Need Help Fuel Pump Circuit

[Josh P]

There is no check engine light present
Would bad ignition switch let the engine crank though?

The bulb for the check engine light maybe burned out or the ecm isn't turning on. Check the fuse, if it is good check for voltage in the socket when you turn the ignition on. A few years ago my van had a problem like you described in the first post, the ground wire in the fuel pump relay was corroded. The crankshaft sensor was starting to go, I had to start the engine several times for it to run.

 

[410Fortune]

When you turn the key does the eec relay click?
same as fuel pump relay except the fpr shuts off after the prime
Ignition switch can cause funky things like this
We need to take a close look at your power distribution box and the wire leads that these relays and fuses click into, many times the wires get corroded or just slip out of their locking pins and cause an intermittent connection.

With a test light or multimeter you can check some simple things out.
We just need the 94 wiring diagrams for fuel pump, pcm and power box I do not have them online
We want to eliminate things until you find the source

First we check power from ign switch to eec relay
Second check acc power feed to pcm from eec relay
Third check power at fuel pump relay from pcm
Finally check that the fuel pump relay is switching and sending power all the way to the tank
Once you do that, you will know the ign switch is good, the fuses, relays and inertia switch are all confirmed good, then you can drop the tank and replace a bad pump or find out why this thing is giving you fits

 

[Turdle]

If you wiggle the relay in the slots, and the pump activates then you have a loose connection. Pull the box away from the fender and turn it over so you can check all of the wire connections. You can pull the box by inserting a flat blade screw driver in the two slots on the mounting bracket.

Yup
If a wiggle test caused the pump to prime you have a bad connection in the relay ( edit and or fuse) sockets. Hard to find by eye really, but basically the lugs are opened too far allowing the relay to slide in without making metal to metal contact. You can remove each lug one by one to close them up a little but be very careful, as too tight will cause the lug to push out the back of the panel when the relay is inserted.

You can also try slightly twisting ( very little, maybe 2 degrees) the pins coming out of the relay which will make them scrape into the connector lugs better. This one fix allowed me to drive home from Colorado when I was actually preparing to drop the tank at a campsite.

edit. don't forget the PCM relay and fuses. If the PCM has no power the fuel pump will not prime.

when doing wiggle test try less aggression to the wiggle. Try to move them one at a time to determine which exact wire's movement causes joy.

 

[massacre]

I may have been wrong about the wiggle test. I heard some clicking when wiggling stuff not 100% sure it was fuel pump.

I don’t really hear anything when I turn the key. That might be the problem.
Just got home from work, going to try a couple more things since it is now over 20 degrees out and I have good daylight.

Really just any checks to do, I have plenty of stuff - meter, test light, power probe etc.
I find it weird that it would not start with the fuel pump relay jumped out, I think it is the eec fuse or relay or something I am not 100% sure it is the fuel pump but am not afraid to change it out if that is the case.
I read to start at the inertia switch since that is the middle of the circuit?
Any links to test procedures would be great. I do have a diagram but it is the gigantic paper ones with every wire in the car listed. Which is fine but it takes longer to trace everything down that’s all.

Thanks everyone for your helpful advice, going outside to see what I can find now.
Been searching the forum for similar threads

The truck doesn’t really have much rot or rust to speak of it was a NC car only been in MA for a couple years so bad grounds were not my immediate reaction but I guess anything is possible.

Also I am alone so no one to turn the key haha

 

[massacre]

Well I can’t believe my dumb luck.
Huge thanks for mentioning hearing the EEC relay click when turning the key.
I could not hear the EEC relay clicking so I removed it. Found power only on the north side of the relay socket with key off. With key on I had power to the north terminal but now also at the west terminal. I replaced the EEC relay with a known good relay, and then I could hear it clicking when I turned the key on. I put an old relay in the fuel pump spot, nothing.
Put a new relay in the fuel pump,spot, turned key wouldn’t you know-
The damn thing primed. Cycled the key on and off like 5 times, primed every time. Started truck right up no problem.

So I guess it was 2 bad relays? I see now that the fuel pump relay gets a signal from the EEC relay so it all makes sense now that I could run the pump with my power probe but it wouldn’t start because the EEC was not working properly.

I will def be keeping an eye on this but for now it seems to be ok?

Thanks again everyone for the helpful advice!
She is backed into the garage so if it happens again at least I can work on it more easily

 

[massacre]

Yup
If a wiggle test caused the pump to prime you have a bad connection in the relay ( edit and or fuse) sockets. Hard to find by eye really, but basically the lugs are opened too far allowing the relay to slide in without making metal to metal contact. You can remove each lug one by one to close them up a little but be very careful, as too tight will cause the lug to push out the back of the panel when the relay is inserted.

You can also try slightly twisting ( very little, maybe 2 degrees) the pins coming out of the relay which will make them scrape into the connector lugs better. This one fix allowed me to drive home from Colorado when I was actually preparing to drop the tank at a campsite.

edit. don't forget the PCM relay and fuses. If the PCM has no power the fuel pump will not prime.

when doing wiggle test try less aggression to the wiggle. Try to move them one at a time to determine which exact wire's movement causes joy.

Yes sir I did that too once I got the back of the relay/fuse block off. Took out a couple of the terminals, tried to pry them a little to get a better bite. Thought about twisting the relay pins too but decided to make that a last resort, as prying them a little seemed to work.

To be honest I think I wasted time chasing the “wiggle” aspect of the whole deal, I apologize for that.
Thanks for your help!

 

[massacre]

failed crank sensor has no affect on the pump priming at key on

it sounds to me like you have either a faulty ignition switch and that circuit isn't getting fed juice or either a short in your fuse box

verify the check engine light comes on with key on every time, a bad ecu relay will have the exact same symptoms

CEL was not coming on with the key, should have been a big red flag. I will keep this in mind thanks for the help

 

[410Fortune]

The ignition switch mounted in the steering column is what provides battery power to the pcm through the eec fuse and relay
The PCM is what controls the fuel pump circuit by sending power to the fuel pump relay via the inertia switch and fuse
In many ways the PCM is a lot like a large relay

Well done!
Glad she is running!

 

[BKennedy]

You have a parts Explorer according to your signature. Pull all the relays out of the box and keep them as spares for your daily driver. I have at least 3 OEM Ford relays that I keep in my center console, just in case.

 

[massacre]

Ok if anything further happens, I will look into the ignition switch.
I will def grab those relays good looking out

 

[decipha]

to answer your questions, yes the starter will still engage if the ignition switch is bad or faulty

the starter circuit is different than the ignition and accessory circuits