Smart CDI Cam Question

[MICR0]

I’ve recently started a project for an experimental vehicle based around a Mercedes/Smart 800cc CDI diesel engine. I’m working first on getting the motor running with an aftermarket ECU but am having a tough time figuring out how the cam position is sensed by the ECU. There seems to be no sensor anywhere along the cam, cam drive or valve train. Since the injection is purely electrical the cam phase must be known by ECU in order to determine when a piston is in its compression stroke (yes?). Does anyone here have any experience with CDI Diesel engines that may offer some insight?

Thanks

 

[dcar11]

I'm also developing a prototype vehicle around the Mercedes/Smart 800cc CDI diesel engine. Odd!

I can't help you on the technicals but I know that we get our ECU (and all other smart diesel accessories) from Shrick. They're in Germany and they're not particularly helpful but you might get lucky.

http://www.avl-schrick.com

Good luck!

d

 

[70btdc]

I have seen small engines like this that 'test' fire the injector with retarded timing at each TDC during cranking and monitor RPM, then lock the correct TDC afterwards. Saves the cost of the sensor.

 

[MICR0]

I recently spoke to someone that suggested that the ECU is looking at the spaces between the timing pulses coming off the flywheel. It’s able to “see” the deceleration of pulses as the pistons are on their compression strokes and can recognize the pattern. I guess with sample rate and processor speed not being an issue this sounds plausible. Can someone confirm this?

 

[WGJ]

Yes. Some European Ford engines do/will do this.

Bill

 

[WGJ]

Just checked on that - the torsional data collected via CPS signals are used for misfire detection and not position.

Bill

 

[70btdc]

I dont think Ford generally use this method. There is one I4 Ford SI engine that uses the difference in spark dwell to determine compression stroke, saving cost of sensor, but its certainly not accross all engines, especially CI.

 

[patprimmer]

Bill might just be in a position to know exactly what Ford use and even why they chose it.

Regards
Pat
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[70btdc]

OK, thanks Pat.