VDO Tach Install - Lessons Learned

[TomH]

Installed a VDO tach on my '06 LQ9. Initially the tach was dead except a momentary blip during start-up. Searching across the boards turned up the solution of a pull-up circuit. A quick trip to Radio Shack and 99¢ later I had all the stuff to solve the problem.

I had a hard time finding a good diagram of the pull-up circuit, so I made up the attached to document what I found:

• The critical part is a 1K-Ohm 1/4 watt resistor (Radio Shack 271-1321).
  • Different articles will show different values and I picked up a couple in the 500-600 Ohm range and they ALL worked.
• As noted in a lot of posts on LS1Tech, the normative config for a Gen-III VDO install uses the conventional (Coil type) ignition settings for a 4-Cyl engine (On-Off-Off) but check with your tuner, as he may have toggled it to an 8-cyl output. (On-On-Off)

Life is good!

[V8Rumble]

Good stuff, I'll bet that this helps a number of people...

[cornetto]

Tried this on my L76\E38 conversion without luck. Does anyone know if the tach signal from an E38 is the same as that off a LS1 ecu?

Cheers,

[TomH]

Originally Posted by cornetto

Tried this on my L76\E38 conversion without luck. Does anyone know if the tach signal from an E38 is the same as that off a LS1 ecu?

Cheers,

Not sure if the E38 is the same deal, but you can try some different resistors to see whether your PCM is looking for a certain value.

I saw a couple of articles that suggested a 680-Ohm value, others in the 1K range. As they were less than a buck at Radio Shack, I picked up 3-4 different resistors and got lucky with the first.

Good luck!

[V8Rumble]

You could also try a variable resistor (aka rheostat) in that range, & if/when you find the value that works, note it in this thread...