I have a 94 Explorer XLT with 39650 miles. For the past few weeks every once in a while it wont start. Ive noticed the fuel pump did not prime when I had a no start situation. It ran fine for about 3 weeks and now it started acting up again. But Ive also had it shut down while driving twice now. The problem is trying to get it to act up while I troubleshoot... I did get one error code out of the PCM which was 543 (fuel pump failure - PCM to battery)... When it dont start I dont have voltage at the pump, Inertia switch and fuel pump relay... When it does run I have battery voltage at the coil windings of the fuel pump relay but once when it didnt start I noticed the voltage down to 10.7... Once when I turned the key to the ON position 10 to 15 seconds went by before I heard the fuel pump prime... Any Ideas?

 

Hi, Vance.
Your problem sounds an awful lot like the problem I was having at the beginning of the summer. Sometimes wouldn't restart after shutting it off and I couldn't hear the fuel pump when I turned on the key. Never would mess up when I got to the shop. They'd keep it for days, mechanics take turns driving it home, etc., and wouldn't mess up until I would get it back. One day one of the mechanics stayed dedicated to it and drove it, parked it, shut off, restarted, etc., until it messed up and he could track down problem for sure (rather than just guess and swap parts). It stayed messed up long enough for him to locate the trouble. He found that the fuel pump had an internal short sometimes when hot and this resulted in about 2# of fuel pump pressure. They replaced the fuel pump and, at my request because of the high current draw when the pump would short, replaced the fuel pump relay and the fuel pump wiring harness. Been long time now with no problems.
I hope the information is useful to you. As I said before, what you describe sounded like the problem I was having.
Robert

 

Hi, Vance.
Your problem sounds an awful lot like the problem I was having at the beginning of the summer. Sometimes wouldn't restart after shutting it off and
I couldn't hear the fuel pump when I turned on the key. Never would mess
up when I got to the shop. They'd keep it for days, mechanics take turns
driving it home, etc., and wouldn't mess up until I would get it back. One
day one of the mechanics stayed dedicated to it and drove it, parked it, shut off, restarted, etc., until it messed up and he could track down problem for sure (rather than just guess and swap parts). It stayed messed up long enough for him to locate the trouble. He found that the fuel pump
had an internal short sometimes when hot and this resulted in about 2# of fuel pump pressure. They replaced the fuel pump and, at my
request because of the high current draw when the pump would short, replaced the fuel pump relay and the fuel pump wiring harness. Been long
time now with no problems.
I hope the information is useful
to you. As I said before, what you describe sounded like the problem I was
having. Robert

Thanks for responding. I dont think my fuel pump is going bad due to the fact that if the pump was the problem then the relay would function normally and due to the high current draw the relays N.O. contacts would be badly burnt. My relay contacts looked almost new and the relay would not function when the vehicle acted up. Due to the fact that I measured low input voltage at the coil windings of the fuel pump relay I got suspicious of the ECC relays contacts that supplys battery positive to the PCM. They looked slightly burnt and pitted maybe enough to cause a voltage drop to the PCM... Since Ive cleaned those contacts the Vehicle hasn't acted up but its still to early to tell. Thanks Again

 

You sound a lot like me, Vance. You'd rather find the problem and know in your heart of hearts that you put your finger on it--and then fix it--rather than just think you're in the right area and throw a bunch of parts on hoping that you got the problem covered. I'm glad for you that you're able to do that.
Because of a disability there is a lot of work that I can't do to my own vehicles anymore. I even have to get someone else to open the hood on my Explorer just so I can check oil and such. I understand what you're talking about with the fuel pump relay and the condition of the contacts. I had looked at my fuel pump relay contacts also (since it was something I was still able to do) and thought they looked pretty normal also. I also assumed that there would be a lot of burning if the NO relay contact had opened up while under a high current load but I didn't see that. The relay coil ohmed out ok and the contact showed good continuity; I only requested that they replace they relay when doing the rest of the work because it was so inexpensive and I didn't want to take the chance that something would go wrong with it while on the road. Because I'm so physically limited on what I can do anymore, I wasn't able to check a lot of things on mine when the thing wouldn't start so, unfortunately, I'm often at the mercy of my mechanic's shop. They've always been square with me and I've always been happy with their work but I still itch to get in there and do the work myself.
What you said about no coil voltage and the fuel pump relay makes good sense and you're probably right--it probably isn't in the fuel pump. Good idea to look at the EEC relay contacts. I hope that that's the "permanent" fix for your problem. I sure envy you on being able to get in there and enjoy the challenge of tracking it down--I wish I still could do that. Good luck.
Robert

 

Aren't the relays sealed? Maybe I'm looking at the wrong relays? Where are the relays you're talking about? Or, are you talking about the relay's plug in contacts?

 

Maybe a dumb question, but did you check that all of the ground wires are clean and tight?

 

normally you can hear the fuel pump turn on for a couple seconds when when turn on the ignition. my problem is with the fuel pump failing to turn on. i only have this problem after it has been driven for a while, engine is already hot and the ambient temp is around 80 degrees or higher. it usually works if i let it sit for a while. i've tried removing and replacing the fuel pump relay and also tapping on it, none of this helps. it seems to be linked to engine temp. i've never had any problems while the engine is running. i'm hoping it's just the relay.

 

The fix turned out to be a relay, but not the fuel pump relay! A bad ECM relay (Engine Control Module Wiring) was the problem. I verified this by applying 12 volts to the relay several times. It would stop working (clicking) occasionally unless I tapped on it.

 

Hmm, I might look into this. I'm having similar problems with my van in extremely hot whether. My pump was replaced last summer, but I don't think the relays were.

 

Yes, the fuel pump is dependent on the ECM relay, fuel pump relay, and the inertia switch. A bad relay can act up on you when it gets hot. You can get the relays at most auto stores for about $7 each.