Gas Gauge

[Brown_Muscle]

Well today I thought my tank was syphoned, I had just filled it up the other day and now it is on E. So I filed a police report, then went to get $10 worth of gas...and the pump kept shutting down like i was full. Managed to squeeze 2.7 gallons into the tank.

So now I think it has to do with the gauge or the sending unit.

The gauge starts out below E and then slowly comes up to the E mark. I was wondering if anyone knew what I should replace in this case. I'm guessing that the tank is full. Any input would be appreciated. Thanks!

[87_crown_vic]

sounds like the float .... sank... not gonna be fun trying to change if its full of fuel.
might be the wires disconected to sending unit or float went bad....
check sending unit wire first then....

siphon gas out best you can into gas cans get yourself a float and rubber "O" ring from the stealership, and pull out sending unit. if the float has never been replaced... you are lucky it lasted as long as it did...

[Brown_Muscle]

ok thanks for that, any way i can check the gauge? maybe put a certain voltage to it to check? Or is it almost definitely the float? I checked the wires and they seem fine.

[87_crown_vic]

if you have slack in the line at the tank that connects the sending unit, connect the plug reversed. if the gauge is good and float is bad, the gauge should go to full since you are reversing the signal to the gauge. if there isnt enogh slack, piece some wires into the plug and connect it reversed to check if gauge goes to full

[1987cp]

The sending unit's rheostat should produce 73 Ohms at empty and 10 Ohms full. It's easy to can bench-test it with a multimeter by just moving the armature. From there, it's also easy to test your fuel gauge by plugging in the sender with it out of the tank and moving the armature (helps to have a friend to watch the gauge).

[87_crown_vic]

The sending unit's rheostat should produce 73 Ohms at empty and 10 Ohms full. It's easy to can bench-test it with a multimeter by just moving the armature. From there, it's also easy to test your fuel gauge by plugging in the sender with it out of the tank and moving the armature (helps to have a friend to watch the gauge).

he doesnt have it removed... wants to see what it might be before removal...

[1987cp]

he doesnt have it removed... wants to see what it might be before removal...

Then I think he'd best siphon out the tank and get cranking!

Techless tip: I have several feet of app. 3/8" diameter transparent nylon tubing specifically for siphoning automotive fluids. It only cost a couple bucks, is easier to get through your filler neck than a dedicated hand-siphon-pump that doesn't work very well anyway, and lets me start the siphon by mouth without swallowing fuel or antifreeze!

[Brown_Muscle]

Allright thanks guys! I got the float and seal for around 10 bux at the nearby dealership...im gunna wait until i use up the gas by driving then do the job, I'll reverse the plug like you said and make sure the gauge is good first too, hopefully it is just the float, interesting how that would go bad when its two pieces of metal soldered together...

[1987cp]

Reverse plug?

[87_crown_vic]

the brass corrodes with age... think of some of the brass fittings on these car ... the place where heater hoses connect into water pump and stuff... i had a 1987 Crown Vic where the heater hose connected to waterpump and the pipe the hose connected to was barely there...

1987cp... read above for the test procedure i gave to figure out if its the float.

[Brown_Muscle]

hmm geez, most of my fittings are pretty good, but then again most of the parts on the car are pretty good, but yeah i know what your talking about. I'll post on how it goes!

[1987cp]

1987cp... read above for the test procedure i gave to figure out if its the float.

It's just that reversing the plug ought to do exactly nothing. The gauge reading depends on the resistance across the sender's potentiometer, which won't change unless the float position changes.

Well, maybe not entirely nothing .... if the tank happens to be well grounded, I suppose you might pop a fuse ........

[87_crown_vic]

reversing the plug makes the float read backwards... so when the tak is empty and you reverse the plug it makes it read full... i know because i have done it.

[1987cp]

Ok, if you say so! I still can't imagine how that could possibly be the case, but I do have both a sender and a gauge handy, so I guess I can test out the concept anyway.

[Brown_Muscle]

oh If you get a chance please test it out, just in case, 1987cp one of your cars is carb'd?