Fuel Guage problem...

When I got my truck it had what I thought was a bad New fuel guage. It was always pegged...I was mistaken.
When I replaced it with a new one from Saturn, it also "pegged". And stayed there until I removed the #27 spider wire connection. It then released and went to E.....
Thinking it was a wiring problem, I jumpered the sending unit straight to the guage, same thing. It pegged to full...

Is it a problem with the fuel sender in the tank, or something off the spider wire harness#27 feed?
I'm open to suggestion?
Thanks
Mike Bogner

Here I go bringing up the fuel tank grounding again, but who knows...Anyway, the fuel tank is isolated from the frame by strips of liner on the supports and is grounded via one wire, #79, which connect the connector housing on the fuel pump to the frame.
The tank itself is grounded via the mounting screws on the fuel pump plate, there are like 8 of them.
The fuel level sending unit is grounded via its mounting screws to the tank, which must be grounded via the fuel pump as explained.
It's very easy for the ground to have a break in this "chain" of grounds, check them! I'm sure many fuel pumps and level sendinding units are replaced because of a poor ground.

Thanks,
I'll do that.
Mike

Here's the info you need to do a complete and thorough check of the fuel guage and components. This is right from the TMs available for free at Steel Soldiers.

Gauges

An observation I've made, is that there seems to be a belief that there is a need for a "good" ground at the gauge panel (gauges to panel via mounting clamp) for the gauges to function properly. As I was recently correcting problems with my gauges, I searched this subject here and printed the wiring schematic for reference. While looking at the schematic, I noticed that only 4 Items on the gauge panel require an electrical ground contact to the gauge panel. They are the high-beam indicater,2 panel lights and the volt meter.(To complete these circuits the gauge panel needs to be secured to the dash) The oil pressure, coolant temperature, fuel level and of course the air gauge(no voltage required), do not need to be "grounded" at the gauge panel. These gauge circuits are grounded at the sending-unit end.

In theory you are right. Try pulling that oil pressure gauge out and get it to work. The oil pressure gauge housing needs to be grounded as well. I went through several gauges and sending units on my wrecker before I woke up to that one.

Eric, I've got to go with Bjorn and Ken on this one. The OP guage on my truck are recieved from the DRMO was giving me all sorts of screwy readings. No oil pressure, normal oil pressure, peg at 120 PSI and stay there. On several occasions, with the truck not running and the accy switch off the guage would read 60 PSI and stay there for several hours with no power to the guage! Try and explain that!

I put a tee in the line at the OP sensor and ran a mechanical OP guage and got normal readings on the mechanical OP guage. I eventually got around to pulling my dash panel, wire brushed the grounding pins on all the guage mounting brackets (those grounding pins must be there for SOME reason) and thier respective grounding locations on the dash, applied copper filled anti sieze compound at all grounding points and reassembled. Started the truck, now the stock OP guage reads as it should, same readings as the mechanical OP guage!

I agree that from the WD, it would appear all you need is +24V and a good connection to the sender for the guage to work, but it ain't so. There must be some internal circuitry in the stock OP guage that requires an external ground for the guage to work properly. Now, if I can just get my fuel guage to read right ......

I remove the #28 wire from the mounted fuel guage with the #27 wire still pluged in and it peg's to full with the power on. I remove #27 wire and with only the #28 wire pluged in its at empty.
Isn't this a bad guage? It looks like its grounding out thru my "new" guage.
I reworked the ground wire at the tank bolted to the frame. Cleaned and replaced the star washers on the sender. Same with the screws on the pump.
Got 28v at wire #27 at guage. Got 1.6v at at sender with guage pegged, power on.
.........................................................................F'ing truck.....
I got to get better aquainted with the features of my Simpson VOM....
Ken, can you tell me what TM you got that procedure from? I looked thru what I thought it would be in and coulditnt find it. My connection is realy doggen.
Thanks
Mike

Start with page 2-120 or the PDF page 206 from TM 9-2320-361-20. It goes through the truobleshooting of all the instruments there. You should have has 28 volts or battery voltage at wire 28 where it is disconnnected from the sending unit. If you don't have 28V there the gauge or wire is screwed up. Rig a test wire from 28 terminal on the gauge to the tank sending unit and try that. Might just be a problem with that wire. Also take that test wire and run it to a known good ground. Gauge should read full (pegged) as long as that wire is NOT grounded. When that test wire is grounded, that tank should read empty.