Quote:
Originally Posted by racerbruce
You guys are freaking amazing.
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That's kind of you to say.
So hey, I now actually understand how the S54 VANOS control is different than other VANOS / variable cam timing, and more importantly, I understand
why. I've never seen this written in one place before so I'm just writing it here in case it helps other folks understand in the future.
Each cam has a separate advance / retard solenoid, and that was bending my head for a long time, especially after I saw that AEM drives that pair of solenoids using exactly inverted maps (i.e. if "advance" is at 80%, "retard" is always at 20%, and vice versa). I've read every bit of technical and training literature BMW made available for the S54 and I still couldn't really grok why that was important until today I read this in the WDS:
"When the relevant optimum camshaft position is reached, the solenoid valves maintain a constant oil volume in the adjustment cylinder on both sides of the chamber so that the camshafts remain in the corresponding positions."
Oh, for crying out loud. The VANOS solenoids control pintle valves between the high-pressure side of things (including the accumulator) on either side of a diaphragm, and it is the difference in pressure between the two sides of the diaphragm that dictates its position and therefore how far the splined shafts push into the cams and therefore how advanced / retarded the cam timing is.
Lots of interesting implications of this, but the most / least interesting implication is that I don't have to do anything even remotely fancy to drive it using the Infinity - just need to convert low-side (ground-switch) to high-side (+12V-switch) PWM with some reasonable amount of current-handling capacity and the rest is straightforward.
Solved the ignition coil situation by ordering a pair of AEM 30-2843 3-channel coil driver modules. Should make things nice and neat.
Finally, I have the whole ECM wiring harness (well, all of it that I care about) for the Z4M mapped out with wire colours and signal names and am integrating that with my previous draft wiring diagram. Should be able to sort out VANOS coil drivers tonight / tomorrow and then actually start building this new harness.