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Old 05-02-2022, 12:21 PM
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I've never had this much trouble locating a problem source before

Originally Posted by RocketyMan View Post
Well if you are for SURE you checked all vacuum leaks, then yeah, I would suspect the MAF next. If you had an issue with the fuel pressure regulator, then it would more likely code fault. Otherwise, I'd be curious what the fuel pressure is at idle. Maybe checking fuel pressure is the cheaper option to check first.
I can not say for SURE that there isn't a vacuum leak anywhere, but I spent hours looking for it. If the fuel pressure check yields no pertinent info that leads to a solution, then I'll starting checking for leaks, again. Isn't P0313 pointing in the direction of low fuel pressure at times? I'm thinking that somethings not quite right with the MAF, but can't throw $160-$$$ at it, getting a new MAF to test, just to find that the MAF wasn't the problem.

Originally Posted by andrewwynn
  • 1) The fuel delivery is calculated based on assumption that fuel pressure is 50.00 psi. If it's anything else even briefly, the wrong amount of fuel is delivered. When wife's FPR was defective she would have random difficult starts but other than than rarely ever any problem...
  • 2) I replaced the whole FPR+fuel filter...
  • 3) see if the needle is dead solid or wiggles (at idle)...
  • 4) leave the gauge on overnight and determine if it holds pressure...
  • 5) the pump itself: does the pressure stay constant at WOT?
My responses:
  • 1) I've never had a difficult start, random or otherwise, and it idles very smoothly
  • 2) the previous owner says he replaced the fuel filter assembly (which I assume means the FPR+fuel filter) less than a year before I got it from him, so odds are it shouldn't have gone bad that fast
  • 3) there'll probably be needle wiggling no matter what, from a cheap Chinese gauge; I'd have to step up to a dampened liquid-filled gauge to get a truer picture, wouldn't I?
  • 4) that's a good suggestion, I'd not thought about; it should test the O-rings at the FPR and at the injectors, too
  • 5) frankly, I'm hesitant to rev the M54 to WOT; it might open a Pandora's box of other problems I don't have (yet)...this X5 is OLD, and retired like myself, not a racecar as in my past
'01 BMW X5-E53 3.0i (born 7/13/01)
topas-blau, Leder-Montana grau,
my new favorite project car

Plus four GM vehicles: 2 Daily Drivers, and 2 modified trucks (for hauling & camping):
3 Chevys:
'09 HHR Panel LS 2.2L,
'08 Cobalt Coupe LS 2.2L,
'04 Silverado 2500HD WT Reg. Cab
+ a '98 GMC Sierra 1500 Ext. Cab

- and 20 others, now gone, that I've had over the last 58 years (not counting the stillborn "1965 ChevyII altered/gasser project")
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