trying to get my car retuned and as soon as boost starts the fuel pressure drops right on the gauge on my fuel rail. didn't have this problem last year and sat all winter and now running a different turbo so i wanted a retune. i have a walbro 255 fuel pump, aem fuel rail and fpr. brand new fuel filter and braided line from fuel filter to line. we just started looking into it today so any advice would be greatly appreciated. running aem version 1 ecu and base fuel pressure is 40

 

Take ur regulator off vacuum and if the fuel pressure doesn't raise then ur regulator is the problem if not then ur fuel pump is going assuming there are no clogs in the system

 

There could also be a voltage drop at the pump. I have seen that cause this on more than one occasion.

 

Voltage drop was my problem. It would hold pressure up to about 6k and then drop off. Wired in a relay and no more pressure drop

 

Yea if you are near the limit of a 255 you can have a voltage issue. the stock wiring can't support the amperage draw.

you need to hardwire the pump with a high current relay (triggered by the ecu fuel pump output) and 8-10awg wire, the negative wire grounded to the chassis and the positive wire straight to the battery with an inline fuse.

 

It doesn't have to be near the limit of the pump though. I have seen widespread voltage drop issues on completely stock vehicles. It is an unfortunate common problem that is even more commonly overlooked.

 

That is true. it seems like it's hit or miss on the OEM wiring. I've seen pumps never have an issue and other times it's like the pump won't even work.

I've noticed that vehicle condition has a lot to do with that.

I personally hardwire every pump on every chassis, especially since most of what I build/work on are high hp turbo cars. NA doesn't bother me as much since the pumps operate within a very narrow pressure range so they don't normally have issues.

also I've found that on newer cars (like 2006+) that the OEM wiring is sufficient, especially given the OEMs move over to more efficient wiring and control systems. although the one issue with most newer models is the returnless fuel system, not so great for high hp and elevated fuel flow so they tend to be converted to return systems.

amazingly the new 2015 launch edition STi we just picked up still uses a return style fuel system and port injection. it has a single feed and dual returns each with their own regulator. seems like STi knows their customers will modify the car in some manner warranting extra fuel flow/pressure.

although I wish they would eliminate the tumble valves lol.