Outer Limits 4x4 Board

I've just put the instrument cluster fro a diesel engine into my petrol vehicle. I need to modify the tacho input for the V8 but how does a diesel get its signal for the tacho? (Obviously not from an ignition coil!!!)

If the signal to a 4cyl diesle tacho is the same as a 4cyl petrol then its easy. If not, I'll have to fork out the $$$ to marks for their adaptor.

Vehicles are Toyota BJ73 dash into FJ73 with Commo V8

Thanks

i have what i believe is a bj42 bellhousing. and it has a sensor hanging off the front of it which points at the flywheel. i cannot see any magnets on the flywheel, maybe it picks up teeth on the ring gear(unlikley). or maybe i'm completly off track. hopefully somebody else can confirm this.

I have just put a diesel in my petrol car, (www.ozsigns.com/aussie/fj80tohzj80) and it[s been nearly 2 months and have not found a decent auto electrician that can get my tacho started, what I do know is that the singal comes from an inductive coil thats on the injection pump.

Ulises

85lux wrote:i have what i believe is a bj42 bellhousing. and it has a sensor hanging off the front of it which points at the flywheel. i cannot see any magnets on the flywheel, maybe it picks up teeth on the ring gear(unlikley). or maybe i'm completly off track. hopefully somebody else can confirm this.

You are correct ,sir. The 3B tacho indeed gets its signals from the flywheel teeth.

Dave

So if I take an input from the back of the coil on the V8, will the tacho read double or will it be out by some random number?

it will probably read a random number, reason being that the sensor on the diesel is reading the actual number of revolutions of the crankshaft whereas in a petrol it reads the electrical pulse from the coil and then the tacho has to convert the signal for the number of cylinders you have.
Cheers
Chris

If thats correct and its definitely 1:1 on a diesel tacho then I should just have to divide the coil pulse by 4 right (8 cylinders firing once each during 2 full revolutions)

If thats the case I may even be able to make something myself to do it instead of coughing up $150 to Mark's for their converter

Thanks

I would suggest that if Marks has an adaptor for $150, buy it. the electronics invloved in making the low frequency, high amplitude output of your coil look like the high frequency, low amplitude of the signal generator of the diesel tach on the flywheel is probably not all that complicated but for the amateur electronics enthusiast it would require about six trips back and forth to Jaycar, three prototypes, and hours of testing to get it right. you might spend less that $150, but remember your time is worth someting too.

if by some miracle the chev ring gear has close to the same number of teeth as the 3B (within 10% would give acceptable results for a low-revving motor) , the get the 3B sensor, drill and tap your bellhousing, and you're set.

Don't some diesels take a tacho signal from the alternator? I'm fairly sure a former colleague was having issues installing a tacho in a diesel Defender, and it connected to the alternator...

Good luck,

Scott

NJ SWB wrote:Don't some diesels take a tacho signal from the alternator? I'm fairly sure a former colleague was having issues installing a tacho in a diesel Defender, and it connected to the alternator...

Good luck,

Scott

yes, many do.