car sitting idleing and all the sudden the gauge pegs all the way past full. sometimes it goes back, seem kinda weird to me

with my tank decided to do that....
sounds like a loose ground or something.

One of these two conditions is what is happening, IMHO

1/ The variable resistor in the tank sender is going open circuit, the wiper is not contacting the wire wound resistor through out it's full travel or the wire wound resistor has a break in it and when the wiper slides past the break it creates an open circuit.

2/ The wire from the sender unit to the gauge is going open circuit. If the wire from the sender was grounding out. The gauge would go to Empty.

There are 3 studs on the gauge that plug into clips in the cluster when the gauge module is inserted into the cluster. The right stud on the gauge (looking at the gauge as if you were sitting in the car) is where the wire from the sending unit connects.
The clips in the cluster and the studs on the gauge can get corrosion on them sometimes and this a place to check for a bad or intermittent connection as well.

To check the wire from the tank sender to the gauge cluster you can take an Ohm meter and measure from the right clip for the fuel gauge in the cluster to the connector at the tank. (Pink wire at the tank connector) You should see something close to 0 ohms if the wire is good. Give the harness at the tank a shake while the Ohm meter is hooked up to these points and if the Ohm meter reading jumps around and maybe shows an open circuit then the wire from the sender to the gauge is the problem.

Hope this helps.
Sidecar 2M6 SE

[This message has been edited by Sidecar 2M6 SE (edited 05-07-2009).]

I think it would also be a good idea to check the weather-pack connector at the firewall. If the connector deteriorates or is damaged, water and/or debris can get into the plug and cause a bad connection.

quote Originally posted by Blacktree: I think it would also be a good idea to check the weather-pack connector at the firewall. If the connector deteriorates or is damaged, water and/or debris can get into the plug and cause a bad connection.

I agree with Blacktree. I forgot that the fuel sending unit wires go through the bulkhead connector too.

There's also a 3-wire connector down by the fuel tank. That's the one I was talking about.

Sounds like your car is jut trying to save you some money on fuel.

When I removed my tank to repair the sending unit, I found there was a layer of some type of junk on the wire wrapped board where the wiper makes contact. I cleaned it off with a razor blade, then wiped it off with thinner. Been working two years now. Some times it gets to acting funny around 1/4 tank. I usually refill it before it gets there. There is a good write up by someone here on PFF on how to do the repair.
Joe

Mine does the same thing and if I give the cluster hood a 'brain duster' it will sometimes come back down to where it should be. I have had the cluster out recently but I didn't see anything wrong with the connectors. I dunno.

Check the published grounds carefully. Grounds which are incomplete, dirty, loose (or tight and dirty or corroded slightly) can produce some really BIZARRE and intermittant manifestations....