Fast xfi rpm issue
 

Fast xfi, analog 7al2, fast dual sync dist. My autometer tach is roughly 500rpm less than what fast data shows. Fast at idle shows 1100 while tach is around 600. Is this normal or if not, what is the fix. I honestly thought I had a low reading tach before I put on efi, just now I have another reference that should be super accurate since its dual sync

Re: Fast xfi rpm issue
 

Sounds more like an Autometer issue.

Re: Fast xfi rpm issue
 

I agree, I think I will try another tach to see. Like I said, when it was a carb combo I really thought it was off then but I had nothing to compare it to

Re: Fast xfi rpm issue
 

Where are you picking up the tach signal?

Re: Fast xfi rpm issue
 

at the 7al2 box, tach terminal

Re: Fast xfi rpm issue
 

Is there an unused tach wire on the FAST harness? If there is, it would be worth trying before changing the tachometer.

Re: Fast xfi rpm issue
 

Have you tried the tack output in the XFI harness if I recall is the white points wire

Re: Fast xfi rpm issue
 

I have not had a tach in my car for a while now. I log & play back every pass. If I had a stick car, I would need one, wouldn’t I? Or a shift light. LOL

Re: Fast xfi rpm issue
 

That's what is firing the msd box. Seems the more people I talk to I am thinking it's a tach issue. Nobody seems to have this problem. And a Tach is a necessity in Stock. Foot brake, and reverse pattern ATI 350 means it's all on me lol

Re: Fast xfi rpm issue
 

I have used a digital hand held tach that uses a small piece of reflective tape on the damper to verify which is correct.
Ernie Neal
SS 354

Re: Fast xfi rpm issue
 

My car is in mothballs in the trailer so can't check without standing on my head. In a couple months will have a much better situation.
Believe you have the right set up. Don't expect the RPMs to match exactly a tach really is a volt meter depending on the quality of the device there may be inaccuracy. Plus there is noise that is tough to get rid of mostly from the MSD the 7AL2 is really bad tons of RF. If you wish to try to arrest some of it set up a Faraday shield around the box with aluminum expanded metal and ground it.
You should probably try a different tach again don't expect them to match exactly but they should be close enough that your staging and shift RPMs on the data log should make sense.

Re: Fast xfi rpm issue
 

My last stocker, a number of years ago had an Autometer tach that was off by 500 at higher rpm and about 200-300 at lower rpm...

That was not the first Autometer tach I've had that was off but was the most inaccurate

I used an MSD ignition tester to fire the ignition and it reads rpm right on the tester. It can be used to test many items rpm related including a tach.....

Re: Fast xfi rpm issue
 

Had an Autometer tach in my car for a while. Was wrong, just removed it. No tach now.