2007 Expedition EL

[GRRRR8]

This had to be one of the craziest things I have seen in 30 years. This may be a bit long, but you will thank me one day.

2007 Expedition EL 5.4 3V / Auto 2WD / 74,000 miles / excellent condition, all maint. current.

It was towed in for a turn over no start last week. 2 psi fuel pressure. Since these are known for melting the connector at the pump(in the tank), it was a no brainer........or so I thought!

Installed a new Motocraft assembly in the tank, it started right up and ran fine. Road tested and all was well. It was towed back in and the customer stated "it's like I have no gas pedal". I checked it and it acts like the ETB is bad, BUT it doesn't really start and stall. It runs bad and stalls and you have no throttle control.

I hooked up the Verus and I see the pump is being commanded 100%. When I can get it to half way idle STFT is 45%. I have 65psi at the fuel rail KOEO. It sounds like a FPDM is bad, but it doesn't have one(no matter what the Ford dealer says!)

No codes and all data with the exception of 100% pump command and 45% STFT are normal.

I was about to test the PCM when I started thinking about how this system works. I unplug both front O2s and the MAF to eliminate fuel control and it starts and I have a gas pedal. Not running well, but running.

It turns out the MAF had failed. I put a new Motocraft one on and it is perfect.

Now the question for Ford is: If a MAF fails with this design, why would you command a pump at 100%? I would be willing to bet that this is why they burn these pumps up especially when the tanks are run low consistently.

Here is the kicker! The dealer a month ago said it needed a ETB due to a hesitation they could not find. A month ago they needed a MAF that turned into a burned up fuel pump assembly.

Hope this helps!

[sbreland73]

Now the question for Ford is: If a MAF fails with this design, why would you command a pump at 100%?

I'll take a guess. If the MAF signal was within limits (and we all know how Ford has WIDE limits)then the PCM assumed it was good, but the PCM saw a very lean mixture (45% STFT) and commanded the pump to max in order to supply the needed pressure for the longer injector pulse?

Good post, thanks for sharing!

[GRRRR8]

That is correct. Poor design or should I say engineered poorly.

[kpkeenan]

Thanks for posting your story, I really enjoy reading these strange circumstances as we try to figure out the puzzle. I do have a comment about the fuel pump command however. You state the vehicle does not have a fuel pump driver module which is correct, instead it uses a mechanical returnless fuel system which modulates the pressure using a regulator integral to the pump in the tank. This system has to have the fuel pump on at 100% whenever it is running, there is no need to duty cycle the pump in any manner. I agree, the scan tool should not read 100%, it should simply say "on" or "off". Since the introduction of the electronic EGR system modules we no longer have the manifold absolute pressure inferred PID in hertz available to help diagnose the MAF sensor, but the abnormally rising SFT at half throttle is usually a great indication that the MAF is underestimating the air entering the engine which is why the fuel trim goes up as engine speed increases. The MAF sensors are more reliable than they used to be, but every now and then ... Thanks for posting.

[TurboJim]

Ford..... if you had used BARO or LOAD pids your dio would have been quick. On TAC cars MAF is very important. If at any time the MAF, RPM and TP dont jive, they go into limited power mode. What I find strange is, there were no TAC codes.

BTW, one of the first quickie tests I do on a vehicle with crazy trims is unplug the MAF. Check for airflow miscalculations. Quick and dirty, but if trims come back to normal you know airflow isnt being sampled right. unmetered air, MAF whatever. I'm sure you know this already, but just a FWIW