Outer Limits 4x4 Board

Can anyone tell me approx how many pulses per revolution a diesel tacho gets? The vehicle is a BJ73 cruiser, 3b engine (4cyl diesel) I'm using the dash from this vehicle in my FJ73 with commodore V8 and need to interface the tacho.

I'm assuming the V8 will give 4 pulses per revolution from the coil

Thanks

A v8 will give 8 pulses per revolution, one for each cylinder. Not sure on diesel though, maybe an intsrument repair shop mnight be able tyo help.

Ringwood Speedometer Service
693 Whitehorse Rd Mitcham 3132 (03) 9874 2260

Give them a ring, Had my speedo fixed there and they did a good job.

TRITON90 wrote:A v8 will give 8 pulses per revolution, one for each cylinder. Not sure on diesel though, maybe an intsrument repair shop mnight be able tyo help.

I come from an electronic background so I could be wrong... but doesn't each cylinder fire once every 2 revolutions being a 4 - stroke engine?

V8 Middy wrote:Can anyone tell me approx how many pulses per revolution a diesel tacho gets? The vehicle is a BJ73 cruiser, 3b engine (4cyl diesel) I'm using the dash from this vehicle in my FJ73 with commodore V8 and need to interface the tacho.

I'm assuming the V8 will give 4 pulses per revolution from the coil

Thanks

conventional (distributor) V8 gives 4 pulses per revolution - if you have coil packs it might be 2,4 or 8 pulses per revolution.

the number of pulses for the 3B tach will depend on if it is a flywheel or pump sensor - the earlier, inline pump engines (to 1987ish?) use a sensor on the bellhousing to count the teeth on the flywheel - so the number of pulses per revolution is simply the number of teeth on the flywheel, which someone with a 3B shuld be able to tell you.

if it is the later motor with the rotary pump, there is a toothed wheel inside the pump that provides the tach pulse, someone who is onto pulling these things apart will know how many teeth - the you have to divide by 2 as the pump does 1 revolution for every 2 crankshaft revolutions.

the frequency is only one part of the equation, you will also have to match the amplitude of the tach signal, the V8 will provide a (messy) 12v square wave, the signal from the diesels will be from a magnetic/hall effect sensor, so the voltage will be very low (probably a fraction of a volt) and be more of a sine-wave shape; the conversion between one and the other is potentially complex especially if the high frequency you require is not a direct multiple of the signal generated by the V8.

if Marks etc have a converter available, it is almost certainly cheaper (definitely if your time is worth anything) to just buy the converter and plug it in. If it was my car I'd fiddle and try and get it right but it is not going to be an easy job.

cheers

Brian

Aaaaahhhh Dumbdunce, it always seems to be you with the answers.

Jaycar has a kit designed for speedo calibration that can increase or decrease the frequency by 1 to 99%. That bi is no hassle. Its more to do with square vs sine wave and as you say, amplitude.

I was thinking of hooking up a signal generator to the tacho and start with a low amplitude and see whether or not it'll read a square wave. Other option is to try and find someone with a 3B who will let me hook up an Ocilloscope and see what the signal is.

I already called Marks cause, as you say, when you work out the time vs money equation, its always cheaper to buy off the shelf. They don't have anything. The other option I am persuing is to trade my instrument cluster for an FJ cluster then use the Marks adapter.

If anyone knows any of the info that could eliminate steps from the trial and error process, please let me know!!!!

Thanks

For anyone who's interested, I hooked up a square wave generator to the tacho the other day and found out that the diesel tacho will work on about a 2V signal and needs a signal 27 times the frequency put out by a V8

I'm sure we covered frequency multipliers in 2nd year at uni... that was a while ago so some head scratching to be done!!

your cruiser is not a MWB but a SWB as i have a fj 73 landcruiser and bj is bundera. i converted to a el efi six in mine and use a 10 pulse for that however i was told that commoders use a 12 pulse and xf falcons use a 9 pulse all from a vdo specialist so i sugest u talk to one as they very.

fj is petrol, f series engine eg 2F 3F (mine was a 3f)
bj is diesel B series engine eg 3B

*j70 is short wheel base
*j73 is MWB
*j75 is LWB troopy

bundera I'm not so sure on but its based on the hilux running gear and one engine I know it came with was a 22R so they get called RJ-something or other

(this has all been done to death in the toyota forum)

That aside, where do I find a VDO specialist?

fastone wrote:your cruiser is not a MWB but a SWB as i have a fj 73 landcruiser and bj is bundera. i converted to a el efi six in mine and use a 10 pulse for that however i was told that commoders use a 12 pulse and xf falcons use a 9 pulse all from a vdo specialist so i sugest u talk to one as they very.

73/74 are all mid wheelbase. BJ is a B series diesel engine powered landcruiser - B, 3B, 13B-T etc engine. Bunderas are LJ or RJ, they are powered by (mostly) 22R petrol or 2L-T turbo diesel engines.

V8 Middy's truck is deifintely a mid wheelbase. the rest of your information really isn't relevant, but thanks for trying to help.