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Troubleshooting Quantum Tach / ISO cruise diaphragm
by
harpy
on 06 Sep, 2021 22:54
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I got my TD Quantum Wagon running this past week (thanks to those that helped me with head gasket questions). This car sounds better than any VW diesel I've ever run. And the AirResearch turbo really gives it a nice little kick! VERY excited that my engine build worked out, though I'll still be on pins and needles for the next 100 miles I'm sure.
One small inconsequential issue is that the tachometer isn't working. The upshift indicator light DOES work though. This tells me that the W terminal is sending out the proper signal which is received in the cluster, but the tach isn't receiving the signal. Would that be a proper assessment? Anyone have any guidance or tips for troubleshooting the tach and getting it working again?
Also, the car came with factory cruise control, but the rubber cruise control diaphragm actuator is shot. I won't be near a VW yard for a while, so I'm just trying to find someone that has an extra one lying around. I hear they were common in gassers, with different brackets, but I've yet to find a good one. Anyway have any leads on one? Thanks!
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#1
by
ORCoaster
on 06 Sep, 2021 23:32
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You might be able to pull the gauge cluster out of the dash and put a dedicated wire on the tach where the signal goes in. Then hotwire the positive and negative wires on the outside of the car. You should be able to see if it is working at the alternator.
Question though? Was the tach previously for a gasser? If so you need to have the electronics modified to be able to use the tach on a diesel. I have done that on a couple of GTI tachs and I have all the proper capacitors and resistors if you need a conversion done. I bought sets of 10 when I did my first one. The price for 10 was about the same as for 1. Strange pricing policy but that was what they did.
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#2
by
harpy
on 07 Sep, 2021 13:24
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I would think that since the upshift indicator works then the blue wire on the W terminal of the alternator would be fine. I figured it was just something in the cluster itself.
The tach is original to the TD Quantum. Says diesel smack in the middle of the tach. I have another diesel tach cluster that I pulled from a junk yard but I'm not ready to swap it out yet. WOuld love to get a proper trouble-shooting plan together. I could conceivably hook the W terminal blue wire up to the spare tach gauge, right? do I just ground the cluster and hook that wire up to the appropriate terminal?
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#3
by
libbydiesel
on 07 Sep, 2021 17:04
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The tach needs to have 12v, ground, and signal connections. If you confirm that it is receiving all three at the tach, then that would indicate the tach itself is bad.
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#4
by
ORCoaster
on 07 Sep, 2021 22:54
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On the back of the cluster, there are three nuts that go to the tach. One is for the signal, one for 12 VDC and the other is the ground. I think they are all well identified. Use that spare tach, and three jumper leads and prove to yourself it works. Then pull the one in the dash and do the same. If it no, wanna go then you have both clusters out, and swapping the tachs is like a short 20 min job.
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#5
by
libbydiesel
on 08 Sep, 2021 11:17
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IIRC the Quantum does not have 'three nuts that go to the tach' but instead the tach has a plastic connector integral to the blue foil that connects to four pins on the tach (one pin is not used).
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#6
by
33B
on 08 Sep, 2021 15:34
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Libby one question, high rpm oil warning buzzer im missing that from my cluster but have a couple of clusters at home. Can I throw that board in my cluster, i have wiring and blue foil has the connector. It goes behind the Speed gauge right?
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#7
by
libbydiesel
on 08 Sep, 2021 18:16
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Yes, I believe you are correct. The board for the warning buzzer is mounted to the speedometer and if your blue foil has the connector and your speedo has the space it should all swap in fine.