M30 - fuel pressure fluctuation; why?

[Jeff N.]

I notice that my FP will change significantly for no apparent reason. I've seen it range from a typical 42 to 44lbs at idle to 30 lbs at idle. When low, it seems "stable" at the low FP. That is, is doesn't jump up/down. Holds at that low FP. Typically, if I shutdown and restart the car, the problem goes away.

Symptoms of low FP show up as the car running lean (reported by the wideband O2 sensor) and then confirmed by the hardmounted FP gauge under the hood.

Seems like there are two aspects to maintaining FP - the FPR and the fuel pump. Is this correct or are there other items involved?

Do FPRs show intermittant problems? Or fuel pumps? Why would shutting the car off seem to reset the FP?

It's strange - any ideas on what might be causing this problem?

thx

Jeff

[Bill R.]

constant or stable then? If not the regulator then the only thing i can come up with is voltage variations going to the pump.. Perhaps poor contact on the fuel pump relay contacts. And when you shut it off and restart it opens and closes these contacts again?



I notice that my FP will change significantly for no apparent reason. I've seen it range from a typical 42 to 44lbs at idle to 30 lbs at idle. When low, it seems "stable" at the low FP. That is, is doesn't jump up/down. Holds at that low FP. Typically, if I shutdown and restart the car, the problem goes away.

Symptoms of low FP show up as the car running lean (reported by the wideband O2 sensor) and then confirmed by the hardmounted FP gauge under the hood.

Seems like there are two aspects to maintaining FP - the FPR and the fuel pump. Is this correct or are there other items involved?

Do FPRs show intermittant problems? Or fuel pumps? Why would shutting the car off seem to reset the FP?

It's strange - any ideas on what might be causing this problem?

thx

Jeff

[Jeff N.]

constant or stable then? If not the regulator then the only thing i can come up with is voltage variations going to the pump.. Perhaps poor contact on the fuel pump relay contacts. And when you shut it off and restart it opens and closes these contacts again?

Good questions - it doesn't seem to do it so frequently that I can test & mess with it. Next time I see it happen I'll pull the vacuum hose and watch what occurs.

I had wondered if I didn't have some blockage in the system, maybe at the pump side, such that the off/on cycle got it freed up. The voltage / contact idea is one I hadn't thought of. (It's likely an old relay from Martin's car so that likely means it's worthless anyways). Maybe I'll try popping the cover and blasting it with contact cleaner...

Also, I'm not 100% positive the off/on cycle fixes the issue. I think it does...pretty sure. It's not a low gas issue - happens with the tank full or empty...

[joshua43214]

Its not unusual to get minor pressure variation if the idle hunts a bit.

Fuel pumps do fail intermitantly as do relays. I don't recall ever seeing a regulator fail in that maner, buts its a big world and all sorts of odd things happen.

[JoeS]

I have the exact opposite issue. I run high fuel pressure during fluctuation - obviously causing a rich condition. I have studied my fluctuation via my external gauge. At first i thought mine gauge was ****, so i threw it away and bought another one. But the new one showed the same results. I have the BAV Auto adjustable FPR, i thought that was the villian so i brought a brand new bosch FPR from BMA. Still the same issue, but the fluctation swings are not as drastic running stock fuel pressure as when they are when i increase te fuel pressure. I have noticed one odd thing, the occurance. It always is there during warm up, and after casual driving, but if i go out can run the hell out of it then come back and watch for it - it never happens. I have just decided to live with it, and i am glad i am on the rich side and not the lean.

[Jeff N.]

This is strange. What part is the Bosch adjustable FPR? I wasn't aware they made one. I have seen 3rd party modified "Bosch" FPRs, is that what this is?

[JoeS]

i just put a regular bosch FPR on. Not an adjustable.




This is strange. What part is the Bosch adjustable FPR? I wasn't aware they made one. I have seen 3rd party modified "Bosch" FPRs, is that what this is?

[Jeff N.]

Had me excited for a minute.

I'll have to poke around and see if it's maybe a voltage / contact issue as Bill has suggested.


i just put a regular bosch FPR on. Not an adjustable.