Crank sensor

[sawood12]

There are two sensors on top of the clutch bell housing at about 12 o'clock. These are the reference sensor and the speed sensor. They are both actually the same part number but do different things. If your car is not starting at all then it could be your reference sensor as this is classic symptoms. If this sensor is faulty then the ECU will not switch on the ignition circuit - engine will turn but not start. However if it does start it wont cut out on you and will run perfectly.

There is a crank sensor also but i'm not sure where this is or what it does (I think it is under the engine somewhere).

I had a problem with my car where it would not start intermittently. I eventually got the RAC man out who was of an older generation and clearly quite experienced. He recognised the type of engine management system straight away from his time working on cars through the '80's and pretty much knew what it was right away. Within 5 mins he had diagnosed it. I went and bought a new reference sensor (£75) and when I went to install it I notced that the original one was loose. I tightened it up and i've had no problems since. So now I have a brand new reference/speed sensor on my spares shelf!

Funnily enough my Focus is in for a new speed sensor at the moment. The symptoms for this was that everytime I would stop at a junction or round about as soon as I depressed the clutch the engine would cut out. It would start perfectly again and run fine but at the next junction it would just cut out as soon as I depressed the clutch. I'm assuming you'd get similar symptoms on a 944(?).

There is an impedance/resistance test you can run to check if the sensors are faulty. Look it up in the workscop manual or Clarkes.

 

[peanut]

the crank sensor is attached just below the speed sensor on the top of the crankcase,

 

[Panzer944]

The offending article looks like this ... (I'm hoping the picture uploads) ... I did find a bracket with metal spring clip at rear of rocker cover and it looks like this is where that sensor may normally reside ... there was another sensor/thingy nearby with a loop of plastic at its end (?). If this post works, I will post another pic of the same sensor in the photo in that clip. Car still runs fine. Thanks for info about Photsohop website ... I did try to join but I had to download Flash v9 and although it downloaded OK the website couldn't subsequently detect it (even after a warm and soft boot). I will persevere. Thanks to all for hints/tips - much appreciated.

 

[Panzer944]

This photo shows the mystery sensor in that spring bracket (similar location to the one that Peanut mentioned) at back of rocker cover (inlet tract for No4 cyl just visible) - you can see other multiconnectors nearby and the damage to the plastic end of this sensor - also you can see the other sender/thingy I mentioned above with the loop of plastic at its end ...

The clip is clearly able to retain something larger (longer?) than this sender ... so although it fits neatly in there - maybe it's shorter than it should be (ie broken?) ... any thoughts?

 

[peanut]

that is exactly the same as mine Robert. It looks like your two connectors have been knocked out of their clip bracket at some time. The connector that has the wire loop is I think a bypass. I think this sender isn't used and the two part connector is simply fitted with a loop instead of being connected to the loom

 

[Panzer944]

Nick - thanks ... car still drives OK ... so, I'll leave that sensor in the clip and hope all is well. As I mentioned in an earlier post, the car had to have a new head gasket recently and I used that opportunity to replace valves, springs, guides and all seals (she has done 165K miles after all) - maybe it got dislodged or even 'mullered' during this work (very unlikely to be the latter ... to be fair, PorscheShopHalesowen have always looked after her). Thanks again.

Update: after downloading the workshop manuals from ProMax' site (much appreciated), and looking through them ... the sender with the loop looks to me like the Lambda sensor (I assume it has a loop to provide a form of resistance to spoof the DME (?)) ... and it is clear that this sensor should be in the clip (as per Nick's photo) so I have removed the mystery sensor and replaced it with the Lambda sensor ... I haven't yet found what this other sensor is for (secondary temp sensor? O2 sensor?), so, I looked on e-bay for replacement O2 sensors and, whilst they all look similar to each other (no real surprise there!), none of them look like the one I found dangling next to cyl block in my car.