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Author
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Topic: I think my fuel pump is toast...or is it FMU?
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Elapid
GOROBGO
Member # 50
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posted
 
 
well, i replaced my fuel filter and the pressure still drops rather than rises when i get into the throttle. I figure it is either the FMU failing or the fuel pumps (has external pump in addition to the in-tank) have taken a big dump.
is there an easy way to test the FMU?
the other question is about replacement. should i replace BOTH pumps with 255 lph units, or upgrade the in-tank pump and ditch the external unit?
I have to get this baby in shape before the dyno tune in 2 weeks!
thanks
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98 Cobra
83 Notch rolling chassis - fs
Posts: 1797 | From: Grass Valley, CA USA | Registered: Jul 2000
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Stimson
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Member # 51
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posted
Hi Rob. You can simply unplug and cap off the to and from lines of the FMU and see if the fuel pressure readings change.
As for getting a new pump.... a walbro 255 high pressure and a vortech 190lph T-rex are safe to upper 400's RWHP on a boosted car depending on how much fuel pressure you run. The more fuel pressure you run, the more strain on the pumps and thus less liters of gas moved per hour (lph)
Posts: 2373 | Registered: Jun 2000
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99gt-UJSTLST
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Member # 584
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posted
quote:
Originally posted by rob:
well, i replaced my fuel filter and the pressure still drops rather than rises when i get into the throttle. I figure it is either the FMU failing or the fuel pumps (has external pump in addition to the in-tank) have taken a big dump.
is there an easy way to test the FMU?
the other question is about replacement. should i replace BOTH pumps with 255 lph units, or upgrade the in-tank pump and ditch the external unit?
I have to get this baby in shape before the dyno tune in 2 weeks!
thanks
I have a brand new external 225 its a walborrow
make me offer
Posts: 2558 | From: SAN JOSE CA | Registered: Nov 2001
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Elapid
GOROBGO
Member # 50
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posted
hehehe!
i don't have the fittings to "simply plug the lines" to the fmu, so that's out.
I don't think is it safe to run boost without an FMU or other engine management system?
(translation: i'm not going to disable the FMU and get heavy into the happy pedal)
99gt...
what do you need to get for it?
i was just looking at the walbro 255
[ November 09, 2002, 09:58 AM: Message edited by: rob ]
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98 Cobra
83 Notch rolling chassis - fs
Posts: 1797 | From: Grass Valley, CA USA | Registered: Jul 2000
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Stimson
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Member # 51
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posted
quote:
Originally posted by rob:
I don't think is it safe to run boost without an FMU or other engine management system?
(translation: i'm not going to disable the FMU and get heavy into the happy pedal)
Rob, maybe I mis-understood you... if fuel pressure is dropping under boost anyways... what's the worste that can happen if you bypass the FMU? Did you mean to say fuel pressure spikes up and then starts to drop? I thought you meant under boost it goes from 38ish psi down to 30psi. Heck, unplugging it and seeing if it'll stay at 38ish psi won't hurt if its dropping to 30psi. I hope my line of thinking makes sense.
Posts: 2373 | Registered: Jun 2000
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Elapid
GOROBGO
Member # 50
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posted
quote:
Sawson said:
"what's the worst that can happen?"
I could blow up a $13k motor...
i really can't afford to replace it again...
maybe i misunderstand the workings of the fmu.
i am under the impression that the fuel pressure regulator keeps the pressure @ 32 psi regardless of boost, it is the FMU that causes the pressure to rise to compensate for boost. this being the case, it would seem that by taking out the FMU and goosing it, i would be at great risk of damaging my motor due to detonation.
sometimes it (fuel pressure) hits 80 psi, and sometimes it drops to 20 psi during heavy boosted acceleration.
fuel pumps being cheaper than cobra motors, i think i'll replace both the fuel pumps and the FMU disk for good measure.
99gt
if that's including shipping, we have a deal.
is paypal ok?
thanks!
rob
[ November 09, 2002, 02:57 PM: Message edited by: rob ]
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98 Cobra
83 Notch rolling chassis - fs
Posts: 1797 | From: Grass Valley, CA USA | Registered: Jul 2000
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99gt-UJSTLST
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Member # 584
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posted
quote:
Originally posted by rob:
quote:
Sawson said:
"what's the worst that can happen?"
I could blow up a $13k motor...
i really can't afford to replace it again...
maybe i misunderstand the workings of the fmu.
i am under the impression that the fuel pressure regulator keeps the pressure @ 32 psi regardless of boost, it is the FMU that causes the pressure to rise to compensate for boost. this being the case, it would seem that by taking out the FMU and goosing it, i would be at great risk of damaging my motor due to detonation.
sometimes it (fuel pressure) hits 80 psi, and sometimes it drops to 20 psi during heavy boosted acceleration.
fuel pumps being cheaper than cobra motors, i think i'll replace both the fuel pumps and the FMU disk for good measure.
99gt
if that's including shipping, we have a deal.
is paypal ok?
thanks!
rob
are you goin to the car show a can take it to you their if not
then it would be + plus shipping wich should be like 10 bucks more for ups ground and I can take pay pal
Posts: 2558 | From: SAN JOSE CA | Registered: Nov 2001
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Unregistered
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Member # 786
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posted
quote:
Originally posted by 99gt-UJSTLST:
quote:
Originally posted by rob:
quote:
Sawson said:
"what's the worst that can happen?"
I could blow up a $13k motor...
i really can't afford to replace it again...
maybe i misunderstand the workings of the fmu.
i am under the impression that the fuel pressure regulator keeps the pressure @ 32 psi regardless of boost, it is the FMU that causes the pressure to rise to compensate for boost. this being the case, it would seem that by taking out the FMU and goosing it, i would be at great risk of damaging my motor due to detonation.
sometimes it (fuel pressure) hits 80 psi, and sometimes it drops to 20 psi during heavy boosted acceleration.
fuel pumps being cheaper than cobra motors, i think i'll replace both the fuel pumps and the FMU disk for good measure.
99gt
if that's including shipping, we have a deal.
is paypal ok?
thanks!
rob
are you goin to the car show a can take it to you their if not
then it would be + plus shipping wich should be like 10 bucks more for ups ground and I can take pay pal
Check pm's
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2001.5 Audi S4
Posts: 1785 | From: Livermore | Registered: Jan 2002
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Elapid
GOROBGO
Member # 50
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posted
hey!
sounds good!
call me @ 800 388 4324
or email me with your details and i'll get you my addy and such...
thanks!
rob
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98 Cobra
83 Notch rolling chassis - fs
Posts: 1797 | From: Grass Valley, CA USA | Registered: Jul 2000
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99gt-UJSTLST
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Member # 584
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posted
quote:
Originally posted by rob:
hey!
sounds good!
call me @ 800 388 4324
or email me with your details and i'll get you my addy and such...
thanks!
rob
check your PM's
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SOUTH BAY STANGS
MINOR BOLT ON'S
www.southbaystangs.com
Posts: 2558 | From: SAN JOSE CA | Registered: Nov 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
Sounds like one of the pumps is not working. Perhaps even an intermitant grounding out of the power wire to the external.
For what it's worth, I do NOT run an FMU, two 255 walbros, 36lbers & a kirban set at 44. FP rises 1-to-1 with boost.
FMU = band-aid for an in-adequate fuel system.
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4266 | From: Fair Oaks, CA | Registered: Nov 2000
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1SLOWLX
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Member # 558
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posted
Does your external pump make a lot of noise?? Cause my T-rex blew up real fast. I think they are the shits. If you have 13k in your motor maybe it is time to think about a fuel system to back up that investment??? Ditch the fmu and get 42 o 50 lb injectors
Albert
Posts: 5231 | From: bay area | Registered: Nov 2001
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Elapid
GOROBGO
Member # 50
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posted
yep, albert!
that's what we are doing, putting 42lb and ditching the FMU, 80mm Pro-M and chip in 18 days!
woohoo
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98 Cobra
83 Notch rolling chassis - fs
Posts: 1797 | From: Grass Valley, CA USA | Registered: Jul 2000
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BOSNA
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Member # 246
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posted
hey 99gt-UJSTLST Ill take your pump for $100
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98 Cobra
97 GT Saleen
Posts: 74 | From: san jose | Registered: Apr 2001
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99gt-UJSTLST
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Member # 584
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posted
quote:
Originally posted by BOSNA:
hey 99gt-UJSTLST Ill take your pump for $100
sorry rob just picked it up
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SOUTH BAY STANGS
MINOR BOLT ON'S
www.southbaystangs.com
Posts: 2558 | From: SAN JOSE CA | Registered: Nov 2001
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