hi all,
just wondering if my fuel pressure is ok, ive got it ticking over at just over 3 bar, when im driving it steady, it goes down to just under 3 bar, but when i floor it, the pressure goes down to 2 bar
i have a new walbro pump and an sx adjustable fuel reg, is this normal?
thanks, phil.

 

FPR on mine is set at 3 bar and increases on boost, shouldnt go down. check the vaccum pipe for any leaks or maybe disconented.

 

Yes mines the same , it ticks over at 3 bar and does not drop at all when floored.

 

oooh thats not good, i didnt think it was right, i know theres no fuel leaks, it must be one of them, or could the regulator be broke in some way?

 

theres been a few references to chinese copied walbro fuel pumps,the proper genuine walbro ones are stamped gss341 or gss342,

 

Yep it will probably be going lean under boost. Dont hammer it till fuel pressure is sorted. Start with a new pump id suggest

 

Mine did the same when the diaphragm in the fpr was knackered, stripped it and rebuilt it and all was well again. Should increase with boost

 

Mine did this, but the pipe from the manifold to the fpr was split.

It now sits at 3.3 bar above boost and hardly fluctuates, except for about 0.2 bar on WOT.

 

fuel pressure should increase on a 1:1 rising rate so with a fpr set at 3 bar atmospheric it should rise to 4 bar with one bar of turbo boost.

 

By atmospheric it means you set your fpr to 3 bar with the vac pipe off and blocked

 

 

thanks for all the replies, ive been out trying to sort it for a few hour, i stripped the regulator and found a piece of metal where the ball bearing closes, put it all back together and it was the same, but whilst the regulator was lose, i noticed that the pipe that goes from under the regulator to the return pipe was leaking, not a lot, but still a leak is a leak, ill sort the leak tomorrow, hopefully its that.
would a small leak drop the pressure to 2 bar?
the pump is ok and stamped with GSS341.

 

possibilty,worth a try, fuel pressure gauge should show 3 bar though and hold even before you start it

 

on ignition it goes up to 3 bar then drops top just over 2 bar over about 10 seconds, then really slowly keeps dropping, sounds like the culprit?

 

,dont suppose you are anywhere near me in Bath? ive a spare walbro here you could try ?

 

return pipe leak unfortunatly wont cause it as thats only got fuel in when it reaches the pressure on the reg..

if sat idling at 3bar then the pressure is about 3.6bar (with vac pipe off) therefore at 1bar of boost you should see 4.6bar pressure..

Has the bit of metal damaged the ball bearing or the mating faces? as the fpr will need to close to increase the pressure.. if it cant seal that might be the issue but 2bar is very low.. fuel pump, or fuel pump wiring (worth checking voltage at the pump on boost, although not easy on the road in your car at all).

Simon

 

hi all again,
thats very true simon, as i found out by fixing it with no joy lol, the ball bearing was a little discoloured so i gentley cleaned it with 800 wet n dry, could it be that? the matting looks to be good.
so today i tried the fuel pressure meter on the pipe straight from the pump and it goes up to 6.5ish and holds, so i next put it on just before the regulator and it went to just over 3 and dropped, this made me think there was a leak somewhere in the parralell lines, so i removed them and fitted the fuel feed to back right, piped both fronts together and the return pipe on back left near turbo, put the meter on the end and it held at 6.5ish again, so no leaks, i fitted the return to the regulator, the meter inline and went round the block, when i try to floor it, it didnt run properly, as its not mapped up there because of this problem, so i gradually built the revs and then tried to floored it, the pressure builds to 3.5 and down to 3, but cant floor it properly, it might be worth mentioning, it only boosts to .5 bar.

 

That sounds better

 

ive just been round the block again and the pressure dropped to 2.5ish? also simon ive just checked the volts to the pump, they are 12.12v on tickover and driving, 11.98v on boost, it drops but hardly anything, would you say thats ruled out?
all the fuel lines are good, with no pressure drop before the fpr, with the fpr piped up, the pressure goes up to 3.5 when the ignition is turned on, after the pump stops, it goes to 3 bar and drops really, really slowly, on driving it drops still so im still thinking its the fpr bearing not being perfectly round, its really the only thing that it can be as thats still not right, is it?

 

So pump appears fine and you have changed it?
Voltage at pump appears fine?
You have no leaks?
Got to be reg then.
At 0.5bar boost the fuel pressure should be 3.5bar if static pressure is 3bar.

 

yes i agree, pump is new and volts ok, no leaks as i tested with the pressure meter at the end of the fuel lines, so has to be the ball bearing in the fpr.
new fpr on its way, so ill keep you posted simon about friday by text, cutting things a bit fine but if the new fpr solves the problem, ill be happy,
thanks for all the help and ill let you guys know what happens with the new fpr,
thanks again,
phil.

 

No problem.

Hopefully that sorts it

 

update for this problem is, a new fpr never solved it, pretty gutted now as ive had to cancel a remap on friday, i really cant see why its doing it now, as youve all said and ive checked everything, the only other thing that i can think of is a bad earth to the pump, it there any other way of wiring the pump up saftley, so i can rule out wiring?

 

leaky injectors ?

 

Yes.

Using a voltmeter on the plug on the top of the tank find which is the ground and which is the pump feed. Wire them directly.

Other thought is the plug thats normally under the rear seat could be corroded.

Think the fuel pressure hold on the reg when engine is turned off and pressure slowly drops? Which generally rules out leaky injector seals. Although unless they only leak with higher pressure on boost but then it would have gone rich due to the fuel in a cylinder and it didnt so I dont think thats the case.

 

yes i thought that, you would have seen it when mapping, it always said lean too, ive just thought of something, when i built the car, i had to swap some wire around on the pump plug, i copied off my impreza based rs200 as its the same, this made the fuel gauge go up to correct reading every time the ignition was turned on, unlike other imprezas which stay up, also when the ignition is turned on and the pump works for the few seconds and stops, i can flash the lights and the pump will work again, could there be some wiring problem at the 3 relays under the dash?

 

Thats deffo not right.

I would buy a new 40amp relay and wire the pump fresh if it were mine.

 

does the relay do anything other than send 12v to the pump with the ignition on? if i just wired it up direct, wouldnt that just be as good for testing?

 

the ecu triggers the relay by dropping the fuel pump output pin to ground.. when you first turn the ignition on to prime the fuel system up to pressure and then when the engine is turning - cranking or running.. so if you stall it or crash and then engine stops so does the pump.. so the only down side to wiring it to ignition trigger is that if you were to crash and sever a fuel line it would continue pumping fuel all the time the ignition is on..
however it would be okay for a test and to prove there is a wiring issue causing the problem and get it mapped etc..
then sort out either using the ecu trigger to you new relay and wiring or repairing the original setup

 

ok, very well put, so ill wire it direct tomorrow and see what happens, ill let you know again tomorrow lol, thanks very much simon.