs
https://cimg1.ibsrv.net/gimg/www.cor...26823f8a26.jpg
New plugs, pre-gapped .050

So finding time to work on the car has been difficult... kinda the reason I sent it to a shop in the first place. Anyway, I finally swapped the spark plugs, with new Champion plugs. The old plugs look......???? I also got around to replacing the wire from the coil to the Opti, which I couldn't find the first time around. So with all new plugs, and wires, it drove great! The engine sounded smooth, and only once or twice was there a hint of the machine gun sound.

Sadly, and after 3 or 4 outings, the engine problems returned. I wondering if I should pull the plugs again, and see if they are crudded up?

Opti spark
 

Are you pulling any codes????

I agree with what MatthewMiller said with one exception. It could be a bad sensor but it also could be the mechanic did not properly attach any sensor connections he may have had to remove for the other work. Also if it ran great after the new plugs but is now back to performing poorly it is not the opti. It could be a sensor not doing its job and now the new plugs are fouled from a rich mixture

No codes right now. I'll look into the sensors. Thanks everyone!

I have a similar issue. Replaced all my radiator hoses and after I get warm and go into closed loop any light load on the throttle I get the machine gun backfiring. Cruise or stomp on it and I'm fine, light pedal and machine gun.

I have a non vented Opti, I just removed the TB and water pump and pulled the opti. I am in a quandary deciding to have opti-doc just rebuild it or go for a vented conversion from him or Petris. I do not want to go through this again. Doing the wire and plugs while I'm busting my knuckles too.

I read a lot of threads on this and it just seems to coincidental that I was changing hoses and had antifreeze all over when this started. 65k on it.

Thanks for sharing! I've considered using Opti-doc if I finally go for opti replacement.
Does the opti-doc test before repair, to confirm failure? I would be interested to see this with yours.

I'm waiting on a reply from him. I'm going to have a vented one in any case. .

Well, I was hoping to check out the MAF sensor. Then I found out, there is no MAF sensor on a 92!

I disconnected the Intake Air Temperature sensor, and I'm not sure that did anything. No codes yet.
I didn't do anything to the manifold air pressure sensor.
I need suggestions on sensors to check.

Pulled one plug (because pulling all the plugs is so fun on this car). No oil or carbon... look ok?
https://cimg0.ibsrv.net/gimg/www.cor...dc1051f725.jpg

Just to let you know about my backfiring in closed loop turned out.

I had my opti rebuilt. Brad said it had staining from maybe from my hose changing job. The bearing was breaking down and there was some red/orange dust in it.
He replaced the bearing and cleaned up the unit. New cap/rotor and sealed up good with something that doesn't breakdown. Converted it to a vented gen II type.

I installed it. Replaced my wires and plugs. Found 7 of 8 we only finger tight. Once assembled I wholly thought it wouldn't start. But it cranked and started right up. I ran it hot and cold in the driveway to vent and settle the coolant level. Took it for a ride. Got to closed loop and no more problems. Just have to change my fuel filter and it's back to doing the cosmetic stuff. :steering: