Fuel Gauge Stuck on "Full"

[espooner]

uel level gauge not working in 2002 Boxster S 2002 Boxster S with 45,000 mi.

While at Watkins Glenn Intl. last weekend, my gas gauge started acting up. It read "full" all day, when normally it is on empty by the end of the day. Turning car off and on had no effect. Filled the tank that evening (14 gallons). By the end of the first run the next day, it read 3/4 full, and was working normally. 2 hours later, it reads "full" again, and has done so since then, even after driving 225 miles back home.

My Bentley repair manual states that the fuel level sensor and fuel pump are all in one, and cannot be replaced separately. The part alone is $372 from Pelican Parts. I don't want to buy it if the gauge itself is the problem.

Before sending for one, is there any testing to do to CONFIRM that it is a bad sensor, rather than a bad gauge? It would seem that as the gauge goes full scale, and at least once read 3/4 full, that it is not the problem. Should I smack the pump/sensor with a rubber mallet to free a stuck float? Anyone have any similar experience?

All replies welcome.

Eric Spooner

[N41EF]

Warning, don't set your car on fire or blow your self up!

It would be possible to remove the battery, the plate and pull the sender out of the tank and power it up and move the sender to see if the gage responds. With the battery removed you'd need a charger or something to power the car whn you turn it on. Remember that to do this your fuel tank is open with a hole about 6 inches in diameter. A less explosive test would be to remove the sender and use a resistance meter to see if the resistance is linear as you move the sender.

When you turn the car off does it drop? Then go to full when you turn the car back on? Or is the needle always full?

I'd check Sunset as well as pelican, I got mine fron sunset because pellican wasn't in stock, the 03 has a seperate pump and sender, so it was cheaper. You may need to find the stupid tool on line to remove the sender, it has a large black plastic lock ring, Mine was less than finger tight when I replaced mine, I tightened it with a strap type oil filter wrench.

[espooner]

Thanks for the suggestion. The gauge needle drops to zero when ignition is off, so I think it is OK, as you imply.

I guess I'll take a look at the pump/sender unit. I think I would probably use a volt-ohm meter to check the resistance change, but don't know which pins to measure across. I assume black = ground and brown-white or red is power, but have not investigated the wiring diagram in the Bentley manual. It also says nothing about how to get to the tank/fuel pump, or how to remove it. I assume from the pictures it is a twist-lock ring - maybe ? I'll try the strap wrench (I have two sizes).

Thanks for your input.

Eric

[N41EF]

The strap wrench I used was a cloth strap wrapped with a one inch square fitting, it came from harbor freight. On the 03 there is only one electrical plug that sends power to the pump and the gage uint. I can let you know what pins or wire colors to check. I'd suggest, in this order:

1. Remove the sender and just play with it, see if it feels smooth through it's range of motion.

2. Resistance check, easier with an analog ohm meter, measure resisteance across the sender as you move it, looking for a smooth somewhat linear arc.

3. Power it up removed and move the arm. Very dangerous.

When you remove it do so in an open garage or well ventilated area, and have one or more fire extinguisheds handy.

As an after thought, it sounds like the gage is working, I'd just order one and replace it. Replacing it is probobly a 2 hour ordeal assuming you can get the lock ring loose.

[casperlabs]

I would like to pass along a recent experience that may help explain a lot of erroneous fuel level indication issues. My 986 has always been in the South, and subject to long periods of storage. The fuel level indicator moved in large increments rather than gradual change with fuel consumption. When the sender was removed for check out, the float arm was found to stay in any position it was placed in (could not fall of its own weight). Closer examination of the steel rod that the arm is made of, revealed a uniform layer of tan colored oxidation over the entire length. The arm can be pulled by opening a couple of snaps, and sure enough, the oxide extended into the pivot bushing hole.

After scraping the oxide off with a pocket knife, and polishing the pivot area with crocus cloth, it was reassembled and found to pivot perfectly. Problem solved!

The 10% ethenol in our gas can hold up to 40% water (by volume ) in suspension and still burn! Just because you cannot see water in the fuel does not mean it is not there. (Do a wikipedia on ethenol for more info.......dry gas is just ethenol) The high relative humidity here in FL just adds to the problem,..... if you don't drive the car and get the fuel cycled thru..

The oxide is probably zinc oxide, coming from a protective coating put on the bare steel arm. It was tan instead of white because of the fuel dye used in motor fuel. The arm should be recoated to prevent rust accumulation in the future. I used a fuel proof epoxy. Nickel, copper, or chrome plating would be better, but perhaps anal on a used car.

Yet another reason why ethenol is better in your favorite beverage than in your mogas.

If you want to check out your float, read Wayne Dempsy's article on fuel pump replacement in the Pelican Parts web site.

His safety emphasis should be heeded in this potentially dangerous part of your car. The job is not very difficult, but I do take strong exception to one step he describes. He advocates removing the tank unit retaining collar with a big screwdriver and a hammer. This is for complete hacks (sorry Wayne, you must have missed that class at M.I.T.). You can do far more expensive financial damage with this method,.... than a trip to the dealership. Buy or make a tool. It took me an hour to make a nice one. This is the same unit in the 996,.... by the way.

Bill Ryan

Casper Labs

[Jager]

I would like to pass along a recent experience that may help explain a lot of erroneous fuel level indication issues. My 986 has always been in the South, and subject to long periods of storage. The fuel level indicator moved in large increments rather than gradual change with fuel consumption. When the sender was removed for check out, the float arm was found to stay in any position it was placed in (could not fall of its own weight). Closer examination of the steel rod that the arm is made of, revealed a uniform layer of tan colored oxidation over the entire length. The arm can be pulled by opening a couple of snaps, and sure enough, the oxide extended into the pivot bushing hole.

After scraping the oxide off with a pocket knife, and polishing the pivot area with crocus cloth, it was reassembled and found to pivot perfectly. Problem solved!

The 10% ethenol in our gas can hold up to 40% water (by volume ) in suspension and still burn! Just because you cannot see water in the fuel does not mean it is not there. (Do a wikipedia on ethenol for more info.......dry gas is just ethenol) The high relative humidity here in FL just adds to the problem,..... if you don't drive the car and get the fuel cycled thru..

The oxide is probably zinc oxide, coming from a protective coating put on the bare steel arm. It was tan instead of white because of the fuel dye used in motor fuel. The arm should be recoated to prevent rust accumulation in the future. I used a fuel proof epoxy. Nickel, copper, or chrome plating would be better, but perhaps anal on a used car.

Yet another reason why ethenol is better in your favorite beverage than in your mogas.

If you want to check out your float, read Wayne Dempsy's article on fuel pump replacement in the Pelican Parts web site.

His safety emphasis should be heeded in this potentially dangerous part of your car. The job is not very difficult, but I do take strong exception to one step he describes. He advocates removing the tank unit retaining collar with a big screwdriver and a hammer. This is for complete hacks (sorry Wayne, you must have missed that class at M.I.T.). You can do far more expensive financial damage with this method,.... than a trip to the dealership. Buy or make a tool. It took me an hour to make a nice one. This is the same unit in the 996,.... by the way.

Bill Ryan

Casper Labs

Hi Bill,

Do you have a photo of the tool you made?

[casperlabs]

I am traveling, and did not take a picture at the time. Can do so after getting back, if you give me an email. There are many ways you can make this tool (a number of designs are evident in the ones sold on ebay). I had a worn out diamond saw blade disk that was the same diameter as the tank ring . I then cut 4 pieces of 1.5" angle steel 3/4 " wide. One side of each angle was slotted 3/4 inch deep about 0.150 wide (to engage the raised ribs on the retainer OD). The angles were then spot welded to the disk 90 degrees apart. If you don't weld, bolts could be substituted. In the center hole of the disk, an old 3/8" sq. drive socket was welded for wrenching. You could also just put a big bolt and nut in the center. What ever you make, it needs to be stiff. Otherwise it will pop off the relatively small drive lugs (which are very soft plastic).

BR

[Jager]

I am traveling, and did not take a picture at the time. Can do so after getting back, if you give me an email. There are many ways you can make this tool (a number of designs are evident in the ones sold on ebay). I had a worn out diamond saw blade disk that was the same diameter as the tank ring . I then cut 4 pieces of 1.5" angle steel 3/4 " wide. One side of each angle was slotted 3/4 inch deep about 0.150 wide (to engage the raised ribs on the retainer OD). The angles were then spot welded to the disk 90 degrees apart. If you don't weld, bolts could be substituted. In the center hole of the disk, an old 3/8" sq. drive socket was welded for wrenching. You could also just put a big bolt and nut in the center. What ever you make, it needs to be stiff. Otherwise it will pop off the relatively small drive lugs (which are very soft plastic).

BR

Bill, I sent you a Private Message