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Old 06-30-2007, 08:44 PM   #1
dwarren
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Member#: 72797
Join Date: Oct 2004
Location: Ontario, Canada
Vehicle:
2005 Legacy GT
Blue

Default Fuel Pressure Problem - Need Help

I have a modied 2006 Legacy GT with a 20G, intake, headers, up and down pipe, CBE, fuel pump and injectors. I also have a fuel pressure problem and don't know the cause as of yet.

When I start my car fuel pressure is about 46 PSI. It stays this way for about 15 seconds while the car idles and then drops down to 31 PSI for some reason. At this stage it idles very poorly.

Under throttle the same issue is noticed. After you floor it, the fuel pressure drops a little and as a result my car leans out tremendously. It takes half a second or so for the fuel pressure to increase at which stage everything is alright again.

We've tried a few different fuel pumps, different injectors, and a new fuel pump controller. Neither worked. I currently have a new fuel pressure regulator on order to see if that's the culprit.

Any thoughts on other causes? Has anyone had a similar problem?

Dave
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Old 06-30-2007, 08:53 PM   #2
mxboy15u
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Wrong forum, but my guess is the regulator.
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Old 07-01-2007, 08:14 AM   #3
ride5000
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12.9 / 105+

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regulator sounds like a good place to investigate.

also check/replace the fuel filter.
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Old 07-01-2007, 09:15 AM   #4
dwarren
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Thanks. I'll do that as well.

On another note, I do have the Perrin PWI meth injection system that was installed on my car. It has been un-installed recently to ensure it was not indirectly causing this fuel pressure problem.

While the meth was installed, the fuse that is part of the system blew twice and had to be replaced. Any thoughts as to why this happened? Could this be related to my fuel pressure problem?

Dave
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Old 07-02-2007, 06:42 AM   #5
ride5000
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it doesn't sound likely.

what it probably is is some debris in the regulator preventing it from closing.

what happens is that at inital startup your fuel pump duty runs at 100% for a while. during this time the regulator is closed enough to produce the necessary rail pressure--46psi. a few seconds after startup the fuel pump duty will drop down to 33%. at this point the regulator must close some more to keep rail pressure. for whatever reason it cannot, and rail pressure drops.

when you turn off the car, or otherwise stop the fuel pump, how quickly does the rail pressure drop? according to my best guess of what the problem is, i would expect it to drop like a rock right back to 0psi as soon as the pump stops (since the regulator cannot close itself all the way).

ken

edit:

i also just considered another issue: if your intake manifold pressure reference line which connects to the fuel regulator is detatched or blocked, you'll see strange fuel pressures. you SHOULD be seeing manifold pressure + 43psi on the rail.. which means that your initial start rail pressure is too HIGH. the 31psi after the fuel pump duty drops down is actually about where it should be. you could be overrunning the regulator at 100 pump duty which artificially produces high rail pressure. the 46psi fuel pressure should only occur when there's about 0-3psig boost in the manifold. be TOTALLY certain that this little reference line is perfectly fine before you swap out regulators.

Last edited by ride5000; 07-02-2007 at 06:46 AM. Reason: more info
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