Fixed Tach... YES!!!
Fixed Tach... YES!!! Thanks to the forum and Parish8 in particular!
I gave up on my factory 1991 vette cluster(frack) every working right and jumped on some autometer gauges. Got the tach all mounted and set up and it didn't work. No needle bounce no nothing. I was using the tach output on my 2004 GTO pcm to feed the signal but it just didn't work.
I saw some posts on the forum here talking about a pull-up circuit and how that would make it work fine. But I didn't really understand for sure how to do it. I PM'ed Parish and got the scoop. I ran a wire from a switched 12v source to a 680 ohm resistor and jumpered into my tach output wire between my pcm and my tach. Keyed the ingnition and the tach reads just like it should have all along. NICE!
Thanks, Parish! I would have been pulling my gauges out and really pissed had I needed to send it in. Instead I just used the forum and spent $5 with good ol radio shack
I gave up on my factory 1991 vette cluster(frack) every working right and jumped on some autometer gauges. Got the tach all mounted and set up and it didn't work. No needle bounce no nothing. I was using the tach output on my 2004 GTO pcm to feed the signal but it just didn't work.
I saw some posts on the forum here talking about a pull-up circuit and how that would make it work fine. But I didn't really understand for sure how to do it. I PM'ed Parish and got the scoop. I ran a wire from a switched 12v source to a 680 ohm resistor and jumpered into my tach output wire between my pcm and my tach. Keyed the ingnition and the tach reads just like it should have all along. NICE!
Thanks, Parish! I would have been pulling my gauges out and really pissed had I needed to send it in. Instead I just used the forum and spent $5 with good ol radio shack
I don't know what all it works on...
Parish did his on a truck with a couple of things that were running off the tach signal that were dropping the signal too low.
I did mine on a 2004 GTO pcm with nothing but a tach running on it.
John B (above) says the LS2's and LS7's need it too.
Anyone else got anything to add? I've no idea how many platforms this is needed on.
Parish did his on a truck with a couple of things that were running off the tach signal that were dropping the signal too low.
I did mine on a 2004 GTO pcm with nothing but a tach running on it.
John B (above) says the LS2's and LS7's need it too.
Anyone else got anything to add? I've no idea how many platforms this is needed on.
Trending Topics
Teching In
Joined: Oct 2006
Posts: 35
Likes: 0
Originally Posted by CHarris
Thanks to the forum and Parish8 in particular!
I gave up on my factory 1991 vette cluster(frack) every working right and jumped on some autometer gauges. Got the tach all mounted and set up and it didn't work. No needle bounce no nothing. I was using the tach output on my 2004 GTO pcm to feed the signal but it just didn't work.
I saw some posts on the forum here talking about a pull-up circuit and how that would make it work fine. But I didn't really understand for sure how to do it. I PM'ed Parish and got the scoop. I ran a wire from a switched 12v source to a 680 ohm resistor and jumpered into my tach output wire between my pcm and my tach. Keyed the ingnition and the tach reads just like it should have all along. NICE!
Thanks, Parish! I would have been pulling my gauges out and really pissed had I needed to send it in. Instead I just used the forum and spent $5 with good ol radio shack
I gave up on my factory 1991 vette cluster(frack) every working right and jumped on some autometer gauges. Got the tach all mounted and set up and it didn't work. No needle bounce no nothing. I was using the tach output on my 2004 GTO pcm to feed the signal but it just didn't work.
I saw some posts on the forum here talking about a pull-up circuit and how that would make it work fine. But I didn't really understand for sure how to do it. I PM'ed Parish and got the scoop. I ran a wire from a switched 12v source to a 680 ohm resistor and jumpered into my tach output wire between my pcm and my tach. Keyed the ingnition and the tach reads just like it should have all along. NICE!
Thanks, Parish! I would have been pulling my gauges out and really pissed had I needed to send it in. Instead I just used the forum and spent $5 with good ol radio shack
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
Yep, hook one end of the resistor to a wire that is IGN hot (+12v in the start and run positions)
Then "T" the other end of the resistor into the wire that goes from pin 10 on the red PCM connector to your tach.
Then "T" the other end of the resistor into the wire that goes from pin 10 on the red PCM connector to your tach.
Teching In
Joined: Oct 2006
Posts: 35
Likes: 0
Originally Posted by G-Body
Yep, hook one end of the resistor to a wire that is IGN hot (+12v in the start and run positions)
Then "T" the other end of the resistor into the wire that goes from pin 10 on the red PCM connector to your tach.
Then "T" the other end of the resistor into the wire that goes from pin 10 on the red PCM connector to your tach.
Another mystery tach issue I had posted here several months ago after I got my V8 MK3 Supra running that one issue I could not solve was the tach. It only worked when the car was shifted into reverse.
Here is my setup:
Engine: 2003 LM7 5.3L
Harness: 1998 F-body six speed
PCM: 1998 F-body, reflashed by HP Tuners
Tach adapter: Baker Electronix module (diagnostic test OK when disconnected, fails when connected to PCM)
Tach: Stock 1988 Toyota Supra
Trans: TKO600 manual
I figured this had something to do with the auto to manual swap I did but everything else worked, and the tach is getting a power feed while the engine is running. It works accurately when shifted into reverse, so a weak signal may well explain the problem. I was going to look into putting a resistor in the power feed to it to duplicate the b/u lamp load.
When I used the same stuff when I built the RX7 (exceptions- tach was a Racepak panel, harness was a converted 1998 A4, and motor was an L33), the tach works with no problems at all.
I will try the above and see if this helps with the Supra tach problem.
Thanks for posting this, yet another reason why this is a great forum.
EDIT-
I drew a diagram to simplify this. I will be giving it a try on my car & will update with results.
EDIT #2
Installed it today & the tach works great. Big thumbs up to the 99 cent solution to a long time bug.
Here is my setup:
Engine: 2003 LM7 5.3L
Harness: 1998 F-body six speed
PCM: 1998 F-body, reflashed by HP Tuners
Tach adapter: Baker Electronix module (diagnostic test OK when disconnected, fails when connected to PCM)
Tach: Stock 1988 Toyota Supra
Trans: TKO600 manual
I figured this had something to do with the auto to manual swap I did but everything else worked, and the tach is getting a power feed while the engine is running. It works accurately when shifted into reverse, so a weak signal may well explain the problem. I was going to look into putting a resistor in the power feed to it to duplicate the b/u lamp load.
When I used the same stuff when I built the RX7 (exceptions- tach was a Racepak panel, harness was a converted 1998 A4, and motor was an L33), the tach works with no problems at all.
I will try the above and see if this helps with the Supra tach problem.
Thanks for posting this, yet another reason why this is a great forum.
EDIT-
I drew a diagram to simplify this. I will be giving it a try on my car & will update with results.
EDIT #2
Installed it today & the tach works great. Big thumbs up to the 99 cent solution to a long time bug.
Last edited by V8 Supra Builder; Feb 24, 2008 at 02:26 PM. Reason: Problem solved
Hey everyone I'm new to this site, I wish I had found it when I started my swap
but now its near finished. I swapped an 05 l33/4l60e into a 91 silverado. I 've been driving it for a few weeks now but am still trying to get some kinks worked out. The main one being the tach. I'm using a cluster from a 98 silverado and I'm wondering if wiring in a resistor will fix my problem. So far everyone seems to be using an aftermarket tach set to 4 cylinder mode.Will wiring in a resistor work with my factory v8 tach? I have an autometer tach adaptor that just arrived today but I'd rather not use it if I can get away with just a resistor. Thanks
but now its near finished. I swapped an 05 l33/4l60e into a 91 silverado. I 've been driving it for a few weeks now but am still trying to get some kinks worked out. The main one being the tach. I'm using a cluster from a 98 silverado and I'm wondering if wiring in a resistor will fix my problem. So far everyone seems to be using an aftermarket tach set to 4 cylinder mode.Will wiring in a resistor work with my factory v8 tach? I have an autometer tach adaptor that just arrived today but I'd rather not use it if I can get away with just a resistor. Thanks 
The resistor 12v+ is only to boost the signal strength enough to excite the tach and make it work. The pulse frequency that comes off LS engines is 4cyl so the resistor trick does not affect this in any way whatsoever. In short you still need to either use a tach that can be set to accept 4cyl pulse or use a box such as you describe to change the tach out frequency from 4cyl to 8cyl or your stock tach will not read properly.
On The Tree
Joined: Mar 2008
Posts: 135
Likes: 2
From: Austin, Texas
Ok... so now I'm having the tach not working issue. Autometer adjustable tach w/ 07 5.3 in 84 C10. Set to four cylinder mode and needle jumps when cranking during start but that's it. So am I reading this right that the resistor is so that you can reuse a factory type tach? I thought setting the tach to 4cyl mode would allow it to work if its an aftermarket tach. If I do still need the resistor w/ my Autometer Tach, I assume I still need to set it to 4 cyl mode. This correct?