Corrected title.... Original tachometer cluster in a 1991 K3500. Fuel gauge not working.

[Dajain]

Here she is in all her glory. This is when I picked her up. All the decals are off now but the glue residue still needs to be cleaned up.
I did take the wheel lift off as it's missing parts and I'll be towing trailers with it instead.

I just set up this account this morning so the signature hasn't been filled out yet. I'm sure I'll be here quite a bit. lol

And before anyone says something, I am waiting on the proper front marker lights. lol

And thanks for all the service manual downloads. Thay are all saved on the computer now.

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[Dajain]

So, if this cluster is from '91, and I find the gauge is faulty, is the motor replaceable?
I need to do more testing.
The truck has the 34 gallon tank, and I put 10 gallons in it. The sender reads 24 ohms right now, which sounds about right for the 10 gallons. But once I plug the sender in, the gauge goes to full grounded position.
Again, I'm just tinkering with her on Sundays and haven't troubleshot forward the tank yet.

Update.... This just came to mind.....
When I got the truck, I did looked up ALL the RPO codes and printed them all out. Just looked at the list and it does have the RPO code "U16" which is specific for engine tachometer. Apparently, it is the original cluster. hmmmm.

 

[someotherguy]

I haven't seen too many of the gauges in these clusters go bad, surely they do, but it's not overwhelmingly common like the stepper motor failures the newer trucks get. (GMT800's are somewhat notorious for it)

I would exhaust all possible wiring issues before suspecting the cluster/gauge itself. When the gauge goes full on power up regardless of sender reading, it's typically an open circuit. Gauge is getting power from the cluster but has no signal from the sender. The factory service manual should help troubleshoot this.

Richard

 

[Dajain]

I haven't seen too many of the gauges in these clusters go bad, surely they do, but it's not overwhelmingly common like the stepper motor failures the newer trucks get. (GMT800's are somewhat notorious for it)

I would exhaust all possible wiring issues before suspecting the cluster/gauge itself. When the gauge goes full on power up regardless of sender reading, it's typically an open circuit. Gauge is getting power from the cluster but has no signal from the sender. The factory service manual should help troubleshoot this.

Richard

Yeah, It's a simple enough circuit and I haven't tested from the tank forward.
Now, when I put a fuel gauge (from a boat and different ohm range) to the sending unit, it reads 3/4 tank. It reads 24 ohms with the 10 gallons in the tank.

If the wire was shorted from the sending unit to the gauge, it would always read a closed circuit (far left) with the key on.
If the ground was broken on the other side of the circuit, it would always read open and full right no matter what.

But I plug the harness into the pump assembly pigtail, turn the key on and the gauge goes full closed and needle swings far left like a closed circuit.
Unplug the pigtail and the needle swings far right showing an open circuit.

It's almost showing that the ohms between the gauge and the sender are in different ranges.

I'm looking for a rheostat to test the gauge from the pigtail to see what that shows.

But I won't be able to dig in to that before Sunday.

 

[Dajain]

OK, here's a quick update and it's a weird one. lol

I had another truck in the driveway that needed a new fuel pump. His gas gauge worked so I took it and plugged it into my truck...

Now, my new pump assembly is new and with the key on, the needle does move to the bottom of the fuel symbol but that's it.

This gauge that I know works, does move the needle BUT the float in the full tank position only takes the needle to the "E" mark.
It's almost like the motor is 1/4 turn out of adjustment.

Is that motor adjustable inside the cluster? That seems to be what the problem is.

 

[Scooterwrench]

The stepper motor is not adjustable but you can pull the needle off and reposition it. May want to make sure you get a full scale amount of movement before you mess with the needle. If you disconnect the sender at the tank and turn the key on it should go to full on the gauge.

 

[fancyTBI]

One other thing on the clusters. The 93-94 clusters have 80psi max oil pressure gauges. 91-92 they are 60psi.

 

[Dajain]

So, I took a little time today to mess around with the cluster and the gauge.
Apparently this was an issue for a while. There are small scratches around the fuel gauge needle.
With the key off, the needle moves to the 3/4 -7/8 full position and not all the way to full
Without power, the needle can be moved from the 9 o'clock position to the 3 o'clock position. That leads me to assume the needle is in the proper position on the motor shaft.
I'm thinking there is a resistor burnt out or something going on with the circuit board

So, I did some looking...
I found a moonie cluster for $75 on E-bay. 90 day warrantee on it.
When I get it, if the fuel gauge works, I'll just leave the moonies in it. I can always add a tach if I want one.
Who knows, If I find a place that will go thru and fix these clusters, I may send it off so I can have the original back in it someday.
But I want the truck going by springtime.

 

[ChevyPilot]

When I got my 1990 K2500 the fuel gauge didn't work, the "PRNDL" was immobilized, and the odometer wouldn't turn. I sent the cluster off to instrumentclusters.com (Southern Electronics) to be overhauled. There are several places that do this. As I recall, the fuel gauge was not available as a separate part, even back in the day. Turnaround was very fast. They overhauled the whole thing, replaced all the bulbs, and bench tested all of the functions. After installation, everything worked.. I think it was about $150.

In my truck you have to pull the bed off to get to the sender, so the cluster overhaul just made sense since it needed work anyway. And then there was no need to check the sender...

 

[Dajain]

When I got my 1990 K2500 the fuel gauge didn't work, the "PRNDL" was immobilized, and the odometer wouldn't turn. I sent the cluster off to instrumentclusters.com (Southern Electronics) to be overhauled. There are several places that do this. As I recall, the fuel gauge was not available as a separate part, even back in the day. Turnaround was very fast. They overhauled the whole thing, replaced all the bulbs, and bench tested all of the functions. After installation, everything worked.. I think it was about $150.

In my truck you have to pull the bed off to get to the sender, so the cluster overhaul just made sense since it needed work anyway. And then there was no need to check the sender...

The bed on this truck has an open access to the fuel pump and top of the tank. Made it easy to get the readings.

My PRNDL doesn't work either. Hoping to get that fixed also with the new cluster