Is it typical when your tachometer is off and reading high, the amount of RPM difference will increase with more RPM?
My tachometer is about 400 RPM off at idle and 1800 RPM near redline.
I probably haven't blown my engine up because I have been short shifting it for 5 years! lol
The only reason I found out it was off at high RPM, is I was using an online RPM calculator to see where my speed and shift points are going to be with the 3.4 DOHC swap and I realized I should be able to get to 80 in 3rd with the 2.8 (5500 RPM) but I can't. 55 MPH in my car reads 5500 on the tachometer when the calculator says I should be turning 3683.
How do I fix the gauge, I have read things from replacing capacitors to installing a potentiometer. I obviously need to fix this before the DOHC swap. Thanks!
Has it always been inaccurate? It may be that someone has replaced the tach or instrument pod with one from a 4-cylinder. It will be off by 50%. At 1000 rpm, it will read 1500. At 2000 rpm, it will read around 3000%.
I was just gonna shift by speed or when the gauge points to "rpm" on the stock tach, but that is a good idea while I'm repairing the tach, who makes the 7k backgrounds anyway?
According to the RPM calculator with a 7k redline you shift from 1-2 at 40 mph, 2-3 at 70, 3-4 at 100, and 4-5 at 150, (not that I will even need that last shift lol) The theoretical max speed is 200 at 7k rpm.
I would expect to need to send in the stock gauge face, then have them make a custom one based on the stock unit.
Since you mentioned 'gauge points to "rpm" on the stock tach', this means you have the backlit gauges (not front-lit) so the face will be a bit more complicated to make.
The numbers you posted seem to suggest you have a 4-cyl tachometer on a V6. Swapping in a V6 tach should fix the immediate problem.
But as the other guys mentioned, the stock V6 tach only goes up to 6500 RPM, whereas the 3.4 TDC can rev to 7K RPM. There are several ways you could address that problem. Probably the easiest would be to take a Fiero V6 tach, and just add another hash mark for 7000 RPM. There is no peg at the rev limit to stop the gauge needle, so it should go all the way up to your new hash mark. Another option would be to modify your existing tach. Doing a little math, you should be able to figure out what capacitor is needed to make the needle hit the redline at 7K RPM. Then you'd print up a gauge face to match. Another option would be to swap in a completely different tachometer that can go up to 7K RPM+.
On a side note, I'm not sure if you plan on using a turbo. But if you are, then you might want to check out this thread, where he installs a 7K RPM tach with boost gauge: https://www.fiero.nl/forum/A...130314-2-110302.html
If the redline is 5500, it's a 4-cylinder tach. V6 tachs redline at 6500. The tach filter might also be at fault. The 4-cylinder tach will also have an oil pressure gauge in it. Just a few ways of telling what you have.
To any one reading this, member J Gunsett messaged me and offered to repair my tachometer. I sent it to him and he replaced a resister and now the tach is accurate again!
He even give you a printout of the before reading and after! Highly recommend him!
