I am trying to specify a pnp system for my 1989 Porsche 964 Carrera 4. The VEMS PnP? unit is built by Peep Paadam of

The car as it is 25/06/2014







Rennlist procjet thread and discussion

964 55 pin DME Motronic pin out here


and here:


further information (some for 993 specifically)


Injector info

Injector flow vs pressure calculation

Standard DME coil dwell time table


Here is a method for measuring dead-time in-car.


Idle car while datalogging, and have a means of changing injector electrical pulse width slowly up and down while logging. Car must have a reasonably stable idle at a fairly fixed RPM, and battery voltage must be constant throughout.

Log MAP, AFR, Battery volts, and Injector electrical pulse width, while idling. Slowly raise and lower injector on time (I did it by changing the AEM's injector dead time vs. battery voltage, across 3 cells, straddling the battery voltage that I was seeing). Slowly raise and lower it until the RPM starts to drop significantly or the car starts to misfire. I could go from 11:1 to 16.3:1 or so and back. Do this several times, it may take you a few minutes.

Then examine the datalogs. Do an XY plot. Plot MAP divider AFR on the X-axis, then injector on-time on the Y-axis. You can use AEMLog for this, or MS Excel. Excel has the advantage of having a linear curve fit ("trendline, linear"). The datapoints should form a line. If you project this line to the Y-axis, the intercept is the dead time. See attached.

In Excel, do a scatter plot, then add a trendline. Select "linear", and in the options, select "show equation". If your data is clean and has little noise, the Y-intercept will show in the equation. If not, select "Set Intercept", and try different values until the trendline appears to describe the quiet part of the data. In my example, it's 930 us. This is for a friend's 750cc RC hi-impedance injectors. Note that on the bottom left of the data, there appears to be an arrowhead shape. This is noise in the data, due to lean misfire, at narrow injector duty cycles / leanness.