Ok, Heres The Deal, My Port Motor Tach Whats To Jump 300-500rpms While The Motor Is At 4k Rpms. We Have Ruled Out The Tach Due To Changing The Sender Wire, Which The Jump Moved To The Other Tach. Also We Had The Scan Tool Hook Up Which Show The Rpms To Hold At 4k On The Scan Tool. So This Would Rule Out The Motor. Please Help. The Motor Has Only 10hours 02 500efis. Thanks Scott

The tach is jumping 300-500 RPM, not the motor, right? If this is the case, I would troubleshoot the various portions of the link between the two motors. It sounds like you have already ruled out the gauge itself, correct? Is there a sender that you can check?

yes, we had the scan tool hooked-up and it was showing to hold on the scan tool. i will say that the scan tool does move a little on the rpms, but i was told that the scan tool would not hold the rpms right on that it would move due to the sedative matter of the computer. so this would rule out the motor. any ideas. thanks scott

Anybody?

Run a jumper wire from distributor and the block! I had the same problem, talked with Mike Lavorsi, and he explained its a comon problem with the hp500's due to the piant. I ran a wire and solved the problem!