Filled up and fuel gauge went nuts

[01rangerxl]

Last night I saw that a "Petro" station in the hood had 87 for $3.03 a gallon. That's almost 20 cents cheaper than most places around here, so I decided to fill up. Gauge was showing between 1/2 and 3/4 full. I added a little over 7 gallons, which is about right for where the gauge was at. I let the pump click off, I wasn't trying to round up or anything like that.

On startup, the fuel gauge went way past full. Normally it goes just a hair over the F mark when full, but this was more like a solid 1/8" past the F...noticeably higher than it has ever read. I had time to burn and apparently a very full tank of gas, so I drove around to see if it would move at all. No movement after 20 miles. I got home and shut the truck off, then turned the key to the on position. The gauge then dropped down to where it should be. I hoped that would be the end of it, but not quite.

Today I started the truck up, the gauge read fine, and I drove a couple miles to a store. Come back out and start the truck up...CEL immediately catches my eye, and of course the fuel gauge is pegged way past full again. The code was P0460, "fuel level sensor circuit malfunction" (oh really?).

So I drive home, shut the truck off, then turn it on again. Fuel gauge drops back to normal, so I cleared the CEL. I've driven it about four times since then and the CEL has not returned, fuel gauge has behaved normally, and it seems to be at the correct level (I reset the trip odo every fill up).

Any ideas why my fuel gauge went nuts after this fill up, and has anyone experienced fuel gauge behavior like this? Does it sometimes take a sending unit a while to die completely? Is it possible the float got stuck or hung up somehow and is now free again? The fuel pump/sending unit are completely original and have never been out of the tank, wiring has never been messed with or disconnected. I am hoping this is just a fluke and not a sign of impending sending unit failure.

I plan on putting some Techron in the tank just in case it's related to varnish or something "gumming" up the sending unit. My truck has had a lot of off brand fuel of unknown quality run through it over the past month and a half, so I guess anything is possible.

 

[GearheadTool]

I usually refill mine when it is 2/3 full, back up to full, and I usually gas mine when the engine is running. It usually takes about 4 gallons or so, before it moves from the "12" mark (gallons, on 18-gallon gauge) to full, slowly.. and it usually skips from 12 to the second fullest notch, before moving slowly.

I don't know, maybe it is the vapors/moving gas.. as to dying completely, maybe it will clear itself out, with use, cleaners, and a lot of fresh gas!

 

[yonyon]

It makes sense. Low voltage/high resistance represents high fuel level. If your sender is getting coated it would act this way. A poor electrical connection either inside or outside the tank should behave the same way just before failure.

If it's the sender as is usually the case, then there may be an area (top 25% or bottom 25%) that seems to behave more consistently than the rest and your plan of using Techron might help. I think you already know that it's more likely you're going to have to drop the tank to get that gauge working properly again.

 

[01rangerxl]

Originally Posted By: yonyon
I think you already know that it's more likely you're going to have to drop the tank to get that gauge working properly again.

That's what I'm worried about. Apparently the tank on these trucks is a [censored] to drop and it's actually easiest to take the bed off if you have help.

If it goes completely, I might just use the trip odo as my gauge until the pump itself shows signs of trouble. My parents did that for two years with their old Ranger.

I went to Wal-Mart a little while ago...yes, at 3:30 AM; I have a weird work schedule. I added Techron in the parking lot to the just over 3/4 full tank. Of course when I start it the fuel gauge is pegged again. [censored] truck. I turned it off and restarted...still pegged. Drove home (4-5 miles), turned it off, turned it back on and the gauge dropped back down. No CEL this time, but if it does it again the CEL probably will come back on.

Seems almost like sitting for a few minutes after running triggers it, and driving it a few miles then turning it off/on again corrects it.

 

[LeakySeals]

You added the 10oz techron (concentrate plus?) from wamlart to how many gallons?

 

[Donald]

The E10 gas does a good job at cleaning the tank. Unless it has sat for a long time (years). Techron is designed to clean injectors, but its real advantage is to clean carbon deposits in the cylinder.

 

[Trav]

Old but still relevant to most cars.
Quote:
"GM has just issued a TSB
on this problem that applies to ALL GM vehicles and
blames the high incidence of sending unit failures
on high levels of sulfur in gasoline. The sulfur
corrodes the sliding resistor mechanism and
produces erratic and inaccurate gauge readings. To
address this problem, GM has released a FUEL
TANK ADDITIVE.
According to GM TSB #06-00-89-07BB, you should
purchase a bottle of GM Fuel System Treatment
Plus (part #88861011 for GM brand, 88861013 for
AC Delco brand, and 88861012 in Canada) and add
it to your tank at every oil change. The additive
cleans the sulfur corrosion from the sending unit
and prevents new corrosion by laying down a
protective film. The additive also removes engine
deposits."


This is a PEA based additive, Techron is just Chevrons brand name.

 

[demarpaint]

Originally Posted By: Trav
Old but still relevant to most cars.
Quote:
"GM has just issued a TSB
on this problem that applies to ALL GM vehicles and
blames the high incidence of sending unit failures
on high levels of sulfur in gasoline. The sulfur
corrodes the sliding resistor mechanism and
produces erratic and inaccurate gauge readings. To
address this problem, GM has released a FUEL
TANK ADDITIVE.
According to GM TSB #06-00-89-07BB, you should
purchase a bottle of GM Fuel System Treatment
Plus (part #88861011 for GM brand, 88861013 for
AC Delco brand, and 88861012 in Canada) and add
it to your tank at every oil change. The additive
cleans the sulfur corrosion from the sending unit
and prevents new corrosion by laying down a
protective film. The additive also removes engine
deposits."


This is a PEA based additive, Techron is just Chevrons brand name.


Imagine that, they recommend an additive? LOL I've had good luck with MMO freeing up two of them now.

 

[volk06]

Originally Posted By: GearheadTool
I usually refill mine when it is 2/3 full, back up to full, and I usually gas mine when the engine is running. It usually takes about 4 gallons or so, before it moves from the "12" mark (gallons, on 18-gallon gauge) to full, slowly.. and it usually skips from 12 to the second fullest notch, before moving slowly.

I don't know, maybe it is the vapors/moving gas.. as to dying completely, maybe it will clear itself out, with use, cleaners, and a lot of fresh gas!


Thats a bad idea. Doesnt all gas stations have signs on the pumps that say shut off your engine?

 

[The_Eric]

Originally Posted By: volk06
Originally Posted By: GearheadTool
I usually refill mine when it is 2/3 full, back up to full, and I usually gas mine when the engine is running. It usually takes about 4 gallons or so, before it moves from the "12" mark (gallons, on 18-gallon gauge) to full, slowly.. and it usually skips from 12 to the second fullest notch, before moving slowly.

I don't know, maybe it is the vapors/moving gas.. as to dying completely, maybe it will clear itself out, with use, cleaners, and a lot of fresh gas!


Thats a bad idea. Doesnt all gas stations have signs on the pumps that say shut off your engine?


Probably not too big of a safety issue, but it can be bad for other reasons. On newer cars, fueling with the engine running can result in a CEL. The computer can see the loss of tank pressure as a leak. In fact, the only times I've ever had a CEL in my car (mouse problems not withstanding) was when I fueled with the engine running. A P0442 I think...

 

[bullwinkle]

I also have this problem occasionally with the GMC and always with the F-450-I just think that fuel senders have a tendency to short when all the way full-the '93 actually went 90 degrees past full the last time I filled it, went back down to normal eventually. Hard to believe that would cause a CEL-a code reader needs to be standard equipment!

 

[Donald]

Originally Posted By: volk06
Originally Posted By: GearheadTool
I usually refill mine when it is 2/3 full, back up to full, and I usually gas mine when the engine is running. It usually takes about 4 gallons or so, before it moves from the "12" mark (gallons, on 18-gallon gauge) to full, slowly.. and it usually skips from 12 to the second fullest notch, before moving slowly.

I don't know, maybe it is the vapors/moving gas.. as to dying completely, maybe it will clear itself out, with use, cleaners, and a lot of fresh gas!


Thats a bad idea. Doesnt all gas stations have signs on the pumps that say shut off your engine?


You would have to be able to read I suppose.

And then there are the people who fill their car with gas cans still in the truck bed, truck running, them smoking.

If you fill an empty 20 gallon gas tank, about 2.5 cu ft of gas fumes needs to vent out somehow.

 

[GearheadTool]

Originally Posted By: volk06
Originally Posted By: GearheadTool
I usually refill mine when it is 2/3 full, back up to full, and I usually gas mine when the engine is running. It usually takes about 4 gallons or so, before it moves from the "12" mark (gallons, on 18-gallon gauge) to full, slowly.. and it usually skips from 12 to the second fullest notch, before moving slowly.

I don't know, maybe it is the vapors/moving gas.. as to dying completely, maybe it will clear itself out, with use, cleaners, and a lot of fresh gas!


Thats a bad idea. Doesnt all gas stations have signs on the pumps that say shut off your engine?


Doesn't matter.. I had a car with a hole in the gas tank once, and dual exhausts.

And The_Eric, my car had a P0422 code. Not "P0442."

 

[01rangerxl]

Originally Posted By: LeakySeals
You added the 10oz techron (concentrate plus?) from wamlart to how many gallons?

To no less than 15 gallons.

Originally Posted By: Trav
Old but still relevant to most cars.
Quote:
"GM has just issued a TSB
on this problem that applies to ALL GM vehicles and
blames the high incidence of sending unit failures
on high levels of sulfur in gasoline. The sulfur
corrodes the sliding resistor mechanism and
produces erratic and inaccurate gauge readings. To
address this problem, GM has released a FUEL
TANK ADDITIVE.
According to GM TSB #06-00-89-07BB, you should
purchase a bottle of GM Fuel System Treatment
Plus (part #88861011 for GM brand, 88861013 for
AC Delco brand, and 88861012 in Canada) and add
it to your tank at every oil change. The additive
cleans the sulfur corrosion from the sending unit
and prevents new corrosion by laying down a
protective film. The additive also removes engine
deposits."


This is a PEA based additive, Techron is just Chevrons brand name.


Thanks Trav! This is a little reassuring that it might be fixable without actually replacing the sending unit.

 

[Trav]

Yes i would give it a few bottles over a month or so. That junk didn't build up overnight so i would think its going to take a little while to get rid of it.

 

[01rangerxl]

Update:

I gave the truck heavy doses of Techron concentrate over the course of about a month. Every tank full or every other tank full I would add a bottle. There was no improvement from this, and I didn't want to replace a working fuel pump just because the gauge was dead, so I left it be. I would say the gauge was working maybe 10% of the time.

Then, as quickly as the problem started, it disappeared a few days ago. The gauge has been working 100% of the time and is reading correctly based on the trip odo and fill ups.

The variable that changed when this happened - outside temperature. We finally got spring weather with temps in the 70s, and when that started, the fuel gauge began working again. It seems to like warm temps. Weird, but true. I'm not sure what's going on there.

When fall/winter rolls around, I'm betting it will act up again, but hopefully it will continue working. We'll see.

 

[artificialist]

Originally Posted By: 01rangerxl

The variable that changed when this happened - outside temperature. We finally got spring weather with temps in the 70s, and when that started, the fuel gauge began working again. It seems to like warm temps. Weird, but true. I'm not sure what's going on there.

Many glitchy old electrical parts do that. Expansion and contraction sometimes cause an open circuit as parts move away from each other or closer together.

Hopefully this means you can delay replacing the fuel module for a while.