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Old 04-12-2015, 09:49 PM   #1
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Fuel gage

I have an 88 mustang lx 5.0 and I have an issue with my fuel gage, wen I turn the ignition key on the gage go to 3/4 and after a few seconds it go to full and beyond. I replace the fuel sending unit and the instrument cluster but no change at all. Please some advice will be helpful.

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Old 04-14-2015, 06:58 AM   #2
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The first thing to check is the secondary ground wire.Its the one attached to the rear side of the driver side head and mounts to the firewall.Make sure its tight and corrosion free.This is the wire that the gauges and lights use.There is also a anti slosh/low fuel module behind the dash/cluster.Its in the wiring between the gauge and low fuel warning lamp/fuel sender.The wiring diagram in the 1st link below should help locate it.Even though you replaced the sender,new or remanufactured parts can still be defective.You would need to lower the fuel tank and raise the fuel sender up enough to move the float rod up and down for testing,but here's how to test it if you wanna do so.Connect one probe of an ohmmeter or multimeter (set on ohms) to the fuel sender signal lead and the other probe to "ground".Push float rod all the way down(closest to filter) to the "empty stop position".If it reads less than 14 ohms or more than 18 ohms,replace the sender.Now leave the probe connected to sender signal lead,but move the other probe to the "sender ground" lead.Pull float rod all the way up(farthest away from filter)to the "full stop position".If the meter reads less than 155 ohms or more than 165 ohms,replace the sender.Leave meter connected and move float rod from the full stop(up)position to the empty(down)stop position.If the reading jumps to an open condition while decreasing,replace fuel sender.If you disconnect the wiring harness from the gauge and touch the ohmmeter probes to the gauge terminals or back probe the harness terminals,the meter should read 22.5 ohms when the needle is on empty.When the needle is at the full mark,it should read 145 ohms.When you open the 2nd link below,you'll see the instrument cluster and connecters " "A" & "B" which have 14 wires attached to each one of these connecters.The wires are labelled 1 through14 on each connecter.Simply match each connecters number and letter to the matching component it plugs into.Example::find the instrument cluster diagram at the top of the page,find the very first component in the cluster which is the slosh module,look under it and you'll see B10.B10 is basically a terminal or pin out that the wiring harness plugs into.B10 matches up with "connecter B,wire #10" So in other words,once you plug wiring harness "B" into the cluster,wire #B10 goes to the slosh module.Example 2: the next component you'll see is the fuel gauge and below it you'll see terminal "B9". Find connecter " B and wire #9" This is the wire that connects to the fuel gauge once you plug the harness in.Do the rest of the wires and components this same way.The reason I posted the link and explained it was so you'll know which wires to check for opens,shorts,corrosion and loose pinouts.The wire can sometimes pull loose from inside the plastic harness connecter which means the harness is plugged in correctly,but the terminal(male/female)that's soldered to the end of the wire isnt touching the blade terminal on the component itself,such as the terminal on the back of the fuel gauge.The wire could also be broken in half or just a few strands of wire could be the only thing keeping the wire and terminal (male/female part thats soldered to the wire)intact.A loose wire there would definitely cause the gauge to act up intermittently.There are some tests you can do that will diagnose a bad gauge or anti slosh module,but you'll need a Rotunda 021-00038 Instrument Gauge System Tester or its equivalent in order to do these tests.I didn't list the test procedures because I assumed you don't own one of these,but let me know if you do own one and I'll post the procedures.....
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Old 04-14-2015, 06:37 PM   #3
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