About 15 years ago, my 1986 IROC 305 TPI LB9 failed emissions. Went through normal troubleshooting and could not find root cause. Had a local mechanic that guaranteed emissions test or your money back. He could not get it to pass emissions. When I started taking the engine apart, I found damage in cylinders 2 & 4 due to a coolant leak. Life happened and I didn't get back to working on the engine until this year.

The engine had minor modifications done. I can provide specifics if needed. However the injectors were replaced with 22lb Bosch D3 injectors from South Bay. After the engine was rebuilt, we ran the engine on an engine dyno. We struggled with getting the AFR tune correct. We upgraded the tune to a $6E to remove the 9th injector. Updated the fuel injector size in the tune and deleted the low pulse width injector correction table (after reading multiple posts about D3 injectors). On the dyno we used a WB o2 sensor to verify AFR. We checked for leaking injectors by putting fuel pressure only at 43lbs for 1 minute. Shut pump off and spun motor over and cylinders were dry.

With all that said, looking at the pictures below, the original exhaust manifolds (from before the engine rebuild) show what looks like to me a rich condition (high build up) on one side and normal/leaner condition on the other side. This failed emissions. After the rebuild, I see a similar imbalance in the new exhaust collectors. We will verify next week (May 16th) what the spark plugs say. Is this imbalance normal, or could this be the original issue that caused the car to fail emissions? Could this be an ECM issue?



After rebuild, driver side

After rebuild, passenger side




Original exhaust manifold before rebuild. Notice lack of build up.

Original exhaust manifold before rebuild. Notice build up