Hello, I have a 2005 F150 5.4l 137000 miles. Three weeks ago, my truck began surging/bucking under heavy throttle. I replaced the original fuel filter (plugged) replaced the original fuel pump (screen was very dirty), neither helped. I then replaced the Fuel Rail Pressure Sensor as well. No help. The problem has evolved into stalling under light throttle and bucking at a much lower throttle position. I tried a new Dorman FPDM (my original is in very good shape) with no change. My scanner shows fuel pressure around 40 psi at idle (which is very smooth). Under acceleration, the fuel pressure will drop to around 5 psi, then spike to around 75 psi. This will repeat 3 to 4 times then somewhat smooth out as the speed increases. At a cruising speed (also very smooth), acceleration will repeat the fuel pressure drops and spikes. The spark plugs are original to the truck and need to be replaced, but oddly enough, once in a while, after sitting overnight, the truck will run perfectly for about 1/4 mile, then symptoms return. The truck never misses at idle or accelerating so I doubt the plugs are contributing. Outdoor temperature is rising and for the past few days the truck stalls and cuts out and no longer has that short time of running correctly. There are no codes, stored or pending. With the vehicle parked and in neutral, the engine revs smoothly. In gear with my foot on the brake, either D or R, I can load the engine with no sputter or hesitation. This only happens when the vehicle is moving. I am at a loss and don't know what direction to look in. ANY and ALL help is really appreciated!

 

137k on the original plugs? Change them. Ford recommends plug changes on the 3V 5.4 at 60k. Betcha that may fix it.

 

That poor engine needs some love! Change the plugs, clean the MAF and the throttle body.

 

I have a Lisle tool on the way. I have cleaned both the throttle body and MAF (with MAF cleaner) more than once. My throttle body was not very dirty to begin with, very minor deposits. I have checked for vacuum leaks using three different methods and can't find any.

 

May be worth inspecting the FPDM on the frame rail by the spare. If it is badly corroded might be time to replace. I don't believe that your fuel pressure should drop like that under acceleration.

Scratch that I see you tried the doorman one.

 

obviously this isnt normal... you might try doing some research and find out wich wires to check for proper signal from the PCM. im not 100% sure how this system works but i know that the PCM and the FPDM control the voltage to the pump wich controls the pressure. ill see if i can come up with anything and post it.
good luck

 

here you go...
i really hope this helps. keep us posted



1. Check the circuits of the Fuel Pump Driver Module (FPDM) to narrow down the cause of the problem. The FPDM is located at the rear of the vehicle on the frame rail on the driver's side of the vehicle, behind the rear axle.

2. The White wire at FPDM pin 5 should show battery voltage whenever the ignition key is on, from the fuel pump relay, through the inertia switch.

3. The Black/Orange wire at FPDM pin 3 is a dedicated ground for the FPDM, grounding to the frame at G300, near the FPDM.

4. The Pink/Black wire at FPDM pin 4 is power out of the FPDM feeding the fuel pump. This circuit should show battery voltage whenever the key is in the run position.

5. The Light Green/Yellow wire at FPDM pin 2 is the fuel pump ground circuit. This circuit is duty cycled with a ground signal from the FPDM based on the command from the Powertrain Control Module (PCM). Back probing this circuit with a jumper wire and grounding it should result in 70+ PSI of fuel pressure if there is power to the fuel pump and the pump is good.

6. The Brown/Orange wire at FPDM pin 6 is the command signal sent from the PCM to the FPDM. This is a duty-cycled signal, with the PCM supplying a duty-cycle between 5% and 50% when it is commanding the FPDM to run the pump, and a 75% duty-cycle when it is commanding the FPDM to shut the pump off. If the duty-cycle is commanded between 5% and 50%, there should be exactly double that amount of ground to the fuel pump on the Light Green/Yellow wire. For instance, if the duty cycle on the Brown/Orange wire is 20%, this would be a command for the FPDM to supply a 40% ground to the pump, and if the duty cycle on the Brown/Orange wire is 50%, this would be a command for the FPDM to supply a 100% ground to the pump.

7. The Light Blue/Red wire at FPDM pin 1 is a feedback signal sent from the FPDM back to the PCM. This is also a duty cycle signal, with the duty cycled at 50% when everything is OK, and changing to a 25% or 75% duty cycle if the FPDM is seeing a problem.

 

Jeebus20, thank you for that information. I am curious though how I can measure duty cycles with a multimeter. I am not familiar with the term 'duty cycle' so I will have to google it.

 

I just read about duty cycles in Wikipedia, I think I know how to measure them with the tools I have. I will ask more questions as they arise

 

Is there software that I can use with my OBDII scanner to monitor the duty cycles?

 

I know there are DIY type OBD II interfaces that can display nearly everything. Google took me to the "AutoTap", but it looks like you may have to pay for the different software packages separately?
I read about one a couple years back that was under $100 for the hardware and all their software was free. Can't seem to find it now though.

 

UpFord, where are you located. if your local in SoCal i can help you out. i have a scanner with all the needed software

 

I am in Utah. For whatever reason, the issue has resolved itself. It had the problem, then the next morning it ran fine and has so for 3 days now. I have a feeling the problem will return since nothing was 'fixed'. It ran fine Friday and I replaced the plugs Saturday. Broke 5, the gap was .056" on the three that came out intact. If the issue comes back I will post again if I figure it out.

 

@UPFord, have you had any more issues with this. I'm having the same problems and just wondered if you did anything other than changing plugs.

 

@ryanW, no. I have gone a year without any additional issues. It seems to have resolved itself. I think it must have been a fuel additive I added just prior to the issues. That is the only thing I can figure since it just went away...