Tac calibration issue??? - ZR-1 Net Registry Forums

Paul Workman · 02-08-2008

When I mentioned to Pete and again to Mark Haibeck (yesterday) that at 7000 rpm I'm only doing about 102mph, the question of tac accuracy came up (Pete). Or, do I have a 4.10 gear? (Marc). I verified my rear gear is a 3.45, and I hooked up my scanner and ran the tac up to a steady 3000 rpm, and the scanner rpm says 2565. Hmmmm.... Pete tells me he's at 122 mph at 7000 rpm with the stock 3.45 rear gear, and if I do the math, 122mph*2565/3000=102mph.

Q: Obviously my tack reads high at steady rpm. Is that to offset tac lag in rpm runup, or is there some calibration issue I might want to address?

What say da Z gurus??

TIA,

P.

petefias · 02-08-2008

What does the tach show at idle? Without the engine running and key on does the needle sit exactly at 0?

If you go into diagnosis mode you can get the exact RPM of the engine to verify the tach.

Paul Workman · 02-09-2008

Quote:

Originally Posted by petefias

What does the tach show at idle? Without the engine running and key on does the needle sit exactly at 0?

If you go into diagnosis mode you can get the exact RPM of the engine to verify the tach.

At idle it sits between 700-800 (hard to tell exactly). However, w/ engine off, it reads below zero; approx - 500 rpm. Hmmmm...sez me.

My scanner reads the rpm off the ALDL connector - the reading I was using to compare with the tac. But, I don't know if the rpm reading there is a DC (analog) voltage which is being interprited, or actual digital "blips" being counted - I'll have to research that some (with the FSM), I recon. In any case, the speedo reading seems to suggest the ALDL scanned rpm are in agreement, FWIW.

P.

Aurora40 · 02-09-2008

Sounds like your tach is off. I believe that's somewhat common. I do not know what the fix is, though. Mine is within 50rpm pretty much throughout the rev range (looking at increments where the needle is right on a line, otherwise it's just a guess). You can slowly rev it up when parked and look at your scanner to see. There's no lag compensation I'm aware of. It should match what the scanner says, or else your tach isn't very accurate.

Pete · 02-09-2008

Pual here is the hi tech way i check my tech

if you have the stock chip cut off is 7100 take her out stay in the throttle till cut off look what the RPM gauge is showing.LOL

Even though this works, i'm J/K.

Paul,time for a shift light.

Pete

petefias · 02-09-2008

Easy fix: just shift at 7500.

02-08-2008	#1
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Tac calibration issue??? When I mentioned to Pete and again to Mark Haibeck (yesterday) that at 7000 rpm I'm only doing about 102mph, the question of tac accuracy came up (Pete). Or, do I have a 4.10 gear? (Marc). I verified my rear gear is a 3.45, and I hooked up my scanner and ran the tac up to a steady 3000 rpm, and the scanner rpm says 2565. Hmmmm.... Pete tells me he's at 122 mph at 7000 rpm with the stock 3.45 rear gear, and if I do the math, 122mph*2565/3000=102mph. Q: Obviously my tack reads high at steady rpm. Is that to offset tac lag in rpm runup, or is there some calibration issue I might want to address? What say da Z gurus?? TIA, P.

02-08-2008	#2
petefias Join Date: Aug 2005 Location: Lancaster, PA Posts: 147	Re: Tac calibration issue??? What does the tach show at idle? Without the engine running and key on does the needle sit exactly at 0? If you go into diagnosis mode you can get the exact RPM of the engine to verify the tach.

02-09-2008	#4
Aurora40 Join Date: May 2005 Location: Leesburg, VA Posts: 2,713	Re: Tac calibration issue??? Sounds like your tach is off. I believe that's somewhat common. I do not know what the fix is, though. Mine is within 50rpm pretty much throughout the rev range (looking at increments where the needle is right on a line, otherwise it's just a guess). You can slowly rev it up when parked and look at your scanner to see. There's no lag compensation I'm aware of. It should match what the scanner says, or else your tach isn't very accurate. __________________ Bob Saveland Former owner of #2517 [IMG]http://a.random-image.net/aurora40/vette.jpg[/img]

02-09-2008	#5
Pete Join Date: Dec 2003 Location: Chicagoland,IL Posts: 2,679	Re: Tac calibration issue??? Pual here is the hi tech way i check my tech if you have the stock chip cut off is 7100 take her out stay in the throttle till cut off look what the RPM gauge is showing.LOL Even though this works, i'm J/K. Paul,time for a shift light. Pete __________________ '91 #1635 PoloGreen 350 LT5 11.09 @ 129.27 11.04 @ 128.86 474RWHP 400RWTQ http://www.youtube.com/watch?v=SFNFOhGGlR4 http://www.youtube.com/watch?v=ZlRIOMwaDYY https://sites.google.com/site/peteszr1garage

02-09-2008	#6
petefias Join Date: Aug 2005 Location: Lancaster, PA Posts: 147	Re: Tac calibration issue??? Easy fix: just shift at 7500.