My 2001 4.0 2WD Explorer started to act up on the way home (loss of spark or fuel). I made it home, but then the truck would not start. I towed it to the mechanic and it started and ran for awhile. After it was turned off it did not start again. So the problem seems to be intermitant. We spent a little time together diagnosing and there were no trouble codes or check engine light. The fuse/relay box in the engine compartment did not have ground turned on from the pcm. (No ground to fuel pump relay and others) Is this a known issue with older explorers? Could this be caused by the PATS? (Dead battery in the key fob or something else?) I head read that PATS would not disable a running vehicle, only prevent it from starting.

I'm new to the forum. If this is in the wrong forum I'm sure someone will let me know.

 

Welcome to the forum! Which 4.0L engine does your Explorer have (OHV or SOHC)?

By "not start" does the starter spin the engine over but the engine doesn't start (like due to no fuel) or does the starter not even attempt to spin the engine over?

A dead battery in the key fob would not cause the PATS to not allow the vehicle to start because the transponder that the PATS is looking for does not require battery power.

-Rod

 

Thanks Rod,
Sorry for the delayed response. This is an OHV 4.0 and it cranks but won't start. I can hotwire the fuel pump and get it to start, so we traced backwards to the relay and the relay is not turning on. I did check the inertia switch and it is good and has continuity. Exploring the relay/fuse box under the hood I found that several relays did not have ground including the fuel pump. I learned that the pcm turns on the ground to control these relays which was new to me. (I am not knowledgeable on Fords, mostly GM experience) Not having a pin-out wiring diagram for the pcm, I stopped here. Currently I am under the assumption the pcm is going out and intermittently not supplying ground, or I have a break in the harness or fuse box. I couldn't see where the fuse box could be further opened up to expose the bottom side for visual inspection or circuit tracing and I was daunted by the task of unwrapping the harness and visually inspecting for a broken wire, knowing that it might be intermittent and a continuity test would possibly give random results.

So I have several questions now. First, is this a common or known problem for older explorers to lose the ground to the relay box? I was hoping this might be a known problem with a known solution. Second, what is a good source for wiring diagrams and pcm pin-outs? Haynes and Chilton manuals are not as detailed in this area as they used to be. I have tried a couple subscription services online over the years for wiring diagrams but have not been impressed or satisfied. Third, forgetting about PATS incompatibility, is there any compatibility between OHV and SOHC pcm's or wiring harnesses? Or are they very unique to each engine? (different sensors etc.) I ask because I have a SOHC parts car available to me if there is any compatibility.

 

I've not heard much, or experienced many, failed Ford PCMs and I don't recall hearing about many issues with the relay coils not receiving ground. Usually the symptoms you describe on a Ford would be due to a failed fuel pump or the fuel pump driver module. Now if this were a Dodge/Chrysler/Jeep/Ram I'd suspect a bad TIPM but that function doesn't seem to be common on Fords.

Years ago I procured a set of Ford factory wiring diagrams for several model years so I have not had the need to go out looking for wiring diagrams for Fords. If you can be a bit patient (my evenings are pretty full currently) I'd be happy to send you PDFs of the related wiring diagrams. The manuals may also have some troubleshooting guides for no fuel pump activation. I'm trying to recall what all the PCM checks to allow the fuel pump relay to trigger. PATS would be one thing. But if the PATS were the issue I'd expect you to have a flashing or constant (I don't recall which) "Security" or "Theft" light on the instrument cluster when you attempt to start the truck.

I'm also not real familiar with that all is interchangeable between the OHV and SOHC. I'm sure there are some sensors and maybe even some wiring harnesses that work for either, but many of the items like the PCM, PATS, etc are tied to the VIN and likely won't swap unless you can reprogram the calibration codes and VIN.

Speaking of that, you might want to look into Forscan to get some more visibility into what might be happening (such as if the PCM can trigger the fuel pump when commanded and if the PATS is in Theft mode) assuming you don't already have a professional-grade scan tool.

-Rod

 

Thanks Rod,
I was just looking at scan tools to see what level I wanted/needed. I will also look again at the PATS Theft light to see what it is doing. I wasn't focused on that last time I was troubleshooting. I have no experience with scan tools and pcm programming or triggering functions of the pcm. It will be an exciting learning curve. If you have time, the pdf wiring diagrams would be great, I appreciate the offer. Not rush. This is a long term project and I have been focused on another project in the garage lately, but trying to get back to this one.

 

I would start by confirming the power and grounds to the ECM.

 

@aquanaut20 thanks, i definitely have power and ground to the ecm. I can supply ground to the fuel pump relay with a direct jumper to ground and it starts right up. So i feel like i am left with an intermitent break in the ground circuit back to the ecm or the ecm is sporadically not supplying the ground.

 

Have you confirmed the ground exiting the ECM,, Back probed ? Monitor the circuit with a scope or graphing meter.

 

Not yet. I just got the pinout for the ecm and that ground circuit so I will be looking at that next. Thanks.