Fuel & temp. gauge problems
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New User
Joined: Jan 2008
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Fuel & temp. gauge problems
Hey, just recently purchased a 88 f-150, 73,000 miles on it, interior and exterior is in good condition and runs great but im having a problem with the fuel gauge, I know the truck has about a 1/2 tank of fuel now but shows way past full, and the temp. gauge works sometimes and sometimes it doesnt.
Any suggestions to fix these problems would be greatly appreciated.
Any suggestions to fix these problems would be greatly appreciated.
Elder User
Joined: Jun 2006
Posts: 805
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The pegged fuel gauge would suggest the sending unit in the tank is stuck. That unfortunately requires dropping the tank to find out or replace. These gauges are excited from the gauge end, and require a drop in resistance at the grounded end to push them up scale. A pegged gauge normally indicates a shorted wire to the sending unit. Does the gauge ever move downscale?
Working or not working is not very descriptive of the temp gauge, but odds are, the sending unit is kaput. Not uncommon. The temp sending unit is the one that's down on the intake near the #5 intake runner, if it's a 5.0, and has a single wire. There is another that sends coolant temperature to the ECM, but it has two wires. The one for the gauge uses the block for a ground. Check the gauge buy connecting the wire to the sending unit to the block, and it should peg out the gauge. Open circuit, (not touching anything) it should read stone cold. That will at least tell you if the IVR (Instrument Voltage Regulator) is working. If it is, pop in a new gauge sender (20 minute job and $10 part) and check it again. If it still is intermittent, you probably have a bad ground to the cluster, or possibly to the block from the frame.
Working or not working is not very descriptive of the temp gauge, but odds are, the sending unit is kaput. Not uncommon. The temp sending unit is the one that's down on the intake near the #5 intake runner, if it's a 5.0, and has a single wire. There is another that sends coolant temperature to the ECM, but it has two wires. The one for the gauge uses the block for a ground. Check the gauge buy connecting the wire to the sending unit to the block, and it should peg out the gauge. Open circuit, (not touching anything) it should read stone cold. That will at least tell you if the IVR (Instrument Voltage Regulator) is working. If it is, pop in a new gauge sender (20 minute job and $10 part) and check it again. If it still is intermittent, you probably have a bad ground to the cluster, or possibly to the block from the frame.
Senior User
Joined: Jun 2006
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You are in the right page.
Does your fuel guage work at all, or does it stay way past full?
If it stays way past full it is probably just grounded out.
You temp guage may be a bad ground. Or it could be the sending unit too.
Does your fuel guage work at all, or does it stay way past full?
If it stays way past full it is probably just grounded out.
You temp guage may be a bad ground. Or it could be the sending unit too.
Posting Guru
Joined: Jan 2001
Posts: 1,124
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From: Rural Florida Panhandle
I remember working on my 88 tank and gauge, and it was the OPPOSITE. When the circuit was OPEN, the gauge read full. I know that sounds backwards, but that's the way it was. Try crawling under the truck and see if you can unhook the connector from the tank and try and see if your gauge still reads full. If so, it could be a broken or unhooked wire instead of a shorted one. I wrote it all up some time back:
http://www.winfordr.com/FordTruckStuff/f150tank.htm
http://www.winfordr.com/FordTruckStuff/f150tank.htm
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