2nd Generation Specific 1986-1992 Discussion

Question About Stock Fpr

Old 02-19-2004, 01:54 PM
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should the FPR flow something when it has no boost or vacuum on it?



Loi



this is for an s4 TII by the way.
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Old 02-19-2004, 02:55 PM
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I think it should. I have never tested it though. I remember pulling the vac line off on an n/a one time. And if the fpr wasn't bleeding off fuel as it should, the car I would imagine would have either started to run dog rich or the injectors would have started leaking since fuel pressue would start to sky rocket.
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Old 02-19-2004, 03:10 PM
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i've got 2 stock FPR's and neither of them flow aything when no vac line is attached. just wondering if both are bad or what?



Loi
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Old 02-19-2004, 06:00 PM
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I've never heard of the stock fpr going out. Seems strange that you have 2 that do that. Maybe they are fuctioning correctly. Why are you testing them anyhow?
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Old 02-19-2004, 06:07 PM
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with no vacuum line attached they should still flow fuel.



no vac line == atmosperic pressure, so having no vacuum line connected is comparable to the condition your FPR experiences around WOT (it will still have around 1-2inHg due to the throttle plates and air filter etc though)



on my setup WOT is like 0 inHg to the MAP sensor.



the fpr is supposed to compensate for vacuum on the other side of the injectors (and boost on a t2), so when the fpr gets 0 vacuum, it is supposed to regulate the static fuel pressure.



when it gets N vacuum, it regulates static fuel pressure - N.... when it sees boost, it regulates static fuel pressure + N psi boost.... so yes, it definitely should flow fuel @ atmospheric.
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Old 02-19-2004, 07:33 PM
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i just checked mine, i cant blow thru it
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Old 02-19-2004, 07:39 PM
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Originally Posted by j9fd3s' date='Feb 20 2004, 01:33 AM
i just checked mine, i cant blow thru it
probably can't blow hard enough.





the fpr will see atmo pressure for a short time when transitioning from vacuum to boost on a turbo car, it definitely has to flow fuel under this condition.
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Old 02-19-2004, 07:41 PM
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yeah i can only blow 1-2psi the fuel pump can do like 40!
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Old 02-19-2004, 08:31 PM
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what the hell are the chances that i would get 2 non-functioning fpr's!!!!



i really must have the worst luck ever!!!!



Loi



o, and i'm testing them cause my car won't start and i'm pretty sure its a fuel thing cuz it starts when i spray starting fluid into it.



yeah, and my car won't turn over when its on the ground but will when its on jackstands. thats a whole different problem though....damn project cars, damn them to hell!!!!!!





i didn't mean that....
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Old 02-19-2004, 08:40 PM
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Sure...

Mazda spec is 35psi at vacuum or under -"0"

At "0" it supposed to step up to 40psi.

If this is a turbo FPR, then it's a 1:1 ratio for boost versus pressure.

i.e. - at 10psi of boost, the fuel rail pressure should be 40psi + 10psi = 50psi.





-Ted
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