hmd

Bingo. Thanks.

Bri Bro

The DL1 already has two RPM inputs, one is high level and the other is low level. Am I missing something here?

TT

No, it just would have made this thread much shorter if he had initially posted what unit he was hooking up.

hmd

Well yes. But at least the thread is half technical.

I was so focus on wiring in the SMT6 that I forgot to look at the high voltage pulse of pin 1 on the DME, I spent all the energy and efforts trying to find the 0-5 pulse.

special tool

"Measure the time-interval between each grounding pulse (t). Then plug into 15/t=RPM"


Danno - 15/t???? Are you sure about this firing for Motronic?

Danno

basic conversion of period to frequency f=1/t and t=1/f
since there are 60 seconds in a minute, we use 60/t
so if t=1, that is 1 second per pulse, we get 60/t = 60/1= 60rpm for a 1-cylinder engine
since there are 4 cylinders, 4 pulses per revolution, we divide by four 60/t*4 = 15/t

if we measure an period of 0.0025s, that means we have 0.0025s*4= 0.010s per complete revolution, 10ms
we can use 60/0.0025s*4 or 15/0.0025s = 6000rpm.

special tool

Danno - the motronic makes only 2 pulses per revolution.

TT

Danno's running a Chevy small block in his car.

Danno did a job with quantitative numbers, now if he can convert them into values appropriate for a 4 cycle engine and everything becomes very clear.

jimbo1111

I'll stay away from this one.

jimbo1111

What's up Special tool. The Vitesse boy's threaten to cut you off if you talk to me?

awilson40

he's Baackkk

TT

For posterity's sake lets get the calculation correct:

basic conversion of period to frequency f=1/t and t=1/f
since there are 60 seconds in a minute, we use 60/t
so if t=1, that is 1 second per pulse, we get 60/t = 60/1= 60 cycles per minute for a 1-cylinder (4 cycle aka 4 stroke) engine
since there are 4 cylinders, 4 pulses per cycle, we divide by four 60/t*4 = 15/t cycles per minute
There are 2 revolutions per cycle so:
15/t cycle/min * 2 rev/cycle = 30/t rev/min (RPM)

So the correct conversion for the 951 is RPM = 30/t where t is the time between ignition pulses.

Jeremy Himsel

= Another blown customer's motor

RobNL

So do you mean he's capable of getting an engine up to 12000 rpm before it blows. Wow, so just with some extra changes to make it stronger it would be awesome .

BTW, TT why do you use the ignition pulse? Would the length between each pulse not be influenced by changes in timing, causing spikes? Why not the speed sensor? That gives just one pulse per rotation and that's only influenced by the change in speed.

Furthermore are the number of pulses to the RPM-display the same as the number of pulses to the ignition?

TT

The ignition signal is a very common element on cars so the automotive dataloggers use it as an input to determine RPM.

An abrupt change in timing can affect the period, but that would be for just one interval. It would be correct after that, easy enough for the controller to filter/average or even throw out the bad one.

You'd have to ask Porsche why they didn't use the reference signal. Most likely the decision was driven by the signal type needed by the available tachs which goes back to the first point about the ignition signal.

Yes.