Fuel Gauge Help!
 

I had previously assumed that my sending unit was bad as my fuel gauge is inoperable. After digging into it a little bit, I have found that there is no voltage to the plug at the sending unit.

The fuel gauge stays pegged past full. I've changed gauges to rule that out, and when you reinstall the gauge it moves from empty to full then stays pegged at full, so the gauge is operating I assume?

The car was originally CrossFire Injection. It was then later switched to a carb, and then a carbureted 350 was installed by me. I have no clue what the previous owner did when they did away with the CFI.

Where should I go from here? Does anyone have a wiring schematic for this? I'll be driving this car from Florida to Ohio so I would REALLY like a fuel gauge. Help!

Keyed power goes to one terminal on the gauge in the dash, and the other side has a ground wire that comes from the sending unit in the gas tank. The sending unit has a float on an arm with a wiper (rheostat) in the body of it that changes the amount of ground (read in ohms at the sending unit) it sends to the gauge, which is what changes it from empty to full. Since your needle is pegging, you know you have power at the gauge. And usually that means that the wire coming from the sending unit is grounding out somewhere between the tank and gauge (full ground=full tank). If you disconnect the wire at the sending unit and the gauge doesn't move, you know at least the problem isn't at the sending unit. But if the meter goes down, then the sending unit is bad.

Thanks, that clears a few things up. This is one of the few areas I'm highly inexperienced in, outside of just changing fuel pump assemblies. A fellow mechanic explained it to me exactly as you described, however he said that full ground=empty. Which one is right?

I plugged in the sending unit from my parts car (that I don't know if it's good or not) and it did not affect the gauge at all. I grounded out the wires coming into the sending unit (center pinkish wire is for the sending unit, correct?) And it had no affect, so I'm assuming that you are right about the ground.

Right now it's looking like I have a ground fault somewhere between the gauge and the sending unit, right? Could I just run a new wire directly to the gauge? Any clue which post on the gauge is for the sending unit?

On another note, I pulled my tank today. I've been going through a fuel filter every two weeks because there's so much crap in the tank. Looks like whoever swapped to carb also dropped the tank and eliminated the pump, and placed a piece of fuel line in it's place. The car must had been sitting for awhile before I purchased it, the inside of the tank was pretty bad.

Took the tank to a local shop to have it split open and cleaned out, then I bit the bullet and ordered a fuel injection sending unit. $180 bucks! Hopefully I won't end up needing it, that's $180 that could be spent elsewhere. Took me about an hour and a half to drop the rear end out, cut the exhaust, and pull the tank. Not too bad when you have a lift.

Is your gauge cluster still in the dash? Once it's out, a test meter will tell which side is powered. Then see what happens when you disconnect the other side. On the 3rd gen, I'm only familiar with the 90-up printed circuit board backed cluster. Is your that way too, or is there separate wiring to each gauge?

It's the same way. I have a couple spare fuel gauges laying around the shop, so I think I can decipher which leads are which. Hopefully I don't have to pull the gauge cluster again, I FINALLY got all the instrument lights working, it's a very sensitive thing.

Alright, I ended up bypassing the cluster and wiring the fuel gauge separate. With the new sending unit, it works perfect. Got the car all put back together today.

Alrighty then! Did you end up running a new wire from the tank, or tap off the one in the cluster loom?

I ran a new wire, I had an open short somewhere in the original wire so rather than bother with tracing it, it was much easier to run a new wire.

I actually had 3 problems. The wire from the bulkhead on top of the pickup that goes down to the sending unit was missing, open short in the wiring, and a problem in the cluster. I'm pretty happy now. Only thing is I have some squeaks from the rear end, must be the new polyurethane bushings.

Bad sending unit, rheostat, or bad gauge?
 

Sorry guys for interupting, but can you checkout my video and let me know what is happening here. Thanks guys. http://www.youtube.com/watch?v=kDfATT_qprU

It's hard to say just yet if your gas gauge is bad. When keyed power is off, the needle should drop back down on it's own. To make sure you don't have a short somewhere, disconnect the battery. Then if the needle doesn't drop, the gauge is bad. Oh, and you should have started your own thread for this.