Ls1 tach reading not accurate

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Sep 16, 2005 | 02:23 AM

mexricanboy26

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Ls1 tach reading not accurate

I have my Ls1 running now but noticed that the Tach readout is way off. I', going 65 miles and it reads at 800 rpm. How can I correct this?

Sep 16, 2005 | 03:34 PM

jdperk-86elco

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From: Kansas City, MO

There is two ways to correct the tach reading incorrect. The signal coming out of the PCM is a 4 cylinder signal and the tach in your dash is a 8 cylinder.

1. Use a tuner program to change the tach signal to 8 cylinder (I would call this the prefered method since it is a computer just change the value.)

2. You can purchase an adapter box that you can set switches to get the correct 8 cylinder signal to the tach. It connects inline between the PCM and tach. The adapter box is on this forum somewhere and I know John B. used one.

Sep 16, 2005 | 03:56 PM

mexricanboy26

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Thank u.. you say the pcm reading is a 4cl...but the pcm it uses is for ls1 5.7l v8..so it should already have the programming for the v8??

Sep 16, 2005 | 04:14 PM

jdperk-86elco

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From: Kansas City, MO

Quote:

Originally Posted by mexricanboy26

Thank u.. you say the pcm reading is a 4cl...but the pcm it uses is for ls1 5.7l v8..so it should already have the programming for the v8??

That would be the logical assumption however the dash for the F-body and Corvette is electronic and it can be programmed to use any signal GM decides to use and they chose a 4 cylinder signal. It's an electronic dash thing and not a independent tach thing.

I am in the same position and I have to change my tach to read correctly, but first I need to finish my swap and get it running. Maybe this weekend.