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Registered
Join Date: Jan 2006
Location: Millersville, MD
Posts: 505
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sporatic tach
sometimes the tach works, sometimes it doesnt move at all and sometimes it bounces all over the place. any ideas where i should look, i figure a loose wire or a bad ground.
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*NEW 1969 911t targa soft window option 1967 912 Targa Soft Window 1989 911 GP White Cabriolet 1970 911t 2001 Chevy Silverado 1500 1997 Audi A4 Quattro 2.8 2003 Acura TL Type S 1973 911t 3.0 track car (SOLD) |
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03-21-2006, 08:33 AM
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Registered
Join Date: Jan 2006
Location: Millersville, MD
Posts: 505
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BUMP
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*NEW 1969 911t targa soft window option 1967 912 Targa Soft Window 1989 911 GP White Cabriolet 1970 911t 2001 Chevy Silverado 1500 1997 Audi A4 Quattro 2.8 2003 Acura TL Type S 1973 911t 3.0 track car (SOLD) |
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03-21-2006, 09:31 AM
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Autodidactic user
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,298
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Check your points. The tach gets it's signal from the points. If the gap is incorrect or there is some oil on the surface this could lead to the symptoms you describe. Make sure the gap is perfect and then run a piece of paper between the points to remove any oil. Don't forget to double check the gap with a dwell meter.
On my 73, the breaker point gap is: .035mm (.014 inch) and the dwell angle: 38º +/- 3º @ 900 RPM Vacuum hose connected (38º or greater @ 6,000 RPM w/ vacuum hose off). It's probably the same on yours but double check to be certain. If this doesn't fix the problem, check the voltage from the alternator and voltage regulator. Incorrect alternator output or a voltage regulator that's not working properly can also lead to a bouncing tach. Hope this helps.
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Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.  1973 911E Targa (MFI) |
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03-21-2006, 12:18 PM
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Slumlord
Join Date: May 2001
Location: Canada
Posts: 4,983
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The bouncing tach has often been attributed to a failing alternator, I haven't been able to figure out why, but it seems to be a common problem.
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84 Cab - sold! 89 Cab - not quite done 90C4 - winter beater |
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03-21-2006, 12:30 PM
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Registered
Join Date: Jul 2005
Location: Somerville, New Jersey
Posts: 484
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As well as the above 2, I would check the electrical connections on the back of the tach. I bumped one loose when changing my gauge lights, afterward the tach was bouncing pretty irratically...
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-Matt 1985 Targa |
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03-21-2006, 12:32 PM
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