Still the cut out / stumble problem with my whipple charged 2000 500EFI. The engine seems to labor and cut out both when coming on plane and when cruiseing. The specifics are as follows:

- the problem seems to only happen when the RPMs are between 2500 & 3300.

- once on plane and cruising in the above RPM range the engine seems to loose rpms with out moving the throttle. when the throttle is then advanced the motor stumbles and the rpms quickly drop back to 1000 - 1500 then bounce back. this is accompanied by a backfire.

- when the engine rpm's are above this range the engine can be throttled with no stumble and the rpm's can be advanced all the way to WOT with no problem. The engine runs perfect at 4000 plus RPM's

- the engine idles fine

Here is what we have checked so far:

- changed the spark plugs

- checked engine compression - all cys are 140 - 150 pounds

- checked the cap & rotor (they look like new)

- switched the fuel pumps between engines

- switched the ECM's between engines

- Switched the TP sensors between motors

- there are no trouble codes

Any help would be great.

have you tryed switching the map sensors, I had a 500 efi that acted like that, the wire going into the top of the cap was broke.

Thanks - I will try switching the MAP sensors

changed the MAP sensors - still does it .... HELP!!!!!!!!!!!!

Just for grins slide an electric fuel pump into the circuit. Sounds like a fuel supply problem.

Fountain 10, I have a 35 lightning ts with the 500E.F.I as well.First off I love them! I had the same (although infrequent) symptoms as you to wards the end of the season. Does it seem to occur more when cold or does that matter? Also the fuel rigging and component selections seems very important Bret at aeromotive is (the man) last but not least Dustin at whipplesuperchargers.com is a class act he is responsive,knowledgeable as well as being very proactive in product development, not to mention he isn"t condescending with his feedback! message me with any questions good luck, i can"t wait for the season.P.S last year I recorded 102 on GPS at the cleveland poker run. This year I will be driving by that !!

Found the problem thanks to Dustin at Whipple. One of the diaphrams at the end of the fuel rail wasn't working correctly and it was letting the fuel vibrate in the fuel rail. Dustin has been a great help in working out any bugs along the way. I can't thank him enough for all his advise and prompt service when needed.

Gotta luv those Whipples!!! And the service!! I've had mine for 2 years with out any problems!!!