Pelican Mini-Technical Article: Repairing the Fuel Tank Sending Unit

Search our site:

Originally posted to the PorscheFans mailing list, and written with the 911 in mind, this procedure can be used on other cars as well.

You may remember I posted last week about my fuel gauge which was stuck at the half way point no matter how much fuel was in the tank. Judging from the amount of mail I received this is a really common problem.

Today I removed the unit, disassembled it and gave it a clean, as well as cleaned the electrical connections and it now works perfectly. These were the steps I took:

Removing the sender unit.

1. Remove carpet from trunk. This is needed as the fuel can leak from the sender during removal. Place fire extinguisher within easy reach. Also, be sure to carry this procedure out in a well ventilated area.
2. Place towels inside trunk around sending unit to soak up any leaked fuel.
3. Unplug electrical system plug.
4. Remove filler cap to let pressure out of the system. (I don’t know if this is required but I felt better about relieving the pressure at the filler cap rather than when undoing the bolts holding the sender in)
5. Remove the five 8mm nuts securing the sending unit.
6. Gently lift sending unit up from its position. I made sure to lift very slowly to allow the fuel to drain from the unit back into the tank rather than into the trunk.
7. Stuff a rag in the now empty spot where the unit was to stop the fuel vapors escaping and to insure against any dirt or pesky type rodents entering the fuel cell.
8. Check sending unit gasket to see if it’s in good enough condition to use again. Mine was.

Disassembly:

The sender is a long cylinder, about 300mm in length and 40mm in diameter with electrical connectors at the top and pin holes to allow the fuel to enter the unit at the bottom. It’s secured by a 4mm nut and locking washer at the bottom.

9. With needle nose pliers, bend the small locking washer flat so you can access the nut to remove it.
10. Slide the float assembly from the housing.

Cleaning the Unit:

It has one thin wire which runs the length of the unit and then back up the other side, as well as a copper earth wire. In fact, the long thin wire looks like two different wires but it crosses from one side of the assembly to the other. This wire supports a cork like float with two electrical contacts that touch each side of the wire. The unit measures the resistance of the electrical circuit depending on the location of the float. There is also a contact at the bottom of the unit that the sender closes to activate the low fuel warning light.

11. Check the integrity of the active wire. The float should move freely up and down the wire. Also check the solders at each end where the wire connects for both the active wire and the earth. My earth was very dirty with what looked like some type of corrosion. If the float or the wires are damaged, you could try to fix them or maybe the easier path would be to order a new sender unit (p/n 901.741.801.00) as it’s quite delicate in there.
12. Lightly sand the active wire and all the contacts with some emery cloth or fine glass paper, being careful not to rub too hard.
13. I then lightly sprayed the wires and contacts, as well as the outer electrical contacts where the lug connects with some WD-40 then left it to dry.

Reassembly:

14. As per disassembly. The float assembly is keyed to the housing by a notch at the top so you can’t assemble it incorrectly, though I can’t see what difference it would make. I guess it’s there for a stronger join. Remember the locking washer before fastening the nut.
15. Reinsert into fuel tank and tighten the five 8mm nuts.
16. Clean the connection points on the plug. I used a cotton bud (I think they’re called q-tips in the US) dipped in WD40 and pushed it into the three connector holes. It came out filthy dirty so I think this was quite worthwhile.
17. Attach plug to connector on sender unit.
18. Reinstall trunk carpet
19. Turn on ignition and see the fuel gauge jump to the correct reading!

This process is not going to be the panacea for every fuel gauge problem, but it’s probably something you should do to at least get a better idea of what might be causing your problem

Terry Steer
1980 911SC Petrol Blue
terry@rpm.com.au

Comments and Suggestions:

Bob	Comments: Good how to article. I have repaired a few by doing this. The one step I would add is to bench test the sender with a multimeter attached. As you move the float the resistance on the meter should increase or decrease smoothly. I have encountered ones with dead spots that couldnt be repaired. Bob.
December 14, 2011

Davey Cracker	Comments: Thank you, Terry! My fuel gauge now works. ;
October 23, 2011

silverstorm	Comments: Hi There..My car has a problem where the fuel gauge sometimes gets stuck on empty and even after shes been re-fuelled so would this proceedure be the same on my car too ? Its a 2003 911 C2..
September 26, 2011

johnstahl	Comments: I remove my sending unit and the fine wire was broken. So I have 3 questions what is the size of that very thin wire and what it is made of. Last question is how is the wire routed at the oposite end of the solder points? I assume it should not touch the threaded rod that holds the casing on, correct?
June 29, 2011

Hambone	Comments: Where can I get the wire that runs down the sender then up the other side? Oh and what type / size wire is it. Don't want to put the wrong thing in there turn my sender into a toaster and Kaboom! JH
May 7, 2011

Hollywood D	Comments: I tried to replace the gasket on my sender '83 but it's stuck inside the tank. I pull it all the way out and theres somethig on the end thats catching. Not sure what it would be. I don't want to force it out because it works fine, I just need to put a new gasket on.
March 2, 2011
	Followup from the Pelican Staff: The only thing that could be on the end of the sender is some corrosion - the sender should be a straight fit into the tank. Pulling it out might release that corrosion into the tank though - I would run the tank down as low as possible, and then pull the sender - then clean out whatever is left behind. - Wayne at Pelican Parts

John	Comments: can the printing format be made more paper friendly? Maybe in 2-column form?
December 4, 2010

chuck	Comments: I am installing a fuel pump on a 1988 944porsche. I got the old unit out without any problems but upon reinstalling i found out the the wires are color coded. I have a brown and also a black and green. Which wire goes on the positive and negative?
June 16, 2010
	Followup from the Pelican Staff: I'm not 100% sure, but on almost all Porsches, the brown wires are connected to the battery ground. - Wayne at Pelican Parts

redbaron3d	Comments: don't forget to replace the cork gasket whenever removing the sender, our host has them cheap. a little gas smell vapour leak can really stink. Also I think the outer shell may be aluminum . mine was super light , if so will not be able to grab it with a magnet.
May 16, 2010

Sonny	Comments: My fuel sending unit was not working,when I removed it the outer housing was no where to found. I assume it's somewhere in the tank, any segestions on how to get it out, I'm hoping it's a metal casing that can be grabbed by a flex magnate
February 6, 2010

justforfun

Comments: Good suggestions. My gauge was stuck @ 1/4 , but by removing the sending unit and cleaning it fixed the problem. The only other thing I did was to test the unit prior to reinstalling it into the car to confirm it was not the gauge.One way to test is to plug the unit in turn on the ignition, check at full, empty and a position inbetween not really a good idea since gas vapors are involved. The other is to use a volt ohom meter and check the resistance change across the unit as the float moves.

October 29, 2009

JJ 911SC	Comments: Had the same problem when I got the car 3 months ago. The previous owner was using Esso Gas. I switch to Shell V Power with Nitrogen Cleaning agent and sure enough a month ago the needle went all the way up. J.J. http://www.pelicanparts.com/gallery/JJ_911SC
September 15, 2009

harry	Comments: it begins to start but then immediatly cuts off. so it wouldnt be the battery
July 24, 2009

Harry	Comments: my 1985,1 944 turns over great and begin's to start but will not start all the way. Do you think that the fuel sender might be the cause of this?
July 23, 2009
	Followup from the Pelican Staff: Nope, the fuel sender has nothing to do with the starter circuit. Try replacing the battery and/or the starter as a first step. - Wayne at Pelican Parts

Search our site:

Guest Technical Article:

Repairing the Fuel Tank Sending Unit

Repairing the Fuel
Tank Sending Unit