GarageBuM

Hello everyone!

first off, this is a 94 z28 rebuilt to bone stock with the exception of being bored .040 over and a K&N air filter. Everything is new and ACDelco except the cat. It's a universal one. The left side of the engine LTFT is 140 and the right side is 128. The opti just got installed last weekend and it is a brand new unused 1994 edition opti. No reman. No crossed wires, or vacuum/exhaust leaks. Can't feel a miss anywhere. I'm lost. There is no water leaks as the timing cover and water pump are sealed with aviation sealant. O2s are reading like they are supposed to and this is not a false lean code as the spark plugs reflect a lean condition. Any help would be greatly appreciated.

GarageBuM

Ok, sorry it took so long to reply, but it took some time to figure this out. Of course, this car failed inspection which actually helped me quite a bit. I was able to go off the report and see, there were times the engine was lean, and rich. I took Injuneers advice and picked up scan9495 and eehack. When I monitored left and right blms in real time, idle and drive, I noticed all these little spikes and drops while driving, and a very slow, constant rise in the blm numbers while idle, all the way till they would max at 160. So I let it idle for several minutes (30 or so) then cut it off and let it cool. When cool, I pulled a plug. PIG RICH. Drove down the freeway for one exit romping all over it, came home and let cool, pulled a plug, lean as well done bison meat. couldn't figure it out to save my life.

Don't remember why, but I was under the car one day with a flashlight in my mouth. Sliding under the car on the creeper on of the tools fell of my chest on the ground. Normal thoughts and words as I blindly felt around for it, turned my head to see it, grabbed it and put it back on my chest, turned my head strait up and BOOM! Flashlight landed on the underside of the driver manifold right under the heat shield of my ole rusty manifold where I saw carbon build up! I immediately pulled the manifold, cut the heat shield off and found a very small, inaudible crack on the very top of the manifold, checked passenger side, same thing. I bought a set of shorty headers and a new exhaust system and BOOM! Problem solved! Passed inspection, BLMs went back real close to factory specs! shbox, you were one hundred percent correct! I should have looked closer. Thanks for all the help and I hope this post helps someone else with a similar issue.

Ananta1369

Actually, I think this might help me. I have very similar issue and suspect that I have a leak somewhere in the header. I will look at this idea more. Thanks for following up and posting the solution. So many never do...

GarageBuM