The fuel gauge on my 89 seems to be stuck at full... Put gas in it 3 days ago (which gave me between half and 3/4 of a tank). Hoped shutting down and restarting would clear up the problem but it didn't. Where should I start in searching for a problem?? :confused:

 

start with the most likely cause - the sender.

and that is one expensive POS... something like $300.00!!!!

The sender is a fancy rig that holds the pump inside the tank. You have to remove the entire unit to inspect it. I don't think its a serviceable part, tho.

My sender is fouled up... the question with these is not if its broke, when will it break.

I just refill at 250 miles on the trip odo!!! 325 when doing a long highway cruise.

 

My 92 just got stuck at full today. Have you found your problem yet? Tom :confused:

 

Check the harness for an open in the signal wire or the ground circuit. Remove fill door and pull the rubber boot out. On the '89 the body side of the harness has 4 wires as it was prewired for the ZR1 fuel pump. Ignore the dark green/white wire. The pump side has 3 wires - the cavity from the dark green white wire is plugged: Tan white is power to the pump. Purple is the signal from the sender. Black is ground. Note that the ground joins another ground that is soldered to the tank. This is the pump ground. Disconnect the harness and jumper the black & purple wires on the female side. Gauge should read empty (you may have to turn the key on & off to get it to change). If not, ground may be bad or signal wire could be open. To verify, jumper purple wire to ground. If it reads empty, follow the harness to the back up lights splice just to the right of the fuel tank fill and check the splice (I'm assuming your backup lights work - if not you will have to investigate this ground circuit further). If it didn't read empty when you grounded the purple wire, you need to check it for continuity. Remove the right side trim in the storage area and check the rear harness connector above the speaker, Pin B. If ok, check at the next connector which is in the passenger side kick panel area, Pin E. If ok, check the cavity connector C8 at the cluster. If the wire is good to this point, ground Cavity C8 at the cluster. If the tank doesn't read empty, the cluster is bad.

 

Excuse my ignorance, but I want to be sure. When you say jumper the wires that is the same as connecting them, not reading the voltage between them?Sorry for the question, but I would hate to spark something around the fuel tank.

 

Yes, connect the wires in the body side of the harness. The tank is grounded, but that's a safety feature to prevent an explosion from static electricity when it's being filled. Shouldn't be a spark, but make sure the cap is on securely and you can pull the harness back a little ways.

 

This just happened after I put a bottle of 3M fuel injector cleaner in a full tank. This did not create the problem did it?

 

I've heard of injector cleaners shorting out the pump wiring, never the sender, and most of the stuff you dump in the tank is pretty weak. I've used 3M port fuel injector cleaner, but only with a direct connection to the fuel rail and with the fuel pump disabled, which is what GM use to recommend (they don't recommend anything now).