Fuel Pressure issues

[aldive]

I have been having a delayed crank to start problem. Well tonight I hooked up a fuel pressure test gauge.

The fuel pump makes the standard noise with the key in the run position; however, the gauge reads about 5 pounds of pressure. This is true after several cycles of key on key off.

Upon cranking, which is immediately after a couple of key on “prime” sessions, the pressure is a rock steady 65.

Further, after turning off the truck, the pressure drops to almost zero immediately.

The truck runs great, with full power and gets typical mileage.

Any ideas or suggestions on what to do next?

 

[RiverRat]

Since it's starting ok (not flooded) IIRC there is a check valve in the fuel pump to maintain pressure. Maybe it went bad.

 

[aldive]

Need some input, pleaee, have a long trip very soon.

 

[JDraper]

FPR on the way out?

 

[aldive]

I am hoping that is the issue and not the pump utself.

Any more ideas or suggestions for testing?

 

[JDraper]

Al, just ran your symptoms through my Ford repair matrix. If you have fuel in the vacuum line of your FPR, it is most likely the problem and needs to be replaced. If you don't have fuel in the vacuum line, the Ford matrix says to replace the fuel pump module.....good luck!

One other note, it also mentions looking for restrictions in the fuel line, but your symptoms don't seem to follow that line of thought.

 

[aldive]

Any other thoughts or suggestons, please?????

 

[Opera House]

Measure the fuel pump current at the fuse. When I had problems, I measured the pump current for a week. Quarter inch spade connectors fit nicely in the fuse socket and lamp cord brings it into the cab. Current is normally about 5A, higher at WOT and lower at idle. First 5 minutes current is about 1/4 amp higher till pump windings warm up. Current is roughly proportional to pressure. Since the fuel system is high bypass, 80%, pump voltage can drop to 6 volts from bad connections and the vehicle can still run. At 2 1/2 amps the engine will have problems and may not run. Below 4A indicates fuel system problem. Current is a little easier to monitor and will tell you some things pressure won't. This will help you document other times the system may be having problems.

 

[aldive]

Any idea why there is so little ( 5-10 psig ) pressure with key on and even when several cycles of this, yet with motor running, there is 65 psig?

The fuel pump check valve "must" be bad since the pressure drops to 0 as soon as the motor is turned off.

 

[aldive]

Originally posted by aldive
Any idea why there is so little ( 5-10 psig ) pressure with key on and even when several cycles of this, yet with motor running, there is 65 psig?

The fuel pump check valve "must" be bad since the pressure drops to 0 as soon as the motor is turned off.

Answered my own question; had a friend do the key on while I looked at the pressure gauge, it went to 65 psig, but dropped to 0 as soon as the key was turned off. When I was doing it myself, by the time I turned off the key and got to the engine bay to look at the pressure gauge, it was 0.

My problem is definately a bad check valve in the fuel pump.

Oh boy, I get to drop the tank to replace it......

 

[aldive]

Thank God for extended warranties; I am not going to have to do the work and it will not cost me a dime.

 

[aldive]

Well the new pump is in and it didn't cost a dime. My aftermarket warranty paid my mechanic friend $504.68.

Truck starts immediately, runs like a scalded dog; I am pleased.

 

[james t]

ouch. i assume most of that cost was for labor, as the pump shouldnt be much over $100. glad to see you got it fixed without any hassle.

FYI- yours is a 99 and doesnt have a FPR. it has a returnless fuel setup and pressure is controlled by the computer.

 

[aldive]

The pump was a Ford replacement paet and was not just the pump but the entire assembly.

You wouldn't believe how nasty the strainer sock was.

 

[tmsoko]

Glad it was fixed. I will shed some light. The returnless fuel system is a completely mechanical system. The EEC is not involved in any way. There is a FPR, but it is in the fuel tank. Just like a rail mounted reg, but instead of having fuel travel from pump to rail reg, then back to tank, the reg and return line are move to within the fuel tank.

As for the pressure drop, your check valve went bad, This happened on my Ranger and it perplexed me for some time. When the check goes bad, all of the fuel in the line above the top of the tank (liquid seeks equil pressure/level) pours back into the tank - back flow through pump. When you turn the key, the few second pump pulse only moves a small portion of fuel - not enough to fill the line / rails back up. If you do several key on-off-on cycles, the pump bursts accumulate and fill the line, thus providing full pressure.