tach not working on new engine - Third Generation F-Body Message Boards

92tracker · 09-02-2009, 10:24 PM

The engine is an o2 LS1 installed into my 92 and the tach will not registor any reading. I connected up the white wire to the new harness and nothing any help on this would be greatly appreciated

3.1EyeCandy · 09-02-2009, 10:26 PM

More than likely the tach needs the bump-up resistor mod. It fixed mine

Search on ls1tech for it.

Basically what you need is a 680 ohm resistor wired up to A) ignition switched power and B) the white wire.

Have fun!

92tracker · 09-02-2009, 10:36 PM

Thanks I will give that a try!
I had my car out today for the first time what a difference the new engine makes

andrew69_04 · 09-02-2009, 11:40 PM

i didnt have to do anything with my tach to make it work. seems to be functioning properly (my cars a 92). only problem i've encountered is it reads the wrong rpm due to the tach signal

V8Rumble · 09-03-2009, 09:02 AM

Try switching the tach to 4-cyl. mode, & see if it gives the correct reading.

3.1EyeCandy · 09-04-2009, 06:59 PM

Quote:

Originally Posted by V8Rumble

Try switching the tach to 4-cyl. mode, & see if it gives the correct reading.

In efilive, my tuner used a 3 for this value. Dead on.

andrew69_04 · 09-04-2009, 09:54 PM

Quote:

Originally Posted by 3.1EyeCandy

In efilive, my tuner used a 3 for this value. Dead on.

From what i have found from reading, a value of 4 is supposed to change the frequency to match the v6 tach. i might try both values and see which works best.

V8Rumble · 09-04-2009, 10:01 PM

Quote:

Originally Posted by 3.1EyeCandy

In efilive, my tuner used a 3 for this value. Dead on.

THAT is weird. I've seen several instances on LS1Tech where people have toggled their tachs over to 4-cyl mode, & it's worked - but I've never seen ANY reference to a 3...

(Maybe you got one of the ultra-rare "Geo Metro" LS1 variants...???)

andrew69_04 · 09-04-2009, 10:44 PM

Quote:

Originally Posted by V8Rumble

THAT is weird. I've seen several instances on LS1Tech where people have toggled their tachs over to 4-cyl mode, & it's worked - but I've never seen ANY reference to a 3...

(Maybe you got one of the ultra-rare "Geo Metro" LS1 variants...???)

Were not talking about a 3 cylinder mode. The ls1 tach runs off a 4 cylinder frequency (#6 value in the pcm). in order to run the ls1 motor on a 6 cyl tach you have to change the tach frequency so the tach will read the correct rpm. from what i have read on tuning forums, you have to change the value in the pcm to a 4 to run on a 6 cyl frequency. make sense?