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Tach needle sticking ???

The Tach in my 89 5.0 LX just started acting up today.

The needle sorta sticks as it climbs and will NOT go past 4800RPMs. :nonono:

BTW, this hapened after I changed the thermostat and reset the timing.

Where is the input to the Tach located ?? Is it possible I bumped a wire loosed somewhere ??

-ERIC

89 5.0 LX Vert w/93 Cobra long block, GT-40 heads, some kind of Wildassed Cam (??), HyperTech Chip, 68.5" Short belt for Smog and P/S DELETE, 73mm Police Interceptor Front calipers w/PFC pads, 73mm C&L MAF, BBK 2.5" O/R H-pipe, Flowmaster 40 Series Deltas, King Cobra Clutch Set, BBK Strut Tower Brace, Poly bushings.
Reply to
Katmandu
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Anyone ???

Reply to
Katmandu

The tach picks it signal up from the negitive side of the coil. I can't remeber if the fox bodies had one or two wires come out of the plug on the negitve side. Being it works until it gets to 4800 rpms I doubt its a wiring problem. Sounds like it might be time to swap it out for another one.

MadDAWG

Reply to
MadDAWG

This has nothing to do with this but:) I had a 87 F150 that had a very weird tach. It would go all the way around and then read correctly. One day I watched it make three complete revolutions in about two miles. 99.9% of the time it was perfect. Here is the killer, sometimes it would go clockwise, and sometimes it would go counter clockwise.

Al

Reply to
Big Al

The tach is driven by the Ignition Control Module (TFI module). The wire from the harness would be the Tan w/yellow stripe...

-- Mike

93 Cobra
Reply to
Mike R

That's not just weird, that's downright possessed, Linda Blair style! :)

Reply to
Garth Almgren

Cool. Thanks Mike!

BTW, I did move the distributor about 90 degrees (or so) to reach one of the bolts to the thermostat housing.

Since I don't have a Timing light, I scribed a mark on the distributor shaft for reference. I set it back after I installed the new thermostat.

I also "adjusted" the Throttle Body's Butterfly valve "a tad". I turned the screw about 1/2 turn in to back the idle down. It did the trick and lowered the idle just fine.

Now I'm wondering since I did move the Butterfly valve, that I "may" have thrown the TPS out of adjustment.

Would is be possible for a misadjusted TPS to give a fugged up reading to the ECM and therefore give a fugged up Tach reading ????

-ERIC

Reply to
Katmandu

Assuming (yeah I know) the idle setting was ok before rotating the distributor, my suggestion would be to reset the throttle stop screw back (as close as possible) to its original position. Spend $35.00 for a timing light and adjust base timing to spec. Tweeking other adjustments only invites more frustration. There is a KOEO self test for the TPS, but there's no need getting into that. You might want to reseat the TFI connector although it probably won't resolve your tach issue. The tach needle could simply be sticking at a certain position. Give it a good Fonzarelli whack and maybe you'll get lucky. On second thought, just give it a tap. Your luck, something else might break :-0

-- Mike

93 Cobra
Reply to
Mike R

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