Hello all;
My 2000 M Coupe has been taking longer to start when sitting for awhile after shutting down. It takes about 5 seconds to fire when cranking. After it starts it runs fine, so it seems I'm losing fuel pressure. I put a pressure gauge on it and looks like it's dropping about 11 psi from 40-29 psi 20 min after shutdown. It had 45 psi at rail when idling. Pulled rail after running, and injectors are not leaking.
I've read that there is a 1 way check valve in the fuel pump. When these fail, does the pressure fall incrementally like mine after shut down or would it drop off more quickly? I've replaced the fuel filter, FPR, and swapped out fuel pump relays. Any advice/help would be appreciated. Thanks!
Last edited by bretto; 07-17-2017 at 01:09 AM.
When the original check valve inside the fuel pump fails, we usually install an additional check valve as described here in the E32 DIY https://www.bimmerforums.com/forum/s...k-valve-repair
Shogun tricks and tips for the E32 series are HERE!
Great, thanks! I will order part and install to see if it solves the starting issue.
I don't think the dropping fuel pressure is your issue. For one thing, it hasn't dropped enough to keep the car from starting. Secondly, if you watch your gauge when you crank it, I think you'll find that pressure pops up almost immediately. On the S52 in an M Coupe, I'm pretty sure that the pump primes with key on, anyway. However: IF you're only seeing 40 psi running, then you are 11 psi short: the engine needs 51 psi.
Check for how long it's taking spark to arrive; see if you have any cam sensor codes.
Chris Powell
Racer and Instructor since, well. decades, ok?
Master Auto Tech, owner of German Motors of Aberdeen
BMWCCA 274412
German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471
Thanks for the reply. The car does start but only after 4-5 seconds of cranking after it has been sitting for a bit. It will fire right up if it has already been running. The pump is priming but doesn't seem to build enough pressure quickly enough to avoid long start time. I measured the pressure at the fuel rail with gauge. Is 41 psi at idle measured at rail within spec for this car?
No.
51 psi is the correct fuel pressure. Now, you need to be aware that your gauge may be wrong.
29 psi after 20 minutes is not a big deal. More likely, that would show a leaking injector, than a faulty one-way valve. How long does it take the pressure to rise?
I have to recommend that you find another gauge, to corroborate the readings you're getting. If indeed, you're getting only 40 psi, you have a problem.
That said, I would still strongly suggest that you see whether you have SPARK right away when the engine begins rotating.
Chris Powell
Racer and Instructor since, well. decades, ok?
Master Auto Tech, owner of German Motors of Aberdeen
BMWCCA 274412
German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471
I would add that, after all the above conditions have been confirmed and fixed,
a faulty fuel tank/canister purge valve can cause longer than normal crank times before starting.
But I will add that this fault is usually indicated by an error code, which is why I recommend a diagnostic scan to confirm.
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