Adding cam sync to VEMS plug-n-play

Talk and Tech about turbocharged 924/944/968 cars
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four0four
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So, I've been puttering about wasting time adding cam sync to my VEMS install for some reason, figure I'll share some progress here :D


(I've also kept it somewhat documented here, but I don't pretend that wiki is otherwise active)

Two parts are pretty easy to adapt: VAG 058905161B and Bosch Motorsport 0232103037. I'm using the latter, but I did fit the former previously (didn't finish the rotor adaptation on that one). I'm pretty sure you could fit a sensor to the rear of the cam too, I've seen some 911s do this with a bolt added to be picked up. That does your adapter seal against oil though, so this is easier...


Anyway, VEMS requires a masking (or really, inverse mask - so allowing?) pulse generated by the cam sense circuitry for their "auditrigger" trigger architecture. If you check their schematic this is Q13. This means you can't have an arbitrary phase offset, the pulse needs to be squarely overlaid with the TDC pulse from the reference sensor. So, I stuck a bolt in the rotor, measured up the angle at TDC, and printed a bracket:
camhall_measurement.jpg
camhall_measurement.jpg (376.81 KiB) Viewed 486 times
camhall_firstry.jpg
camhall_firstry.jpg (209.16 KiB) Viewed 486 times
And, well:
shit.png
shit.png (98.62 KiB) Viewed 486 times

Some help parsing that:

yellow: width of cam sensor pulse, 13.74ms
green: period of cam rotation, 113.67ms
magenta crank rotation 1, 57.87ms
orange: crank rotation 2, 55.91ms
purple: desired shift of cam pulse, 8.86m


Not sure why, but that didn't line up. Probably to do with precisely where along the face of the sensor it triggered, but even that doesn't account for 30 degrees! That's a lot!

Anyway, shifted it by 28 degrees to land the crank TDC smack in the middle of that cam pulse, reprinted (forgot to take a picture), and:
perfect.png
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Perfect :)

Just finished making the modifications to the ECU to support this - basically needed to swap some inputs around and solder in a single NPN transistor that masks the TDC signal unless the cam signal is also present. Will test it probably tomorrow, and hopefully document the VEMS configuration differences required (basically just doubling of teeth and rearrangement of the tooth trigger table for now - I don't have a harness in place for sequential inj/ign).

Of course I'll be sharing the models and some general directions once I know it works to...any standard.


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four0four
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OK, I know why it was off by 30 degrees - TDC mark comes way prior to TDC, obviously.

Hooked it all up tonight, seems to work great (VEMS sees 24 pulses per reference pulse). Puzzling over the trigger settings and really wishing VEMS was properly open source...The trigger system is really flexible, but also really....well, more evolved than designed :')

I think this is correct, but I'm going to need to rig up a remote hotwire and get out the timing gun to check some things first:
Screenshot 2024-01-09 143320.png
Screenshot 2024-01-09 143320.png (89.67 KiB) Viewed 419 times
Attached is the STL, since this seems to work. Probably going to iterate on it a little bit to add a removable cap at some point, but I don't feel bad putting this out since it seems to function :)
Attachments
cam_sync_adapter_boschmotorsport_+28deg.zip
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Thom
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Good effort, nice work. I am sure you will experience a smoother engine with sequential injection.
What size injectors are you running?


'90 944T - modified somehow

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four0four
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I imagine so! I'll need to do the "make a whole engine harness" project to go fully sequential, but that's probably next anyway. If I could only identify the alternator/starter connector now...

The injectors are Siemens 110324 ("80 lb"). I had stock, and then briefly Bosch 0280155968 in previously, but quickly ran out of fuel.


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