Fuel pressure ?

[Methodical]

How long should the car hold fuel pressure after the car is turned off.

My pressure goes from about 38-40 to under 20 psi in about 1 hour.


Thx

 

[HGFireHazard]

I can't give you a definitive answer, but I know from night to morning the pressure is gone. Judging by my experience it seems like a few hours (3-4) would do the trick, but that's only an estimate.

 

[Methodical]

I can't give you a definitive answer, but I know from night to morning the pressure is gone. Judging by my experience it seems like a few hours (3-4) would do the trick, but that's only an estimate.

Is that with a mechanical or electric fuel pressure gauge?

 

[Black95GTS]

Is that with a mechanical or electric fuel pressure gauge?

Good question.

I think he means in general. You can basically do two things if you want to work on the fuel system but don't want to deal with pressure:

1 - Let the car sit over night, it will be gone by then

2 - While the car is idling, kill it by triggering the inertia switch in the trunk. This is will cut off the fuel pump and there will be no fuel pressure. The car will stall out and a CE light will come on, but, after you are done and enable the switch and start it up, it should go off. This is how I always do my fuel system work.

Adam

 

[HISSIN50]

Al, that's normal. The system is designed to not hold pressure indefinitely (there's no reason to). Otherwise a more robust check valve would have been used and the prime-out could be omitted.

When people post, they should note if they have aftermarket FPR's since they almost always lose pressure very quickly after shutdown.

 

[Methodical]

Good question.

I think he means in general. You can basically do two things if you want to work on the fuel system but don't want to deal with pressure:

1 - Let the car sit over night, it will be gone by then

2 - While the car is idling, kill it by triggering the inertia switch in the trunk. This is will cut off the fuel pump and there will be no fuel pressure. The car will stall out and a CE light will come on, but, after you are done and enable the switch and start it up, it should go off. This is how I always do my fuel system work.

Adam

I was asking him if he used a mechanical or electrical gauge when he observed his fuel pressure because I know there can be a slight difference between the 2 types of gauges in pressure readings. But thanks for the tip.

 

[Methodical]

Al, that's normal. The system is designed to not hold pressure indefinitely (there's no reason to). Otherwise a more robust check valve would have been used and the prime-out could be omitted.

When people post, they should note if they have aftermarket FPR's since they almost always lose pressure very quickly after shutdown.

I sure hope so because I don't want to have to fool with the fuel pump.

 

[HGFireHazard]

I have a mechanical unit on the fuel rail that sends an electrical signal to the gauge in my car. I didn't want any fluid coming in nor to have the gauge outside of the car.

I also have the stock FPR, as JT noted that many aftermarket FPR's do lose their pressure quite quickly.

 

[Methodical]

OK fellas. I am 100% convinced now that it's my fuel pump. I think it was slowly dying on me. Today I started the car and let it run at 2K rpms with some WOT revs and the fuel pressure never went pass 25psi. This while viewing the pressure under the hood with a mechanical gauge on the fuel test port. Do ya'll agree?

 

[HISSIN50]

If you know the gauge is good and have checked that it's not the FPR that's causing the loss of pressure (one can carefully use a pair of fuel-injection hose clamps on the return side to see if pressure shuttles back up), then the pump is the reasonable option left.
To be sure you could open the delivery side and do a volume test.

Good luck.

 

[Methodical]

If you know the gauge is good and have checked that it's not the FPR that's causing the loss of pressure (one can carefully use a pair of fuel-injection hose clamps on the return side to see if pressure shuttles back up), then the pump is the reasonable option left.
To be sure you could open the delivery side and do a volume test.

Good luck.

The FPR is new - stock not adjustable. I thought about doing the clamping method but since Ford no longer manufacturer our fuel lines and no one else seems carry them, I will stay away from that method (see fuel line thread at Corral).

Thanks for the tips

 

[txmustang6933]

check your fuel filter, depending on the # of miles on the car, i have seen a car not run at all because of a clogged filter. you should run 35 lbs at idle when its normal

 

[Methodical]

I found out the problem was a bad stator in the MSD distributor. Replaced distributor and all is good now.