So, I have been having some problems lately with the car not running like it should. I have checked just about everything I can think of. The car is running lean under boost. It has nothing to do with rpm's. If I'm light on the throttle, the AFR are fine all the way up the rev range. I have checked for leaks in the connections in the intercooler piping, adjusted the valves, changed the spark plugs, coil packs, fuel pressure regulator and fuel pump. Still acting the same.
Any ideas what it could be?? Would really appreciate any help!

 

What engine management are you using? What MAP sensor?

 

The tune ?

 

retune

 

I'm using AEM (series 1). The MAP-sensor is Omnipower (4 bar). How can the tune just change all by itself?... Or could it be since the engine was brand new and has "worn in", so I now need to retune? The engine has about 2000 miles on it now.

 

Sounds like loss of fuel pressure under high flow demand

 

This.

What fuel pump?

I had a Walblow when mine was tuned to about 11.5 A/F. It gave out after about a year. Put in a DW 340 after the failure, at the same base fuel pressure, and found i was running really rich afterwards.

Something to check anyway.

 

I had a Walbro 255, but just put in a Aeromotive Stealth 340. Same thing happens.

 

Check the map sensor..for leaks and the plug connection. I had problems with one of the pins in the plug and had the same problem. Inspect it clean the map with carb cleaner..etc.