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

[lolwat]

first up new filter BAM!!!!!!!! then if it still drops a pump and check your tank(drain it, check for water etc etc)

[Golberg]

Are you running a stock fuel pressure reg?

[Nikkojoe]

...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

Its still gotta be there (the brown/red one) because thats is for the fpr. Blue one can be removed as that controls the abv.

And that setup is wrong with the vac lines. Will mean your abv is open on boost all the time....

[hugh]

I just crimped the return with the pressure guage in the engine bay, and the car idled around 50psi, but still dropped a little when revving..does that mean that the pump is doing a bit, by pressurising it more than normal because no fuel is returning, but not good enough to produce the correct pressure when revved? ie. it's on it's way out but not there yet..good enough to idle, but not good enough to rev?

KE_Slider: I ran it quickly yesterday with no filter, just the pipe straight through to see if the filter is blocking it, but made no difference.

Goldberg: As far as I'm aware, I am running a stock FPR. I got two others sent to me from a friend, one was all one piece, with the vacuum and fuel line joined to it which I think is a NA 4age one and one had the thread in the top, which my fuel return line has a banjo on it, and that is the one I used...I think it is the 4agze one.

Nikkojoe: I didn't set up the vacuum lines, John (Sprinterman68), who was recommended off the forum did. I can have another look tomorrow at where the vacuum lines go because I may have made a mistake.

[lolwat]

ok buy a new pump BRU

or (sorry if someone has said to already) check for clogged lines(doubtful)

[Nikkojoe]

Yeah I understand. Just get a picture/diagram of where the vac lines go to and then we can see if its correct :)

[hugh]

So I bought a new pump, and the pressure does the same thing, idles at 30psi, then when you rev it, it bounces around between 20psi and 40psi...I've been told that the vacuum lines may not be connected properly, so I have taken a photo...hop it makes sense...

There is a little pipe out of the top of the ABV which has no vacuum lines running to it at all, and as far as I can see, no VSV

http://www.ae86drivingclub.com.au/dcimages/5/2/8/29561.jpg

[Nikkojoe]

Incorrect.

Your abv is constantly open so you wont make consistant boost, and the fpr works off the red/brown vsv which you are missing. To make it atleast half decent, there is a vac line port on the intake manifold, move the hose that connects to the throttle body to the intake manifold port and see how it goes. Really though you should need a vsv....

[hugh]

interesting...as I didn't do the vacuum lines, I am unsure or why the red/brown VSV would have been removed...I will have a look at my manifold for the vac line port..
Would I need to vacuum cap the line on the throttle body?

[Nikkojoe]

Yep, block it off.

Best off googling for abv mod, lots of stuff out there.

[hugh]

Is this the vacuum port you were talking about??

Also, do I need to do anything with the little vacuum pipe out the top of the ABV??

http://www.ae86drivingclub.com.au/dcimages/5/2/8/29565.jpg

[Nikkojoe]

Yep, that's the one.

The port on top of the abv should be left open (the one seen in your pic above). I believe its a vent for the abv. I also doubt you could fit anything to block it anyway...