[leomarcotte]

I have a 1990 36' Land Yacht with a Chevy 454 that I purchased a few months back (70K miles). The engine appears to run fine at first with good acceleration and smooth operation.

After about 30 minutes on the road it develops a backfire while climbing grades at highway speeds. Depressing the accelerator to the floor seems to rectify the problem in most instances but it does occasionally still occur. In addition, when coming to a stop and starting to accelerate again the engine idles and runs very rough. While it eventually gets back up to speed the first 30mph of speed increase is very slow and painful. Eventually, it appears to kick in and start to have a more normal acceleration.

The dealer (Huffines Chevrolet in Lewisville Tx) has replaced the spark plug wires, spark plugs, both fuel filters, and done the 60K service that included tune up and injector service. The problem still persists.

Anybody have any idea what is causing this problem?

I am considering a vacuum leak, fuel lines being weak, fuel pump replacement, coil replacement, or possibly bad new spark plug wires. What priority should I attack these or what others should I add to the list?

Thanks