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lazy fuel gauge and broken odometer, '92 325ic

Discussion in 'E30 (1984-1993)' started by Moonbeem, May 28, 2008.

    Moonbeem guest

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    The fuel gauge on my car reads full whenever I get in (wouldn't that be nice!) then reads accurately (I think. I tend not to let it get much lower than half full) after 15 minutes or so. In the meantime, is the "range" feature on the obc an alternate way to judge tank contents? Is there a fix for this?,

    Without a working odometer and trip meter, I don't really have a way to tell how much fuel I have in the tank. Any suggestions?
    Thanks.
    Steve
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    az3579

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    I would consider that 'normal'. I replaced both my SI board batteries, fuel gauge, AND my fuel sending unit and it does that to me occasionally, just not 15 minutes but instead like 5.

    I would consider your fuel gauge to be working properly. There are other things that these units tend to do that are much worse, like when mine read full at all times, even when the low fuel light was on! (before I replaced everything)
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    Brian A

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    OBC gives reasonable estimate of remaining range

    Regarding the OBC "Range", if the system is working properly the OBC provides a good estimate of remaining miles of fuel. Likewise, the Average MPG is accurate too. The OBC uses the average MPG plus the fuel level to estimate remaining range. At least for my car (a 1987 325ic), there is less than 1/2 gallon left in the tank when the OBC shows 0 miles range (ummm, ... yeah, I've "tested" it). I believe these are all calculated independently from the analog gauges in the instrument cluster.

    There are also hidden functions for the OBC. For your car, if you push the "10" and "1000" buttons simultaneously, and follow the steps in the below document, I believe the OBC will show "fuel in tank".
    http://www.bieveien.com/home/bmw/obc/obc_tips.htm

    Moonbeem guest

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    lazy gauge

    Thanks, guys. I talked to a tech guy at Bavarian Auto, who suggested replacing the circuit board. He said its a straight forward job and the board for my model is only about $110. after you get the core charge back. He said the ni-cad batteries go and can damage other stuff on the board. I'd like to repair the odometer anyway for maintenance purposes. It'll probably wait until I take 'er off the road for the winter. I'm having too much fun driving right now!
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    Brian A

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    You can also just replace the SI board batteries

    If you keep your old Roundel's, check the May 2007 issue for my article titled "Move 'Em Out!". Its relatively easy to move the batteries off of the Service Indicator circuit board and reuse the existing board. Depends on how much you like doing stuff like this.
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    az3579

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    Not if they're soldered in... if they are, they're a bit more trouble than it's worth to take out and replace. If he can live with $110, then I would say by all means go for it. That would guarantee that there are no problems with the SI board and batteries, which might help him diagnose if the fuel gauge is still FUBAR.



    But if you're unlike me and you actually like desoldering things, then by all means go for it. Just remember, you're gonna have to get the batteries online somewhere because RadioShack does not carry them, and I've tried before, trust me.

    Moonbeem guest

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    Yea, I'm inclined to replace anything that' exposed/easily accessable on my car thats original (16 years old).
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    Brian A

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    I'm not sure we're talking about the same batteries. On my car - a 1987 325ic - the Service Indicator circuit board has two plain old AA size NiCd batteries soldered onto it. I've replaced them (and now moved them to a remote location) with AA size NiMH batteries with no problems. Maybe modern replacement boards have something different than the original AA size.

    No matter what the size, I agree though that its a question as to whether or not one thinks all that work is worthwhile compared to shelling out the $110. I have a main battery kill-switch installed in my car, so really tramatize my SI batteries when I cut the power to the car for extended periods. I can now change the SI batteries in a couple of minutes without taking anything apart.
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    az3579

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    That's strange. My batteries are really short and nothing like AA batteries.

    Why on earth did BMW use different size batteries in their E30's? What gives?
    My old board had the really short batteries. My new board has longer batteries but they're still not AA's. You say you have AA's... :confused:
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    AWuorinen

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    I brought my board to a Batterys Plus store, and they soldered in the new ones for under $20. They have a special soldering gun that makes the job look easy.

    Bob Balbirnie guest

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    I have had this wonky fuel guage experience on more than one E30 and it seems that somehow the connection to the cluster that connects the fuel guage to the sender becomes less than desireable. I removed the instrument cluster from the dash, disconnected all wiring then removed the fuel guage and re-installed which solved the problem. It was not related to the SI Battery failure, in my experience, which initially made the Tachometer fail to function properly. I did not let it go futher than that.

    Cheers and good luck, Bob

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