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 NOT need a 1 wire interface), a 4+4 ignition driver (just incase I'm wrong about the logic level), 400kpa onboard MAP sensor, LCD & PS2 for ease of use, knock and EGT sensing, screws
- 30V flyback since you have a resistor pack (and you'll finally use high impedance injectors like the 630cc/min at 3 bar) anyway
- primary trigger=VR
- 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 injectors.
- stepper motor (or in general idle air valve) adds AIR
- injectors add fuel
Trigger - current state
Please keep an updated version of the current state here. Organize thematically, not historically (or not only historically).
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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.
Update 27MAY2008
I have managed to get the RS232 up and running. I am slowly working my way through attaching the sensors.
Update 19JUN2008
For now, I am solving the primary trigger issue by lasering a 36-1 wheel which will be mounted on the camshaft pulley. Then using a sensor, preferably HALL and using that instead of a crank sensor.
Update 29JUN2008
Finally have a rpm signal from v2 36-1 triggerwheel on the camshaft. However, the VEMS gurus are concerned about my trigger wheel design, so I'm fabricating two 12-1 variants, one with missing tooth, one with missing gap. I am now using a VR sensor from a Citroen XM/BX. I hope to scope the wheels tomorrow and undestand a bit more about the amplitude.
Update 22NOV2008
Better slow than never. I have now taken the car off the road and almost finished the wiring harness. I have a few grounds to do before I attach the VEMS, and start configuring.
A few pics:
The TDC sensor signal was checked with a scope and now looks very neat. My configuration concern is how to setup the VEMS to deal with the 36-1 trigger wheel on the camshaft (one tooth is 20 crankdegrees. We have one event every 9th tooth). It allows setting up for sequential injection of course. Ignition will still be wasted spark for starters. Almost like a standard 36-1 (number of wheel on teeth is like that: 35), but some variables resemble a 18-1 setup.
- tooth_wheel=23
- another_trigger_tooth=09
- h[1]=00 1B 12 09 FF FF FF FF
- tooth_wheel_twidth1=50
- tooth_wheel_twidth2=00
The last 3 variables make no difference with 1.0.x firmware.
I'm als unclear on what the modification values for the rpm in megatune are supposed to do, or what they relate to. I would expect a multiplier there, not a number in the hundreds or thousands. Essentially, in one trigger wheel revolution I want 4 injector events (one per injector) and 4 ignition events (2 per ignition module).
Update 30 Nov 2008
First run and first drive today, after an epic battle with the primary triggers... on to tuning!
Update 7 Dec 2008
Finally have the WBO2 properly calibrated. Still wrestling with some cold start issues. EGT sensor has already died. New one ordered with DP engineering. I think knock sensing still needs some work, as does the harness need some cleaning up. Boost control needs attention soon too. I have a few mundane maintenance jobs to do also.
The care drives quite well now. I think it's getting to be time to schedule some time at DP-engineering for tuning.
RPM (tachometer gauge) output for the dash gauge
- some dash only require a 1k pullup to +12V, and that's all. (or a stepper output that can pull to +12V, not only towards ground).
- VEMS can be configured to send a frequency signal out via this output channel. Calibration allows fine-tuning, or even that a 4cyl dash-gauge can be used with a 5cyl or 6cyl engine.
Other (mostly older) dashes require high voltage input: an IGBT output and 220 uH for RPM output "inductive pullup" See [shop item] inductor
As requested, here's the info on the ignition map:
These are the OEM settings, which I copied into the vems.
Here's the current config: