Front Fuel pump started buzzing on and off while parked.

[BillRod]

Hi All

88 Ranger, 2.9L 4x4, 5spd, Ext Cab.

Yesterday afternoon the front fuel pump started buzzing on and off while the truck was parked, engine off, key out of ignition.

I could feel the fuel lines vibrating telling me the pump was cycling on and off.

It would be on for 2 or 3 seconds then off 2 or 3 seconds, on, off in this same pattern. Not sure how long it was doing that as it was parked in the driveway.

First thing I did was I start it, the engine ran fine so I turned off the key and all was quiet for a while.

A little while later the pump started the same thing, pulsing on and off.
I now have the battery disconnected until I can figure it out.

Anyone have any thoughts as to what would make te front pump come alive and pulse on and off like that?

Thanks
Bill

 

[Psychopete]

Hello. Sounds like your computer relay is either defective / allowing this behavior, or it's somehow getting 12 volts intermittently from the ignition switch when it's not supposed to. The fuel pump relay depends on both the computer to ground the energizing side, and the positive side comes directly from the computer relay. Sounds like the computer is powering up.

 

[BillRod]

First diagnostic result:

I have 12 volts coming out of the small terminal on the solenoid.
Key in the off position.

Bill

 

[BillRod]

So it's not the two easy ( Cheap ) things.

Replaced the ignition switch and the started Solenoid, but the Fuel pump still comes alive with the key off.

Any diagnostic routines I can go through to check things further?

Thanks
Bill

 

[Psychopete]

I think the wire you are testing is R/LB (start), where the one in question may be R/LG (start & run) to the computer relay. Going to be hard to test, try pulling the computer relay (brown) when it does it again. If it stops, the problem could be the computer relay or intermittent power to trigger it on. If it continues, fuel pump relay is probably shot.

Edit:
This is from an '89, our wiring colors are different, but the general circuit works the same. I am too lazy to update all of the wiring colors for each, but I may get around to it at some point.

 

[BillRod]

Thanks

I'll try those 2 relays tonite.

Bill

 

[BillRod]

It's the darndest thing! Not sureif I should be glad or not...

Monday during lunch I went to the Upullnpay and got 2 Fuel pump relays and 2 Computer relays, $13 total.

After work I hooked up the Negative battery terminal and the fuel pump was quiet.
Cycled the key a few times, turned it on and off a few times all that and fuel pump never came alive on it's own.

I did not change anything, the issue simply went away sometime between Sunday (when I swapped the Ignition switch and solenoid) and Monday.

Maybe the new ignition switch was seated incorrectly, I don't think so but?

So now I am back driving it, hoping it either it is fixed or waiting for it to happen again so I can continue to diagnose it.

I hate it when issues go away like this, not sure if it's real or not.

Thanks for your help.
Bill

 

[silver88ranger]

Same issue

Just thought I would add my 2 sense.. I had a very similar issue on my ranger I pulled all the electrical connections sprayed them with contact cleaner and that seemed to fix the buzzing and now it only runs when the truck is running so my guess is just a bad connection or ground

 

[BillRod]

Truck sat for a few weeks, went to start it last week and no fuel.
The fuel pump was quiet.

I removed the relatively new FPR I got from AutoZone and put in one I had picked up from the UPullnPay and it started.

Has not had any other symptoms yet, I'm keeping my fingers crossed!!!

Bill