Fuel pressure creep?
Turbo Mini Forums

Bit of an odd one!

Since fitting a fuel pressure gauge it has become apparent that my fuel pressure creeps up gradually? So far ive checked the following...

* Took cap of tank and ran pump to check for blocked breather on tank causing pressure build up-No change when cap removed.

*Ran return hose into seperate petrol can to illiminate restriction in tank return as return runs to bottom of tank-made no difference

* took my FPR off and used foot pump to check it was opening at 3Bar-got face full of fuel at 3Bar so thats working ok

* blew down the return, all seemed clear and could here bubbles in tank when blowing down return hose

After all these checks I put it back together and all seemed fine, running at 3Bar continuously for a good few minutes. Took it for a drive and after 15-20mins I noticed fuel was being taken out on my LCD display and then noticed the fuel pressure at 4.5Bar.

Anyone got any ideas why this could be? Im yet to check the fuel pressure when the fuel is cold again but it doen't seem to be heat relateed from what I can tell...

Cheers in advance
Matt

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1/4mile in 13.2sec @ 111 terminal on 15psi

could the pump not be giving constant pressure?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Hmmm good point, any suggestions of how I could check though? Ive already got a pressure gauge in between the pump and inlet to FPR.

Just had a though I suppose I could possibly put a gauge on the return aswell, although this would restrict the flow any way because of the fittings being pushed into the hose?

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1/4mile in 13.2sec @ 111 terminal on 15psi

Having had the regulator plumbed in backwards originaly and pressures of 90psi, maybe the regulator cap is damaged?

I'm confused.. probably because I know Nowt about Fuel Injection

...But...

Isn't the point of a fuel regulator to make sure a constant fuel pressure is supplied to the injectors? who cares what the pump output is as long as the pressure AFTER the regulator is constant? Thats the point of a regulator ..it regulates the varying pressures coming out of the fuel pump..

<<Edit>>Just thought, does the regulator regulate by returning unused pressure? Is that what I am missing?

Edited by Turbo Tel on 2nd Jul, 2008.

website:- http://www.terryhunt.co.uk

I thought Joe's point could be valid if for some reason the pump isn't staying a constant speed and the return hose is no longer sufficient to return the excesss fuel?

The way ive got it plumbed is tank, pump, gauge, fuel rail, FPR, tank.

I dont think it is really possible to damaged the FPR really as it is an aluminium piston that moves inside it, I'll take it apart and have a look though.

Tel, the FPR in this case goes after the fuel rail and regulates the pressure by limiting how much gets returned to the tank.

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1/4mile in 13.2sec @ 111 terminal on 15psi

Could it be a sensor problem?

Is it being affected by heat etc.?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Elaborate please!?

could the seal on the fpr be leaking slowly ,and letting fuel above the piston.. that gradually builds up pressure on top of the piston and creatres a rise in the fpr setting .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

sounds pretty feasable robert, possibly due to connecting the wrong way?

i'd pull it apart and have a nose.

You should be referencing boost at the top of the piston, so pressure should not creep due to leakage.

Is the boost reference line clear? A blockage would hold fuel pressure high after boost.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

is this a standard metro rising rate fpr? If so, is your new fuel pump too strong for it?

I'm sure i read something on here a few years ago posted by either wil or ben about putting a bmw pump on their car and it trashing the diaphragm in the fpr.

Might be worth a look.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Matty is on fuel injection on his K1100 Turbo in this instance.

He is going to need 4-5 bar.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

The best method is to maintain a fixed differential pressure across the injector, so fuel pressure goes up with boost.

This is so that the injector then provides a fixed flow rate. Much easier to map that way.

Most injectors are designed to operate at 3 Bar differential pressure. If you run without boost reference, the differential pressure drops and the injector will not work correctly.

You cannot use the Metro FPR on injection. The Metro one controls downstream pressure. You need upstream control with injection.

Edited by Paul S on 2nd Jul, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Ive taken the FPR apart and think I may of found the problem! Will confirm later!

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1/4mile in 13.2sec @ 111 terminal on 15psi

Well looks like all is well!

Turned out to be some what could only be described as string/fibrey material in the piston of the FPR? I cleaned it out and fitted a second filter and taken it for a 45min drive and the pressure stayed around 3Bar give or take the pressure difference in the plinenium!

I also noticed that the fuel pressure was also ALOT more responsive with vacuum which is all good! Cheers for the suggestions lads thought that was going to be one of them probs that takes ages to figure out! :Laugh:

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1/4mile in 13.2sec @ 111 terminal on 15psi

i rekon your problem is a peice of string/fiber in the FPR try taking it apart and cleaning it out then going for a 45 min drive. should sort it out i rekon!


EDIT: OH i didnt see your last post honest i really am that clever.....

Edited by James_H on 2nd Jul, 2008.

Paul is right about fuel pressure. The DON works like this, fuel pressure falls with vacuum and rises with boost to maintain a constant differential pressure.

was the fibry shizzle on the fuel or air side of the FPR?

i ask cause when i pulled the sender unit out of my tank it was covered in what looked like fireglass/wool.

That's something else I've learned about injecting a turbo. It'll all come in handy when I dig the K100 head out of the shed.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

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1/4mile in 13.2sec @ 111 terminal on 15psi