M20 fuel pump pressure test

[Bonymaenjack]

I'm having a problem locating a current fault with my 325i. I appear to be losing pressure in the fuel system or perhaps not creating enough in the first place, I fitted a pressure gauge between the in line fuel filter (newly fitted) and the injector rail and the reading I had was 2.2 bar which was constant even when revving the engine, this didn't fluctuate in the 15 minutes the engine was running . I then fitted the gauge in line between the FPR and the tank and I had no reading at all, zero even when I removed the vacuum pipe from the FPR and inlet manifold .Is this two issues and also am I carrying out the test correctly .?
thanks

[rix313]

FPR to tank will never show a pressure as it is just a return. So your initial test is correct but it should be higher than 2.2.

[Bonymaenjack]

Thanks for the reply, should the pressure vary when revving the engine when testing the fuel feed and if it should and mine doesn't have you any idea of what it could be , duff fuel pump? ,

[rix313]

The demand for fuel will spike when revved or underload so it should rise slightly but settle down again.

[Bonymaenjack]

The demand for fuel will spike when revved or underload so it should rise slightly but settle down again.

It never moved an inch but held pressure for ten minutes .I thought the operating pressure should be around 40+ PSI and then moved as the throttle opened ?.I have a number of issues with the fuel supply and if I can eliminate one then hopefully the rest will become clearer

[Brianmoooore]

Fuel pressure on a M20B25, measured by connecting a 'tee' into the supply hose near the fuel rail, should be 3 bar (approx. 45 PSI) above the pressure in the inlet manifold plenum. With the engine idling, and the throttle nearly closed, the pressure in the plenum will be half a bar or so less than air pressure outside of the engine, so your gauge should read around 40 PSI or a bit lower, as you say. If you snap the throttle wide open at low engine revs, the plenum pressure will increase for a short while to approximately outside pressure, so the gauge should blip up to 45 PSI, falling back as the engine revs rise and manifold pressure decreases again.
If you are seeing only 2.2 bar, then the first thing to do is to start clamping off the fuel return hose from the pressure regulator, and see if you can bring the pressure up to 3 bar. If you can, the pressure regulator is faulty, but if you can't, then it is a pump problem or a blockage in the supply line. Moving the pressure gauge to the outlet of the pump at the tank will determine which.

[Bonymaenjack]

Fuel pressure on a M20B25, measured by connecting a 'tee' into the supply hose near the fuel rail, should be 3 bar (approx. 45 PSI) above the pressure in the inlet manifold plenum. With the engine idling, and the throttle nearly closed, the pressure in the plenum will be half a bar or so less than air pressure outside of the engine, so your gauge should read around 40 PSI or a bit lower, as you say. If you snap the throttle wide open at low engine revs, the plenum pressure will increase for a short while to approximately outside pressure, so the gauge should blip up to 45 PSI, falling back as the engine revs rise and manifold pressure decreases again.
If you are seeing only 2.2 bar, then the first thing to do is to start clamping off the fuel return hose from the pressure regulator, and see if you can bring the pressure up to 3 bar. If you can, the pressure regulator is faulty, but if you can't, then it is a pump problem or a blockage in the supply line. Moving the pressure gauge to the outlet of the pump at the tank will determine which.

Cheers Brian. I've just completed testing as you suggested and this was the results after the following :
after a long time cranking form cold I started the engine with in line pressure gauge fitted near to fuel rail, this showed no pressure . I then clamped the return feed from the FPR and this raised the pressure to 50 psi but the readings didn't alter with either a small opening or large opening of the throttle it remained the same reading regardless
I then stopped the engine reset the gauge and restarted the engine this time the gauge went up but only to 1.5 bar but I clamped the return pipe and the gauge went up to 50 psi but again held without moving when operating the throttle
Also I noticed a slight misfire ,so I pulled off each lead and the number 4 showed no difference to the idle speed and the misfire remained when I reconnected it , I swopped the spark plug from no 1 cylinder which did appear to be ok and the same symptoms were present. I appreciate it could be a lead but I also took out the plug in number 4 and started the engine and no fuel shot out of the cylinder so perhaps the injector is also faulty .
The fuel pump , FPR and plugs are new and the injectors cleaned and refurbished .

[Brianmoooore]

The FPR shouldn't flow ANY fuel at 1.5 or 2.2 bar, so with the gauge showing these sort of readings, clamping off the fuel return hose should do nothing. It looks very much like your FPR, new or not, is leaking badly.
Any chance that the two fuel hoses were connected the wrong way around at some point? I remember a case on here where a FPR was damaged by this, although it eventually 'repaired' itself some time after the hoses were put back as they should have been.

[Bonymaenjack]

The FPR shouldn't flow ANY fuel at 1.5 or 2.2 bar, so with the gauge showing these sort of readings, clamping off the fuel return hose should do nothing. It looks very much like your FPR, new or not, is leaking badly.
Any chance that the two fuel hoses were connected the wrong way around at some point? I remember a case on here where a FPR was damaged by this, although it eventually 'repaired' itself some time after the hoses were put back as they should have been.

There is a good chance that the pipes have been reversed , earlier in the summer I replaced the injectors and to gain access removed the FGR pipes etc (that was replaced in the spring) so there is a chance that may have happened , so for my benefit the pressure created by the pump may have split the diaphragm ?. If it is that which is what's happened then I'm guessing the diaphragm is deteriorating rather than repairing due to the recent problems I'm experiencing?

[Brianmoooore]

I don't think the diaphragm has split, since this would result in fuel being drawn into the inlet manifold along the small bore vacuum pipe. I'm guessing it's more along the lines that hydraulic pressure where it shouldn't be has moved whatever the fixed end of the spring its on, altering the effective spring pressure, and thus the fuel pressure at which the valve opens.

[Bonymaenjack]

I don't think the diaphragm has split, since this would result in fuel being drawn into the inlet manifold along the small bore vacuum pipe. I'm guessing it's more along the lines that hydraulic pressure where it shouldn't be has moved whatever the fixed end of the spring its on, altering the effective spring pressure, and thus the fuel pressure at which the valve opens.

Cheers Brian .It s a pity these items are not serviceable but when I replace it as it seems I must then I'll have a go at stripping it down to satisfy my own curiosity. What is your opinion on adjustable regulators is it worth investing in one and also Pierberg have been around for a long time would it be wise to replace my one for one of those or stick with the Bosch .

[Brianmoooore]

Unless you have a reason for needing a non standard fuel pressure, then there's absolutely no point in using other than a standard regulator.

[Brianmoooore]

Just seen your quote from Cotswold for a new FPR. Wasn't aware that they're hewn from solid gold these days!
They are normally very reliable, and easily checked, so I'd have no hesitation in using a second hand one.

[Bonymaenjack]

Just seen your quote from Cotswold for a new FPR. Wasn't aware that they're hewn from solid gold these days!
They are normally very reliable, and easily checked, so I'd have no hesitation in using a second hand one.

Yep a bit of a shock and the one I bought is only a year old so I'll go through my receipts to see where I bought it from because it wasn't that much .
I've just found the receipt for the one currently fitted , from Euro car parts Bosch original £59.49 purchased in June 2016. I'll try them tomorrow in person as I've tried the online service with no luck

[reggid]

bosch sell one for about half the price of OE (same unit) though bosch ones are apparently no longer been made so get one while stocks last 0260160249

[Bonymaenjack]

bosch sell one for about half the price of OE (same unit) though bosch ones are apparently no longer been made so get one while stocks last 0260160249

Thanks I'll give them a call on Monday

[flybynite]

bosch sell one for about half the price of OE (same unit) though bosch ones are apparently no longer been made so get one while stocks last 0260160249

Are you sure of the part number? Everything I see says the part number for the Bosch FPR is 0280160249. They are certainly not half OEM price here now

Are they still that cheap in OZ? I see that part is listed for Holden too which might explain it.

[reggid]

i buy from US, your PN is correct. they were half the price. last one i bought was 90 GBP not that long ago either