tleed

The fuel gauge on my '98 5.9 Grand Cherokee just started going wonky a couple of weeks ago. It will drop to just over 1/2 tank right after I've filled the tank. It stays there until it drops below 1/2 tank, then drops on to empty.

But last Tuesday it was showing 1/8 tank by the needle & 90 miles to go on the trip computer when it ran bone dry. 24 gallons later I was back on the road.

So I suppose it's time to fix the gauge. But apparently the sending unit is part of the fuel pump assembly. And that's not cheap. How likely is it that I can pull it out of the tank & clean it up & have the sending unit work? Is this a matter of a sticking float? Or is this an electrical problem that won't be fixed w/o a new pump assembly?

I only want to drop this tank once, and I don't want to have to wait for parts to come, if possible.

andrewmp6

Have you tested the voltage coming from the sending unit ?

tleed

Nope. How? And what would I be looking for?

Bustedback

I think you have a bad sending unit. Replace the complete pump assembly to save headaches later down the road.

97grand4.0

He's right, I did mine once for each component. Do the unit.

dave1123

IF the fuel gauges are the same as always was, you be lucky to find about 1.5v at the sender. The supply voltage is the ground leg of a delta shunt circuit with the gauge and a resistor as the other 2 legs. I don't believe the float and resistor in the tank are serviceable separate from the pump assembly.

97grand4.0

[QUOTE=dave1123;3294497] The supply voltage is the ground leg of a delta shunt circuit with the gauge and a resistor as the other 2 legs.

As a licensed electrician of 21 years, I'm going to have to make the coffee a little stronger this morning to wrap my head around that one, Dave. lol.

freegdr

[QUOTE=97grand4.0;3294632]LOL

dave1123

Well, I'm not an electrician but that's the way it was explained to me. I can't draw the circuit, but I understand the resistor is across the supply, gauge, and sending unit in a triangular arrangement so that the whole circuit is balanced with very little actual current flow. I know I've put a multimeter on the sending unit wire and only got about .75v-1.5v. when the gauge was supplied with 12v. I had a problem with the gauge in my Chevy truck and it turned out the resistor was loose on it's mounting studs inside the gauge.

tleed

So how did you fix the issue? Replace the sending unit in the Chevy?

dave1123

No, just removed the resistor, cleaned the terminals, and reinstalled.