Misfire when cold
Thread Starter
Pro
Joined: Nov 2013
Posts: 518
Likes: 264
From: Jasper GA
Misfire when cold
I thought I had solved this but apparently not. 94 LT1 with about 46k miles, has been running great. Last week it started misfiring and when I lasered the exhaust manifold, two cylinders were 120 degrees cooler than the others. Figuring it was due for a tuneup anyway, I replaced plugs, wires, coil and ignition controller. The only things I haven’t replaced were the actual coil wire and the opti (might be regretting that). I have new O2 sensors and those will go in this weekend.
It ran great at first, then the misfire came back. It seems to happen only when the car is cold. As it heats up it gets better, and eventually runs great again. Then next cold start its running on 6 or 7.
Looking for ideas on where to start. I figure I’ll be checking fuel pressure, spark, etc. any suggestions are really appreciated!
It ran great at first, then the misfire came back. It seems to happen only when the car is cold. As it heats up it gets better, and eventually runs great again. Then next cold start its running on 6 or 7.
Looking for ideas on where to start. I figure I’ll be checking fuel pressure, spark, etc. any suggestions are really appreciated!
Thread Starter
Pro
Joined: Nov 2013
Posts: 518
Likes: 264
From: Jasper GA
I went ahead and replaced the upstream O2 sensors and the coil wire, still misfiring when cold. Now all ignition components are brand new, except the optispark. So with it idling I started pulling injector connectors. No idle change on 1, 5 and 8. I'm afraid it's the damn opti, but what's strange is how it gets better when it's hot, which makes me think it's a fuel problem. I should have replaced it when I did the water pump, but at the time it ran great and I didn't want to pull the factory one. Now I think that was a bad decision.
I'll still check fuel pressure before I start the optispark job, but if anyone has a good idea please let me know. I've read a ton of threads on this, and so many of them never come back with a definitive solution. Seems to be a real Achilles heel of the LT1.
I'll still check fuel pressure before I start the optispark job, but if anyone has a good idea please let me know. I've read a ton of threads on this, and so many of them never come back with a definitive solution. Seems to be a real Achilles heel of the LT1.
Thread Starter
Pro
Joined: Nov 2013
Posts: 518
Likes: 264
From: Jasper GA
Following up with the solution. Fuel pressure tests were good so I bit the bullet and replaced the optispark this weekend. Winner! Now from a cold start it runs perfectly, pulls great, misfire totally gone. And now I have a brand new ignition system from end to end, and I know fuel delivery is good.
Le Mans Master
Joined: Dec 2005
Posts: 8,534
Likes: 921
From: Communist Colorado
I hope you were able to get a Petris opti or youll likely be doing the job again sooner than later. Anything from local parts houses or cheap Ebay optis are not good quality. Several years ago I used an MSD and it only lasted about a year, so even a decent name in ignition parts like MSD still wasnt good enough.
Thread Starter
Pro
Joined: Nov 2013
Posts: 518
Likes: 264
From: Jasper GA
At $150 vs $500 I did go with the cheaper option, picked up a Cardone from Summit. We will see how long it lasts, hopefully I’ll get a long term fix. From reading the posts, it seems like a 50/50 bet. Some last just fine and others fail relatively quickly. I’ve done this job twice now so if I have to do it again, I could probably have it buttoned up in 3-4 hours.
if this one fails, yeah I’ll spend the money next time. But for now I’ve got other things to spend the budget on.
if this one fails, yeah I’ll spend the money next time. But for now I’ve got other things to spend the budget on.
