1996 Camaro Z28 LT1 Project

[alone_and_insane]

Swapped in all new plugs over the weekend. All of the plugs on the driver's side (1,3,5,7) were carbon fouled:



And all the ones on the passenger side (2,4,6,8) looked like this:


After swapping in new plugs, the car ran probably smoother than I've ever seen it run...for a time. After about 5-10 minutes, once the car gets warmed up, it still starts sputtering and misfiring all over the place, and it doesn't want to idle without stalling. I'm wondering if it's a problem with the tune with the new exhaust, or if it's something more sinister...

[MP81]

I mean, given you had a similar exhaust setup on before, I can't imagine it would throw the tune that far out of whack - normally exhaust doesn't have much of an effect on the tune, or at least, not to that extent.

No codes?

[alone_and_insane]

The only code I've gotten is the P1441 (evap purge) one that I've gotten periodically for years. I get a flashing SES light when the misfiring happens, but of course, no other codes to go on. I wonder if a lot of the DTCs got tuned out.

[MP81]

Wow - the flashing SES light should almost always set a code. That's the only way we found out that my brother's Buick was missing hard on cylinder 3 - he got on it on the freeway, it got really bad, and starting flashing the light at him, then set the code.

Flashing and then not setting one is very strange...

[DynoDave]

Interesting that it's entire banks running one way or another. I'm not intimately familiar with LT1s, but I would think that rules out certain common things, like the pump, regulator, etc. And any common sensors, like coolant temp, MAP, etc., would it not?

[alone_and_insane]

Is it possible it could be related to the upstream O2 sensors? Do those tend to fail with brand new exhaust components? They both looked pretty carbon-covered when I took them out for the new headers, but I wasn't entirely sure if that was typical/expected or not. Maybe one of them's gone bad and the other is on its way there.

[DynoDave]

That seems logical / possible. An O2 can "slow" with age, and you can see that in a scan tool, looking at the data stream. So if you can borrow a scan tool, that might show you a little of what's going on. If the difference between the two is not great enough, it won't set a check engine lamp.

[alone_and_insane]

So I finally bought one of those fancy Bluetooth OBD data logger things, and here's what I found upon checking the O2 sensors. I also found a P0131 code for O2 sensor voltage low. So hopefully new O2 sensors will get this thing running well enough to get to the M&G. Cutting it close this year

[alone_and_insane]

Pulled the O2s last night, here's what I found. Installed new ACDelco sensors, and the car seemed to drive reasonably well. No sputtering or falling on its face like before. Hopefully the issue is fixed! The thing still leaks oil like a sieve, but that's a separate problem

[MP81]

Man, that driver-side O2 does NOT look good. Passenger-side one looks pretty normal.

Fun fact: If you run E85, your O2 sensors look beautiful. Pristinely clean.

[alone_and_insane]

Yeah, hopefully the crapped out O2 is the culprit, and not just a symptom of something more sinister.

[MP81]

My guess would be that it was a circular loop - O2 crapped out, caused that bank to run like shit, making the O2 see bad readings, misinterpret them, and run shittier.

[alone_and_insane]

Did this yesterday. I think it will be a nice touch!

[MP81]

I presume that is the underhood insulation? Looks good!

[DynoDave]

Nice! Done on a new pad? What paint or product did you use? Home made stencil? Come on man, we need the deets!