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Topic: Tach inop - How to calibrate (Read 681 times) previous topic - next topic

Tach inop - How to calibrate

I have a 1999 U270 with the 8.3 ISC Cummins.  When you turn the ign. switch on it makes a sweep and the hour meets puts up some letters.  When the unit is started the hours show and never change and the tach hand never moves.  I was told it may need to be calibrated.  Has anyone experienced this?
Jerry & Nanci
1999 U270 34'WTFI
2011 Malibu
A smart man knows what to say, a wise man knows when to say it.

Re: Tach inop - How to calibrate

Reply #1 –
My guess would be a disconnected sense wire, as for calibrating it, if you have the VMSpc setup, that will give you very accurite info, just maybe if the tach is not working, maybe the VMSpc would not indicate either, so a guess from this end.
Good luck
Dave M

Re: Tach inop - How to calibrate

Reply #2 –
You might try a reset. On my coach the button is inside a hole at the very bottom of the back side of the tachometer. Mine was showing gibberish in the hours display window. It did correct that problem. Maybe you'll be lucky.
Jim Frerichs
2002 U320 42'

Re: Tach inop - How to calibrate

Reply #3 –
I appreciate any possible help with this issue.  I am new to this blog and basically blogs in general.  I contacted VDO and got the procedure to reprogram the Tach.  But I am going to paste one piece from that procedure. 
By the input of the known pulse-per-revolution
for the diesel engine and ignition system being
used with the tachometer...  What I need to know is the pulse -per-revolution.
Again any help is appreciated.
Jerry & Nanci
1999 U270 34'WTFI
2011 Malibu
A smart man knows what to say, a wise man knows when to say it.

Re: Tach inop - How to calibrate

Reply #4 –
Everyone, just for future info.  I have a 1999 U270 with 8.3 ISC  350 HP.  The pulse per revolution on that engine is 12.0
Anyone who replaces the tach will need this info. to calibrate.  Easy process, I tried this evening but it looks like the head will need to be replaced.
Jerry & Nanci
1999 U270 34'WTFI
2011 Malibu
A smart man knows what to say, a wise man knows when to say it.

Re: Tach inop - How to calibrate

Reply #5 –
To check the pulse generator is easy, using a freq meter, you get the pix real quick, on most of the units I have checked, the reading was the actual rpm of engine, provided the correct adaptor was used with the right gear ratio. most of my speriance is with the DD engines, and different places to pickup the gearing, so different ratios, Ya, I know sort of useless info on the Cummins.
Dave M

Re: Tach inop - How to calibrate

Reply #6 –
I just installed a new tach (totally fried) and speedo (worked, but LCD getting faint). I paid a little more for both units through NSI, but they were able to program the original mileage (~75,000) and set an estimated hours (~1500, tach was so fried he couldn't recover hours from it) their info: Nichols Speedometer & Instruments - Speedometers, Tachographs, Service and

All in it was around $350 ~120-130 for each piece and then 30 or 40 a pop to program them. A little more than I wanted, but it's done right now.

Anyway, he couldn't get the pulse setup off the tach and he set it to 120 for cummins. But, this is too fast. It's easy for me to change the pulse setting.

Does anybody know what the mechanical c8 cummins pulse setting is for the tach?

As of now, I'm doing trial and error using a cheap photo tach (see what engine is running at, then adjust pulses to get matching tach reading) This likely will be the best way, lol.
1998 U270 34'

Re: Tach inop - How to calibrate

Reply #7 –
When I set mine it was 12.0.  With that said mine is a 99 model and it is electronic.  Have no idea how much difference this makes.  A Cummins dealer should be able to give you that info.
Jerry & Nanci
1999 U270 34'WTFI
2011 Malibu
A smart man knows what to say, a wise man knows when to say it.

Re: Tach inop - How to calibrate

Reply #8 –
Here are our notes:

Press & hold back button, then turn on ignition Continue to hold button, display scrolls: Select, Pulse, Adjust Let go when display shows Pulse

As each single digit flashes, press & hold back button until correct value appears

When correct value is entered, wait for Tach to enter numer in memory When tach resets back to hours, calibration is complete

Pulse count is xxx.xx, where last digit is always zero and not changeable

Foretravel correct count for our motorhome is P 138.00 P 138.00 was on orig broken tach and also same number was on another 1997 U270 36' Foretravel

We calibrated our spedo with our Garmin GPS.