Fast xfi rpm issue

jamie2370 · 04-08-2020, 10:45 PM

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

Ed Wright · 04-09-2020, 08:26 AM

Sounds more like an Autometer issue.

jamie2370 · 04-09-2020, 08:34 AM

Quote:

Originally Posted by Ed Wright

Sounds more like an Autometer 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

GUMP · 04-09-2020, 09:25 AM

Where are you picking up the tach signal?

jamie2370 · 04-09-2020, 09:57 AM

at the 7al2 box, tach terminal

GUMP · 04-09-2020, 10:34 AM

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

Signman · 04-09-2020, 10:36 AM

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

Rich Biebel · 04-10-2020, 12:12 PM

Quote:

Originally Posted by jamie2370

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

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.....

Ed Wright · 04-12-2020, 05:27 PM

Quote:

Originally Posted by Rich Biebel

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.....

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

04-08-2020, 10:45 PM	#1
jamie2370 Member Join Date: Dec 2014 Location: Perry, GA Posts: 331 Likes: 11 Liked 239 Times in 90 Posts	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

04-09-2020, 08:26 AM	#2
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: Fast xfi rpm issue Sounds more like an Autometer issue. __________________ Ed Wright 4156 SS/JA

04-09-2020, 09:25 AM	#4
GUMP VIP Member Join Date: May 2002 Location: Shelby, NC Posts: 1,817 Likes: 2,143 Liked 2,323 Times in 546 Posts	Re: Fast xfi rpm issue Where are you picking up the tach signal?

04-09-2020, 09:57 AM	#5
jamie2370 Member Join Date: Dec 2014 Location: Perry, GA Posts: 331 Likes: 11 Liked 239 Times in 90 Posts	Re: Fast xfi rpm issue at the 7al2 box, tach terminal

04-09-2020, 10:34 AM	#6
GUMP VIP Member Join Date: May 2002 Location: Shelby, NC Posts: 1,817 Likes: 2,143 Liked 2,323 Times in 546 Posts	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.

04-09-2020, 10:36 AM	#7
Signman Senior Member Join Date: Oct 2003 Location: Lower Slower Delaware Posts: 535 Likes: 22 Liked 269 Times in 99 Posts	Re: Fast xfi rpm issue Have you tried the tack output in the XFI harness if I recall is the white points wire __________________ Frank Ferrucci I/SA 1271 "Be Thankful for the Gifts You are Given"