Hi all, my "old reliable" 2001 F250 SD LB, 5.4L V8 has become unreliable. Initial symptoms were engine shutdowns while I was driving. Happened twice in 3 weeks. Both times the engine turned over fine, but had no fire. Oddly, about 30 minutes later it started fine and ran for several days. Took it too a shop and they installed a new fuel pump ("definitely the problem!") and filter. Few weeks later died again, same symptom. Left it with the same shop and they drove it for 2 weeks without failure, stated the GEM module was functional but damaged, along with the fan switch (which was!) replaced them and declared there was nothing else they could do unless it died and stayed dead. Drove about 700 miles without issues, stopped at my home office to drop off things, got in, and it wouldn't start. Towed it 500 feet to my house and started to diagnose it a few days later and it started right up. Then wouldn't the next day. Figured engines wouldn't start for one of four reasons: No spark, No fuel, No air (rather unlikely), bad timing (computer issue). Bought a fuel rail pressure gauge and when running have about 35PSI. When it doesn't start - 0 PSI! OK, "No fuel" it is! Thought perhaps it was the inertial fuel cutoff switch, and reset it. Trunk ran for first 2 tries, then died again. Pulled the switch (during a down time) and the switch appears to be fine. Tested for power at the switch and nothing! Moved to the fuse box under the hood, owner manual images below for reference:



Much to my surprise, with the key on, fuses 1,3,5,7,9, and 11 had no power to them (occasional got something like 4.6v - guessing just stray voltage - its an old meter), All the other fuses tested fine at ~12V. Progress. Swapped the six relays around with no luck. Randomly (???) the truck decided to start, several times in a row. Rechecked the fuses and fuse 5 (Fuel pump relay) showed ~12V. (Note: I do not have a factory trailer hookup, nor a trailer installed with my after-factory plug)

Obviously something is funked in the electrical system. A bad wire? A bad steering wheel key switch (although everything else inside works when I turn the switch on)?

At least managed to move the truck out of the way to a more serviceable spot. Also threw a battery charger on it since it had several dozen failed attempts at starting. Suspect the battery is slightly depleted but worth noting that the problem exist even after it battery is fully charged (again, this has been going on for 6ish months - this long post has a somewhat abbreviated history).

Any suggestions?

 

Okay, time to focus on what is necessary for the fuel pump to have power.

What's needed?

The PCM MUST "boot" up. That means it needs to have its power and ground before anything else will work.
The PCM must send a signal to the fuel pump relay to turn it on.
The relay must switch power through the inertia switch to the fuel pump.

So, you need to check all of the prerequisites for the fuel pump to operate. You may have been operating and searching too far "downstream".

Quickest way to see if the PCM powers up is to observe the check engine light. If it comes on when the ignition switch is turned from OFF to RUN, the PCM powered up.

 

Paid attention to the check engine light - PCM is being powered up.

Found a lot of good info I can check on the next nice day in the related topics. Does anybody have a pin-out of the test block connectors they can share?

Of course, now I need to wait for it to refuse to start. Maybe. If anybody has some ohm values I can take some resistance readings???

Just to be complete, no engine codes via my OBD reader. Getting a couple of initialization errors on oxygen sensors but that is it (part of this journal was replacing the two front oxygen sensors, but still getting initialization errors on those - I'm pretty sure its an unrelated problem).

 

Don't know what you mean by "test block connectors".

I like to recommend connecting a meter or an incandescent test light (preferred) to the fuel pump power wire at the inertia switch. That will allow one to see if the problem is upstream or downstream from that point in the circuit. Normal operation would be to see the light come on for 2-3 seconds after the key is turned from OFF to RUN then come on continuously after the PCM detects the engine is firing.

 

Awaiting the next failure to do additional testing. Just need to get my nerve up to try and drive it again and risk getting stranded.

"test block connectors" - saw reference to a test block in some of the related post, specially to "ground the fuel pump via the test block". Was guessing this is the approximately 2"x4" set of connectors under the hood right next to the fuse box. Opened the cover to that block and it looks like 2 unused relay connectors, but suppose it could be the afore mentioned "test block"???

 

This has all the symptoms of the typical relay failure that's been posted here several times. You still need to do the checks and diligence like projectSHO89 suggests to be sure instead of just swapping parts, though.

I don't know if the 01s have the same micro relay for the fuel pump soldered onboard that the 02-03-04? has. I bet projectSHO89 knows that. If it does have that micro relay and the relay is the problem, there are a few write ups in the v10 forum that shows a bypass for that. If the 01s just have the standard relay for the fuel pump, you can just swap that out easily.

 

I posted the fuse panel/relay from the owners manual. I did not see a fuel pump relay, just the 20amp fuse to the fuel pump relay coil (fuse #5). Note that the fuel pump was replaced by the repair shop as their first attempt at swapping parts... I did swap relays around to see if that fixed it and it didn't. So guessing the fuel pump relay itself is elsewhere?

 

No, it does not. The 01 still had the discrete plug-in relay in the instrument panel relay block. Last year for it on the SD trucks. It's not documented in the owner's manual.

See this thread, correct info is in post #13: https://www.ford-trucks.com/forums/1...ont-start.html Schematic for the system is also posted in that thread (5.4 and 6.8 fuel pump circuits are the same).

Regarding that, I'd simply ignore it. Doesn't exist to my knowledge.

Check the fuse sockets that hold the fuses that are critical to fuel pump operation. Sometimes the "fingers" loosen and cause a poor electrical connection that is intermittent. Same for the PCM Power and Fuel Pump relays. Sometimes, fuses that "look" normal can develop internal hairline faults that also cause intermittent connections.

 

Thanks for all the information everyone! Those wiring diagrams are gold - made hardcopies. Sounds like the fuel pump relay is going to be a pain to get to, but will do what needs to be done once it dies again.