ok, on winaldl the rmp is 500 at idle and my tac said 750, winaldl 1900... tac 2600, winaldl 4000... tac 6100, at least from the best of what I can remember from yesterdays tuning, anyways, how can I fix this?

 

ok does your car have a stock motor? is it the original tach?

 

not stock motor, stock tach though, see sig...

 

ok then the answer is simple....you swapped from a 6 to an eight, you have 2 more cylinders than your stock tach is programmed for, so it will always read 33% higher. Get a tach out of an 8 and replace the one in your dash, easy fix.

 

Actually, using a V 6 tach on a V8 car will result in lower tach readings, not higher. Since the tach signal is a single pulse ( say for argument sake #1 cylinder firing) with an 8 cylinder engine that pulse will happen less often than a 6.

 

Much as I hate to disagree with you, I think I am right. Had the problem first hand. I think the solid state circuit board actually "counts" the number of ignition pulses sent from the HEI distributor i.e.: one pulse=one cylinder fires, and is programmed for 6 or 8 pulses per turn. I've seen tach circuit boards that were marked V6 or V8. Whichever one of us is right, I bet if he gets a tach out of a V8 car or even just the board off the back (what I did), it will read a lot closer...g*d knows that the stock tachs are about as accurate as Enron's accountants.

 

Would it be possible to put a resistor in line to the tach? I dont want to change the tach again , besides I tried the tach out of a V8 when I got the new 145mph speedo, It read the same, but I liked the looks of my original better, a little bit beter condition, so I put the original back in.

 

you are supposed to be able to fix it by placing a new capacitor on the board, but I never had any luck with it. Do a search on tach fix on this board, there are several threads discussing ways to actually fix it. It is a very common problem for the stock tach to fail and read wrong.

 

I got a tach off E bay to replace my failing tach and installed it without looking to be sure it was for a V8, Well, the rpm's read way low for any given speed of the vehicle. I pulled the tach and flipped it over, low and behold, there was a little sticker that read 6 Cyl.

The guy swore the tcah was from an IROC....don't remember any of them having 6 bangers in them.

Then, I replaced the large capacitor (on the v6 tach) with one of another value ( forget what exact value) and it read correctly.

 

thats wierd, because both of the 6 cyl tachs that wound up in my IROC read high, always about 1/3 higher....I did try to do the fix like you did, but it didnt work right...so what I have now is a circuit board from a V8 tach mated to the guage head and face of a V6 tach that matches the rest of my guages, works great its as accurate as a stock tach is gonna get

to rsc350: I say try morley's fix, I know other people have had good luck with it. Do a search on tach fix, that should find the thread. If it doesnt work you'll be out some time, about a $1 in material and probably a lot of cussing and if it doesnt work you can do what I did.

 

Hay thanks for ths info guys, i apreciate it. I'll give it a whorel.

 

I looked all over the place and I cant find anything on a tach fix, nothing except replaceing it, I know there has to be a way, you guys know too, any directions you can tell me, or maybe you guys can find a link to a fix??

 

Check this thread.
https://www.thirdgen.org/techbb2/sho...hreadid=109181

It describes how to make a V6 tach work on a V8 engine.

I gave a pretty good description of where the capacitor is on the tach on this thread. https://www.thirdgen.org/techbb2/sho...hreadid=114057

Look at my second post on that thread, the first one I was a little off in the position of the capacitor.