Tach & mileage (efficiency) meter do not work - suggestions?

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Tach & mileage (efficiency) meter do not work - suggestions?

Postby vvurdsmyth » Sat Sep 08, 2012 12:51 am

when I got the car (cheap because of a number of problems, like... ) the tach and mileage meter did not work; sometimes when it is really cold, the tach will show some life, but no where near normal... Bently doesn't have anything about how the tach works; anyone know what the problem is, or could be..?
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby Yoshi » Sat Sep 08, 2012 1:17 am

have you tried punching the cluster panel? Sometimes the connections in the rear are weak. I like to open it up and grease everything, then put it back together. Without the tach, the odo won't work nor will the mpg meter.
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby vvurdsmyth » Mon Sep 24, 2012 4:23 pm

Thank you Yoshi, the cluster panel has been removed several times (speedo gears, and to check connections to the temp gauge); all connections in the cluster were hit with a connection cleaner; Bently doesn't get into it, but where does the tack get its signal..? .. do you know... thinking.. that would be a good place to start.
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby Yoshi » Mon Sep 24, 2012 5:06 pm

tach gets the signal directly from the coil. it's simply 1 wire. It's pretty hard to fuck that one up unless it's cut.
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby M20_fever » Mon Sep 24, 2012 7:27 pm

have you tried another known working cluster?
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby vvurdsmyth » Mon Sep 24, 2012 7:51 pm

Than you Yoshi, going to check out the coil.. and M20Fever... no other cluster to try /~:
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby blasphemy101 » Mon Sep 24, 2012 7:57 pm

Yoshi wrote:tach gets the signal directly from the coil. it's simply 1 wire. It's pretty hard to fuck that one up unless it's cut.


I'm pretty sure the tach signal comes from the DME...
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby vvurdsmyth » Mon Sep 24, 2012 11:18 pm

Thank you blasphemy101, but what is the DME and where is it.. I checked out the coil and there are only 2 wires to it, so if the tack gets its signal from it, there is another connection somewhere... over the BMW rainbow.. (~;
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby Yoshi » Tue Sep 25, 2012 12:40 am

I forget the order but the ECU gets a signal from the coil but so does the ECU. It's a single wire to both.
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby blasphemy101 » Tue Sep 25, 2012 7:39 pm

Yoshi wrote:I forget the order but the ECU gets a signal from the coil but so does the ECU. It's a single wire to both.


The what gets a signal from the what? :P Does it go Coil --> ECU --> Tach, or Tach <-- Coil --> ECU? From going over my MS issues with whodwho, it seemed like the Tach got its signal from the ECU.

vvurdsmyth wrote:Thank you blasphemy101, but what is the DME and where is it.. I checked out the coil and there are only 2 wires to it, so if the tack gets its signal from it, there is another connection somewhere... over the BMW rainbow.. (~;


DME = ECU. Sorry, I use the terms interchangeably.
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby Yoshi » Tue Sep 25, 2012 7:50 pm

When I ran an MS, I ran a single wire to the tach from the main harness. I had no ECU. So it can't go to the ECU then to the cluster. It might split somewhere. I do not know.
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby blasphemy101 » Tue Sep 25, 2012 8:03 pm

Yoshi wrote:When I ran an MS, I ran a single wire to the tach from the main harness. I had no ECU. So it can't go to the ECU then to the cluster. It might split somewhere. I do not know.


Interesting. Is that how it was stock? I'm not saying you CAN'T run a wire from the coil - that's how many tachs get their signal, but it might be an inappropriate voltage. IIRC, pin #32 on the ECU is the tach signal. I'm at work so I don't have the electronic troubleshooting manual, or I would check.
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby Yoshi » Wed Sep 26, 2012 1:05 am

you have the extent of my knowledge sir.
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Re: Tach & mileage (efficiency) meter do not work - suggesti

Postby blasphemy101 » Wed Sep 26, 2012 2:47 am

Yoshi wrote:you have the extent of my knowledge sir.


And you have mine...and I still don't know who's right! -dizzy-

vvurdsmith - the electronic troubleshooting manuals will be your friend in this project. Another option - could the batteries in the service indicator light board be going bad? Many of the signals for the instrument cluster (tach included, I believe) go through that board. Weak or failed batteries can cause all sorts of issues with the instruments.

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