F Press Regulator not controlling the flow of return

[Gene in NC]

Fuel pump seems to be overpowering the fpr or the fpr not controlling the flow and causing flooding or at least gross over rich running. Very rough runnng and no power. !/2 block from home more than enough road test.

1) Pulled both vac and return lines on the FPR. Engne started right up, idled OK, fuel flowing from jury rig return line into a container. No flow from the Jury rigged line from Vac port on FPR.

2) Tried again as (1), luckily, but no flow from the return line.

3) Tried to start with FPR vac line attached to manifold, no return flow.

What the heck can be happening that FPR worked correctly (1), then blocked all return (2) and (3)?

Can't do pressure test until I rebuild another FP test rig, but tests (1) to (3) are indications of what must be happening to FP.

[Gene in NC]

Fuel pump seems to be overpowering the FPR or the FPR not controlling the flow and causing flooding or at least gross over rich running. Very rough runnng and no power. !/2 block from home more than enough road test.

1) Pulled both vac and return lines on the FPR. Engne started right up, idled OK, fuel flowing from jury rig return line into a container. No flow from the Jury rigged line from Vac port on FPR.

2) Tried again as (1), but no flow from the return line.

3) Tried to start with FPR vac line attached to manifold, no return flow.

What the heck can be happening that FPR worked correctly (1), then blocked all return (2) and (3)?

Can't do pressure test until I rebuild another FP test rig, but tests (1) to (3) are indications of what must be happening, no control of return flow.

[632 Regal]

sounds more like the injectors arent shutting down between pulses to me, even with an abundance of too much FP they shouldnt have an issue bro.

[Gene in NC]

M30 in '85 535 is the problem. Posted here because FPR probs are generic, FPR in e34 looks just like e28, and finally cause there seem to be some smart and very experienced people on this board. Also, if I'm right, diagnosis may be helpful to others.

May be very close to final diagnosis. Found wet/gas on end of FPR vac line attached to intake manifold. Oil level overfull by more than 1/2 quart. Sounds like cracked diaphragm which could explain over rich, stall, and blocked return/very high FP.

New FPR early next week. Will test for cracked diaphragm if I can find my MityVac.

[Gene in NC]

Fuel injectors holding back excess F pressure sounds right. Seems unlikely that all six leaking heavily. Faintly recall report of FPR diaphram failure dumping fuel directly into the intake manifold. Could that be the problem?

[genphreak]

Hmm. maybe i don't read this right-

1) Pulled both vac and return lines on the FPR. Engne started right up, idled OK, fuel flowing from jury rig return line into a container. No flow from the Jury rigged line from Vac port on FPR.

- there shouldn't be any surely... unless the FPR is broken internally.

2) Tried again as (1), luckily, but no flow from the return line.

- what does this mean?

3) Tried to start with FPR vac line attached to manifold, no return flow.

I am no expert but;

Have you not therefore isolated that the FPR is actually faulty? I believe the only other problem that can contribute to over pressure would be a blocked/stuck return valve in the tank...

I am pretty sure that if you over pressure the injectors they will flow more fuel at each pulse...

Time to try a new FPR? They are expensive little buggers though... perhaps go for one from a breaking yard- AFAIK they either work or they don't, or on eBay you can get variable ones with gauges on them very cheaply.
Nick

[rob101]

Time to try a new FPR? They are expensive little buggers though... perhaps go for one from a breaking yard- AFAIK they either work or they don't, or on eBay you can get variable ones with gauges on them very cheaply.
Nick

NAAAAAAAAHHHHHHH, got mine for about 150 AUD shipped (can't remember exactly) from REPCO (aka RAPECO or "**** off i am not paying that much for an oil filter")
it was a bosch part as well

[joshua43214]

Fuel pressure regulators do fail stuck closed and will dead head the fuel pressure. If you have too much pressure in the fuel line, and the return hose is removed, you need a new regulator. If nothing comes out of the return line, and the pressure is normal, then something is wrong with fuel supply; bad fuel pump,filter, or pick-up.

I am not sure I follow the rest, there should be nothing coming out of the vacuum line.

Bad injectors will cause the fuel pressure to leak off or be too low. The injector spring is very light and is well bellow the regulated pressure.

[Gene in NC]

Wow! Wild effect by FPR on fuel pressure. With 100psi FP tester in place and return hose rerouted to container, started engine. Idled a lttle weak with FP around 38-40 and unsteady. Pinched return hose lightly by hand and controlled pressure fleetingly at "steady" 43.

Suddenly engine stalled and pressure jumped past 100psi to pin, maybe 120+ psi. Tester has relief valve so I dropped press quickly and it stopped at 10. Thought maybe gauge damaged but second tap on relief dropped reading to "0".

Engine is m30 with Walbro 255lph pump replacing OEM as we are thinking about turbo.

Obviously unreliable FPR, but how bad was the 120psi on the fuel system? Anything damaged? Bentley calls for FP tester range to at least 75. 120 from the high flow Walbro seems credible.

[Alexlind123]

Maybe the FPR wasnt designed for that high flow fuel pump.