Installing a VEMS unit on a stock 89 Porsche 911 Carrera 3,2.
http://www.vems.hu/files/MembersPage/MacB
Engine specs
- Motor 3,2litre normally aspirated
- number of cylinders=6 (even fire)
- trigger system is 2 VR sensors on flywheel / starter ring gear (crankwheel)
- rev sensor is sensing 129teeth per crank rev
- 43*3, so divide-by-N N=43
- the rest like reference tooth almost like with 3 teeth on the crank: a c003 trigger if sectrig comes just from 1 crankpulse, ( or c006 if camsync is also installed - which is not, at least initially )
- TDC sensor is sensing 1 pin on flywheel (don´t know yet how many degrees before TDC). Will likely need to have (access to) a strobelight to verify all is well.
- stock NTCII at cylinder head #3
- AFM (flap type) will be removed, will use TPS instead (exchanging stock idle and WOT switch)
- idle control valve is the "silver cigar" BOSCH thing, two wires to ECU, so PWM
- IGN distribution will remain untouched in first step, stock coil, stock distributor
- stock fuel injector BOSCH 0-280-150-158 low-Z (2-3 Ohms)
- wideband O2-sensor will be used intead of stock narrowband
- no MAP. It would be easier to tune with a MAP sensor, but also possible with TPS, with more work
- no airtemp sensor planned. The MAT sensor is almost a MUST (in a normally aspirated engine MAT sensor can be an NTC in the air-filter, very simple and cheap, just make sure the engine will never inhale it)
- Firing order is 1-6-2-4-3-5 for the Carrera
- wiring should remain mainly stock with stock-DME-connector and only additional wires for wideband, TPS and so on
- planning to use alpha-N only
Trigger: div-by-43
- primary trigger: 129 is 43*3
- that is 43 per event: 43 is a prime number so cannot be divided. Therefore divide by 43 is the way to go with this trigger: the only way
- 129 means 258 for a full engine cycle, the max value for "Coil-type" + "normal" is 255 ! (and using divider is a must anyway, because only that allows a race-condition between secondary trigger and primary trigger, should the 2 falling edges of primtrig-VR and sectrig-VR be close)
- So I need to use "Auditrigger DivbyN" option and a "Audi trigger divider" of 43.
First trigger tooth will be 0
Next trigger tooth 1
Angular width of teeth is 120°
reference tooth is 0-5-4-3-2-1
"Auditrigger" option for the ECU.
- any drawbacks due to the 129 teeth variant, like rev limit or so ?
- timing from 3 pulses means that (crankhome-VR) pulse must be 35-75 crankdeg BTDC. Also, during cranking, relative angular acceleration is high (does not double, but RPM * 1.3 is possible) between consecutive events, so, as a result the actual spark will be slightly delayed during cranking when the engine suddenly comes alive - this can be somewhat compensated with a few degrees higher sparkadv at 400 RPM. Does not effect normal running (even quick acceleration in gear1).
- if really 129, than 43 tooth per event per (if 6cyl). But with divby3 (and 43 tooth total,) next_trigger_tooth=14, 14*3=42 tooth (~2.75 degree percylinder spark delay) can be used to compensate this tooth...
- important: divby4 (11*4=44) is clearly invalid, there is no integer T=tooth_count for which 4 * T = 129 so trigger error would always be on with that (if it would run at all)
- secondary trigger is the TDC-mark on flywheel
- what to do for the low-Z-injectors ? is the 30V flyback ok and do i need the inline resistors (6,8 Ohm) ?
- order with "low-Z extension" option if you keep the high-Z injectors (and configure PWM-ing: ~35% PWM duty after 1msec full-voltage)
Here is what I ordered:
- 1 x Wideband connector
- 1 x Econoseal18-Wire side
- 1 x EconoSeal36-Wire side
- 1 x ECU VEMS V3
- 1-wire interface: no
- EGT input: no
- Flyback: LowZ active flyback 8ch
- ignition driver: 8
- Knock input channels: 0
- LCD connection: no
- MAP connection: offboard(electronic)
- mounting-style: no-screws
- primary_trigger: EC36/27 VR
- PS2 connection: no
- secondary_trigger: auditrigger w/camHALLinverter
- Service: normal
- withSDcard: no
Other stuff:
- TPS from E36 (Hella): 6PX 008 476-111
- WBO2 (Bosch): 0 258 007 351
- MAT (Bosch): 0 280 130 039
Related projects by other users:
Looks like a similar setup: MembersPage/KevinBlack/PorscheTurbo