Tachometer

[Special Ed]

I have a '94 Suburban that I got a little over a month ago and the first time I drove it, I jumped on it and the tach went to 3600 RPM. I know that the 6.5 redlines at 3400 and it didn't sound like it was any where near that rpm. The truck has a fairly new alternator that was put on before I got the vehicle so my dad (sixnickel) and I thought it might be the wrong size pulley or something. We measured the pulley on my alternator and then the ones on my dad's 2000 K3500 6.5TD and my mom's 1999 Surburban 6.5TD and they were all 2.5" diameter pulleys. My dad brought a Tech 2 home from work and while cruising on the highway @ 60 mph, the tach was reading about 2150 rpm and the Tech 2 read about 1750-1800 rpms. Any ideas?
Thanks Eddie

[Scrufdog]

mine is also off by about 200 RPM, with the proper sized pulley. Just one of those things I guess. I dunno why they didnt run the tach of the PCM.

[njdevi11]

Check this out, if you want an absolutely accurate tach you can do it digitally, im thinking about doing this to my 6.2. You can put a digital encoder wheel on your injector pump sproket and pick it up with a photo sensitive diode. Its accurate to the revolution. The signal must be amplified to be used with a traditional tach.

If this offends the admins please remove the link.

http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml

[Garth J]

what I did on my 6.2 was get a programmable tach the one with dip switches inside it comes with a photo sensor and I drilled a hole in the pan at the bottom of the bell housing and welded a 1 inch nut to it then count the gear teeth on the flywheel set the switches as per instructions screw in the sensor and set it to the instructions and it was perfect

[njdevi11]

Garth, Could you post some info on the programable tach you used? who's the manufacturer?

[Garth J]

It was a ISSPRO tach from a dealer. Like I said it had a little pannel at the back with I think 9 little DIP switches inside. You order it with the sensor and just follow directions. What I did was get a 1 inch nut and a 1 inch jamb nun drilled a hole in the pan at the bottom of the flywheel ,welded the big nut on it cleaned out the threads from weld splatter ran the jamb nut on on the sensor and screwed it all the way to the flywheel teeth then backed it off a half turn then jambed it with the jamb nut (dont forget to count the flywheel teeth when you have the pan off) set the switches as the directions tell you for that many pulses per revolution and you will have a great tach.
Originally the tach was for reading pulses from the alternator but that didnt work so ISSPRO gave me the sensor