moronputz

For years I have been living with a fuel gauge that never reads full and have been unable to fix it.

I've tested the sender and the ohm readings are within spec. Likewise I've tested at the gauge connections and also get ohms within spec, so clearly the fault lay in the gauge itself.

After a little detective work I found that it may be possible to recalibrate the gauge itself fairly easily.

The following is offered as a suggestion only with no guarantee of success - though it seems to have worked for me. This also assumes that the fuel sender is accurate.

You need to know exactly how much fuel is in the tank so that you can calibrate to that reading.

Remove the carpet to access the fuel sender unit in the top of the fuel tank.
Remove the wires and using an ohmmeter check the sender unit reading so that you know exactly where the gauge should read. There are 2 wires on one side and one on the other side of the connector. Resistance is checked across the two wires (or actually the two posts on the tank unit). Resistance figures are in the workshop manual page 90-17, but for reference they are
- Reserve - 63.2
- 1/4 - 42.2
- 1/2 - 21.2
- 3/4 - 8.6
- full - 2.8

Once you have this info you should be able to work out approximately where the gauge should read - of course it would be easier with a full tank, but may not be accurate across the whole range.

Remove the instrument pod.
Separate the glass.
Remove the fuel gauge.
On the side of the fuel gauge is a small potentiometer which adjusts the internal resistance.
My gauge always read low and I found that turning the pot a little anti-clockwise raised the reading.
Work using very small adjustments and always know exactly where you started so you can get back there if you need to.
You may need to try a few times and each time you need to reassemble the instruments and reconnect to test them.
After some trial and error I now have a gauge that reads close enough at 1/2 tank and at full

Once you are happy simply reassemble and away you go.

I also note that the other gauges also have these potentiometers so I assume they are all adjustable the same way if needed.

Good luck and cheers.
John
1990 944S2

Van

Some great sleuthing there!

My gauge has always been a little low. But after 11 years, I'm inclined to just live with it. Maybe I'll fiddle with it if I have the instrument cluster out for another reason.

God_Bot

I always wondered about the accuracy of my gauge. It's never read full and I've always be afraid that it would be empty before the gauge read empty.

I don't recall seeing anywhere what the tank capacity is, any know it off-hand? I'll keep this thread in mind when I work up the courage to open up the dash.

tjbreen

Mine read low for years and I ended up buying a completely new sender, which made no difference. I finally fixed it by installing an IceShark power and ground cable kit, as well as cleaning the football shaped contacts on the back of the gauge panel. Did both at once so I am not sure what made the difference but my fuel needle now reads full.

Moving the pot sounds easier but may just be compensating for an increasing resistance somewhere in the system. I have never gotten my temp gauge to behave (won't show anything past horizontal) so I might try using this technique on it.

acorad

fwiw, I just dug into my sender a few days ago (and my car now smells like gas because of it!) and took the sender apart and found that the float was getting caught on the the copper wire w/in the sender when it floated up and that was stopping the float from ever reaching the top.

I also cleaned everything inside the sender (which seemed pretty darn clean already) and cleaned the contacts on the top of the sender.

I haven't filled the tank up yet, as I'm doing some other things as well, but the sender seems to be working better.

Van

'85.5 cars and later had 21 gallon tanks (that's the plastic tank). The early cars had a steel tank which, I think, was like 16 gallons.

docwyte

I fixed mine by installing a V8. With the modern alternator, all the gauges read properly...

ozzie951

Just a couple of extra things. Follow the instructions up to "...instrument cluster (4 screws, 3 cable connectors)". Once out, then go inside your house and find a nice table to put the instrument cluster on face down. Remove all 8 or 9 screws around the outside of the cluster. Don't lift the board off yet. Remove the two nuts that are hold the fuel/temp instrument. The nuts sit on top of a black (almost diamond shape) plastic piece (or U conductors). Then you can pull up on the two U conductors which have two poles underneath. Now seperate the board from the cluster housing and the fuel/temp instrument will be sitting there on the housing all on its own! Take it out and sit the board back on the housing. Re-insert one of the U conductors under the fuel guage, but don't press it all the way in (leave the poles exposed).

Go back to the car. To double check the fuel guage is fine, attach alligator clips to each pole. Hold one alligator clip lead to one battery terminal and tap the other alligator clip lead on the other terminal. If meter does not jump, reverse polarity. Go to the fuel sensor on top of the fuel tank. Wire the fuel guage in series with pin 1 and 3 (pin number shown on the female plug) and -ve battery and +ve battery last. If your tank is full, the fuel guage should read 4/4. If not, then you need to fiddle with the pot as described. IF it reads 4/4, then the wiring between the sender and the guage is faulty.

At this point, take everything off the battery, put the plug back on the fuel sender and take the guage back in the house. Clean all contact points where the U conductors sit on the circuit board as well as the "pins" where the cable connectors go. There are two sets that are parrallel to the bottom and one vertical. The vertical one holds the single 'pin' that goes to the fuel sender. That pin is near the center. I use 'deoxit'... its a fluid filled pen that I use to clean electronic contacts. Clean the contact points and pins. Then screw everything back together and put the cluster back in the car and recable everything. Turn on ignition and check the fuel guage. If you are lucky (like I was), it should now read 4/4 full !!! If not, then there is a wiring problem between the cluster and the fuel sender (bummer).

Hope that helps.

Tom M'Guinn

Great post, thank you! I posted some pictures below to help people visualize. Also, I noticed that the mechanical stops on the needle may need adjustments too. The first pic below shows were the needle stops mechanically on one old gauge I had sitting around the garage -- I could peg it to that point, but not beyond without adjusting the stops. More gauge talk in the thread below...

https://rennlist.com/forums/944-turb...l#post10287516