Need Help! Losing Fuel Pressure!

[LTZ MACH]

Ok, a little background on the car

• KB 2.4 making 17 psi (and 24 psi on high boost)
• 60 lbs injectors
• KB BAP
• Fore Precision Hat
• One cobra pump and one focus pump
• Modified to return-style
• Fuel Pressure Regulator

Well, I had the car out this weekend noticed the fuel pressure dropping off. I do not have a wideband yet, so I got a little worried. At idle, the fuel pressure is reading almost 70 psi. Rolling about 60 mph in 3rd gear, I noticed the fuel pressure is around 58 - 62 psi. I then hit it and as fast as boost came on the fuel pressure dropped. At max boost (17 psi) I noticed the fuel pressure was 38 psi. I immediately got out of it. This does not seem right to me at all. I thought the fuel pressure should be 45-50 at idle and increase with boost 1-to-1. Could someone please give me a little insight on this and hopefully give me a few things that I should check??? Some of you tuners or fuel guys should have some idea, I hope! Please let me know what you think.

LT

 

[03cobramanIII]

Ok, a little background on the car

• KB 2.4 making 17 psi (and 24 psi on high boost)
• 60 lbs injectors
• KB BAP
• Fore Precision Hat
• One cobra pump and one focus pump
• Modified to return-style
• Fuel Pressure Regulator

Well, I had the car out this weekend noticed the fuel pressure dropping off. I do not have a wideband yet, so I got a little worried. At idle, the fuel pressure is reading almost 70 psi. Rolling about 60 mph in 3rd gear, I noticed the fuel pressure is around 58 - 62 psi. I then hit it and as fast as boost came on the fuel pressure dropped. At max boost (17 psi) I noticed the fuel pressure was 38 psi. I immediately got out of it. This does not seem right to me at all. I thought the fuel pressure should be 45-50 at idle and increase with boost 1-to-1. Could someone please give me a little insight on this and hopefully give me a few things that I should check??? Some of you tuners or fuel guys should have some idea, I hope! Please let me know what you think.

LT

why you got a foukous pump and one cobra pump? you need to go to amazon site there a vender here and talk to them about your problem they hooked me up good.

modified to return style??? omg! theres no telling call them # in my sig tell um cobraman III sent you LOL.

 

[LTZ MACH]

Thanks! The focus and cobra pump set up is in there from the previous owner. My plan is to convert to twin walbro 255s since the car is return style.

I will try giving Amazon a call as soon as I get a chance.

LT

 

[JedWele]

Probably something else, but I would replace the fuel filter just in case its clogged.

 

[LTZ MACH]

I will check that too, but it is only a few months old. I will probably due that when I replace the pumps.

LT

 

[69gt4speed]

Possible issues
1 there isn't a proper rising pressure fuel regulator installed or the vacuum/pressure hose line isn't hooked up from manifold port to pressure regulator port. Reg has to see what manifold pressure is doing.
2 One pump could be failed causing fuel pressure to return through bad pump, u need a check valve maybe with a focus pump?
3 I wouldn't run 2 mismatched pumps in parallel anyways
4 Ya I'd probably use at least 2 walbros at least no fpdm w check valves unless they are built in. 255's
5 It almost appears the regulator is hooked up wrong port wise, I don't know if u can do that.
6 I'm surprised it runs at all.

There are many things to check out, really u don't need a fpdm or the frps w a return type system. Hard to say really what's going on. U are correct 39 psi - idle vacuum is good at idle and rising 1/1 w boost.

 

[LTZ MACH]

Thanks! I am now leaning towards the FP reg being bad. I checked the vac tube going to it and everything looks fine. No leaks, bad connections, etc. and I know it is correct because my boost gauge is reading at the same point. When I disconnected the vac gauge from the reg at idle, nothing changed, which it is my understanding that the FP should have increased since I removed the vac from the reg. This is why I am thinking it is the reg.

Yeah, I don't like the different pump set-up either and especially since they are on full time now and now adjusted duty cycle because of the return system. I am afraid that they are going to burn up too soon. The FPDM has already been bypassed!

Thanks for the help. Hope it is just the reg because it is an easy replacement.

LT

 

[69gt4speed]

I wouldn't worry turbine pumps will burn up just not sure if a focus pump has a check valve built in since it is used in a single pump application. If it failed might bypass fuel back into tank.
As far as reg goes that is the easiest to check out. I assume a ext reg w 03 fuel rails. Prob left the frps hooked up? I'd check the port connections for sure. Fuel pressure almost goes backwards from what u want.
I am surprised it isn't throwing codes from the fpdm being bypassed. There's a wire that goes back to ecu to indicate it's working. But i've never tried this let me know how it goes.

 

[2004silvercobra]

i would say frps might be bad and messing it all up.. it could either read 0 or read really high.. mine went out and said i was at 70+ at idle.. pull the plug off the sensor and see if it drops..

 

[LTZ MACH]

Yes, it is an external reg with the stock rails. The frps is still hooked up, which is what I am readying the fuel pressure from.

This weekend I put a mechanical gauge on the valve on the rails to verify my gauge in the car and they are within 3 psi of each other. With the vac line removed from the reg I tried adjusting the pressure down to 40 psi but it would not go any lower. It was already at its lowest setting. I then hooked up a hand-held pressure calibrater I borrowed from work and pumped up to 12 psi into the reg and the fuel pressure never changed. This makes me think that either the reg is bad or I have a restriction in the returnline somewhere that will not allow me to adjust the pressure any lower than 60 psi. Any other thoughts?

LT

 

[69gt4speed]

Prob regulator is bad. I'd check the return line though, take the gas cap off and blow air through the return line make sure it isn't pinched off. Make sure the reg is hooked up right meaning inlet, outlet and return to the right line. U can take a lot of better regulators apart, get repair parts for them.