A new "my lt1 runs like poo" thread :p
 

Ok, wound up driving the z an hour home in the pouring rain after work Thursday night. Car was running mint but now not so much. It started popping, sputtering, and backfiring randomly on the highway on my way home and now, even after the rain has stopped, is still doing it.
I did a quick look around at all the wires and everything looks ok but it feels like it's down a cylinder or two.
At first anything under 2500 rpm was horrible and almost undriveable. Now, it's cleared up a little, but still not so great under 2000 and downright horrible under 1500. It does however idle great and starts right up fine. It will pull all the way through to redline without too much drama but you can definitely tell it's just not all there. My other half said it best when she drove it, "the gas pedal feels like a spongy brake would react"
Not throwing any codes so could it still be the opti? It really feels just like a plug wire is shorting out but they look fine everywhere. Any ideas before I tear the front of the motor off, AGAIN!!!

opti or coil but you aren't alone not many lt1's have been running right lately :P

Tell me about it. I'm getting ready to either do an ls swap, or eliminate the opti.
Been seriously considering opening up a hole at the back of the intake, dropping in a regular distributor, and just running a megasquirt.

Speaking as the owner of an LT1 that runs like a top, I can tell you that my car has zero issues driving in the rain, ever. Refresh my memory, is your opti vented? And you checked for simple stuff like vacuum leaks and fuel pressure? Connections on the coil are good? And there is definitely not a plug wire touching something hot?

Yes, opti is vented, none of the wires are touching anything hot, triple checked.
Didn't see any vacuum leaks, all of the ignition plugs look good.
Didn't check fuel pressure cause whatever caused it happened after it got wet the other night so I'm pretty sure it's ignition related. You can definitely smell unburned fuel from the exhaust.


I used to love lt1's. My old 9c1 caprice was awesome. I beat the daylights out of that car. Went through 3 transmissions and 2 rear ends but the motor was always strong and trouble free.
I don't want to hate lt1's but this one is making it hard not to. Grr...

Yeah I just realized fuel pressure issue wouldn't make sense. Is there any chance it could be a bad coolant temp sensor causing the computer to see a cold engine and dump fuel? If yours is the same as mine there are separate sensors for the gauge and the PCM so the gauge can read correct and the PCM can still be getting bad info.

I can't believe it's running that bad and not throwing codes. I'm just trying to come up with anything other than the opti that could cause it.

i have heard stories of the vented optis getting water in them and they start running just like that but i dont speak from experence.

i know you said no codes, could an o2 cause a problem.

Mine used to run beautiful. But I did an emissions delete and race headers with ory and now the air fuel ratio is all tweaked.. Still trying to track it down but Now its running good till about 3200rpm goes lean as you all saw on the dyno 17:1!!! WTF So, at least my ignition is good... knock on wood.

17:1 is leeeeean...