Ok, my poor old IROC has developed the dreaded Gas gauge/sending unit, reading over full problem. I bought this car about two years ago and have replaced almost everything on it, interior, engine/transmission, exhaust and brakes. I'm planning on regearing the rear end next, but now this gas gauge issue has reared it's ugly head and I want to fix it first.

I've already checked the gauge to make sure it's not sticking on anything and checked the ohms from the tank. I'm getting an infinite ohms reading indicating a break in the circuit. Last time I encountered this problem on a GM it was a bad sending unit, I think my plan on fixing it at this time is to buy a new sending unit and replace it; I want it fixed right the first time and not have to worry about it down the road.

If you replace the fuel sending unit (which I'm guessing may be the problem as well), I'd consider replacing the fuel pump at the same time with a GOOD pump like one purchased from GM or some other well known reputable brand.

It's a pain to get these tanks down, and if your pump hasn't been replaced, its only a matter of time before it goes out. I had to take off my exhaust and axle to get my tank down to replace my pump, and I don't look forward to doing it again (I may to put a higher power pump in now that I'm going to be upgrading to a 350.)

Edit: I just noticed your info says you have a carburated car.... so yeah you don't have to worry about the electronic fuel pump problem.

You still have to take the tank down for that sending unit though...

Yeah, somebody swapped my car to carburetor years ago, used a tiny dead head 6 psi external pump and the car was prone to vapor lock on a warm day. After I bought the car, I swapped to a 45 PSI electric pump mounted on the rear subframe, to a return style pressure regulator under the hood to prevent vapor lock. I will finally get to see if they replaced the old in tank pump with a pick up hose and a sock or if it's actually drawing through the old pump.

I have the same problem however mine started with the addition of an aftermarket fuel gauge. I haven't done any circuit testing however I'll be dam*ed if I'm going to drop the tank. Last time I did that I had to cut the exhaust off and I'm not ready to do that again until I have a new system ready to install.
I hoping that I can rework the circuitry and satisfy whatever sort of voltage the gauge needs to operate correctly. I'd rather pull the dash apart than drop the tank.
Keep us posted with what you find.

In my quest for horse power, I installed long tube headers and dumped the exhaust just before the rear axle, so thankfully I won't be dealing with the exhaust.

When I did my V8 swap this is how I did my exhaust, sounds mean and its out of the way.

I'd put money on it your issue is with the sender, in all the third gens I've seen with fuel gauge issues 90% of the time it's been the sender. Unfortunately a good one is $120 or more.

Yep, I just paid 160 bucks for one through Summit; It'll be here tomorrow.

I got lucky guys, found a dirty connector where the tank harness connects to the body harness. Cleaned, reconnected and it works like new again. I put the new sending unit on the shelf in my shop, I figure as long as I have a new one in my shop I'll never have a sending unit problem.