Tach Bounces on Start Up, Drops to Zero (DIES) and Check Engine Light Comes On
 

ARGH! My poor little piglet! 89 FC GTUs. Just on the road this past June for the first time since '04. Thread title says it all. A/C on/off-no diff. Behaves-BEAUTIFULLY in every gear/whine/speed EXCEPT for the no-tach/check engine. NO power loss.

Haven't had a chance to find a mechanic that can read a code. Is this a known issue? Suggestions on where to look?

Bill

:dunno:

I had something similar and it was the thermowax (Idle Air Control) that had the plunger stuck.
I don't have the money to fix it so I pulled the throttle body off and removed the screw that contacts the plunger and gave the whole throttle body a good cleaning. It smoothed things out, but when it's cold I have to use my foot to hold the throttle down till the engine warms a little that it holds it own idle.

Hope that helps.

You have a Green Check Connector plug near the leading coil that has but one Orange wire to it. You ground this wire to the negative battery terminal and w/key to on the Check Engine Light will give you any error codes.

And does the car die when the tach dies or just the tach itself?

Dunno...but don't think so...I don't have to coax her
 

On start up she revs high like always....while revving the tach drops to zero/disappears...and shortly after engine (sounds like) she drops back down to where she should. I can't hear/feel any different behavior. ONLY thing is the tach gone/engine light on!

Just the tach, then check engine light comes on....NOTHING I can hear/feel is any different...gonna have to get her coded....

I'm hoping it's just a bad ground. (ha ha) I've been running her daily on the street with a track suspension...I'm waiting for any/every cold solder to bust loose one at a time.

Ohhh, so the tach is bouncing and the engine is still running ok? I'm sorry I was confused lol. I agree, the most probable source is a poor ground connection lol. Please post the results of the coding and what you find! lol

Am taking the dash out early Oct to replace the heater core...will chase it down then...this morning...tach was fine...ugh...

Your tach receives its signal from the trailing coil so make sure the plug w/four wires is connected properly. The specific wire is the Yellow/Blue wire.

Edit: repost of what satch said, forget to refresh the page.