oxides
Well-Known Member
Old fashioned petrol tachos run off the distributor/coil connection and take the ignition pulses and divide by 4, 6 or 8 depending on the number of cylinders to get rpm.
Old fashioned/aftermarket diesel tachos count alternator output pulses pre diode/regulator and have to perform a more complex division based on the number of poles in the alternator and the ratio of engine revs to alternator revs.
Modern tachos have a dedicated sensor on the crankshaft/flywheel and count engine revs directly (this may be integrated into the engine ECU and be part of the injector/ignition timing). Sounds like yours is the latter. I presume there's some form of electronic box running the engine which may have a tacho output.
Old fashioned/aftermarket diesel tachos count alternator output pulses pre diode/regulator and have to perform a more complex division based on the number of poles in the alternator and the ratio of engine revs to alternator revs.
Modern tachos have a dedicated sensor on the crankshaft/flywheel and count engine revs directly (this may be integrated into the engine ECU and be part of the injector/ignition timing). Sounds like yours is the latter. I presume there's some form of electronic box running the engine which may have a tacho output.
dr pepper
New Member
Yep thats true, the alty ought to have a w terminal if it came from a diesel engine.
T'other way is to put your own w terminal on, do a google for alternator phase tap.
You just connect a wire to one of the 3 windings going into the rectifier.
It just so happens I have a rev counter on eblag now, its 24v though, i tested it on 12 but i wouldnt guaranntee it'd stay working on 12.
T'other thing is the belt ratio, if you use a tacho from a vehicle with a diffo belt ratio it'll read wrong.
The lucas ACR range of altys on landys are 11 pole and produce 22 pulses for rev, multiplied by the pulley ratio.
Prestolite do a tacho with a dipswitch on the back to program the number of poles and belt ratio, but your looking at ££££££££'s.
T'other way is to put your own w terminal on, do a google for alternator phase tap.
You just connect a wire to one of the 3 windings going into the rectifier.
It just so happens I have a rev counter on eblag now, its 24v though, i tested it on 12 but i wouldnt guaranntee it'd stay working on 12.
T'other thing is the belt ratio, if you use a tacho from a vehicle with a diffo belt ratio it'll read wrong.
The lucas ACR range of altys on landys are 11 pole and produce 22 pulses for rev, multiplied by the pulley ratio.
Prestolite do a tacho with a dipswitch on the back to program the number of poles and belt ratio, but your looking at ££££££££'s.
