Fuel Pressure Going Down?? Need Help!

[hugh]

Hey Guys,

I am in the middle of tuning my GZE and am having a problem with the fuel pressure. When you go about 2000rpm, the engine leans out and looking at the fuel pressure gauge in the boot, the pressure goes down as the revs go up.
Engine runs at 30ish psi on idle which is fine but as you rev it, the pressure goes down. I have replaced the VL fuel pump and the FPR with no success. Car is running surge tank in the boot.
Need to get this fixed ASAP as I still have other things to do on the car before I go away overseas for good, very soon...

Any help would be great!!
Hugh

[Hen may possibly be a nut]

If your fuel pressure drops with revs then you have a problem. Could be blocked filter/pickup, dying pump or too small/crimped lines (actually scratch that last one, you're measuring BEFORE the lines).

Also just check that your FPR is getting a manifold pressure signal (runs through a VSV stock, you can run it straight from manifold as a test though to see if anything changes).

Hen

[slide86]

agreed.

ensure that the reg is closing coming up on load so there is actual pressure in the rail rather than just allowing the fuel to go back down the return.

try crimping the return line with some pliers and then revving up the engine. if the fuel pressure stays at 30psi, then you know you have a return problem and not a pump/rail fault.

[hugh]

If it makes a difference (on where its reading the pressure from), the gauge is between the pump and the filter. I have a new filter but it requires some hose fittings so haven't been able to test that yet.
It is running a VL pump and I took it off and replaced it with another second hand one which I pulled out of a perfectly running VL, so no reason to think there was a problem with it, but it has just sat around for a while, so possibly could be the pump.
I may be wrong, but if I crimped the return line, and pressure stayed at 30psi, wouldn't that mean the return is fine and there is a problem with the fump or something??
I'm a little confused...

[slide86]

yeah you are right bout crimping the return to diagnose the fuel pump, BUT you can also crimp the return to simulate the pressure reg operation.

what i was hinting at is, if the reg is staying open, there will be no pressure in the pump side under RPM....so the fuel will just flow back to the tank. by crimping the return you simulate the reg closing thus building max fuel rail pressure.

you really need to have the gauge on the rail, not at the pump. this is the proper way to measure fuel pressure.

[hugh]

Thats just how the system was when I bought it and ahven't really changed anything as there hasn't been problems till now. I can move the gauge to the fuel like..but do I put it on the line just before the FPR, or return line?

So if the return is fine and I crimp it, the fuel pressure should go up...and if it doesn't, the return is the problem...correct?

Sorry about being a bit shit

[slide86]

yeah thats right, if you crimp the return and the pressure goes up and stays high, then the pump is working fine.

if you crimp it and the pressure doesnt go up, then you have a problem with your pump.

fit the gauge just before the inlet to the fuel rail. im interested to see what is happening at the rail end.

do GZE have a fuel damper also? i know on normal 4age they have a damper on the start of the fuel rail, this looks like a pressure reg.......you arent getting these two confused?

[hugh]

nah...damper is the thing like you say, that looks like a FPR, but doesn't have any vacuum line to it, sitting right on the end of the rail..if so, yeah I have one...

You just contradicted yourself I think though...In your first post, you said, crimp the return line and if it doesn't go up, its a return problem and not a pump/rail fault, but just said the opposite in your last post...When I get home, I will crimp the return line and tell you what happens...

Could it be a vacuum problem? After I put the engine, the wiring and vacuum lines were set up by John (Sprinterman68) and I noticed he has done the ABV mod, so not many vac lines left...

[Nikkojoe]

How is the red vsv setup? One end should be from inake manifold, other should go to fpr

[hugh]

Alright, so I have done a few tests...

Crimped the return line, when the pressure gauge was still in the boot, between the pump and the filter and the pressure dropped down like before when I revved the engine.

Moved the pressure gauge to just before the damper on the fuel rail and when I revved that, the pressure didn't drop so much, but stayed around the 30psi mark...

Just realised that I forgot to crimp the return and try it with the pressure gauge in the engine bay, but it is pissing down now and don't want to head back out...

I'm thinking fuel pump, someone let me know if thoughts are different..

I think my VSV was removed when ABV mod was done, does that sound right?
Off the top of my head, I think the vacuum line goes from ABV to throttle body, with a t-piece in the middle going to the FPR