when I'm cruising at a steady pace my gas gauge gives a fairly accurate reading, but as soon as I hit the gas or brake it jumps all around erraticly. What is wrong? Is it the float or the gauge? It just started to do it.

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1986 CAMARO Z28 ->
151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, B&M Ripper shifter, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframe connectors, all bushings are urethane, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.32@ 106.4MPH 3300lbs less driver and speakers Next mods-> Extreme Energy 268 cam, Holley street dom intake, ported heads.

1987 TRANS AM ->
73,000 miles, 305TPI, auto, gutted air box, gutted cat.

 

My new (to me anyway) 86 IROC does the same thing. No idea why unless the connections inside the instrument panel are getting dirty/loose after 15 years. I say this as my oil pressure ga. does the same thing.

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Z's r Best

 

Some electronic gauges can twitch due to interference from the ignition system. I've heard of faulty plug wires, or wires with poor insulation causing gauges to dance around. As for the fuel gauge jumping I've got a question. Does it stick when the tank is full or close to full and stays there until the tank is about half full or less; then the gauge falls to the correct level.

If it's only happening during hard acceleration/decceleration, I'd probably say that it's just the fuel sloshing around moving the float around. Does the gauge dance around when the tank is full?

 

Does
it stick when the tank is full or close to full and stays there until the tank is about half full or less

My gauge does this. Goes all the way to the top and higher then after it gets to a half tank it seems to work. Why does it do that?




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1986 SC Camaro
Mods: Threw 2.8 in garbage, put in rebuilt
350 .060 over, XE268H Comp cam, Edlebrock
Performer Intake and Edlebrock 600 CFM Carb,
Pete Jackson noisy GearDrive (which sounded
cool for about 5 minutes, now I'm sick of it)
Rebuilt TH350, 3.42 Rear Gears. LCA RLB's.

 

bhaas, if you have a mechanical fuel pump I'd probaly say that it's your float that is sticking. When you're driving around (and your tank is half full or less) and hit a bump, decelerate/accelerate hard enough, the force of that probably jars the float enough for it to fall down to the correct position.

If you have an electric fuel pump it could also be the float sticking. Another possibility could be the sending unit. My dad had a truck with dual tanks and when he switched over to a tank that he knew had fuel, the gauge would give an improper reading.

Those would be my best guesses. Anyone else out there want to put in their 2cents?

 

One more thing guys. Never over-fill a gas tank. When you're pumping gas and you hear that thump telling you that you've filled up, stop. Be careful though sometimes I've just started to pump and I hear that thump; when I know a lot more gas is still needed. The reasoning behind my precaution is this.
At the gas station, the fuel is stored in these large tanks underground, where the temperature is nice and cool. The ground is cool, the tank is cool, and the fuel is cool. Therefore the fuel is more dense.

So when you pump the gas into your car it is in a dense form. When the gas is in your tank it's going to warm up(the molecules spread out). In other words the gas goes through an expansion process. Endurance racers used to (probably still do) cool down the fuel before they'd put it in their fuel cells. The reason being-if you had a 20 gallon fuel cell, by cooling down the fuel and making it more dense you could probably cram a gallon or two more into the cell (maybe more, maybe less). Doing this could give you extra laps around the track, while others would be pitting for more fuel. Now fuel cells (for racing) don't use a measuring device like floats; at least none that I know of. That is why you see racing team crew members that are calculating how much fuel they have and how many more laps that they can go before refueling.

What I think starts problems with floats is that when you overfill the tank with cold fuel and then it expands, the float is then pushed beyond where it is designed to stop. This then leads to the float sticking. Of course I could be wrong. Anybody have any thoughts on this?

 

Gas tanks have a domed top above the fill neck to catch vapors, so even when you DO fill it to the point of having it pour out the fill neck there's still room for it to expand.

I've also heard it's unsafe to overfill the tank in case you get hit on the side and your car goes BANG.

As for the gauges going crazy around cornering and accelerating/decelerating... That's normal. I haven't seen ANY thirdgen fbody that doesn't do that. I like to think of my gas guage as an accelerometer. heh

In fact, every car does this, really. The float's going to stay in the same spot, but the gas is going to slosh all around, so.. When you brake, all the gas goes to the front of the tank, making the back of the tank appear more empty to the float. When you accelerate, it all goes to the back, making it seem more full. Same with turning: When you turn left, gas goes right. The gauge is just reporting what the float is reading at the time.

All cars do this, actually. It's just that newer ones delay the electric signal for a little bit before reporting it to the gauge. I'm sure if there was a way to get a newer car to keep a constant acceleration for a minute you'd see the gauge change. Of course, it would probably go down from losing gas. lol.

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89 iroc-z 305 tbi
k&n filtercharger, open element air filter. nuffin' else

 

Thanks for the info, Enkil.

 

My car does this too. It used to be WAY worse before I swapped gauge cluster for a newer one. I think its just a matter of the gauges and sending units getting old. I know of at least a dozen camaros that have this problem.
I used to be going on the highway and the gauge would be down to almost empty, then I would get off to get gas and the gauge would go up to almost half a tank. some things you just have to deal with. unless of course someone knows an easy way to fix it then I am game.

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Jay

black 85 Z28, t-tops, 4bbl carb, flowmaster 80 series muffler w/ custom tips (hollowed out cat), edelbrock chrome air cleaner, Infinity 4" 2 way front speakers and Infinity 3 way 6x9s, Alpine CDA-7863 head unit. many more mods planned (holley carb 4160 and edelbrock performer RPM intake coming very soon)
Jay's webpage

 

No I think you are mistaken the gauge doesn't smoothly "jump" around, I mean it twitches like a freak. Even if accelerating at part throttle and give it just enough it will twitch. It doesn't do it when it is full it does it any other time though. Like someone else said too my oil pressure gauge does the same thing.

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1986 CAMARO Z28 ->
151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, B&M Ripper shifter, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframe connectors, all bushings are urethane, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.32@ 106.4MPH 3300lbs less driver and speakers Next mods-> Extreme Energy 268 cam, Holley street dom intake, ported heads.

1987 TRANS AM ->
73,000 miles, 305TPI, auto, gutted air box, gutted cat.