weird voltage at the fuel pump | Ford Explorer Forums - Serious Explorations

  • Register Today It's free!

weird voltage at the fuel pump


New Member
August 10, 2013
Reaction score
City, State
Glendale Arizona
Year, Model & Trim Level
1991 Ford Explorer
`I am looking for help concerning my fuel system. I first thought that i needed a fuel pump, and replaced it.

I still am unable to get the truck started.
Once again, I am stumped.

1991 ford Explorer sport 4x4 4.0 v6. auto tranny.

I checked the voltage at the fuel pump connection at the tank and found that it is only getting 1.2 volts.
It does not spike up or down after the standard 2 seconds that it should.

Do you think my eec/ecm may be fried? bad ground?

I am so confused.

I have replaced the relay for the fuel pump, the fuel pump itself, and the fuel filter.

I had some pressure in the fuel rail, but was unable to get a measurable reading and guess that the vaccuum of the engine may have cause some of that pressure.

Desperately seeking help.


Join the Elite Explorers for $20 each year.
Elite Explorer members see no advertisements, no banner ads, no double underlined links,.
Add an avatar, upload photo attachments, and more!

Check for voltage on both sides of the fuel pump inertia switch. Oh, you might check that it isn't popped "open"

You will only see the fuel pump voltage for about 2-3 seconds after the key is turned on, so a helper to work the ignition switch will be handy.


Actually, I removed the inertia switch just to be sure that it had not gone bad. It is jumpered through.

And I am getting the same voltage there.

There is also no spike up or down. I am watching it as I turn the key on. When I run the starter, It drops to 1.0 volt and when I let off, it returns to 1.2 v

Ok, now check for voltage to the fuel pump relay primary coil terminal in the relay box. You will see 12v on both legs, one should switch "low" for 2-3 seconds when the key is turned on. no need to crank the starter.

SecondsI get the same voltage reading there on the back side of the Relay. and the front side of the relay has 12 volts. nothing changes after The 2 seconds. are the relays supposed to reduce Voltage?

I also get reduced voltage on the EEC relay.It has 12 volt on the front side and two volts on the rear(output).


I think I found the issue

I talked to a mechanic and he suggested replacing the ignition switch. After replacing the switch, I had the same symptoms.

Lastly, I tore apart the relay powering the eec. It was rusted and corroded which was causing an almost full closed circuit which reduced the voltage.

After the dealer told me that they don't make the relay any more, I replaced it with a general purpose relay.

Now I am getting correct voltage behind both relays and at the fuel pump connection.

Thanks for all the input.