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'91 744 Fuel Level Sending Unit 700 1991

posted by  145Guy on  Mon Jan 18 05:31 CST 2010
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last visit: Wed Mar 14 07:46 CST 2012
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So, I just got out the fuel sending assembly out of a recently acquired '91 744.
The previous owner had a "reputable" garage install a new regina fuel pump. The fuel guage worked before the pump was replaced.

The car ran no problem, but the fuel guage was at empty and the red light was driving me nuts. I had to fix it.

Well, whoever did the job didn't bother pulling the harness through the rubber grommet, they just cut all the wires about 6" from the sending unit. Now that would be ok, but when the put the unit back in, they wired the white/grey & brown wires FROM the sending unit together, and somehow then tied into the same wires on the harness side. Needless to say it was a mess, and they used WIRE NUTS to splice the stuff together, and then sloppily wrapped the entire mess up with duct tape and then over that, electrical tape. At least they got the fuel pump and ground wired to the correct harness wires. Of course they neglected to address the big crack in the pump wire about an inch from the top of the outside of the sending unit....left it totally exposed and only half of the wire strands were still connected.

To my dismay I troubleshot it down to the sending cylinder itself....oh, and the morons didn't solder wire to the two terminals, they clamped a butt connector to it with wire clamped on the other end.

I pulled the canister apart to find that the little criss-crossed contacts had slipped and were only touching one rod, and the windings on the top of one rod were coming loose to boot.

I took them out, re-wrapped the windings superglued with a glue that petrol doesn't break down. Had to re-bend those little crossed contact setup...which took quite a while to get just right so they rode upon the rods with solid contact and didn't get jammed up. Put the canister, float, rods back in to test the movement of the float.

Aha, the float jams part way....took back out, discovered I had slightly bent both rods when disassembling it the previous time, so I had to very gingerly roll the rods to find the humps and tweak them straight.

Got the assembly back together, float moves freely, contacts looked good when I put the float in....ohmmeter tests from top to bottom.

Test in car just hooked up to harness leads to top of terminals = success!!!!!!!!!

It's strange how slowly the guage reacts to movement of the float, but I guess that's due to the balast resistors that are used to smooth out the needle on the guage....I remember bypassing those resistors for the temp guage on my '86 240 to get more accurate readings and no more shorts.

Now I've got to put the assembly back together (correctly this time), install it and hope it still works......

Just my 2 cents worth, and despite the royal pain in the posterior, well worth saving the ton of money to have to buy an entirely new assembly.







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    '91 744 Fuel Level Sending Unit 700 1991

    posted by  way2kool on  Mon Jan 18 12:52 CST 2010
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    last visit: Fri Dec 27 11:16 CST 2013
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    Congratulations on your successful repair. Your description of how to repair the broken tank level sender is well done. I might have to tackle this on mine.








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      '91 744 Fuel Level Sending Unit 700 1991

      posted by  145Guy on  Sat Jan 23 10:46 CST 2010
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      last visit: Wed Mar 14 07:46 CST 2012
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      Well, it actually took until today for the total fix to get accomplished. Found a great sealant for the banjo fittings. Indian Head Gasket Shellac from Permatex. It's like molassess, but a very thin coating works like a charm.

      I used it on the sending unit tank gasket as well, but after I PB Blastered the seal two days before and let it sit. I also used it around the electrical fittings where the wires pass through the plastic block into the sending unit and on the butt-connectors I put on to hook up the sending unit and where the outside harness was reconnected. I've found it doesn't affect continuity and it's so gross that it'll keep anything out of those little crevices.

      As for the final fitment, the note on the walk-through here on the FAQ section for 700's says to use a string and a wedge to push the level sender up when inserting into the tank. I didn't have the opportunity to try that but got the unit in just fine, however, I'm wondering if I tweaked the level sender cylinder just enough to only get my guage to go to 7/8's of a tank. It's tough to say now, but when I refill the tank I'll know for sure if the sender unit is working completely properly. Either way, I'm not doing it again. Being 6'3" and in the trunk in 30 degree weather is just awesome.







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