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Tach Wackiness, Bucking At Stoplights


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Recently purchased a 2000 Mercury Sable LS Premium Wagon 143K.  Did the following to get it roadworthy:  Cosmetic stuff, Rear brakes, front ball joints, inner/outer tie rods, alignment, replaced PS pulley, water pump, S-Belt, spark plugs, intake manifold gasket, PCV valve, several coils, AC Compressor/liquid line/orifice tube/condenser. Today, at Bull Geeks suggestion, today I replaced the crankshaft position sensor in reaction to the car not starting after a short ride on a blazing hot day. 

The car cranked up perfectly after the installation.  Purred like a kitten.  But when I revved the motor, two out of three times it acted like it was missing, stumbling it's way up to 3K.  One of three times, though, it was perfectly smooth.

I drove to the auto parts store (about a mile).  The ride was uneventful.  When I put the car in park, I noticed the tach dropped to 0, alhough the motor was still running smoothly.  Somrtimes it would hang at 150 RPM.  When I revved it, the tach would stick at zero for about half a second, then leap up to five hundred,then leap up to 1K, then ride up smoothly to 2K.  The tach was very clearly not shwoing what the engine was doing.

A few days before all of this, I was sitting at a light, when the car suddenly began bucking with the engine revving (I had my foot on the brake. It bucked about four times before I shifted to neutral and the bucking stopped.  Shifting back to drive showed nothing unusual.  It acted normally again.  What!?!

Any ideas would be welcome. 

 

 

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While I've never experienced this first hand, I've read many threads about failed transmission range sensor causing all kinds of strange, seemingly unrelated issues.

I would start by checking all grounds and main electrical connections.

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Perhaps that sensor isn't 100% perfect?

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  • 4 weeks later...

The tach is still acting weird, but the stumbling/missing is resolved. 

Replaced the entire intake manifold.  There was hissing from the rear of the engine compartment and the Scotty Kilmer smoke test reveled leakage.  I could not verify exactly where the leak was, but confirmed it was not coming from the vacuum hoses.

After the new manifold was replaced, she purred like a kitten and roared like a ...well, Sable.  But the new (junkyard) manifold did the trick.

The tach still acts strangely sometimes, but it does not seem to affect anything at all.

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  • 4 weeks later...

i know this is an older thread sorry.

 

when the tach is acting up, smack the dashboard above it a few times, if it fixes, its your cluster.  mine does it all the time, gets worse over time. 

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