Gas gauge pegged - Team Camaro Tech
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post #1 of 11 (permalink) Old Jul 16th, 10, 03:39 PM Thread Starter
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Terry
 
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Gas gauge pegged

After taking two years to do major mods (200 4R, 8.5" Nova posi, Classic Auto A/C, Alum radiator, Hotchkiss susp) to my '68 Camaro I decided to prepare for a road trip. First, I siphoned the old gas out of the tank. There was only about a gallon of old gas in the tank. Still smelled like gasoline. Had not turned to gel or varniish. Second, I poured 4 gal of fresh fuel in the tank. Third, I disconnected the fuel line at the carb and stuck it into a Miller's quart bottle. Poured some gas into the carb and started the engine. Did this a couple of times until I got about a quart and a half of old fuel out of the line. Connected the fuel line to the carb. The engine started right up and ran good. But, the gas gauge is pegged at 3:00, and doesn't move. Is it possible when I siphoned the old fuel out with a garden hose the hose disturbed the fuel level float??

Last edited by IRON MAN; Jul 25th, 10 at 04:24 PM.
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post #2 of 11 (permalink) Old Jul 16th, 10, 04:03 PM
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Wink Re: Gas gauge pegged

That's possible, but not likely unless you were really thrashing that hose around in there
Most likely, the wire to the sender is grounded somewhere along it's route to the tank
If you did or had any exhaust, suspension or body/frame work done it may have gotten pinched into something causing it to short to ground and peg gauge.
I've even seen a screw for the door sill plate go into th ewire and mess up the gauge signal

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post #3 of 11 (permalink) Old Jul 16th, 10, 08:05 PM Thread Starter
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Re: Gas gauge pegged

Quote:
Originally Posted by Vintage 68 View Post
That's possible, but not likely unless you were really thrashing that hose around in there
Most likely, the wire to the sender is grounded somewhere along it's route to the tank
If you did or had any exhaust, suspension or body/frame work done it may have gotten pinched into something causing it to short to ground and peg gauge.
I've even seen a screw for the door sill plate go into th ewire and mess up the gauge signal
Vintage68, Thank you for the quick response. I disconnected the wire plug that goes to the sender on the gas tank near the base of the trunk lock. Ran a wire from the batt (+) to the brown sender wire and turned the ignition switch to on. The gas gauge remained pegged at 3:00. Should I fill the tank up 16 gal, drive it, and see what happens as the gas is used up? Don't know if that would determine anything.
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post #4 of 11 (permalink) Old Jul 16th, 10, 08:27 PM
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Re: Gas gauge pegged

Look underneath the tank on the front side (by rear axle) where the passenger side tank strap loops through the hanger on the underside of the trunk pan. See if the black ground wire coming from the sending unit is screwed on there good.

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post #5 of 11 (permalink) Old Jul 16th, 10, 10:54 PM
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Wink Re: Gas gauge pegged

Actually, you do not want to power up the 'brown' wire to the sender
The power (+12) goes to (and through) the gauge and then to the level sender unit in the tank - so the "sender" is actually a 'reciever' as a path to ground for the gauge
So if you unplug the sender wire at the tank, and the gauge still stayed 'pegged' (or reads high level) then the problem is in the wiring between the gauge and the where you unplugged the sender wire.
If, after you've unplugged that sender and then turned the key to 'on' the gauge no longer reads high - the problem is the sender or float in the tank ...

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post #6 of 11 (permalink) Old Jul 17th, 10, 09:40 AM Thread Starter
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Re: Gas gauge pegged

Vintage68, Thank you for the very clear explanation. So the level sender unit acts as a " receiver" as a path to ground. You have convinced me to trace the float sender wire to the gauge. I suspect the wire is grounding on top of the gas tank. I've got the '68 on jack stands to make tracking the wire easier. I will post where the problem was (hopefully) when I get this solved.
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post #7 of 11 (permalink) Old Jul 17th, 10, 09:50 AM
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Re: Gas gauge pegged

Ground the brown wire in the trunk. There should be a connector there. Make sure you have the wire going to the guage. Turn the key on. Does it go to empty. If it does then its between the connector going to the sending unit or ground/ sending unit.

If it still stays at the 3 oclock position then its the wiring to the guage or the guage.

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post #8 of 11 (permalink) Old Jul 17th, 10, 11:20 AM
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Re: Gas gauge pegged

I would do as Mike (prostreet69camaro) stated.

By unplugging the connector in the trunk, you will have two terminal ends. If you ground the end going towards the gauge and then turn on the ignition, the gauge should read empty or below. By grounding this wire you are creating close to a 0 ohms resistance just like the sending unit should if the tank was empty. If the gauge reads empty or below, go in the back and take the jumper wire going to ground off of the connector end and the gauge should then read full or above. With an open circuit there is an infinite resistance which is higher than 90 ohms which the sending unit should have when the tank is full.

With grounding and leaving open the connection in the trunk you can find out which way the problem is. Either forwards towards the gauge or rearward to and through the sending unit and then to the ground wire connection to the body of the car. I've seen both gauge problems and sending unit problems in vehicles so if after the test forward things are made to work you may still have a problem with the sending unit and it's wiring. You just have to go through the steps to find the problem(s).

I've also seen a fair amount of original crimped connections onto wire look good and be mechanically solid but electrically they are bad. You may have to get out a meter to do some advanced troubleshooting.

Jim

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post #9 of 11 (permalink) Old Sep 2nd, 10, 08:16 PM
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Re: Gas gauge pegged

Hi Guys,
Trying to fix my next problem( gas guage) With the sending unit wire plugged in the trunk (tan wire) my guage is pegged @ 9 oclock with key on and doesn't move. When i diconnect that tan wire and turn the key on then it goes past full ? I have a new tank ,wires from the trunk to main harness and new sending unit. Can anyone help me narrow it down as I'm not to good with wiring problems.

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post #10 of 11 (permalink) Old Sep 2nd, 10, 10:12 PM
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Re: Gas gauge pegged

This is a good fuel gauge/wiring diagnosis methid:
http://www.chevelles.com/techref/ftecref18.html

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post #11 of 11 (permalink) Old Sep 3rd, 10, 09:04 AM
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Re: Gas gauge pegged

Thanks

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