Cummins Tacho pulse

[Liambennett]

Hi all, I’m trying to work out the pulse setting for a new VDO tacho that I have installed.
The engine is a Cummins VT555m.
The Tacho generator runs off the fuel pumps.

The workshop says the following

The V-555 engine fuel pump operates at 0.786 times engine speed. Because of this reduced fuel pump speed, a 1.57:1 fuel pump tachometer drive must be used in V-555 fuel pumps instead of the standard 2:1 drives used in other applications. This 1.57:1 tachometer drive ratio permits accurate engine speed reading for applications that are connected directly to the fuel pump tachometer drive shaft.


It is extremely important that the proper tachometer drive be used on V-555 engines. For example: If the standard 2:1 ratio drive is used on a V-555, low tachometer speeds would be indicated and any on-engine governor adjustments would be made dangerously high. Conversely, if a 1.57:1 ratio drive is used in a standard fuel pump, speed reducing adjustments might be erroneously made. Refer to Table 5-1 for comparison of V-504 and V-555 engine, fuel pump,


Any ideas how many pulses I need to set on the Tacho ?

 

[Comodave]

Contact Lauderdale Speedo. They programmed my VDO tachs for a very reasonable amount. Quick turnaround.

 

[EngNate]

Why can't you use a hand held photo tach and set your VDO to match?

 

[Comodave]

My VDO tachs are programmable. There may be a way to do it manually but the directions were not very clear so I had Lauterdale Speedo do mine. For two they charged about $60.

 

[Liambennett]

I’m able to program the gauges, I just need the number of pulses taking into account the fuel pump is slower than the engine

 

[Comodave]

My tach sensor comes off the gear teeth that the starter drives, forget the correct name right now. Probably call Cummins tech support for the pulse info. 800-286-6467