Fuel Pressure Too High

[Hanaldo]

Hey guys,

Just having a bit of a high fuel pressure problem after installing my new Walbro 460lph fuel pump, was hoping someone might be able to think of something I have done wrong here.

So to give you all the information, I have just replaced my old Walbro GSS-342 with a brand new genuine Walbro F90000262. Straight swap over really, just removed the old pump and installed the new one, had to modify the cradle a tiny bit to fit obviously, but nothing drastic, very simple stuff. The only thing I did differently was instead of using the stock wiring harness, I ran wires from the pump directly through the lid using Superben's idea:

Then from there to the relay and earth point, all as per normal. I otherwise haven't touched anything, didn't touch the fuel pressure regulator or anything in the engine bay from when the car was last running. I am using a Sard FPR as well.

After finishing everything off, I primed the pump to check it was working and it seemed to be, got this:

Seemed all good, so I primed it a couple more times for good measure, checked the pressure was still at 43psi, and then started the engine. Everything sounded fine, didn't suspect any issues until I looked at the gauge:

This is just at idle, no throttle being applied. I checked everything over again, but for the life of me I can't figure out what I may have done to cause the fuel pressure to go out? Only thing I can think of is maybe having the lid/hoses off for a couple of days may have let air/something else in to upset the regulator? OR, perhaps there was an issue with my old fuel pump? I wouldn't have suspected so, it never surged or gave any trouble. Tuners never mentioned the car starving of fuel at all.

Any ideas? I would simply adjust the regulator again, but I'd like to know why the pressure has jumped up in the first place...

[Hanaldo]

Orrr, new thought... Is the Sard FPR perhaps too small for the 460lph pump? Can't keep up with the flow?

[zebra]

Return line probably isnt big enough

[Marcus89]

There are the higher rated sard Type-R fuel regs but I couldn't see that being a problem at idle. The FPR doesn't actually feed any fuel back to the return it only really comes in play under boost as far as I understand. Really got me stumped trying to work out whats going on. When you prime the car does the pressure go to the correct 43 psi again now or does it jump the higher pressure?

[zebra]

at idle its the worst case, 460l/h pump and the engine would be swalling 3-4l/l means 455l/h of fuel has to be bypassed by the reg and down the return

[Hanaldo]

Return line probably isnt big enough

Yeh? Standard return line... Surely not everyone using this pump has upgraded fuel lines?

There are the higher rated sard Type-R fuel regs but I couldn't see that being a problem at idle. The FPR doesn't actually feed any fuel back to the return it only really comes in play under boost as far as I understand. Really got me stumped trying to work out whats going on. When you prime the car does the pressure go to the correct 43 psi again now or does it jump the higher pressure?

Nah when priming it always goes to 43psi. It's only when the engine is running that it goes to 60psi.

[Marcus89]

Ah disregard my post I just read a little more to get a better understanding (haven't mucked around with aftermarket fuel regs yet) I'd have to agree that increasing the fuel return is likely cause couldn't be much else at idle coming into play

[Hanaldo]

Dammit

Well that's something you don't read in the brochure.

[89CAL]

Do you have some spare fuel line lying around that you can run from the FPR outlet to a large container/bucket, then start the car and see if theres a different in fuel pressure. It's not the safest way to do it but will give you an answer as to wether it is the FPR or return line that is causing the issue.

Obviously be careful if you decide to do this because of fuel vapours and stuff, probably best to do it outside

But yeah if you use the largest size fuel line that will fit on the Reg then you should have no restriction there. I can't say I've ever heard the return line being a problem, but thats not to say it isnt the problem.

[scotty nm35]

The return bypass hole in the reg is probably only 2mm in size so I don't think the return line size will matter much. Are you sure the reg is genuine? I assume all was well with it before the pump change?

Can you perhaps try fitting another reg? I run the relatively cheap SX reg with twin Walbros on e85, no issues here.

[Ben C34]

Not that I have put a gauge on my car, but I have the same pump and haven't had any running issues you would expect with high fuel pressure. I'm running stock reg.

[Hanaldo]

Unfortunately I don't have another reg I can try, or any fuel hose

I am pretty sure the reg is genuine, I bought it from a seller on here... Hmm, this is a bit trickier than I thought it would be

[White GTS-T]

What voltage is present at the pump now, as apposed to before? Is the FPR adjustable?

[Hanaldo]

What voltage is present at the pump now, as apposed to before? Is the FPR adjustable?

Was 14v, haven't actually checked this time. I'll have to borrow a multimeter. The FPR is adjustable yeh. I was going to try to adjust the pressure, I just don't want to cover up any problems by doing so. It was all working fine with the old pump, so just want to be sure everything is ok.

[White GTS-T]

How hard is it to try the old pump with the new wiring configuration and double check the pressure again, to rule out the new pump?

[boostn0199]

I get around 62psi pressure before it reaches the fuel reg so it sounds like maybe the reg isnt doing its job and is just running full pressure straight as it comes out of the pump.

[Ben C34]

I get around 62psi pressure before it reaches the fuel reg so it sounds like maybe the reg isnt doing its job and is just running full pressure straight as it comes out of the pump.

what does that mean? The reg creates pressure in the system before it, all the way back to the pump.

[scotty nm35]

Yeh, sounds like the reg can't bypass enough fuel unfortunately. It can keep up at 12v but not at 14v when the engine is running.

[STATUS]

what injectors? i would not be too concerned unless its bouncing, its not uncommon to to run 60-80 base pressures depending on target boost and pump capabilities. ID recommend a base of 60-100psi depending on application. I generally run 60psi on bigger injectors ie 1000 and 2000cc.

Basically keep TOTAL pressure under the injectors limits.

ID725 - 8.5 bar, 123.5 psi.
ID850 - 7.0 bar, 101.5 psi.
ID1000 - 7.0 bar, 101.5 psi.
ID2000 - 9.0 bar, 130.5 psi.

[kitto]

Have you tried adjusting the base pressure when the engine is running?

If not, do that and report back