jonand 0 Posted May 16, 2006 Hi All, Having completed my autograss racer chassis - the engine will not now start. Its a 405 unit running Motronic 4.1, and ran fine before the build . I have done all the normal checks and it seems to point to a failed CAS sensor as I can get no signal back to pins 23 and 25 on cranking. This in turn presumably is telling the ECU that the engine is stationary and therefore doesnt energise the pump relay. Can anyone advise on how to test this sensor before splashing out on a new one ? And does anyone have a 405 Mi wiring diagram with the two row Motronic 4.1 (I have the Bx version - but wire numbering is different) Thanks Jon Share this post Link to post Share on other sites
Dream Weaver 2 Posted May 16, 2006 Put a multimeter onto 2 of the pins of the CAS (trial & error) and you should get a reading of approx 515 ohms resistance. If you do then the CAS is OK, if not its buggered. Share this post Link to post Share on other sites
jonand 0 Posted May 17, 2006 Put a multimeter onto 2 of the pins of the CAS (trial & error) and you should get a reading of approx 515 ohms resistance. If you do then the CAS is OK, if not its buggered. Hi Dream Weaver, I've done that and got 512ohms, but I cannot generate a voltage signal back from the sensor when cranking the engine - I've also noticed that the tachometer doesn't move on cranking either. Do you think my original diagnosis is flawed ? Cheers Jon Share this post Link to post Share on other sites
C_W 3 1 Cars Posted May 17, 2006 I'm not sure whether my revcounter is sticky but I find that it doesn't move on cranking (i'm sure it used to bounce a bit) but now it only moves when its started. I'd say its unlikely to have failed whilst the engine was out and is most probably a power fault somewhere. Share this post Link to post Share on other sites
Dream Weaver 2 Posted May 17, 2006 I had severe problems with the CAS on mine when I finished the build. The engine wouldnt crank (Emerald has an LED to tell you whether its getting the signal). Tested the 1st CAS and it read 0ohms, so got a new one which was reading 515. Tried that and it still wouldn't work. In the end it was the immobiliser on the ECU that was still switched on. Thats all the experience I have of them though. May be worth checking the shielded cable back to the ECU to make sure there are no cracks anywhere??? And you could try connecting it to the ECU then testing the readings by lightly tapping the CAS against something metal? Share this post Link to post Share on other sites
jonand 0 Posted May 18, 2006 I had severe problems with the CAS on mine when I finished the build. The engine wouldnt crank (Emerald has an LED to tell you whether its getting the signal). Tested the 1st CAS and it read 0ohms, so got a new one which was reading 515. Tried that and it still wouldn't work. In the end it was the immobiliser on the ECU that was still switched on. Thats all the experience I have of them though. May be worth checking the shielded cable back to the ECU to make sure there are no cracks anywhere??? And you could try connecting it to the ECU then testing the readings by lightly tapping the CAS against something metal? Thanks Guys I have checked continuity from the sensor back to the ECU and appears OK, I have connected the sensor back to the ECU with it removed and tried to pick up a signal by moving it across metal - no signal. Ultimately I'm not sure whether the sensor should be generating a voltage signal (which I have tested for - with result = 0) or some other signal form e.g. resistance change (note static resistance = 512ohms) Ideas anyone? Thanks Jon Share this post Link to post Share on other sites
