The fuel gage on my 1990 240 wagon is stuck on full. When the ignition is turned off, it moves to empty, but returns to full and remains there as long as the key is on. What would be the problem?

A couple of comments on previous posts:

I don't know about a 544 fuel guage, but I think our guage actually works the same way as the one in my 1800 (as did my dad's 122, if I'm not mistaken). There's no "comparison of resistances" going on. Rather it's a fiendishly simple but terribly twisted plan that makes the needle move. The needle itself is suspended on a bimetallic strip. Just as you might assume that's a thin strip of two different kinds of metals laminated together. The two metals have different expansion rates, so as the strip is heated, it bends. The metal on the outside of the bend expands faster than the metal on the inside of the bend. There are thermal switches on Volvs that work the same way. As they are heated, the deflection causes them either to make or lose contact with another contact in the switch.

So, the circuit works like this: there guage sender is simply a rheostat attched to a float: the higher the float, the lower the resistance in the circuit. The less resistance, the more current. Inside the guage, that bimetallic strip is wrapped in wire. With the increased current, the wrappings heat up and the strip bends causing the needle to move. So, if there's a short to ground, the needle heads north but quick.

So, the first thing to do is to pull the instrument pod anddisconnect its wiring. Pull out the floor in the back of the car. This is a pain in the butt. Find the plate covering the guage sender and remove it. Pull the connector and probe the grey wire with an ohmmeter, with the other probe connected to good ground. If you get anything but infitite ohms, you've got a short, which would suck badly. If the wire is good, then the guage sender is bad. As indicated, it's a pretty simple circuit, and since the guage itself works, there are few other things to go wrong.

Now, despite my infinite respect for "Sven's Manitainer," I have to qualify his description of the simplicity of the job of replacing the guage sender. I tried recently, and if it hasn't been done before on your car, it might be a pretty bad job. It certainly was on mine, which ended up off to the shop behind a wrecker. If you're going to do it yourself, be prepared with the proper Volvo tool, rather than a wood or brass drift and a hammer. Also, if you don't know the age of your pre-pump, be prepared to replace it, too.

The hole in the floor is not much bigger than it has to be, and although access is definitely easier in a wagon than in a sedan, it's not by much. Also, it's apparently not unusual for the hose connections to snap off while you're trying to remove the hoses. Then, if you do find you can't get the assembly out, you're screwed (this is what happened to me).

At any rate, this is one job I hope I won't have to do again soon.

By the way, if you should suspect the guage to be bad, you can test it by hoking up various resisters from 0-350 ohms between the grey wire connector at the guage sender and ground. Under different resistances, the guage should read different levels, the more resistance, the lower the needle.

Good luck!

-EdM.
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'90 240DL Wagon 'Lola' -- '72 1800ES 'Galadriel'

Despite the many years separating our cars (I drive a 1964 PV544) the problem with the fuel gauge remains.

As you probably know from the many discussions about the subject here, the gauge has two grounds on it.

One is direct to the frame, usually a short wire inside the dashboard, while the second one goes through the fuel tank level sending unit.

The resistance on the sending unit in the gas tank ckanges as the fuel level float moves up and down, and the gauge on the dash compares the different resistances and a small coil inside the gauge causes the needle to move in conjunction with the sending unit float.

Since your gauge is indicating EMPTY all the time, I'd examine the sending unit and its wire.

If it indicated FULL all the time, I would say that the short wire to ground is either corroded or broken.

If I could pull your sending unit and take a quick look at how it's set up, I could tell you in a second where the problem is...

Of course, I may have this all backwards, but at the moment my gas gauge is doiing the exact same thing as yours, and I know where my problem is because I somehow mixed up the two ground wires when I re-installed the dash last week.

Let's see if someone has a service manual for your model and can help us out here. I don't think my vintage 1964 manual would be of very much help!

Steve

Whatever you do, do not follow any advice you may receive instructing you to whack the dashboard firmly above the fuel gauge location. I've been given that advice a couple times, and I definitely don't want to damage anything in my instrument cluster.

The fuel sender assembly also includes the top cover plate for the fuel tank, with all it's termninals and connectors for fuel, vapors, and electricl lines in and out of the tank. Over the years that top plate and it's terminals etc. disintegrate into a rusty mess. I've had to have a couple of those replaced on our bricks over the years.

Since yours is a wagon, you can see it fairly easily by removing the carpeted plywood panel (screws at sides and on forward side of long hinge). There's a sheet metal cover plate under that, remove and you can then see the top of the tank. Just possibly the level sender wire is grounding on some exposed metal. Possibly the whole thing is a mess. The cool fuel running through the lines causes condensation on the outside which hastens the corrosion, in spite of pretty good plating on the exposed parts.

Removing the fuel level sender's big bung nut requires non-steel tools to avoid sparks. I've had others do this job; proceed with proper cautions if the job is needed and you do it yourself.
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Sven: '89 245, IPD sways, electric rad. fan conversion, 28+ mpg - auto tranny. 850 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).

Thanks, Sven. I'll check this out tomorrow.