MD2B rpm sending unit

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Vronsky

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Hi All,

My RPM gauge is not working, and I'm suspecting the sending unit is defective.
I believe this unit concerns a Hall Effect sensor.
Does anyone know how I can test this sending unit, ie. how much resistance (Ohm) should be measured if okay ?
Also, how much voltage should I normally read on the two connecting wires ?

Also, one of the blade connectors has now broken off (unit was already defective beforehand):
can this be restored/soldered by a workshop ??

THANKS,
V.
 
Vronsky said:
Hi All,

My RPM gauge is not working, and I'm suspecting the sending unit is defective.
I believe this unit concerns a Hall Effect sensor.
Does anyone know how I can test this sending unit, ie. how much resistance (Ohm) should be measured if okay ?
Also, how much voltage should I normally read on the two connecting wires ?

Also, one of the blade connectors has now broken off (unit was already defective beforehand):
can this be restored/soldered by a workshop ??

THANKS,
V.
Click to expand...

The RPM sender unit is most likely be a VDO unit

The various units are listed here

https://www.vdo-instruments.com/sensors/speed-rpm-and-rotational-sensors.html

It will be easier to to identify is you can post a picture

It looks like item 21 on this breakdown draving

https://www.marinepartseurope.com/en/volvo-penta-explodedview-7742090-30-13792.aspx
 
Last edited by a moderator:
Rogershaw said:
The RPM sender unit is most likely be a VDO unit

The various units are listed here

https://www.vdo-instruments.com/sensors/speed-rpm-and-rotational-sensors.html

It will be easier to to identify is you can post a picture

It looks like item 21 on this breakdown draving

https://www.marinepartseurope.com/en/volvo-penta-explodedview-7742090-30-13792.aspx
Click to expand...

I believe that the Volvo unit is inductive and senses the timing gear teeth . The items at the bottom of this page seem to match especially. P/N 340-804-007-002A. 28.5 mm thread length 18 mm .

I get a reading of around 1500 ohms one from my md2b. These things certainly fail from time to time and cost around £70 from Volvo.
 
Thanks, I'll check your readings with my unit, but are you sure this is an inductive sensor?
Inductive sensors usually have 3-wires, while 2-wire sensors seem to be Permanent Magnet Generators >>
https://axleaddict.com/auto-repair/DIY-Auto-Service-Pemanent-Magnet-and-Hall-Effect-Sensor-Diagnosis-and-Testing

Bilgediver said:
I believe that the Volvo unit is inductive and senses the timing gear teeth . The items at the bottom of this page seem to match especially. P/N 340-804-007-002A. 28.5 mm thread length 18 mm .

I get a reading of around 1500 ohms one from my md2b. These things certainly fail from time to time and cost around £70 from Volvo.
Click to expand...
 
You can get a new rev counter for £50 and connect it to the W terminal on your alternator if you have one, as most seem to.
 
Thanks! Yes there are alternatives, even much cheaper than the W-terminal solution, but I first like to try to restore the original thing (in a cost-reasonable way)

Cheers,
V.
 
Hi,

This is of a Swedish forum, a guy measured his sensor on a MD17 (which has the exact same sensor).
I am having this issue with the sensor on my 2002, so hopefully you solution can help me too.

Resistance: 1.06 kohm. (1060 ohm) when disconnected.
DC with ignition on (position 1): 0.26 V
Idle (800 rpm): 0.22 V DC and 0.97 V AC.
2000 rpm: 0.22V DC and 1.66 V AC

Please post your measurements if you can.
I did not get anywhere near these figures with mine, disconnected resistance is infinite so I believe it is dead..

Cheers,

Otto
 
Hi there...did anyone get to the bottom of this one? Is it a 'hall effect' or other type of sensor. There seemed not to be any conclusion. My sensor is also playing up on my MD2B and I've tested the gauge at it is ok.
 
In the end, I used a handheld laser RPM tool (Aliexpress) to check RPM of the flywheel (idle & WOT).
Worked fine as alternative for me.
 
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