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 vems.ee
The car as it is 25/06/2014
- 6 cylinder
- Upgraded "cup" cam of unknown lift and duration
- Decat pipe
- Permanent 4WD with centre and rear active differentials
- 55pin Motronic
- Twin spark
- Twin distributor
- Twin coil (not coilpack or cop)
- Standard 218cc/min at 3.8bar high impedance injectors (Bosch p/n 0-280-150-731 193.9cc/min @ 3bar 16ohm). Note while there is agreement on the flow at 3bar, when run at 3.8 suggested flow values run from 218cc to 250cc)
- 2 wire style Bosch ISV
- Intake "resonance flap", vacuum actuator, electrically activated
- Carbon canister vacuum switch
- VR crank trigger on flywheel 60-2, missing tooth is 84 degrees BTDC
- Hall sensor in distributor
- 4WD wheel sensor on rear diff, Hall
- 2x ABS wheel sensors
- Cylinder head temperature sensor (NTC)
- 2 knock sensors
- Narrowband O2 is fitted to most models, but this car had a factory option selected to remove this
- Standard AFM (Flap style)
- AIT (NTC type inside AFM)
- Altitude potentiometer
- Standard idle and wot switch (no analog TPS)
- Source Porsche 964 PnP? unit from Peep Paadam (vems.ee) to agreed specification, with suitable base map.
- To begin with I will keep the twin coils and distributors, unit will be supplied with additional earths to allow coilpack/wastedspark at a later date.
- Fit an analog/potentiometer TPS (from Opel Omega A - as per Peep's suggestion)
- Remove AFM and add a separate MAT.
- Add wideband 02
- Convert to Speed Density (MAP) operation
- Test idle and review if AplhaN?+Map compensation would be better
- Check duty cycle and review if uprated injectors are required
- Measure and make bracket for TPS
- Measure and make AFM replacement pipe and hose joiners and either source top-hat adapter to keep std airbox
- Wire old AFM plug for AIT/MAT sensor (neatly and reversibly)
- Check continued operation of HVAC (this car does not have AC). There is one pin on the ecu which comes from the HVAC instructing not to cut fueling on overrun if heater is on - this is to maintain heat exchanger temps
- Check continued operation of ODB for ABS and 4WD diagnosis and testing
- Operation of "central informer" check engine light
- Find standard DME injector dead time table
- Find standard DME injector sequential vs batch fire operation
- Find standard AIT vs ignition retard and fuel adjust tables
- Check the distributor hall sensor is sufficient for ecu to camsync for full sequential injection and standard injectors will fuel adequately in full sequential mode.
- Check Peep will have performed O2 calibration on supplied unit
- Check best location for MAP sensor take off (before or after)
- Check best location for AIT/MAT sensor
- Is EGT sensing desirable and retrofittable to PnP? unit
- Find guideline EGT for aircooled 911
- Find compatible uprated injectors, and establish if mods to ecu will be required to run low impedance aka "low-z" injectors.
Rennlist procjet thread and discussion
964 55 pin DME Motronic pin out here
further information (some for 993 specifically)
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.