fuel pump relay power supply problems

[Tired Iron]

I've been fighting a fuel delivery problem for a while. i just finally found that i have 12v going to both sides of my pump relay. i have 12 v on relay pin 30 (ok), 86 (ok), and 85 Not Ok. I don't have a print that will show me what is putting full 12v power on 85. This in not phantom power, it is a nice bright test light.

other things i'v done for my fuel problem are test and verify the pump, the crash reset switch, verify good relays- all fine. i can jam a jumper in the relay socket between 30 and 87 and get pump power although my pump and tank are not in the truck right now to actually run it. (i am injured and cant get my tank back in until i heal in a month or so and my wife wont do it either)

Any experiences with this? I think power is supposed to grounded on blueish grey w/orange tracer in the fuse socket. I'm wondering if i should just chop it off and ground it so my switch will run the pump correctly. I prefer repairs over cobbling it together.

 

[Tired Iron]

http://repairguide.autozone.com/zne...96b43f/80/21/19/6d/large/0996b43f8021196d.gif

As soon as I post something i find my own answer. This diagram shows bluew/org wire goes to magic box, it looks like a PCM failure. that means I should chop the wire, ground the relay side and hope i can get away with not replacing the magic PCM box.

Does this sound right?

 

[MrShorty]

i have 12 v on relay pin 30 (ok), 86 (ok), and 85 Not Ok.

Actually, this sounds right to me (KOEO condition). I cannot remember the pin assignments, but, there should be +12 V at 3 pins:

1 pin is a red wire that comes from the EEC power relay and should have 12 V with the key on. This circuit energizes the coil side of the relay.
1 pin (blue/orange) goes from the coil side of the relay to the PCM, which acts as a ground side switch. When the PCM part of this circuit is open, this should show 12 V as well. This also goes to the self-test connector where you can manually ground it to force the relay to close.
1 pin (Black/Yellow) coming from the battery through the fuel pump fuse.

These three pins should all show 12 V KOEO. If you ground the test lead (blue/orange) in the self-test connector, the green wire going to the fuel pump should also show power. I think this is the next thing I would check -- see if the fuel pump relay can close when this part of the circuit is grounded.

 

[Tired Iron]

mr shorty-
that test connector short brought the relay to life! I am encouraged. would that mean it is a PCM failure? it doesn't fire the pump for a second when the key comes on before cranking. this tells me it's not a engine cranking signal that is preventing pumping or it would start and then stop right away.

i need to get my tank back in, that will help me do real pump testing. I hate being a gimp.

FR-
the previous owner had an aftermarket alarm system at one time it has never worked since the 12 years i've had the truck. I don't know of any theft system beyond that. It has never run for a second since it was parked for a couple months and wouldn't restart. That was about 3 years ago, sometimes I take my time to get things done.

 

[MrShorty]

that test connector short brought the relay to life! I am encouraged. would that mean it is a PCM failure?

Possibly. Remember that "by the book" diagnosing of a bad PCM is usually process of elimination. Eliminate "all" other possible causes. When those are tested, then you conclude a bad PCM. With that in mind:

Have you verified the wiring between the relay and the PCM? Verified the PCM's grounds? Verified that the PCM is getting power?

 

[Tired Iron]

I've never worked on PCMs before. I am going to do some studying and see what comes up. I am really leaning toward a failed ground, i know i have solid 12v+ power coming out where I don't want it. maybe a short in the wire loom, who knows what gets in there having lunch. I guess this is my next adventure.

 

[shucker1]

Try this old post.

http://www.explorerforum.com/forums/showthread.php?p=2954012#post2954012

It might help. Read post #3 .

Like Mr. Shorty said the PCM acts like a power to ground switch.

No ground = No Go.

 

[Tired Iron]

Mystery solved!

I closely followed an old post from another member, scaterline, in 2010 on his fuel pump issue. I started testing my PCM power and grounds and I found that PCM pin # 20 and 40 were not grounded. I searched the harness for the other ends of those wires, what i found was a plug, right next to the battery, a black wire and a black w/wht wire. still plugged in with it wires pulled out from somewhere.

My question for someone with an explorer close at hand, do both of those wires get connected to a frame ground where the battery pig tail terminates? Possibly crimped into the same lug at one time? I know laying the blk/wht wire in the neg. terminal will solve my problem but i don't know what to do with the second all black wire.

This has been 3 years sitting since it stopped running. I guess it must have been around the time I pulled my winch off to put it on my pickup. I must have got a little excited about yanking wires. I guess hind sight is 50/50.
Next, in 6 weeks, my shoulder should be healed enough to put the tank back in and actually run the beast. That will be the proof.

 

[Tired Iron]

Fuel tank is back in, pump works great. No new parts at all, just alot of headache and labor for my own mistake of letting a couple wires get left off the battery ground terminal.

I've been driving the truck for a week now with no issues at all.