500EFI whipple engine stumble
 

I have a HP500 EFI with Whipple Chargers which is having an intermittent stumble when coming on plane (or right after coming on plane with the rpm's around 3000 - 3500) or when running close to WOT. This problem does not happen on a constant basis but does seem to be related to the load on the engine. The best way to describe it is the ignition is cutting out. The rpm's will drop from 3500 down to 1000 or so then come right back. I have changed the ignition coil and spark plugs but this did not fix the problem. Could it be a problem with the ignition module or knock sensor ? I have a scan tool so I am going to plug it in tomorrow as well as check the fuel pressure under load. Any help would be great.

call Dustin, he should be able to help!

Sounds like a knock sensor shutting down the ignition, You have good gas?

I will check the knock sensor. I just cleaned sand out of the water pressure fitting in the block which is right next to the knock sensor. Maybe I loosened the wire hooked to it. The gas is good 93 octane from the same place I always get it plus it is only happening on one engine.

I had a similar problem in the past with a carbureted engine which actually turned out to be the possitive wire from the starter to the alternator shorting on the block almost caused a fire. Just a thought.