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

Ed Wright · 04-09-2020, 11:31 AM

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

jamie2370 · 04-09-2020, 02:57 PM

Quote:

Originally Posted by Signman

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

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

Ernie Neal · 04-09-2020, 08:57 PM

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

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: 2,142 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: 2,142 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"

04-09-2020, 11:31 AM	#8
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 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 __________________ Ed Wright 4156 SS/JA

04-09-2020, 08:57 PM	#10
Ernie Neal Senior Member Join Date: Feb 2009 Location: Columbus, Indiana Posts: 527 Likes: 162 Liked 322 Times in 77 Posts	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