No tach ms2pnp
11-28-2015, 11:00 PM
#1
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No tach ms2pnp
I have a 1991 with a 1994 turbo motor. I can't get a tach signal. I tried the resistor trick in the dignostic port and still nothing. What am I doing wrong lol
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11-30-2015, 02:51 PM
#14
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i wrote a huge reply and lost it explaining why the resistor works and why the tach goes dead when you pull out stock ecu, even though the 90-94.5's tach is driven through coils.
i dont feel like writing it again right now. :(
i dont feel like writing it again right now. :(
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11-30-2015, 03:17 PM
#18
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because the stock ecu provided the pullup to power the tach signal.
the coils go to ground with each spark event.
the signal must have voltage to start with.
when coils ground, the tach sees constant voltage, then none -- the rate it sees those events is how it knows the engine speed.
1K from B+ (12v) to the tach signal (IG-) puts power back on the wire. otherwise there's no activity on the wire, cause youre going from no voltage to ground -- no signal.
the coils go to ground with each spark event.
the signal must have voltage to start with.
when coils ground, the tach sees constant voltage, then none -- the rate it sees those events is how it knows the engine speed.
1K from B+ (12v) to the tach signal (IG-) puts power back on the wire. otherwise there's no activity on the wire, cause youre going from no voltage to ground -- no signal.
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11-30-2015, 04:11 PM
#20
SADFab Destructive Testing Engineer
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I don't think the mspnp's even have tach output hooked up. Or at least the jumper shouldnt be set. Adding the resistor is emulating the stock ecu. If adding the resistor isn't working you have bigger problems.
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