Fuel Gauge tomfoolery


chewy012

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So i've got a '94 f150 4x4 with the dual tanks. My I don't drive that many miles, so I typically rotate the tanks vs. filling both up amd then going a month between fill ups.

Anywho, I filled up the mid ship tank the other day and the gauge went straight to E, which is not where I left it when I switched to the rear tank. I usually refuel at 3/4 tank. Anyway, after about a day of driving the full tank on E, the gauge finally crept back up to full. Turn the truck off, sat over night, back to E in the morning. When I backed into my work parking spot this morning, I kinda bumped the curb stop pretty good and the gauge breifly shot up to 1/4 and then dropped to E.

I checked and cleaned the pig tail connection. Is this a "normal" flaw? I'm wondering if there is a weird short somewhere and it's functioning backwards.... I guess I'll find out as I burn through this tank...

Gauge works normally when I switch to rear, and no amount of flipping back and forth fixes it haha

Any thoughts?


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rusty ol ranger

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Hole in the float is my guess.
 

adsm08

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Yeah, either a hole in the float, or a dead spot in the sender.
 

chewy012

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Cool, I'm thinkin' dead spot cause it did go back up to full at one point, and the tank before it was working fine. Thanks guys!

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chewy012

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I always forget about dead spots being a thing that happens to mechanical electron connections haha

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RonD

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I would guess wiring

1989 and up Ford fuel gauges use 10 ohms EMPTY and 158 ohms FULL

A short to ground on a sender wire would be 0 ohms so EMPTY would be shown
If shorted wire was bumped or otherwise separated from the Ground then gauge would read sender ohms and go up until grounded again

Disconnected wire would be infinite(high) ohms so would read FULL all the time.

Short could be in the sender itself

Since the other tank registers OK then you just need to check the one wire from the switch on the dash back to the effected tank, the short could be in the switch itself or in the sender, but my guess would be somewhere on the wire run the insulation has worn through and it is rubbing on a metal part.
 

chewy012

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Thanks for the numbers Ron, I'll bust out the ohmometer and see what she says

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scotts90ranger

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Have a similar issue on my '97 and forgot about the reverse ohmage... going to drop that tank in the near future to try to fix the issue, been living on the rear tank keeping the front empty waiting on weather and time to cooperate together... I do have a spare sender and tank for front and rear (rear tank was dented enough to break the pickup screen off and make the bottom 1/4 tank useless... not sure how one of the previous owners managed that...).

Hopefully you get yours figured out, mine will work intermittently like yours, rear tank works fine, front sometimes works but most of the time is at empty.
 

chewy012

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Have a similar issue on my '97 and forgot about the reverse ohmage... going to drop that tank in the near future to try to fix the issue, been living on the rear tank keeping the front empty waiting on weather and time to cooperate together... I do have a spare sender and tank for front and rear (rear tank was dented enough to break the pickup screen off and make the bottom 1/4 tank useless... not sure how one of the previous owners managed that...).

Hopefully you get yours figured out, mine will work intermittently like yours, rear tank works fine, front sometimes works but most of the time is at empty.
Glad I'm not alone. Have fun pulling the tanks, sounds like the PO high centerred backing over prius or something....

I'll be poking around and pressing buttons and checkin wires this weekend. I'll let you know if I find anything that might help you.

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chewy012

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Looks to be one of those "inside the tank" issues. I'm betting a hole in float now. I was able to get my ohmometer on it a pulled an even 14 ohms, corresponding to near empty.

I'm not sure why it starts to find its way back up after a while though.... Maybe the fuel trapped in the float vapors out with tank venting? Not sure, but the wiring seems to be in check.

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RonD

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Did you rock the truck with ohm meter connected, float will go up and down changing OHMs as it does.

Float hole issue would just go to EMPTY and stay there, wouldn't see gauge go back up at any time, IMO

But yes, could be sender is shorted out inside and it might read correctly below 3/4 or 1/2 tank, but you would need to get at the sender regarless
 

chewy012

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Did you rock the truck with ohm meter connected, float will go up and down changing OHMs as it does.

Float hole issue would just go to EMPTY and stay there, wouldn't see gauge go back up at any time, IMO

But yes, could be sender is shorted out inside and it might read correctly below 3/4 or 1/2 tank, but you would need to get at the sender regarless
Yeah I rocked it, it looked like it briefly (fraction of a second) jumped up on ohms, but then flat lined at 14.... That jump could have been more attributed to the $10 multimometer.

Thanks for the input, I think i'ma just have to keep an eye on it. Do some boyncing around when the tank is lower. I've only put 35 miles on it since the issue started

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chewy012

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Woooaaahhhhh, can anyone tell me why the sending units are like $130!? Yikes. I was gonna order one but after seeing that, I think I'll just smack mine with a hammer.

Also, as this will be the second time going into the tank, I'm thinking i'ma cut an access hatch in the bed. Anyone got a method they like? I'm thinking just weld on a piano hinge and a tab with a magnet to keep it down.

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RonD

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In my previous Ranger I cut out an access hatch, then I went to wrecking yard with the cut out piece, to match the humps, and cut out a larger section from a damaged bed so I could just screw it down, I think I paid $5
 

chewy012

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In my previous Ranger I cut out an access hatch, then I went to wrecking yard with the cut out piece, to match the humps, and cut out a larger section from a damaged bed so I could just screw it down, I think I paid $5
Yeah thats what I was thinking, theres no u pull near me though :/ and I don't know how these other yards around here operate

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