I'm thinking of installing a VEMS in my Citroen CX 25 Gti Turbo 2. It's a 4 cylinder, side cam 8 valve, 2500cc, 1:8.5 compression turbocharged, intercooled, wasted spark engine.
I think I have all of the technical documentation to the vehicle, though there are still some minor things to figure out.
Factory standard, it has a Bosch fuel injection system with 285cc 0 280 150 802 injectors (2.4 Ohm impendance, but there is a resistor pack), and the documentation states a max fuel rail pressure of 2.5 bar, less at idle. Max mid range boost i 0.560 bar and at 5000 rpm it drops off to 0.440 bar boost. I have tightened up the wastegate to a max midrange boost of ~0.9bar and 0.8 bar at 5000 rpm. In the last 25,000km or so this has not caused any problems, even though I have no idea how it's possible as 285cc injectors at 2.5 bar in a 2500cc engine at +0.440 bar should only just be able to service the factory 167hp. At 0.8 bar the Hp should be in the region of 200, which would seem to indicate something like a 97% duty cycle on the injectors. The turbo is a garrett T3 type.
Airflow and airtemp signals come from a mechanical airflow meter. There is a GM 16 038 77 MAP sensor, but the signal is only used by the electronic ignition, not by the injection. There is a watertemp sensor, no lambda or EGT. There is a knock sensor type E 001T - 90272. It looks to me like the ignition modules are logic level as the Revue Technique speaks of two circuits one at 1-1,2 Ohm and one at 3500-4000 Ohm.
The RPM pickup is done from the flywheel which is a 72-1 setup with a BDP sensor (which I am now thinking must be a HALL (partnumber EA 20 165 653 with a claimed resistance of 50 Ohm according to the Revue Technique).
- if it's HALL, you can measure output with DVM (ignition on). Push the car a bit in gear 5 and the output will switch between 0 and 5V as the teeth pass
I would like to set up a VEMS for the vehicle in order to increase fuelling and accomodate anything I would like to do in the future. For now, my objective is about 250hp, which should be equivalent of about 1.2 bar boost.
Now, the first thing I need to set up is a buy list. I'm thinking a pre-built VEMS, (do I need a 1 wire interface?), a 4+4 ignition driver (just incase I'm wrong about the logic level), 400kbar onboard boost sensor, LCD & PS2 for ease of use, knock and EGT sensing, screws, power flyback (seems sensible, but I'm not completely clear on the details), primary and secondary trigger hall.
Obviously I'd also want a WBO2 sensor, and some wiring, like the 36pin and 18 pin harnesses and plugs.
As I have an air meter, I'm going to want to replace that, and will probably need a replacement air temp sensor. Are there any suggestions for that?
See genboard/sensors under WebShop (MAT sensor; and Temperature sensor (NTC) - latter only for the experienced.
The car doesn't have a stepper motor, in the factory setup cold enrichment is done through the standard inejctors.
- stepper motor (or in general idle air valve) adds AIR
- injectors add fuel
Update 03APR2008
I've placed an order for VEMS kit with the local dutch experts, and look all set to get started. All the issues with BDP sensors e.d. have been resolved. More as I get around to it.
Update 18APR2008
I\m in the very opening stages of installing my VEMS, essentially at step 1 of the guide. I've made the power/ground lines and soldered the RS232 connection.
At the moment however, I am halted in my tracks because the communication on the COM port is unreliable. I am using a linux laptop and have tried contact both with Megatunix and Megatune over Wine. Initially I thought this convoluted setup might be the problem, but even over terminal, I can generally talk to the vems initially fine, but after a period of time, or really a number of commands, communication becomes impossible. I've checked battery voltage a steady 12,3 volts (engine off obviously) between VEMS grounding and the +12v line. I have yet to check resistance on the serial wires, but obviously I checked them for damage or bad contacts extremely thoroughly already. If there's anyone who has any thoughts I'd love to hear it. I can get a succesful comms test to the VEMS once or twice but it quickly seizes up until the unit is power cycled.