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Old 25-08-2019, 10:59   #1
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Choosing correct COdE value for VDO tachometer after alternator replacement

I have replaced my original alternator on my Volvo Penta MD2040 with a Balmar 120A alternator and a serpentine belt conversion kit.

After the installing the new alternator the tachometer shows incorrect values. After googling a bit a found some manuals of other CDO tachometers where you could set the correct Pulse value. Replaced the broken display for the hour meter on the tachometer today and was planning to set the correct Pulse value. Replacing the hour meter display was fairly easy once the display was delivered.

In all the manuals I find from other VDO tachometers you are supposed to hold down the bottom while turning on the ignition until PuLSE is displayed and then enter the correct Pulse value.

But when I hold down the bottom on the tachometer when turning on the ignition there is only CoDE displaying where you are supposed to set some specific Cd value.

Where do I find what Cd value to enter for my alternator?


- The new alternator is a 12 pole alternator with a 1:2.166 ratio (Pulse = 12 x 2.166 = 25.992)
- The tachometer is labeled with both a VDO and a VolvoPenta part number.
VDO: N 02 070 109
VP: 873588
- The engine is a Volvo Penta MD2040-D

The current Cd value on the attachment is just me fiddling around and not something that is correct....
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Old 25-08-2019, 11:17   #2
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

Here are some pictures of the tachometer



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Old 25-08-2019, 14:06   #3
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

The V.P. Tachometer is not truly adjustable for any pulse freq., but is set up to match the frequencies that are put out by V.P. engines.

That said, most alternators put out pulses per revolution that are 1/2 the number of poles, and you might find a VP code that matches your Balmar.

Code 12 will match 25.8 pulses per crankshaft revolution, and that is very close to the 25.99 pulses that you mention, and should work if you indeed have 25.99 pulses per crankshaft revolution.

Code 7 will match 12.36 pulses per crankshaft revolution, and that is about 5% off from 25.99/2. If code 12 doesn't work, try this one.

If code 7 gets you closer, use the fine adjust feature to dial in the 5% difference.

Hope this helps.

DougR
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Old 25-08-2019, 16:36   #4
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

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Originally Posted by DougR View Post
The V.P. Tachometer is not truly adjustable for any pulse freq., but is set up to match the frequencies that are put out by V.P. engines.

That said, most alternators put out pulses per revolution that are 1/2 the number of poles, and you might find a VP code that matches your Balmar.

Code 12 will match 25.8 pulses per crankshaft revolution, and that is very close to the 25.99 pulses that you mention, and should work if you indeed have 25.99 pulses per crankshaft revolution.

Code 7 will match 12.36 pulses per crankshaft revolution, and that is about 5% off from 25.99/2. If code 12 doesn't work, try this one.

If code 7 gets you closer, use the fine adjust feature to dial in the 5% difference.

Hope this helps.

DougR

Thanks a lot DougR!

The calculation of 25.99 pulses based on poles and ratio is from Balmar who has made both the alternator and the serpentine belt conversion kit for the MD2040. They suggested that I should calibrate my tachometer for 25.992 pulses. I am assuming that this is correct.

I will try with both Code 12 and Code 7 to see which one is closest to the actual RPM on the engine. I expect that as you write the Code 7 for 12.36 pules will be close to 25.99/2=12.996 if half the number of poles output pulses. While Code 12 for 25.99 pulses will be very close to 25.992 if all the poles put out pulses

Next time I am at the boat I will try both Code 7 and Code 12. Don’t own a handheld tachometer so will try using tape and a phone app strobing the flash. Hear that they are fairly accurate.

I’m not a tachometer expert by far and are still wondering where can I find data about what the "COdE" settings actually mean and what pulses each code are used for? The VDO site gives no information for older models.
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Old 26-08-2019, 19:11   #5
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

If it is the same as the usual alternator, 6 North and 6 South poles, then the W terminal only puts out 6 pulses not 12 so the formula is Crankshaft puller / alternator pulley * number of poles / 2 = number of pulses.

The part number on the taco is more than likely a Volvo only VDO part number so is not listed in any VDO parts lists.

Hold down the calibration button and then power the unit up, the display should read PULSES.
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Old 26-08-2019, 23:48   #6
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

Quote:
Originally Posted by aualby View Post
Hold down the calibration button and then power the unit up, the display should read PULSES.
I really wish that was the case. If I press/hold the button when the ignition is on I can set a positive/negative value. I assume this is fine tuning.

If I hold down the button when turning on the ignition I only get the option “COdE”. That is why I try to find an explanation of the different Cd values for COdE.

The options ”SELECt”, ”PuLSE” and ”AdJuSt” on other VDO tachometers does not seem to be available on this model.
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Old 27-08-2019, 10:44   #7
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

[QUOTE=jonase;2963648] If I press/hold the button when the ignition is on I can set a positive/negative value. I assume this is fine tuning.

Correct. Pressing the button when the ignition is already on puts you into the adjustment mode, and you can scroll in both positive or negative direction. The number you see ( 2.5, 4, -3, etc.) represents the % difference between the pulses that the tach is seeing and the reading on the dial.


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Old 01-09-2019, 13:28   #8
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

Thanks for the help. Code 7 was the closest match and I could easily adjust the fine-tuning using a tachometer app on the phone and a wite tape on the engine (-9).
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Old 30-09-2020, 01:16   #9
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

@jonase, or anyone else here. May i ask for a quick advice please. I have exactly the same gauge you have (Part number 873688) in my boat. I had an AD41 before but changed engine to a Kad44 for some more power and the Volvo mechanic that sold it to me said i can use the same instrument panel for both. I just changed the to digital throttle from the old mechanical and left the old instrumentpanel in. I cant get in hold of this mechanic again, and i know why, since there was many faults on the enging but that is another topic.. Anyway, the RPMs show more or less double now than before with my old engine, even if i can find that the gauge are suppose to work for both so i assume this is an adjustment thing!? First, you talk about a button to puch, but what button is this? I have 2 buttons on the panel (alarm test and light on/off) and no other button. I have not taken the gauge out but cant see one on the back side either (have an inspection hatch behind the panel). So, what button are you puching to get in to settings? According to another mechanic this one do not take impulses from the Alternator, but i dont know about that? He said anyway that it gets it from another place. With the original Alternator it was same issue but it had a lining broken so i bought a new upgraded 100 amp Alternator but same with this. No change.. I have had the Vodia service instrument on the engine and that shows correct, and now i bought an NMEA 2000 adapter to get engine data on the GPS from diagnostic port and that works great and showing correct. Obviously i would like to get the RPM gauge to show correct also, can anybody assist in this matter?
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Old 30-09-2020, 01:29   #10
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

This might help. https://j109.org/docs/vdo_programmab..._hourmeter.pdf
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Old 30-09-2020, 01:39   #11
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

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Originally Posted by hlev00 View Post
Hi, Thanks for your reply.
It helps in the sense that i now understand the button is on the back but that is not he same tach, looks totally different in the back.
It might also be that i can use the instructions on the settings since i am sure they are similar on this as on mine.
Think this is the one that replaced mine.
I will take it out and look for a button on the back..

Thank you very much! I see light in the tunnel
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Old 30-09-2020, 01:44   #12
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

You can use the above link to a manual to find the button on the back for the calibration setting and how to enter calibration mode.

But the calibration settings are a bit different with the predefined COdE values on these VolvoPenta tachometers (made by VDO). You would need either a handheld tachometer or something similar. I used a piece of white tape on the crankshaft and a techometer app on my phone as a handheld tachometer.

Once you have the handheld tachometer you would just have to test different COdE values to find the one closest to the correct rpm. Once you have the best COdE value you can fine tune the remaining difference.
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Old 30-09-2020, 01:48   #13
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

Quote:
Originally Posted by jonase View Post
You can use the above link to a manual to find the button on the back for the calibration setting and how to enter calibration mode.

But the calibration settings are a bit different with the predefined COdE values on these tachometer. You would need either a handheld tachometer or something similar. I used a piece of white tape on the cramkshaft and a techometer app on my phone as a handheld tachometer.

Once you have the handheld tachometer you would just have to test different COdE values to find the one closest to the correct rpm. Once you have the best COdE value you can fine tune the remaining difference.
Thank you! And i have the right RPM´s from my NMEA 2000 from diagnostic port to my GPS so i can just make sure they are the same.. I will try the different codes until i am close enough for the calibration part :-).

Thank you guys..
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Old 30-09-2020, 05:17   #14
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

Use code 14 for your KAD 44.

To set the code you need to use the small button on the back of the tach which is found in a small hole at about 4 o’clock position. Push in the button with a stiff wire, small screw driver, etc.
Set as follows:
- Key off, push the button in and hold in
- turn key on, then release button.... tach will say “code”
- again push the button in and the tach will begin to count up thru the code numbers. Release the button when it gets to 14.
- wait 10 seconds for the code to be accepted and when the code goes back to engine hours you can turn the key off.
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Old 30-09-2020, 09:47   #15
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Re: Choosing correct COdE value for VDO tachometer after alternator replacement

Quote:
Originally Posted by DougR View Post
Use code 14 for your KAD 44.

To set the code you need to use the small button on the back of the tach which is found in a small hole at about 4 o’clock position. Push in the button with a stiff wire, small screw driver, etc.
Set as follows:
- Key off, push the button in and hold in
- turn key on, then release button.... tach will say “code”
- again push the button in and the tach will begin to count up thru the code numbers. Release the button when it gets to 14.
- wait 10 seconds for the code to be accepted and when the code goes back to engine hours you can turn the key off.
Hi there!

Perfect info..
Much appreciated

Regards
Jan
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