New User Looking for Help

[T_Auto]

Hi all! I don't own a truck but work at an automotive repair shop and these forums can be helpful at times. We have been working on an 86 Ford F250 and have been having trouble with the fuel gauges working.

I decided to join because I saw where a poster had been having problems finding the correct fuel pump assembly for the rear tank. We had this same problem and was beating our heads against the wall. The local parts house got us a fuel pump assembly that looked similar but the gauge would read opposite. We found out the assembly the parts house got us came out of an 87 which Ford changed the wiring. We just thought the sending unit was defective. After looking at wiring schematics we noticed the 86 5.0l and 7.5l fuel systems were almost identical. I looked at the 86 F250 5.0 fuel pump assembly and bam, it was the correct one.

The way I found this group is because the customer came back complaining the fuel gauge isn't working. So, I have been checking out forums to see if others have ran into these problems.

[Gary Lewis]

Welcome!  Glad you joined.  Your help can be invaluable and we may also be able to help you.

Toward that end, have you seen the Troubleshooting tab on the page at Documentation/Electrical/Gauges?

[T_Auto]

Gary Lewis wrote

Welcome!  Glad you joined.  Your help can be invaluable and we may also be able to help you.

Toward that end, have you seen the Troubleshooting tab on the page at Documentation/Electrical/Gauges?

I did not. I will look at that. Thanks so much!

[grumpin]

Welcome!

[ArdWrknTrk]

Welcome to the Forum!  

Yes, the hot fuel handling system can be quite problematic, and not many know of it's various iterations.
83-84 and 85-86 control those pumps differently.
'87 was a "one year wonder" and those sender/pump assemblies are VERY rare.
You have a fantastic parts store!

Senders went from 10-70 to 160-15 ohms beginning in '87 because the instruments changed from thermal gauges to what is essentially a stepper motor attached to the needle.

[mat in tn]

welcome. we are doing an 86 right now. same basic situation. the sender wire from the tank to the guage should be dark blue with a yellow stripe. if you were to ground it for a "second" while someone watches the guage it should go to full. this should prove it to be a problem with the sender. or at least its ground.

[T_Auto]

mat in tn wrote

welcome. we are doing an 86 right now. same basic situation. the sender wire from the tank to the guage should be dark blue with a yellow stripe. if you were to ground it for a "second" while someone watches the guage it should go to full. this should prove it to be a problem with the sender. or at least its ground.

When we ground it, it goes to full. It's the second pump we put in so we were having a hard time believing it would be the sender. The gauge works if we turn the key on but when we start it the gauge stops working for the rear tank.

[ArdWrknTrk]

I'm in the Dr, but let me look in detail at the thread.
I'm pretty good with troubleshooting these 460's....

[ArdWrknTrk]

I had a similar problem with my 87 truck, but note the later gauges and sender work in reverse.

So, this only happens with the rear tank, and not when switched to the front?

My problem is that with the engine running the ground potential essentially becomes zero, and the gauge won't read.

I guess I'd really have to be looking at the truck to see what id need to, to diagnose from what I've been presented so far.

[FuzzFace2]

T_Auto wrote

mat in tn wrote

welcome. we are doing an 86 right now. same basic situation. the sender wire from the tank to the guage should be dark blue with a yellow stripe. if you were to ground it for a "second" while someone watches the guage it should go to full. this should prove it to be a problem with the sender. or at least its ground.

When we ground it, it goes to full. It's the second pump we put in so we were having a hard time believing it would be the sender. The gauge works if we turn the key on but when we start it the gauge stops working for the rear tank.

Dose this do the same on the front tank too?
Wonder if the IGN switch is not making a full connection after it is turned to start?
Anything else not work like radio, power windows, etc.?
Dave ----

[mat in tn]

good point. it is not unheard of for an old ignition switch to have a weak connection