H964

hey guys, i went to the gas station, put 30$ and the fuel guage didnt even move, it stays in the bottom and the light is flashing.
has anyone addressed a simillar problem before?

PC2

It could be your Fuel Level Sender Unit, number 22 on the attached diagram. Try cleaning the connectors and see if that will work.

H964

i will try that tomorrow
thanks a lot

JasonAndreas

If cleaning the pin contacts on the sender and the back of the fuel gauge doesn't work, as a last resort the procedure for checking the fuel tank sender unit with a multimeter is;

1. Hold sender unit vertically, with the threaded flange pointing up:

Reading: 70.1 Ohms to 74.7 Ohms

2. Turn sender unit over; threaded flange points down.

Reading: 1.1 Ohms to 2.5 Ohms

You want to flip the sender unit over rapidly and read the resistance immediately after the float has audibly bottomed out. The one problem with removing the sender unit is Porsche recommends that you DON'T reuse the sealing ring and to coat the new one with an acid-proof grease. The tightening torque on the sender unit is 30Nm (22 ft lbs.)

H964

well i fix it . iam proud of my self.
i ended up taking the #22 part, and took it apart. inside of it, there was a very thin wire that goes around, and it carries a floating sensor. my wire was broken. so i took one off a speaker wire and replaced the old one, and voila, now its working perfectly. no more flashing, and its reading correctly
hope this helps someone

Smokin

I have a flashing fuel light but my gauge reads correctly. I am curious if you needed new gaskets or if not, what type of sealer you used to button it back up?
I'm glad you tackled the job... It always feels good to solve problems like that... Knowing you just saved yourself hundreds of dollars!

John Boggiano

Interesting, thanks.

I thought there WASN'T a float.

H964

well there are so seals in there, when you pull the top plastic cover, it conects to this long round pipe. in the bottom of it, there is small screw, you take it out, and everything opens up. inside you find a very simple mechanism, once you get there iam pretty sure you will figure it out.
iam positive that any shop will charge you an arm and a leg for such a job

Marc Shaw

Well done!

Marc

Smokin

Mike... Thanks for this DIY! I finally got around to taking out my control unit and tank gauge unit today. My fuel gauge worked but my "low fuel" light would flash intermittently regardless of how much fuel was in the tank. I removed the sending unit and took the end cap off as you described. I was surprised how much fine particulate matter (dirt) was built up everywhere. Here's what I did...

Removed the control unit and then carefully unscrewed the tank gauge... Letting all the gas drain out. I then unscrewed the nut holding on the end cap. There are two fine wires running the length of the tank gauge. The float rides up and down on the wires, sending info back to the control unit. My wires were fine. I just cleaned the dirt that I could find, blew it out with compressed air. Then I carefully flipped the tank gauge up-side-down and back to get the float to run up and down over the fine wires. I guess they were dirty... Or the contacts hooking up the control unit were... Anyway... I hooked it all back up and - VOILA!.... No more flashing lights!

I appreciate your posting the info on how you did yours. It made it a lot easier for me to tackle this job!

H964

wow, great to hear, i didnt believe how simple it was to fix and save at least 100$ .
i hope it serves other rennlisters

HiWind

Just what I was looking for thanks - 964 fuel guage float remove service fix fault

Ps - should you disconnect battery or any other safety measure if you open fuel tank?

Richard Curtis

Hmm. I took my part #22 apart a year ago or so, after seeing some of the same problems. But could not find a float (could this have changed over various models? Mine is a '93). I cleaned whatever I could see with brake cleaner, blew everything off with compressed air and reassembled. The gauge worked correctly for several months but now is showing only three quarters full after I completely filled the tank. I've never seen the "low fuel" light.

HiWind

found this on the net (SeanR of Texas on RW) ... useful (tho applies to 1980 pcar) although it seems mostly the same in essence:

When a fuel gauge starts to read empty all the time, the most likely reason is due to a stuck/inoperative fuel sending unit.

The unit is located in the hatch area, under the carpet on the passenger side. Typically covered by a plastic, round cover, that is black (HW: mine is white). Pop that off and you will see the top of the gas tank, the sending unit that has one hose (hw: no hose, just the wires with a connector to top) and a wire connector attached.

To remove the sending unit is very simple, take the hose off (one hose clamp) and gently pull the hose off the unit. By now most of our hoses are close to crap, so be careful. I usually take the clamp off the hose, and then work the hose off the nipple, not putting any bends in the hose. (HW: wasn't necessary)

Pull the wire connector off. From the connector you can actually test and see if it is in fact the sending unit, sometimes it is an actual cluster issue, but chances are it won't be. Take a jumper wire, with the ignition key on, and jump 2 of the three connectors. I don't remember the sequence, but it really does not matter. As you are jumpering, you will see the gas gauge jump to full. This will tell you that the gauge works, and the sending unit does not.

* do not remove the sending unit if you have a full tank, you will end up with over flow, do it with 1/2 tank or less.* (HW: is this true? could be for 964 too. Gonna wait a 100km)

Removal of the sending unit. For the guys with just a basic tool set, take a large cresent wrench, one that will open wide enough to get to both sides of the black/ribbed plastic nut, and unscrew it. Once you get to a high point on the large nut, you will need to unseat the sender either by lifting or twisting, once it is unseated you can pull the sender up a bit and then remove the large nut. (HW: same)

Pull the sender out, above the gas tank level and tip is sideways as you lift it out, you will see the fuel empty from the sending unit. Once that is drained a bit go ahead and pull it out and get it out of the car.

At this point, you can either install a new unit or try to refurbish the old unit yourself.

Once you have the old unit out, at the bottom there is a 5mm nut that needs to come off, pull it and the washer, then pull the funnel off the unit. (HW: this is a far as I got as tank full) Under that you will see another 5mm nut that does not have a washer. Take it out and then gently pry the black plastic cover off the bottom of the sensor.

At this point, the cylinder that holds everything together is free to come off, slide it off gently and you will see why they fail. Massive amount of varnish and corrosion along the return tube, the slider for the float, and the electrical connections. On the one in the pictures, I sprayed a bit of brake clean on it, then took a small file and removed all of the corrosion I could. Cleaned up everything that looked varnished and put it all back together.

You will notice that there are three wires that guide the float, do not kink those, these are what helps give the reading to the gauge. Do your best and make sure the float moves smoothly from top to bottom.

Once the varnish and corrosion are cleaned up, it will give the sensor more life.

Metal Guru

It is but instead of being on a lever arm it moves along the I.D. of a tube. It's a popular design in the heavy truck industry, known for it's durability.
Porsche spec'ed most likely because it didn't have room in the fuel tank to use a lever arm float.