Hello,
I have a 1984 Z28 5.0 I started restoration on about a year ago. The car was put into storage in 1990 with a full tank of fuel. I knew when I started the restoration, I would be replacing the fuel tank and fuel sending unit with new. I got the car running with a fuel can and the gauge still showed FULL. I drained the old fuel from the tank and the gauge still showed FULL. I installed the new tank and new fuel sending unit and the gauge still shows FULL. I put 5 gallons of fuel in the tank, and the gauge still shows FULL. I ran the car with the new fuel in the new tank with the new fuel sending unit and it runs great, but the gauge still shows FULL. I put a camera in the tank, and the float is floating on top of the fuel as it should and not stuck all the way up. I checked the wiring and there are no cuts in the wiring where it would be grounding out. It doesn't matter if the car is off, ignition on, or running. the gauge always shows FULL. At this point I don't think it is the fuel sending unit. Has anyone encountered this before? Is it possible that the gauge is stuck on full and what do I do to fix it?
Thank you all,
Dave

 

Clearly, yes.

Take off the bezel covering the gauge and see if the pointer is merely stuck on something. Like maybe, the stop at full-scale.

 

A short to ground on the pink wire from the gauge to the sender would create an "empty" indication. An open circuit would create a "full" reading.

Try connecting a 50Ω resistor (or thereabout) from the pink wire to a good ground, and power on the ignition. That should pull the gauge indication down. It might be easier to access that wire at the C200 connection or at the C313 connector at the rear axle hump.

 

everytime I do a fuel tank sender I always check the level switch with an ohm meter at the plug. Ive had DOA units before. You should be able to see the 0-90 sweep.

 

Thanks Sofakingdom. I hope this is all it takes. I don't want to take the fuel tank back out again.

 

Unfortunately, this is the first one I've done. I hope this is not the case. I really don't want to remove the fuel tank again. What else could it be before I resort to removing the tank again?

 

Did moving the gauge pointer with your finger straighten it out?

 

I was unable to get to it last night. I am planning trying that tonight. I hope it's anything but a DOA sending unit. I really don't want to drop the tank again.

 

Well, of course, nobody likes dropping the gas tank. So try the simple quick eeeeeezzzzy cheeeeeeeep free HIGHLY LIKELY fix before getting all wound up in worst-case doom & gloom.

 

HaHa! Thanks for your support! I feel better already!

 

It worked! I need to do some more things to the car and test some more, but I think it works! It slowly creeps up to full with the ignition off then drops and settles at the fuel level with the ignition on. If I remember correctly, that is what it used to do. I noticed the clear plastic panel lens is scratched really bad so I'm replacing that too while I have it off.
Thank you very much! I appreciate it!

 

 

Hey Vadar,

My car is currently doing this. The fuel gauge is sweeping to EMPTY and locking there when I turn the key to the ON and START position.
So you're saying this is a short, as in the PNK wire that terminates in the brown gauge plug in (port 10) is grounding out somewhere between there and the sending unit in the tank?

 

In a nutshell, yes.

Connector C2 (forward side of the instrument cluster), Pin 10, should be the pink wire to the fuel level sending unit. If the cluster is still in position, it might be easier to access the circuit back at C313 to test at the pump end, using jumpers/connections to test the complete harness. Measuring resistance at a disconnected C313 should provide good information. If the harness is grounded somewhere between C313 and the cluster, it will be necessary to check at the connects right on the cluster.

If that pink wire is disconnected from the instrument by any means, it should sweep to the FULL end of the scale. When grounded, it should sweep to the EMPTY end of the scale. I suggested about a 50Ω resistance (47Ω is a lot more common) to test for somewhere between 1/2 and 3/4 fuel load, since the gauges are never quite linear. If that all works, the instrument itself is about as good as it will ever be, and any problem is likely outward from the C2 connector.

Also, your "export" RH drive version may have that circuit also routed through the C200 connector, as earlier domestic versions did.