Gas gauge is stuck

[stangGT97]

The gas gauge on my '98 has been stuck at full since I bought it back in May. I've just been living with it, assuming it was something to do with the fuel pump module which would be a pricey fix. Then something weird happened today (outlined below)
1. After replacing my coil packs on Thursday, the stupid 'Theft' warning kept coming up on me. The battery had been disconnected while I was performing the service and for about 1/2 hour after.
2. Today, without warning, the car just would not start when I was trying to leave the grocery store. The radio had reset itself (clock and all settings) and the starter wouldn't crank at all. Oddly enough, in this condition, the gas gauge moved from the Full mark to where it should have been given the # of miles driven. Cycling the ignition back and forth kept moving the needle, although the car appeared to be immobilized (probably related to the Theft light flashing at me for the past few days).
3. Luckily I had a 1/4" ratchet and 8mm socket still in the console so I just reset the battery and the car fired right back up.
4. Now the gauge is back to being stuck at Full.

I'm puzzled. I did find a mouse nest in where the spare tire is, so maybe one of those critters chewed out a wire which is causing a short somewhere. Any ideas??

Thanks!

 

[wmburns]

IMO the problem is in the fuel sending unit located in the gas tank.

There is a limited amount I can do for you because my Ford reference CD that covers the 96-98 model years will not let me copy/past diagrams.

Connector C420 should be near the gas tank right side. The V/W and BK are from the sender. Disconnect the connector and measure the resistance. This should be the fuel level.

I am having trouble reading the diagram but I believe it says 224 Ohms empty and 150 Ohms full. Report the results.

If the readings from the sender look OK, then the problem is in the cluster.

Also, if you are handy, you could try going to Radio Shack and get a variable resistor. This could take the place of the fuel sender. By varying the resistance you could confirm if the cluster guage works.

I think it may be necessary to drop the tank to replace the sender.

It may be a good idea to get your own Ford Service CD off of ebay. They are not very $$. The diagrams will help you a lot to trouble shoot this problem. This goes double if needing to make repairs after rodent damage.

 

[stangGT97]

OK thank you for the suggestion. I'll see if I can get under the car this week to take those measurements. As far as the rodents go, the only place I have found nesting is in the trunk by the spare tire, so I am optimistic that they did not do much damage.

FYI, if you need to copy a picture, you can always hit the Print Screen key on your keyboard, then paste the image into Microsoft Paint and save it as a JPEG. Thats how I circumvent copy protection lol