Incorrect Tach

[kgoodrich]

I have an 89' IROC with a 350 TPI. I have a problem where my tach is reading about 1000 rpm higher that what I the engine is actually running. When cranked and idleing, the tach says I am running about 1700 rpm. I know that I am running about 700 rpm actually. This problem started after I replaced my head gaskets. The engine blew a head gasket a while back, I changed the head gaskets, put it back together, and now the tach is 1000 rpm off. Also for some reason, the car is very cold natured. It used to fire right off and idle no problem. Now you crank it first thing in the morning and you have to monitor it for about 2 min or it may die. Even after that, for about the first 10 minutes of driving, when you give it gas, it seems like it almost wants to backfire through the intake. Does anyone have any suggestions on the Tack/Idleing problem??????? Please Help!!!!!!!!!!!!!!!

[ikeyballz]

old cars seem to like to do that first 2 min warm up..

but, try take off the back wire connecting to your tach and grease it up.
sounds like a sticky wire to me..

[kgoodrich]

This car is completely factory, so the gauge cluster is a printed circuit board on the back. All except for the Speedometer. As far as the distributor, it is not like the good old HEI ignition with the coil in the cap, where the one black wire coming out of the cap feeds the tach. This one has the smaller distributor, coil mounted separately, and a 2 wire and 3 or 4 wire plug coming out of the module from the distributor. These problems did not start until I replaced the head gaskets. Every since then, it has not been exactly right.

[ikeyballz]

oh, wow..i didnt know the 3g's had electronic tachs? cool O_O;

[Morley]

Your inst cluster isn't really printed circuit. What you have is a plastic (flexable) "printed circuit" that just replaces the wiring that powers the instruments and backlighting. It is just a plastic sheet with copper traces on it.
The thing with the tach being off...welcome to the world of a third gen getting old, they all do it or will soon.
The idle problem sounds like a vacuum leak, and a pretty good sized one at that.
Get the car warmed up to where it will idle on its own. Next take a propane torch and turn on the gas but don't light it. Now, direct the gas at every area that could possibly have a vacuum leak. Don't forget the EGR valve up under the plenum. If the idle quality changes while using the torch, find the spot where you pointed the torch to make it change and you have found your vacuum leak.

[ikeyballz]

hahaha! thats a pretty nifty way to find a leak... kinda dangerous sounding tho.

[Morley]

Originally Posted by ikeyballz

hahaha! thats a pretty nifty way to find a leak... kinda dangerous sounding tho.

Less dangerous than using carb cleaner.

[wrightz28]

Originally Posted by Morley

Less dangerous than using carb cleaner.

Both can be dangerous in the wrong hands, however when done correctly, propane is the lesser of the 2 evils. Anyway, sounds like a intake manifold end seal isn't right, they take some finese.