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Stupid Fuel Gauge 900 1993

posted by Milanomike on Sat Dec 7 09:30 CST 2013
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last visit: Sat Oct 11 22:27 CST 2014

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OK, this fuel gauge is a pain, would like it to work, say 75% of time for daughters who drive this machine.

I've reluctantly considered the solder technique mentioned in the FAQ, but am not confident I won't melt the flexible plastic circuit board. So, I was thinking hey, why not conductive electronic paint under, at and over top of the 3 screws?

Anyone been there with this idea? I've had good ideas before that were bad ideas....

Mike

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Stupid Fuel Gauge 900 1993

posted by Milanomike on Mon Dec 9 12:37 CST 2013
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last visit: Sat Oct 11 22:27 CST 2014

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Thanks guys, I 'll give it another go once weather warms up a bit.

Mike

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Stupid Fuel Gauge 900 1993

posted by Mike91 on Mon Dec 9 14:27 CST 2013
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last visit: Wed Sep 17 19:52 CST 2014

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I have 93 and 94 940s. Both of them had fuel gauge failures caused by these problems:

1. The flex circuits on the back of the Yazaki cluster can fracture. These can be fixed by resoldering and possibly adding jumper wires. Fractures are not necessarily at the fuel gauge screws. I had to use an ohmmeter (cluster unpowered) and voltmeter (cluster powered on workbench) to discover and fix all the fractures. See the FAQ and link to Turbobricks.

2. The fuel gauge itself contains a circuit board with soldered parts. Some of the solder joints can fracture and must be resoldered. I removed the gauge and resoldered every thru-hole connection on the circuit board.

On my cars, both of the fixes above were necessary to restore the fuel gauge operation. I would look for problems with the Yazaki cluster flex circuit first. It is possible to test the instrument cluster with the cluster sitting on a workbench. A 12v power supply and some resistors to simulate the fuel sender unit are needed. That is how I discovered and fixed the fractured Yazaki flex circuits.

If you are concerned about soldering, perhaps try to find an electronics hobbyist who is familiar with the use of a small soldering iron.

It is helpful to connect an ohmmeter to the ground and fuel gauge sensor wires at the instrument cluster electrical connector. Make sure the resistance of the in-tank fuel sender unit is stable (see the FAQ). This rules out a fuel sender unit or wiring problem.

Regards,

Mike

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Stupid Fuel Gauge 900 1993

posted by dinomartino on Mon Dec 9 07:57 CST 2013
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last visit: Fri Oct 24 04:43 CST 2014

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I've used conductive paint (out of a defroster grid repair kit) to repair broken traces on my 1993 Yazaki cluster with good success. If there's a broken solder joint where a component attaches to a trace, I'm not sure that conductive paint will do the job, as the part can still wiggle within the solder blob and cause an intermittent connection or a higher resistance one--the paint doesn't have the mass to immobilize the part like a large contact patch of solder would.

Reflowing the solder is a better bet, although you are right to proceed with caution doing it. And the other suggestion, about removing the screws and GENTLY cleaning all the contact areas, is spot on. After 20 years, the connections benefit from a little freshening up.

john
--
1989 245 245K / 1993 945 131K

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Stupid Fuel Gauge 900 1993

posted by dm960 on Mon Dec 9 09:31 CST 2013
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last visit: Fri Oct 24 06:41 CST 2014

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Like Dino, I used the paint to repair contact to a light on my old '78 BMW bike. It is a flex board tucked in the inst. cluster and I'm sure hitting it with a soldering iron would have damaged it. It's very fragile.

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Stupid Fuel Gauge 900 1993

posted by ktuuri on Sun Dec 8 16:27 CST 2013
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last visit: Tue Sep 30 23:32 CST 2014

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I have brought on back to life just by removing the 3 screws and cleaning the screws and broad under the screws with deoxit.

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Stupid Fuel Gauge 900 1993

posted by HillBilly on Sun Dec 8 12:07 CST 2013
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last visit: Thu Oct 16 08:26 CST 2014

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I've tried the solder repair on my wife's 94 model 940 with no success.
I was able to reflow the solder with no problem but the problem is apparently somewhere else.
She has to tap on the fuel gage with the end of her hair brush to get it to work.
It will drop at random.

You should try the solder repair.
It's not difficult if you have a small pen type solder iron.
The #1 rule to soldering is to allow time for the solder iron to reach full temperature before soldering.
The #2 Rule is to know when good enough is good enough...aka....knowing when to quit.
Flow it once then stop.

Just my opinion
steve

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