I have a problem that both me and my tunner are stumped over if anyone could help that would be awesome.

So I took my S in to get retuned due to a new 3.5 map...and it felt kinda funny the last two weeks at WOT

Well we found that the fuel psi was only 60 at WOT and when it was at the top end it was only 40psi!!! not good at 15 pounds of boost.

So we reconnected the vortech FMU and it hit 100psi at start of WOT then 80 then 60 at top still not good.

We replaced the old 255 fuel pump with new 255...NO

Replaced the Fuel pressure regulator...no

checked all lines for a pinch...no

My compression in 8.8 and I'm running 650's all the rest of the mods are in the sig...

O and the fuel filter is on the fuel pump right?

If you need to know anything else of what happpened I'll let you know...thanks for any help-Rob

 

Did you use a model 342 HP pump? The pumps tend to wimp out if you are using too high of a static fuel pressure. The difference between 60 and 50 is dramatic so if you are using high pressure to compensate for small 650 injectors this may be your problem. If you run 750s at 45 to 50 psi the pump won't wimp out.

 

Moving to FI

 

As an experiment, I might try running a different source of 12 volts to the pump and make sure the pump ground is good. Maybe it simply's having a problem drawing sufficient current.

Your fuel pump is a high volume/High pressure or just high volume? Walbro sells both kinds. The Comptech is either a Walbro or a Bosch right?

 

The fuel pump is the 255 from Vortech...or at least both of them were.

 

I think I'm going to go with the 750's like you said Sideways....I just can't think of anything else...I've been racking my brain.

I figured 650's would be able to handle this power though....

O and the fuel filter is on the fuel pump right??