Q: I have a 402 big block motor in my Chevy truck. It runs great from 1,800-2,000 rpm, on up. It has a Crane RV cam, Edelbrock Performer intake, and Performer heads. The rest is stock Chevy and pretty new (10,000 miles).

At idle, it has a bad miss on cylinders 5 and 7 (we put the engine on a diagnostic machine to find out for sure). I have changed the lifters, carburetor, plugs and plug wires, distributor shaft, even new heads. I still have the miss.

Could it be a bent distributor shaft? The two dead cylinders are next to each other on the distributor cap.

A. We have a few questions as well. Do you have spark at low rpm? Did you do a compression comparison on all the cylinders? Did you do a leak-down test? Have you had the same intake manifold on the engine while this was happening? If all of this checks out, then we’d say you have a fuel distribution problem or a cracked manifold causing a vacuum leak. We don’t think it is a bent distributor shaft, because then all cylinders would be affected.

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