ive got a 1985 ford f150 351w and when i bought the truck it looked like the fuel guage was working fine but the more i drove the truck,the fuel guage was droping fast,very fast so i checked for leaks and couldnt find and and i went and filled the tank back up and it took about 6 dollars worth of gas?whats the problem here?theres some thing wrong with the guage or sending unit..or ive got a 6 gallon tank on my f150 haha..thanks chuck

 

Chuck,

How are all of the other gauges reading? If they are all reading lower or higher than they should then you probably have a bad Instrument Voltage Regulator that is located behind the instrument cluster. It is supposed to regulate voltage to your gauges at about 5 volts. Replacement is about $10. If the gauges are OK, then check the ground(s) at your fuel tank(s). I use plural here because some trucks have dual tanks. There is a wire that runs from the tank to the truck frame that is notorious for breaking or making a poor connection. I had a similar problem with my rear tank and found the ground connection had broken off. I cleaned the connection points and reaattached the ground and everything worked fine. I spent a lot of time troubleshooting the sending unit, the gauge, etc., before I found the problem.

John

 

I've got a similar problem with a dual-tank setup; guage doesn't read right for either. Sending unit has a two-wire connector running to it. Are you saying there is another wire that should ground the tank to the frame, or is one of these wires supposed to be grounded? I had heard that it could be a sending unit harness problem, the harness is supposed to be inside the tank. Thanks.

 

I will check the wiring schematic to determine the grounding setup for the dual tanks. I am pretty sure they are separately grounded but I will let you know for sure.

John

 

thanks because i drive it all the time and it really starting to get on my last nerve..i dont know when ive got any gas or im getting ready to have to walk..thanks chuck

 

Checked the wiring schematic for my '82 Van and it shows a separate ground wire for both tanks. I climbed underneath to see for myself, and sure enough, the ground for the back tank is connected to rear crossmember and the one for the midship tank is attached to the left framemember above the fuel selection solenoid. I also adjusted my Instrument Voltage Regulator behind the instrument cluster with both tanks full to where the gauges read exactly Full. The IVR has a small adjustment screw that you can turn to adjust. Clockwise to raise the gauges CC to lower. I did it with the motor running. The IVR isn't a very sophisticated piece of electronics, just a bimetal heated by a coil at 12v causing the bbimetal to open and close at a rate to meter voltage to the gauges. Suppose to be at about 5 volts at the gauges, but my guess is that at the Ford plant they adjust the IVR to get the gauges within spec. I have replaced the IVR at least three times and found each one caused the gauges to read differently. Only after I adjusted one did I realize that this is probably the main reason for gauge misreads along with poor connections at ground and at the sending unit. Pop the sending unit connections off at the tank and clean the contacts, put dielectric grease on to reduce corrosion, adjust your IVR and you should be in business. If this doen't work my guess is you either have a bad gauge or bad sending unit, which if you have bad readings on both tanks not likely to be both sending units.

One of the things I love about my old '82 is that I can fix just about anything without having to deal with sensors, computers, etc. I am thinking about getting a new 2000 but know it won't be near as much fun to work on. If I take it to Ford I am never sure they do it right and it takes all the fun out of it!

John

 

I have the same problem with the fuel guage in an '88 5-speed f150, the gas tank was replaced by the previous owner and i think the ground could be the problem. Where is the ground normally attached? (I can't see any wires going to the tank from anywhere on the sides or the back of the tank, is the ground attached at the front under the guard of the front of the tank?, and what does it look like (bare wire, insulated, other?)
Thanks
Cliff

 

this one sounds like a bad sending unit, I just went through the same thing with my 82 F250 4x4 . it read right, down to about half tank then dropped to quarter tank in about ten miles or less, then stayed on quarter forever then would go on down to empty. this got old quick.