Before you blame the Sender..

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Southernboy
Joined: Thu 07 Oct, 2010 13:39
Posts: 6414

  Z3 roadster 3.0i
Location: Johannesburg

Before you blame the Sender..

Post by Southernboy » Thu 20 Sep, 2018 12:53

I bought a project Z3 around January time. I drove it from Cape Town back up to Johannesburg without a functioning fuel gauge... scary stuff with lots of fill up stops.
Since then, I have had the fuel pump / sender out no less than a dozen times. A previous owner had obviously had a go at sorting out the common Z3 / BMW fuel gauge issue - erratic or non functioning display on the cluster. In the process he had broken one of the small clips which holds the housing carrying the float arm and ceramic card sensor. When I first removed the unit, I found a cable tie holding it to the main body housing the actual fuel pump..
I bought a new replacement ceramic sender card, and using a broken unit for the part that holds the ceramic card and the float arm, I replaced the plastic clip on housing which holds those components.
Prior to buying a new ceramic card, I had had the pump out to replace the broken housing as described above, I refitted the unit but still had a zero reading on the cluster gauge. After several attempts at cleaning the original card with rubbing alcohol and using 2000 grit paper on the two little sprung contacts which ride across the ceramic card, I still had a flat liner... That's when I decided to replace the ceramic card.
When that arrived, I pulled the unit again, fitted the new card and..... still no cluster reading.
Pulled it again and found another assembly error from the previous owner. The two sprung contacts have a very specific way of being housed - he hadn't refitted them correctly. So, that sorted, I re-fitted the unit, but again nothing.
Today I pulled it for the last time. I had checked all the connectors, the wiring from tank to cluster and the ceramic card for correct operation and resistance reading on my multi-meter. Everything was working including the cluster gauge which I had taken in to a specialist repair shop for testing.
Finally I had a good look at the fully assembled unit, and I noticed on the inner side, there is a small round plastic button covering a little rubber diaphragm. I popped the little button off, removed the rubber bit and managed to easily thread a piece of cotton through the hole which emerges at the upper hose connection on the outside of the unit. I then tied the inner side end of the cotton to the float and popped the unit back into the tank.
I didn't replace the screw on nut thingy, but lined it up as per the mark at the bottom, and pulled on my piece of cotton which raised the float arm inside the tank.
The cotton managed about 20mm before the float arm got stuck inside the tank.
That was the beginning of 3 hours of trial and error bending the float arm one way then another and checking by putting the unit back into the tank each time to check if it would move freely.. finally I found the right combination and for the first time since I got the car I have a fully functioning fuel sender. Cluster gauge is working 100%. I checked by filling the tank in 4 stages.. 1/4 at a time and each fill reflected the correct reading on the cluster.
Unfortunately I can't post any pics to illustrate the required bends, but if anyone else is suffering you can PM me an email addy and I'll mail you a "how to" with a photograph of the required bend alteration to the float arm.
"Normal is overrated"
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Gazza
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  M roadster S54
Location: Romford Essex

Re: Before you blame the Sender..

Post by Gazza » Thu 20 Sep, 2018 21:51

10/10 for persistence

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"Understeer is when you hit the wall with the front of the car, oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall and torque is how far you take the wall with you"

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BonBon
Joined: Tue 08 Jan, 2008 21:10
Posts: 1195

  Z3 roadster 1.9

Re: Before you blame the Sender..

Post by BonBon » Mon 08 Oct, 2018 11:34

If you look carefully at the tank you may find that it deformed over time and the plastic wall is interfering with the arm. I saw scratches on the inner side of my tank done over the years by the arm.

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Southernboy
Joined: Thu 07 Oct, 2010 13:39
Posts: 6414

  Z3 roadster 3.0i
Location: Johannesburg

Re: Before you blame the Sender..

Post by Southernboy » Mon 08 Oct, 2018 12:00

That's exactly what was happening inside my tank - the arm was catching.
However, I doubt the tank has deformed, although I admit it may be possible in a very hot climate.
On the pump / sender unit you will see that the float arm pivot shaft fits into a plastic tube housing. These 2 parts actually wear and the arm becomes quite floppy, which allows it to eventually catch on the inside of the tank. I considered making a thin bush to compensate for the wear, but since the shaft and it's housing are somewhat conically tapered, this becomes tricky because a perfect arc of material needs to be cut so that the two ends mee cleanly at the join, or a perfectly machined bush with the correct taper is required. Machining is a non starter since the thickness of the bush would need to be no more than the thickness of the wall of an aluminium Coke can, which is probably about 1/8mm thick.
I considered using a washer to make the wire arm push the shaft into the tube so the taper would fit more snugly, but this is also not possible - the wire arm is pretty much held in position by the plastic clips of the swivel part and won't allow as much benefit as I needed... Anyhow, the only practical remedy is adjusting the arm and float position so it can move freely given the wear of the pivot shaft and tube.
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