Fuel Pressure= Low Diognosis? (99.2.5L)
 

Recent problem : Truck starts normally from cold start, but after stopping, sometimes has to sit for 30-45 minutes before able to start ( cranks over strong, but will not fire).

Fuel pressure test results:

Key ON-Eng. OFF: the pressure only went to 32 Psi, then rapidly dropped to zero; so the system is not holding pressure static.

Key ON-Eng. running: Pressure held at a steady 62 PSI at idle.

Could this be an Injector leak? (I've been getting a # 4 Cyl. Misfire Code); or is it a failed Check Valve in the Pump assembly?

Also, don't know how low "static" fuel pressure would allow initial, cold start without a problem--then prevent starting when "warm "?

Leigh

UPDATE-Fuel pressure check results

Key ON-Eng. OFF: the pressure only went to 32 Psi, then rapidly dropped to zero; so the system is not holding pressure static.

Key ON-Eng. running: Pressure held at a steady 62 PSI at idle.

Could this be an Injector leak? (I've been getting a # 4 Cyl. Misfire Code); or is it a failed Check Valve in the Pump assembly?

Also, don't know how low "static" fuel pressure would allow initial, cold start without a problem--then prevent starting when "warm "?

Leigh

Fuel pressure should hold for a few months.
No lower than 50psi on your year, Returnless system.

Simple test for leaking injector or leaking Pulse Damper, is using the Clear Flooded Engine routine.

All fuel injection computers have this, if engine is at 0 RPMs(off) and computer "sees" WOT(wide open throttle) voltage from TPS(throttle position sensor) it will turn off fuel injectors but leave spark on.
Allowing driver to "Clear a Flooded engine"

So key on(computer on)
Press gas pedal to the floor and hold it down(computer "sees" WOT voltage, injectors off)
Turn key to START
engine should just crank without firing or trying to start

If it doesn't fire then yes fuel pump check valve is the problem
If it fires then fuel is leaking into the intake, could be injector or from the vacuum line on the Pulse Damper, easy to check that vacuum hose for fuel or fuel smell.

As soon as you release the gas pedal injectors will start working, even while cranking.
If engine does fire with gas pedal to the floor the computer may exit Clear Flooded engine routine on its own so engine will start, I think if RPMs reach 400 computer will exit the routine.

This works if TPS sensor is working correctly, at throttle closed the TPS sends computer under 1 volt, .69-.99volts is spec.
At WOT TPS sends computer over 4.5volts.
Throttle cable can stretch over the years so WOT voltage is below 4.5v, so no clear flooded engine routine.

Popular mod on older Rangers is the throttle cable mod, fairly simple, you put a ziptie on the end of the cable in the cab, this in effect shortens the cable back to spec, some need 2 or 3 zap straps, and can't believe the increase in power now that they have WOT back, lol.
The stretching of the cable happens so slowly that it isn't noticed, people just assume the engine is getting older and "tired".

Thanks Ron,

The engine did not Start, or attempt to Start with the Gas-pedal to the floor, and when I released it started right up, so check valve likely failed.

It's my understanding that the Check-valve is integral with the pump Assy.: so I suppose a complete Pump Assy. replacement is in order???

Best regards,
Leigh

Yes it is part of the fuel pump.

On some years there was a 3 port fuel filter, it has an IN and OUT and then a 3rd port which returned fuel to the tank, and I assume it did this with a check valve inside the filter that would open above 75psi, so system couldn't be over pressurized.
Failure in the filters check valve could produce the same symptom, but never seen one up close so can't say for sure.

On others the computer turned fuel pump on and off while engine was running, cycling the pump according to fuel demand which it is calculating anyway.
On these the filter would just have an IN and OUT no 3rd port.

Thanks Ron,
I'm about to order a Delphi DHP 10227 Pump module; but I'm still not sure how with this "0" static fuel pressure condition the truck starts right up, Cold, but refuses to start after a short trip without setting for 30-45 minutes?

Key=ON evidently supplies adequate pressure for immediate cold start---Why would it differ after "run"???

Best regards,
Leigh

Did you try the engine off pressure test on cold engine and then warm engine?

Could be the warmed up pump isn't getting up to 30psi even briefly???

Don't know other than that.

RE. Pressure Check.
 

I only did the Pressure-check on a "cold" engine, & it dropped rapidly from it's max 32 psi to "0".

I'm wondering if the lower pressure in the system, when warm, could allow the fuel to vaporize, resulting in a vapor-lock blocking fuel flow to the injectors?

That would explain why it starts normally again after setting / cooling off for 45+ minutes?

Leigh

Possible, but not as likely as failing fuel pump being the issue when warm.

Mechanical fuel pumps located on the engine and the metal fuel line feeding it were the source of vapor lock in the old days.
Electric fuel pump located near fuel tank virtually eliminated vapor lock issues.
Fuel injection always uses electric fuel pumps, most inside the fuel tank, so while it is possible, vapor lock is not likely.