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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 12-17-2004, 11:09 PM   #1
grabbem88
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Default signs of a bad fuel pump??

well i finally had enough,and dropped off my car at ford.
to see what the hell was going on with it cutting out.
found out with the o2's plugged in the fuel pressure
dropped like a bad habbit. it was like 26psi when the car was
put under load,and they even tried with the vac. unhooked off
the fuel regulater. i'm thinking it's my pump,although it is only 1yr old
it wasn't a name brand...walbro 190lph.ford said it might be my regulater.
what i don't understand is when my o2's are unplugged it goes into rich,and
my runs fine,except for the fumes. does anybody have any advise?
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Old 12-17-2004, 11:24 PM   #2
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Default RE: signs of a bad fuel pump??

damn dood.. strange problem... walbro's are good pumps, **** they prolly make the pumps that get the brand names put on them! ... if it's only 1 year old.. I doubt thats the problem.. if your pressure isn't going up without vacuum.. the regulator is bad.... from what I have seen.. with fuel pumps its usually all or nothing.. if they are getting proper voltage either they are working properly and give you full pressure.. or they don't pump anything at all.. but again that is just what I have seen....

When you say cutting out.. do you mean stalling or missing? since fuel pressure affects all cylinders it won't cause a miss/hesitation... but if its stalling out... that could definetly be your problem...

I can't see how having the O2's unplugged could tie into the fuel pressure, are you positive that is the case?.. unless like something with them is causing low voltage to the fuel pump? I don't have a wiring diagram so I dunno if that is even possible.
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Old 12-17-2004, 11:56 PM   #3
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Default RE: signs of a bad fuel pump??

thats what i thought too,how can you unplug o2's it's fine....plug them in you lose fuel pressure? i'm stumped on this one too.
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Old 12-18-2004, 12:09 AM   #4
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Default RE: signs of a bad fuel pump??

can the o2's tell the computer to go lean?
on the dyno it didn't show any signs of ill fue/air problems.it stayed 13.2 on the widebands.
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Old 12-18-2004, 12:19 AM   #5
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Default RE: signs of a bad fuel pump??

Quote:
ORIGINAL: grabbem88

can the o2's tell the computer to go lean?
on the dyno it didn't show any signs of ill fue/air problems.it stayed 13.2 on the widebands.

yea.. but the ecu does it by adjusting the injector pulse width.. not varying fuel pressure
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Old 12-18-2004, 12:21 AM   #6
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Default RE: signs of a bad fuel pump??


Quote:
ORIGINAL: grabbem88

can the o2's tell the computer to go lean?
on the dyno it didn't show any signs of ill fue/air problems.it stayed 13.2 on the widebands.

what the??... did you see for yourself the low fuel pressure.. did the shop tell you this? maybe the dude had a bad gauge.. cause if you are 20psi down on fuel pressure... its gonna show up on the wideband...

what are the symptoms like .. does the car stall?
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Old 12-18-2004, 02:13 AM   #7
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Default RE: signs of a bad fuel pump??

the ford guy said the pressure was fine at idle then dropped when he put it under load.
where are all the diagnostics geeks when you need one???
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Old 12-18-2004, 03:57 AM   #8
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Default RE: signs of a bad fuel pump??

26 psi ?!?!?! holy shiznit.... be careful dude you could hurt the engine if its running that lean. heres what i can tell you, when you unplug the o2's the computer senses this and will run a rich mixture in 'safe' mode to keep from accidental leanness. how this ties in with your problem, you will have to figure out. i say your pump is ok though. the problem might be in your regulator, did you change your fuel filter? that might get clogged up...
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Old 12-18-2004, 01:08 PM   #9
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Default RE: signs of a bad fuel pump??

yeah,i changed the filter........i have a fuel gauge on it myself,and it shows the same
reading as what ford got.
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Old 12-18-2004, 04:37 PM   #10
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Default RE: signs of a bad fuel pump??

i really don't believe its my regulater.....how many mustangs do you know that lost fuel pressure that bad?
36psi to 26psi.because of a bad regulater?
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Old 12-18-2004, 04:37 PM
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