1988 F250 460ci. This is a recent purchase and the gauge has never work on either tank. I pulled the tank selector out and when I check the voltage on the tank selected, the pump voltage is 13 volts. The gauge side of the switch is 1.8 - 2.0 volts. Is this correct? Same readings no matter what tank is selected.


Thanks in advance.

 

Any one know what the Fuel float circuit voltage should be?

 

Open to any ideals yall might have.

 

The only way I have ever troubleshoot a fuel sender problem is using a DVM set to Ohms then measure the fuel sender level resistance. On an 80's vintage truck the resistance should be high when the fuel level is low. The resistance will be low when the fuel level is high. bass-ackwards from a '90s vintage truck.

A diagram from subford:



A low resistance value should be in the 10 Ohm range. A high value is a bit fuzzy for me because I do not have an exact value but I have found several references to a 70-75 Ohm range. You can measure this at the Fuel Tank Selector switch, key off.

 

I found an old thread on the subject. In the thread it stated empty should be 22.5 and full 140. Right now mine reads 24 and gauge is sitting at empty as it always does. I pulled the tank but have not taken the pump assemble out. I will do that later today. to see if the float has a hole or dirty.

 

And I have been corrected by Subford more than once. 80's vintage trucks have fuel sender values opposite the 90's.

Perfect opportunity to confirm the documentation.

 

90% of the time the brass floats are bad. Full of fuel and setting on the bottom. I have changed dozens of them. Part number C0AZ-9202-B. The same float they have been using since 1960. It is hard to get a voltage reading on these since it is a pulsed 6v dc voltage

 

I would assume that would make it read dead empty? mine is like that on the front. Just drop the tank and replace the float? I've read it may be a tank sending unit problem. One last thing, do you know if the part that causes cross fuel contamination easily replaced by dropping one tank or the other?

 

Yes replace the float. You will know when you get it off. No the fuel tank selector is frame mounted it will be a pot looking thing with 6 lines on it. If you can get connector off on top of the front tank short the db/y wire to ground and see if the gauge moves when in the front position if it does then it is the float

 

I pulled both tanks and the floats had holes in them. Now for the chore of getting the tanks back in.

 

So the debate continues....

Perhaps this thread may help: https://www.ford-trucks.com/forums/1...e-problem.html

Maybe not.

 

Glad to see you found the problem. Still seems odd some folks say the resistance values are different for 80's series trucks? I never had one so I have no first hand experience. Plus no EVTM.

 

Is this what you guys are calling the floats? This is what another member called a tank sending unit but it looks like it has a brass float like mentioned
http://www.partsgeek.com/gbproducts/WC/5302-01142176.html?utm_content=YN&utm_term=1990-1996+Ford+F150+Fuel+Level+Sending+Unit+Motorcraft+ 90-96+Ford+Fuel+Level+Sending+Unit+1991+1993&utm_sour ce=google&utm_medium=ff&utm_campaign=PartsGeek+Goo gle+Base&gclid=CjwKEAiAsJanBRCgnpfa0orvyz4SJAAbxEq-saZQTJtiTq15zrO_79jpmdVdydaQgo6HfPEz1-T0ChoC3Yrw_wcB

 

I replaced the brass floats only. Ford is a month behind on getting new floats so I went to the junk yard and they had a bucket full of the for a $1 each. I picked out a few and I complete tank unit just in case I needed it. Tanks are back in and gauge is working. I tested the senders before reinstalling and they where 18omh empty and 150.