Crazy fuel pressure fluctuations..

[Trav4011]

My 04 GT that I just picked up is having some crazy fuel pressure fluctuations.. It's got a single Ford GT pump installed, and the car makes around 540whp with a built motor/t-trim.

I've noticed that while cruising around, from time to time, the fuel pressure gauge will start bouncing around wildly (back and forth), between 30 and 60psi of pressure. The car runs like crap and surges in tandem with what the gauge is doing. Usually, stepping into it past 1/2 throttle makes it stop.. but, it's getting worse and worse. Sometimes, pressure is at 30psi.. sometimes 40.. other times 60. I've never seen this happen before.. Anyone else have this issue?

Travis

 

[avengence85]

What is your pressure at idle?

Also, have you replaced the filter? Sounds kinda simple but I would try it first.

 

[avengence85]

I just noticed you said you have a t-trim. Are you running draw through?

If you are, you are back washing the maf. Data log your maf readings.

 

[SaleenGT2001]

a single GT pump with 540???

i would think you are WAY past the duty cycle of that pump.

my twin GT pumps with PPRV delete and wiring upgrade was hitting 100% DC's at 5200 RPM with 612 rwhp

 

[Trav4011]

It's definitely out of pump.. that's for sure. I purchased the car like this, so I'll be doing some upgrading for sure.

The previous owner ran a -6 feed line from a Mallory fuel filter (in the stock location), up to the fuel rails. It is pretty new (6K miles).. The pressure at idle is usually around 35-40psi, and once I'm crusing around, ranges between 50 and 60psi. The fluctuation starts usually after I've been driving around for a while, and usually in stop and go traffic. The gauge will start bouncing around, back and forth, between 30 and 60psi.. I've logged it all over the place with my Predator, so it's not the gauge. Stepping into the throttle, past 1/2 or so, makes it jump to 60psi, and it usually goes away.

The MAF is draw through.. and the recirculation is about 12" upstream from the MAF, with a 90* bend between. I will log the MAF though, and see what's up.

I plan on doing a new tank with twin supercar (GT) pumps, divorced, with an external "Y". Where can I get the upgraded wiring?



Travis

 

[avengence85]

Pumps aren't going to max out at a low throttle. Its def back washing the maf. I drove my friends car when it was draw through and it did it BAD. He did his own blow through setup and now its perfect with now fluctuations.

My friend has a SQ trim on a blow through with a 4 core front mount intercooler and he gets charge temps of ambient. He is also doing the dual super-car pumps but is making his own Y harness because he didn't want to spend the 130 or whatever it is they want for that harness. Right now he has the termi tank and pumps but they max out at full throttle.

 

[SaleenGT2001]

there is a write up on modular fords about the wiring upgrade.

i used 8 ga. amp wires for mine.

basically you eliminate the stock tiny wires that feed the pumps with the much larger amp wire.

i heard it was good for +10% on the DC but i didnt log it before and after so i'm not sure.

i'm running the twin GT pumps PPRV delete, wiring upgrade and BAP on my car. my DC doesnt get out of the low 80's

 

[Trav4011]

I'll have to look into going blow through.. I set up my last Mustang that way, and it ran great.

The wiring seems easy enough..

Travis