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Old 19-04-2012, 07:01   #1
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GM 8v71 Tacho problem

I have a Detroit 8v 71 2 stroke diesel which runs well. The issue I have is the tacho under reads the engine revs. At full noise, it shows about 1400 rpm and the needle appears very sluggish. I would like to check the connections but I can only locate 1 wire which runs off the alternator. Does anyone know where the other wire is connected to? I guess if the other connection is fine then I have a dodgy tacho.
Any advise would be greatly appreciated.
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Old 19-04-2012, 07:43   #2
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Re: GM 8v71 Tacho problem

Your tachometer probably has a “range selector switch”, which adjusts for differing numbers of flywheel teeth, and must match your flywheel.
The Proximity Sensor (on Bell housing) may have a Grey wire, which goes to the Sender Terminal, and a Black wire which goes to the Ground Terminal (both on Tach’).
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