i just bought an 89 iroc with a decently built (smog legal) 350 and a 97 6 speed; i looked at the cam sheet that was in the car and it says to shift at 5500 and valve float is at 6500, but the tachometer quite easily tops out past 7 grand before it sounds like i even need to shift.
im guessing when it says 7000 its probably at 4500 or 5000 by the sound of it.
i would like to keep the stock look of my car so would like to just fix the tach instead of putting in an aftermarket one.
how would i go about doing that?


(by the way, im hoping this is the right forum to post this in. if its not please point me in the right direction.)

 

Note that the tach could be a 6 cylinder or worse a 4 cylinder tach. In this case they would read high on an 8 cylinder engine.

Here are a couple of decent links that explain the other reason they are off so much. Along with fixes:

https://www.thirdgen.org/forums/elec...meter-fix.html
https://www.thirdgen.org/forums/elec...aayyy-off.html

RBob.

 

its definitely not been a 6 to 8 cylinder conversion, its a factory 350, so thats not the issue.
from what i read in those threads they havent really found a fix for it so i guess thats just one more thing ill pick out of a junkyard car.

 

Uh, maybe re-read the first thread linked. There is one resistor in particular that causes the issue. Even has many pictures of how folks went about replacing it. Note that the issue isn't the actual tachometer, but the driver board for it.

I suggest you re-read the thread.

RBob.

 

so the resistor would cause it to read high?
or was it a capacitor?
i saw one or two things on that but i didnt think it would cause that specific problem and more people had said there wasnt a specific fix for it.

 

It is the 196K (or there about) resistor across pins 4 & 10 on the resistor chip. The capacitor is just to steady the needle (what is known as ripple).

What happens is that over time that resistor value increases. Which causes the tach to read higher.

Can get 100K 1/4W resistors and use 2 in series to provide the 196K. If you have a DVM measure some and find ones that are lower in value. They are usually +-5% which gives some play room on the actual value.

RBob.

 

ah ok.
and yea i just realized the second thread was the one i read.
i think i completely forgot to look over the first one. i feel kinda dumb haha.
i should be able to fix that with my dads help.

thanks RBob.