Then what could be the cause of a stutter and lurch while accelerating?

 

Thanks for the heads up Injuneer.

 

Even misfire detection in OBD-2 is of limited use. With a "GM Enhanced Parameter" capable scanner you can pull up the misfire count by cylinder and determine which cylinder it is, or if it's a more general random misfire on more cylinders. But it doesn't tell you the cause (although you might infer the cause if you have signs of two cylinders cross-firing for example).

That's why we need the codes that turned on the SES light. If you have to, drive it as suggested above by squarehead, and hope the SES light comes on again while its misfiring. But then you have to have a way to scan it and pull the codes. The code may be enough to point you to the problem.

Scan9495 is a good way to try and track down the problem. It will pull codes, so that's all that is needed. If you are lucky enough to be logging while the misfire occurs, there's a good chance you can spot the anomaly that caused it. Not always, but usually. You would look at the things I mentioned in post #6 - coolant temp sensor, O2 sensors and long term fuel trims, IAC counts vs. RPM.

I was reviewing data logs for people for 20 years, but recently decided it wasn't worth the effort. As I've explained, it take a lot of my time, and may require the owner to do some additional diagnostic work. That's where the process falls apart. Seems like most people don't want to do the diagnostic work, or follow up with "trial" fixes. They want a single sentence telling them exactly what the problem is. When they don't get it, they revert to "parts replacement roulette", and I've wasted my time. Or they just give up and never post a follow up telling what they ultimately found the problem to be.

 

Well a little update. This morning it backfired and recently the exhaust reeks of gasoline. This paired with the fact that the idle will kick down to like ~400 rpm randomly makes me think it's not getting enough air. So less of a case of too much fuel and more of the case of not enough air. We've had significant problems with the throttle body so could that be the issue? Or could it be something else? Still no codes so I'll keep yall updated on that front. But I mean there could be so many problems related to air from just a simple clogged air filter to a valve stuck closed. (The air filter is not clogged, I just inspected it a couple days ago; simply an analogy.) The iac has also been replaced so I wouldn't expect that to be the issue either.

 

The PCM measures the air mass entering the engine using the MAF sensor. It only adds the mass of fuel that matches the mass of air, based on the target A/F ratio. If the air filter is plugged, or the throttle body is blocking air flow, the PCM will alter the injector pulse width to reduce the flow of fuel. Your logic is unsound.

You indicate the problem only occurs when the engine is cold. When the engine is cold, the PCM alters the target A/F ratio to richen the mixture. Might be a faulty coolant temp sensor….. see post #6, first listed possible cause. Have you made any effort to verify the accuracy of the coolant temp sensor, and the two wires that connect to it?

4th Gen LT1 F-body Tech Articles

No guarantee that is the problem, but a simple DIAGNOSTIC might rule it out as a possible cause.

 

I have no validation that it works. If it is truly that simple, as explained in the external link you provided, to test if it works then I will try it. I know it's in the water pump, but what is the best way to get to it?
Edit: nvm seems quite straightforward.

 

Finally!!!! We got it to throw a code and immediately got it scanned. The code is for the optispark, and the left side of the manifold was cold while the right side was hot. So we, hopefully, finally have a source. While we are getting the optispark replaced we have decided to also replace the water pump and the coolant temperature sensor. Along with plugs and plug wires because we don't know the condition of these parts, an I want to do some preventative maintenance. I thank you both for some great insight on what to look out for. I will be back if these unfortunately don't work.

 

DTC 16 or DTC 36?

 

They didn't specify. What's the difference between the two?

 

The engine can't run if DTC 16 is active. if it runs at all it appeared briefly at cranking, or early startup, and it is a stored code. PCM shuts down the injectors, can't sequence them, can’t sequence/set ignition timing. Engine will run with DTC 36, but it may or may not run OK. Unlikely either would cause just one side of the engine to shut down and run cold. Odd that either would only occur when the engine is cold. Usually it's heat soak that will upset the cam position sensor circuitry and cause things to break down.

Takes a few minutes with a multi-meter to use Shoebox's procedure to test the resistance of the coolant temp sensor, and to verify that key on, the PCM is supplying the correct 5 volt reference on the two wires at the connector. Specially when you're pulling the water pump.

What Opti are you planning to buy?

 

you better do some research on the Opti your getting, 90% are trash and will cause 10 times more problems than you started with before replacing it.

 

Which optis should I stay away from and ehat are the ones that are generally believed to be okay?

 

It appears that one of the previous owners put a new one on in 2017 u Der the brand name "smp" but I can find nothing about them online it seems. I believe poor product choice is most definitely the reason it is bad today.

 

Standard/SMP is sold by Summit (and probably others). It could be replacement cap & rotor:

https://www.summitracing.com/parts/s...iABEgKTX_D_BwE

If you actually need a new Opti - and it is not evident from your description - you would need a complete unit. The only reputable brand out there, with no one reporting any problems to date that I am aware of, is Petris:

https://petrisenterprises.com/collections/frontpage

 

So the water pump was leaking oil directly into the optispark and causing it to not fire correctly. We replaced those but now the coolant hoses that go from the radiator to the water pump keep backing themselves off and causing a massive leak. This has happened two different times on different hoses now.
Edit: To clarify there was 0 problems with the cooling system before we replaced these parts. The water pump was leaking oil so we replaced it. Now hoses keep popping off? Is this a pressure issue or what?