Tach output looks DEAD.
Thread Starter
Teching In
Joined: Dec 2008
Posts: 40
Likes: 0
From: In the Woods
Tach output looks DEAD. Hey all, I've read all the threads about creating a pull-up circuit to get my tachometer working with the LQ4 in my Jeep, but when i check the output with the engine running, with my digital voltmeter I see next to NO voltage (like .02 volts or so).
I read that, since this is a 9 (or so) volt square wave signal, I should be seeing around 4.5 with my voltmeter, but like I said...I'm only seeing .02 or so.
I have no reason to suspect a problem with the PCM as the tune was done by SpareECM and they do this sort of thing all the time, but I suppose it still could be... (Can you even shut the engine speed output off in the tune?) The Tune in question is just a basic 2007 Silverado 2500/MW3 (NV4500 5-speed) with the VATS, EVAP, secondary O2 sensors and Torque management turned off. The engine seems to run perfectly.
Could this be a problem with my digital voltmeter? It's nothing fancy--just a cheap Radio Shack one.
Thanks,
Jake
I read that, since this is a 9 (or so) volt square wave signal, I should be seeing around 4.5 with my voltmeter, but like I said...I'm only seeing .02 or so.
I have no reason to suspect a problem with the PCM as the tune was done by SpareECM and they do this sort of thing all the time, but I suppose it still could be... (Can you even shut the engine speed output off in the tune?) The Tune in question is just a basic 2007 Silverado 2500/MW3 (NV4500 5-speed) with the VATS, EVAP, secondary O2 sensors and Torque management turned off. The engine seems to run perfectly.
Could this be a problem with my digital voltmeter? It's nothing fancy--just a cheap Radio Shack one.
Thanks,
Jake
Thread Starter
Teching In
Joined: Dec 2008
Posts: 40
Likes: 0
From: In the Woods
I'm assuming that even if everything was working correctly I'd need a pull-up circuit to get it to register on my tach because it needs a 12V input. Perhaps I'll just try that and see if I get anything. From what I've read on here, you just connect a key-switched power source/680 Ohm resistor to the tach wire...Right?
Thanks,
Jake
Last edited by Jake Harsha; Oct 25, 2009 at 10:04 AM.
Thread Starter
Teching In
Joined: Dec 2008
Posts: 40
Likes: 0
From: In the Woods
To anyone else having the same problem that finds this thread... It was the Multimeter. I hooked the pull-up circuit (680-ohm Resistor to B+) and my VDO Cockpit Series tach (set to 4-banger mode) worked like a charm!
Hope this helps someone else,
Jake
Hope this helps someone else,
Jake
Okay, I'm about to go get the resistor, re-read this and want to be sure I understand. I need to put the resistor in series w/ the 12v power to the tach, or put an additional 12v source w/ resistor in parallel w/ the tach wire coming from the PCM?
Here's an article to guide you, scroll down till you see the pull-up resistor part, ignore the diagram labeling as this isn't for a tach hookup, but will help illustrate what needs to be done:
http://www.msextra.com/doc/ms3/ignition.html
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
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 I have used this technique multiple times, with no PCM failures to date. The oldest swap I have running around is around 3 years, daily driven.
That instruction link I provided was straight from Megasquirt. Surely if this causes problems with the PCM they would have known by now.
Just wanted to report back. I wired in two 680 ohm resistors in series for my pull up circuit, works perfectly. I admit, I said a prayer, "please don't fry my PCM", and turned the key and all worked great.
Thanks for this thread and the help 96gt'.
Thanks for this thread and the help 96gt'.
TECH Fanatic
Joined: Jun 2013
Posts: 1,163
Likes: 16
From: Avon, Ohio
Bumping an old thread....
I have a VDO tach I brought back to life with a 1k ohm resistor. The issue is the tach reads low (abotu 750rpm low @6k), and is slower to react than my Summit gauge I have as a back up (Summit is too large to fit the space though) I have seen a few threads where people with VDO tachs are experiencing the same issue.
SO my question-
1) Would wiring MORE resistors to bump the signal help more? Would it have potential to damage the ECU?
2) Has anyone with a VDO tach gotten them to work 100%?
3) Do people seem to truly have ZERO issues with the Autometer or Autogauge units? I dont know who made the Summit brand unit I have, but it reacts fast. and is dead nuts on at redline.
Thanks!
I have a VDO tach I brought back to life with a 1k ohm resistor. The issue is the tach reads low (abotu 750rpm low @6k), and is slower to react than my Summit gauge I have as a back up (Summit is too large to fit the space though) I have seen a few threads where people with VDO tachs are experiencing the same issue.
SO my question-
1) Would wiring MORE resistors to bump the signal help more? Would it have potential to damage the ECU?
2) Has anyone with a VDO tach gotten them to work 100%?
3) Do people seem to truly have ZERO issues with the Autometer or Autogauge units? I dont know who made the Summit brand unit I have, but it reacts fast. and is dead nuts on at redline.
Thanks!
