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Old 12-31-2004, 06:47 PM   #1
IowaRS
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Default Suddenly, Low Fuel Pressure at idle??

Howdy folks, for some strange reason, all of the sudden my fuel pressure is down to 20 psi at idle?

I've been running the walbro 255 with a stock 1.8L FPR and Cartech FMU for over a year now.
Fuel pressure at idle has always been at least 28psi, and then up to 38psi at 0psi boost.

Now, all of the sudden it's down to 20psi at idle, and if I disconnect the vacuum line to the FPR fuel pressure only goes up to 26psi.

I also seem to lose pressure rather quickly after the car is turned off.

I'm thinking there is a leak somewhere, but I can't find any.

Do you suppose one of my injectors is stuck open?
And if so, how would I test it??

Thanks
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Old 12-31-2004, 08:46 PM   #2
BAN SUVS
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Your pump went bad. Get a new one ASAP.
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Old 01-01-2005, 11:57 AM   #3
IowaRS
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Hmmmm, you sound very sure of this.

The pump will still make 60 psi of pressure at WOT though.
Why wouldn't it be able to make the normal 28 - 38psi in the NA range of manifold vacuum?

Thanks
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Old 01-01-2005, 05:36 PM   #4
BAN SUVS
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It could also be the FPR, but Walbros are known to have short service lives. The FPR could also be masking the pump's lost capacity at boost because the regulator is helping out. And the rapid loss of pressure when you kill the engine also points to the pump being bad.
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Old 01-02-2005, 11:59 AM   #5
Portly
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If it was the pump, it certainly wouldn't be able to make 60 psi at high flow rates (WOT) if it struggles to make 20 psi at low flow rates (idle). The pump theory doesn't make sense.

Perhaps your Fuel Pressure gauge is bad.

_Jeff
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Old 01-02-2005, 12:36 PM   #6
Unsung Boxer
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Quote:
Originally Posted by Portly
If it was the pump, it certainly wouldn't be able to make 60 psi at high flow rates (WOT) if it struggles to make 20 psi at low flow rates (idle). The pump theory doesn't make sense.

Perhaps your Fuel Pressure gauge is bad.

_Jeff
there is a one way check valve in the fuel pump that could be partially sticking. Which would explain these symptoms.

Test this by

1. run the car
2. clamp off the fuel return line, (the fuel line that doesnt go thru the fuel filter)
3. turn off the car to see if the fuel pressure drops.

-If the valve is working properly, then fuel pressure will not be able to bleed past it (or past the clamp on the return line).

-If the valve is failing, fuel pressure will drop (slowly or immediatly).

The valve is part of the fuel pump, if you do this test and determined its failed, then you will still have to replace the fuel pump.

(unsung)

Last edited by Unsung Boxer; 01-02-2005 at 12:43 PM.
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Old 01-02-2005, 01:30 PM   #7
IowaRS
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I did something along those lines yesterday.

I clamped the line off with vice grips and looked at the fuel pressure gauge.
I had it up around 90psi.

I let it sit for about 10 minutes it bled down to 84psi and then just stayed there.

I'm going to verify pressure with a different gauge.

Then go from there, starting at the fuel pump.

I can swap my stock fuel pump back in and see if the idle pressures come back up.

Thanks!
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Old 01-02-2005, 06:32 PM   #8
IowaRS
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Hmmm,
Well, I went out and bought another pressure gauge.
Granted it's a very cheap one, but it reads 35 at idle and 43 with the vacuum line removed from the stock FPR.

If this gauge is accurate at all this would indicate my gauge has gone south.
Which sucks, because I use fuel pressure to tune my AFR's and I don't know how long the gauge has been bad..........

EDIT/UPDATE:
I borrowed yet another gauge from a friend
It also indicates my gauge isn't working properly.

I guess either my gauge or my isolator.
I'll put the cheap gauge on the isolator sometime soon and see if that's an issue before dropping $40 on a new gauge.

Last edited by IowaRS; 01-02-2005 at 10:46 PM.
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