1999 Suburban fuel gauge going nuts

[01rangerxl]

The fuel gauge on my coworker's Suburban has started to act up. The truck is a 1999 C1500.

When the truck is on, the fuel gauge will go back and forth from E to F. It does not wobble like fuel is sloshing around, it is E OR F, nothing between. It will stay on one reading for a few minutes, then suddenly flip to the other and stay there for a few minutes. It seems electrical in nature, not something going on inside the tank. The sending unit was replaced when the fuel pump went out a while ago, but not ruling that out as a possible culprit. This is the old body style, but is there any possibility of a bad cluster/stepper motor like later models had issues with? The truck is stock electrically (down to the stereo) and doesn't have problems with other gauges, but the battery did die the other day after sitting for 8+ hours. Not sure if it is related or not, the truck was fine all day today except for the erratic fuel gauge.

 

[LeakySeals]

Many have resolved the wandering gauge with a couple of bottles of techron concentrate complete fuel system cleaner.

 

[01rangerxl]

What are the symptoms of wandering? This one doesn't bounce around in the middle at all, it's E or F.

Interestingly though, when the truck is turned off the gauge goes to what seems to be the correct reading.

 

[LeakySeals]

I think the answer your looking for is a sticky sending unit. The techron concentrate can possibly clean that up so the float doesn't stick. Worth a easy try. If no success you walk away with a clean fuel system and combustion chamber. Use at least 2 bottles to clean that huge tank

 

[01rangerxl]

It's definitely worth a try before replacing parts...I think the tank is around 35 gallons, lol.

 

[LeakySeals]

Whoa thats a expensive fill. Read the instructions on the bottle I think its 12oz for 18 gallons or something. add an extra bottle for good measure, wont hurt anything So I think 3X12 oz bottles for 35 gals would be good.

 

[01rangerxl]

Oh yeah, it's over $100 to fill this thing up from E. Three bottles of Techron won't add much cost to that! Hopefully that will do the trick...fuel gauge is kind of important on this truck because we use it a lot and nobody wants to be pushing it.

 

[abycat]

My front tank gauge never worked for the po so he didnt use the tank. After a tank or two of me using it the gauge worked fine after that.

 

[94 saturn sl1 2000 saturn sc2]

42 gallon capacity.... or about 160 dollars at current price levels . 15.1 MPG lol

 

[RF Overlord]

Very interested in this thread. My company-issued van ('01 GMC Safari) has had the same issue with the fuel gauge for a few years now. It just reads what it wants, when it wants. I have to rely on the trip odometer to tell me when to fill it. Since the company doesn't want to fix it, if I can do so with a couple of cans of Techron, that would be sweet.

 

[mechtech2]

Marvel Mystery oil in the fuel has helped bunches of fuel sensors read right.
Well worth a try. BTW, it's not an overnight fix - give it time with a healthy dose.

 

[01rangerxl]

I suggested Techron to him today, and I know he has MMO laying around.

The battery turned out to have a dead cell, so that was probably unrelated.

 

[Jarlaxle]

I had a GMC pickup (an early GMT400) doing the same thing a while back (when I wrenched)...the owner was mystified. I disconnected the sending unit wire & tested it...gauge worked fine. Apparently, the transmission had been replaced, and the trans shop hit the sending unit wire. Result: it alternated between open circuit (empty) and short to ground (full). The fix was a new wire.

Cliff notes version: check the sending unit wire for a break.

 

[4x4chevydude]

its probably the sending unit on it...tell him to use mileage until his fuel pump goes out and it comes as one assembly....IMO not worth just changing it for the gauge.

 

[stevejones]

Sending unit contacts are worn out (ground down) is my guess. Same problem on my S10 after 125K or so. Replaced whole unit. Worked like new.

 

[The_Eric]

Guys, he said the pump/sending unit was replaced a while ago... Given the instant switch between empty and full, I'd be inclined to say the gauge is at fault. In fact we've got a similar vintage Chevy truck who's oil pressure gauge does something close to what the truck in the o/p is doing. This one, once it goes over a certain pressure, just snaps to pegged and comes back down just as quickly when the oil pressure drops even a pound or two. Also, the oil pressure sending unit is a new AC Delco unit that was installed with the replacement engine.

 

[01rangerxl]

That's kind of what I was thinking. The E to F switch with nothing in the middle seems kind of electrical in nature, but some Techron would probably be good for this Suburban anyway. Next thing to check if Techron has no effect is the wire, then the gauge cluster.

This truck has had the transmission replaced before, so it's certainly possible something got knocked around.

 

[ltslimjim]

As others have said, I've heard any PEA FSC might save it specifically on this forum.

Otherwise; perhaps the unit itself or 'maybe' the wires only.