rpm tacho promlem

[steve rees]

ok all you tech people out there
gqtd42
what would be causing tacho neddle to be jumping all over the place for ex sitting at 110 rpm normally sits 2600rpm it might sit there for few seconds then drop down to 0 then backup to1000rpm and so on basiclly all over the place
anyone had simular prob or know why this has happened never done it b4 in 10yrs ive owned her
any help would be appreciated
cheers steve

[threedogs]

@mudnut is the go to person you seek

[AB]

It could be your wiring on the taco sensor

Have a look at this pic left hand side of the alternator where the wiring is hanging down

Check the wiring condition right behind the sensor

It's common for the wiring to fray right behind the sensor which could cause erratic behaviour like you're getting

[PeeBee]

ok all you tech people out there
gqtd42
what would be causing tacho neddle to be jumping all over the place for ex sitting at 110 rpm normally sits 2600rpm it might sit there for few seconds then drop down to 0 then backup to1000rpm and so on basiclly all over the place
anyone had simular prob or know why this has happened never done it b4 in 10yrs ive owned her
any help would be appreciated
cheers steve

This happened on my 2.8 TD before the conversion. I could not get to the root cause, so sent it like that to WA for the conversion. BD ended up taking it out, blew up the replacement then 'did something sexy with a converter box' and replaced it with an RB30 tacho - all good. The comment I got from them was a voltage spike was killing the tacho control board. they also replaced sensors and wiring. I can ask the question as to what they did to get it to function, but it may not be your specific issue. Must admit, sounds similar though.

[mudnut]

If the wiring to the sensor and the loom is OK, then check the socket connection of flexible plastic circuit and the copper conductors for creases or breaks. If no problem is found then check the circuit board of the tacho, They are very easy to remove from the cluster. A lot of the time the fault will be caused by a dry or cracked solder joint, or corrosion of component legs.

[AB]

How'd you go with this Steve?