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03-14-2017, 12:44 AM | #1 |
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Tach reads 1/2 of what it should
Factory Tach reads 1/2 of what it should coming from ecm. I put a 1K ohm, 1/2 watt resistor in line as suggested with no results. Any body have any other ideas
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1970 CST LS 1 6 speed Ford 9 inch Detroit Tru Track, Dakota Didgital, Vintage Air, QA1 Coil Overs Front & Rear Lots of FUN 2013 GMC PU, Oldest Son 71 GMC LWB. QA1 Suspension, Angry SB. Youngest Son 2019 GMC Diesil Dually. Youngest Son 2017 Toyota SUV Daughters car 2018 Traverse , Wife’s Ride Pittsburg Ca 94565 |
03-14-2017, 08:23 AM | #2 |
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Re: Tach reads 1/2 of what it should
I had the same problem . Tuner changed the setting in the pcm . Cant remember if he had to set it on 4 or 8 cylinder . But it fixed mine from reading 1/2 .
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03-14-2017, 08:42 AM | #3 |
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Re: Tach reads 1/2 of what it should
Needs to be 4 cylinder
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03-14-2017, 09:03 AM | #4 |
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Re: Tach reads 1/2 of what it should
I just looked at my setting . There is an engine section . From there go to tach output . It has resolution low & high . Tuner set mine at 3 & 3 . Not sure how it is calculated but it works for mine . If you have HP tuners its an easy fix .
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03-14-2017, 10:25 AM | #5 |
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Re: Tach reads 1/2 of what it should
What is HP tuners?? Something I can buy??
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1970 CST LS 1 6 speed Ford 9 inch Detroit Tru Track, Dakota Didgital, Vintage Air, QA1 Coil Overs Front & Rear Lots of FUN 2013 GMC PU, Oldest Son 71 GMC LWB. QA1 Suspension, Angry SB. Youngest Son 2019 GMC Diesil Dually. Youngest Son 2017 Toyota SUV Daughters car 2018 Traverse , Wife’s Ride Pittsburg Ca 94565 |
03-14-2017, 01:13 PM | #6 |
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Re: Tach reads 1/2 of what it should
Google hp tuners.
It's about 650 ish
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03-14-2017, 02:06 PM | #7 |
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Re: Tach reads 1/2 of what it should
Unfortunately it is expensive . Did you have someone do any tuning on your pcm . If so they can do it for you . If you have someone local to you you could pay them to do it for you as well . I do not know of another way to fix it .
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03-14-2017, 06:32 PM | #8 |
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Re: Tach reads 1/2 of what it should
Factory output from the ECU is a 4 cyl signal. Simply set up your tach per the instructions for a 4 banger and you're good to go. Sometimes that involves clipping wires on the rear of the tach.
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03-14-2017, 06:56 PM | #9 | |
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Re: Tach reads 1/2 of what it should
Quote:
clint
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1987 Silverado - L83 5.3 w/ 6L80e ,A/C,P/W,P/L,TILT, HID projectors, Wilwood C-10 Pro Spindles w/ 2018 silverado front brakes & C-5 Corvette Rear Disc Brakes 1999 BMW 528i - 5.7 LS1 w/ 4l60e, Ford 8.8 IRS w31 spline posi & FX-r projector retrofit New project: 2006 BMW x5 6cyl AWD to L83 6l80e 4wd to 2WD / RWD A poor man buy's it twice finally got my domain name back, 87chevy.com.... site rework in progress |
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04-20-2017, 11:01 PM | #10 |
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Re: Tach reads 1/2 of what it should
Watch this video. I just made it yesterday.
Common LS swap tach issues and how to fix them https://www.youtube.com/watch?v=FS7aRfYkFAQ
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74 Stepside"Steppin Wolf":78mm Turbo LQ4/4L80e,BTR stage 3 Truck cam,3.73 12 bolt with Detroit True-Trac Project Steppin Wolf Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=670303 My Youtube channel "Bad Luck Garage" https://www.youtube.com/channel/UCRP...XkeEPCu_HmRfuw Last edited by Liltroy; 04-20-2017 at 11:58 PM. |
04-21-2017, 01:34 PM | #11 |
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Re: Tach reads 1/2 of what it should
$80 adapter box can convert 4-cyl to 8-cyl and back and forth. I use this in my LS3 Camaro to drive the factory tach and it works great:
https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
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04-21-2017, 07:15 PM | #12 |
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Re: Tach reads 1/2 of what it should
converter box is unnecessary unless you just have money to blow.
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74 Stepside"Steppin Wolf":78mm Turbo LQ4/4L80e,BTR stage 3 Truck cam,3.73 12 bolt with Detroit True-Trac Project Steppin Wolf Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=670303 My Youtube channel "Bad Luck Garage" https://www.youtube.com/channel/UCRP...XkeEPCu_HmRfuw |
10-24-2019, 01:17 PM | #13 |
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Re: Tach reads 1/2 of what it should
I realize this is an older thread but some of you may be having similar Tach Issues with your aftermarket tach's on your LS powered projects.
seems as though that installing the resistor helps some but I found it did not work. Here is what I have: 2004 5.3 LS3 Truck motor 2-1/4" Autometer tach mounted on dash of my '51. Connected: red to 12V power Black to ground Green to White Signal wire out of ECM Autometer tach was set on 4 cylinder position Nothing. I then bridged the signal side of the tach with 12 volt power side like in the video in the previous post. I tried this bridge different size ohm resistors starting with a 1000 ohm 1/2 watt resistor Tach worked but was registering double RPM than what it should have been I then bumped up to a 5000 Ohm 1/2 watt resister- with same type over sensitive / i.e. tach registering 6k when should only be 3k. I am also getting code:P0654 "Engine Revolutions Per Minute Output Circuit Malfunction" I then called Autometer tech line. Tech guy told me that my signal was corrupt out of ECM. I need to buy the $100.00 autometer 9117 tach adapter box. This gets wired in from the coils directly abandoning the white ECM tach signal wire. So I am thinking that BP Harness set my tach signal within my ECU that is somehow corrupting it/ not allowing it to
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10-24-2019, 02:08 PM | #14 |
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Re: Tach reads 1/2 of what it should
You have the opposite problem of the original poster (you're reading double the RPM instead of 1/2). It actually sounds like BP set your ECM for 8 cylinder output and you set the tach to 4 cylinder. Have you tried setting the tach to 8 cylinder with the 1K ohm pull up resistor? It sounds like that would get you up and working.
Last edited by dayj1; 10-24-2019 at 04:34 PM. |
10-24-2019, 03:30 PM | #15 | |
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Quote:
Posted via Mobile Device Last edited by Liltroy; 10-24-2019 at 03:55 PM. |
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10-25-2019, 11:59 AM | #16 |
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Re: Tach reads 1/2 of what it should
Thanks for the Heads up guys. I will try flipping the dip switch on the tach from 4 cylinder to 8 and go back to the 1000 ohm resister.
Question about the factory ECM tach settings: What does the factory setting on the Gen III ECM 4 cylinder or or 8 cylinder? Why does every LS forum that I read including the Autometer website say to set the tach to 4 cylinder?
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10-25-2019, 01:22 PM | #17 | |
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Quote:
Posted via Mobile Device Last edited by Liltroy; 10-25-2019 at 01:38 PM. |
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10-25-2019, 01:40 PM | #18 |
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Re: Tach reads 1/2 of what it should
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