fitting a rev counter to a oil burner

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dvb668w

dvb668w

Active Member
Posts
257
Location
Gillingham Kent
Hi,
I have a Prima engine fitted to my SerIII LWB and I would like to fit a rev counter,

Anyone know who I go about fitting one to a diesel engine ??

Thanks JJ
 
I have been told from teh supplier...
"only work with vehicles which have a standard clock pulse train"

Now I need to see if the montego lump and a clock !!!
 
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.
 
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.
 
Just had a look at the prima engine and its all mechanical so no direct pulse output for the tacho I'm afraid. Looks like the alternator route. Unless you do what this bloke has done... integerspin.co.uk/rev-counter.html
 
hi, thanks for the link. had a very quick scan and at the end it mentions the "W" terminal. so if my alty has a W connection couldnt i just connect the rev counter to that??

Thanks jj
 
Your 'counter will have 3 wires, a neg, pos and the w, you have to sus out which.
A 'counter for a petrol engine wont work, or at least will wildly overread.
 
It'll only work if your tacho is designed to fit the alternator w terminal which it doesn't sound like it does. Connecting it up may result in in reading about 22 times higher than it should!
 
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