what happens if FPR vacuum hose is leaking?

[hahmeta]

as I'm changing my spark plugs tonight I realized the vacuum hose from FPR to intake manifold is almost cut in half right at the FPR. what does this mean? should I not drive the car?

thanks a lot guys

[e30evolution]

means your fuel pressure will be higher than it should be, and you have a vacuum leak... replace the hose, but you can drive it

[hahmeta]

is it a BMW specific hose or can i get the same diameter from any auto parts store?
thanks for the help.

[hahmeta]

also should i expect any difference in engine behavior with vacuum hose leaking? for instance should the engine idle at higher rpm? or something like that. i'm trying to understand if i should check the fpr while i'm at it.

[jlevie]

At idle the fuel pressure would be too high and thus the injectors would be delivering a bit more fuel for each firing pulse. But with the hose severed, you'd have an intake leak which would tend to counter the fuel increase. So there may not be all that much of an affect.

The hose in question can be replaced with generic vacuum hose, which you can get at any auto parts hose. Take the existing hose with you and then can match up the ID.

[eugeman]

Or, you could cut the hose off before the cracked part and slide it back on, voila, problem fixed. Then you could find an equivalent hose thereafter at your convenience.

[SpecM]

yea, just get some cheapo generic rubber hose

[hahmeta]

thanks guys. took care of it today along with new injectors. old ones were filthy! time for seafoam i guess.

[nando]

means your fuel pressure will be higher than it should be, and you have a vacuum leak... replace the hose, but you can drive it

you have it backwards, it will be lower. fuel pressure *increases* with engine load (vacuum), it doesn't decrease.

[SpecM]

you have it backwards, it will be lower. fuel pressure *increases* with engine load (vacuum), it doesn't decrease.

no, he was right. Manifold vacuum decreases with higher load.

engine load goes up (more throttle), engine vacuum DECREASES, the FPR valve closes (kinda), and fuel pressure goes up.

[nando]

a bit on the semantics side, but that's what I meant. Fuel pressure increases with engine load (proportional to vacuum).

[Mike]

I am actually having something a little different. At idle, I have my needle shaking between 40-43 psi, and the pressure goes down to mid 30's when revved. If I pull the vaccuum line, and plug the manifold side up, fuel pressure stays a constant 43psi when revved. The needle also smooths out. What does that mean? This is no stock m20, btw...