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Old 05-22-2010, 12:33 AM   #1 (permalink)
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Fuel Issue--2000 Grand Marquis

I checked my fuel pressure the other day and it was at around 30 psi. Book says "key on" should be around 45-50 psi. When I take the vac. line off the regulator it jumps up to 45 psi. I plugged the line and the car drives much better with the line blocked. Any idea what could be the problem and will I hurt anything if I leave the vac. line blocked?
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Old 05-22-2010, 12:54 AM   #2 (permalink)
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Re: Fuel Issue--2000 Grand Marquis

The first thing I would check is your fuel filter. More than likely, that is your culprit. If that isn't it, then your fuel pump is getting weak. It even could be the fuel pressure regulator itself, but that is pretty uncommon in fords. If it were a Dodge it wouldn't surprise me.
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Old 05-22-2010, 12:58 AM   #3 (permalink)
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Re: Fuel Issue--2000 Grand Marquis

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Originally Posted by mrboomy View Post
The first thing I would check is your fuel filter. More than likely, that is your culprit. If that isn't it, then your fuel pump is getting weak. It even could be the fuel pressure regulator itself, but that is pretty uncommon in fords. If it were a Dodge it wouldn't surprise me.
Well I've replaced the filter 3 time in the last 10 15k but I have run the gas down low a few times
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Old 05-22-2010, 06:38 AM   #4 (permalink)
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Re: Fuel Issue--2000 Grand Marquis

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Originally Posted by tomrzk View Post

Book says "key on" should be around 45-50 psi. When I take the vac. line off the regulator it jumps up to 45 psi. I plugged the line and the car drives much better with the line blocked. Any idea what could be the problem and will I hurt anything if I leave the vac. line blocked?
You should have a fuel pressure diagnostic gauge hooked up. The pressure is OK (check with vacuum signal removed) but volume may be down. This is checked by slowly opening the pressure release valve on the test gauge asm. If it hesitates/wants to stop running, you have a problem with delivery.

Before replacing pump, check volt supply to the pump.
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Old 05-22-2010, 01:58 PM   #5 (permalink)
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Re: Fuel Issue--2000 Grand Marquis

Both Mitchel and Alldata says key on engine off pressure should be 30-45 psi.

As previously stated you may have an insufficient fuel flow problem.

A couple of tests you can do...

With your fuel pressure gauge hooked up, Find a flexible rubber portion of the fuel return line and briefly pinch it shut. Be gentle and don't damage the line. This will tell how much pressure your pump is capeable of putting out. It should be at least 60psi. If it doesn't increase much or not at all then your pump is weak.

If your fuel pressure gauge hose is long enough, duct tape the gauge to the lower corner of the windshield and drive it. The pressure should stay steady and not drop under wot. Make sure the gauge hose isn't against anything hot and doesn't get pinched shut when you shut the hood. Also make sure it's not raining so you don't have to use your wipers.

If you think it's running lean don't overlook the MAF. Try disconnecting it, if it runs better then it likely is bad.
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