Impulse Sender / Sensor

Guys, what exactly does this do? I know it feeds info on the timing to the ECU, but how does it work in conjunction with the hall sensor, and what is it's specific purpose. Does anyone know what the symptoms would be of a faulty one? I've looked everywhere on the net and can't seem to find any info. In the Porsche tecknik they call it a pulse generator, and in the parts catalogue a pulse sender, but I am stil none the wiser. Cheers, Steve

I'm not sure what the "it" is you're referring to, but I'll take a stab and guess it's the crank sensor. If so, the failure mode is that the engine won't run at all. The ECU needs the signal to know when the crank completes a full revolution; all the ignition timing runs off it & when it's not sending the pulse, the ECU has no idea where it is in the cycle. As far as the ECU is concerned, the crank is not rotating.

Hi, thanks for the reply. I believe I have a faulty CPS or Hall sensor as the car runs until warm, and then if left at running temp idling for a while it will shut off. It then will not restart until the engine temp drops to around 40 degrees. The symptoms are very much like vapour lock but I have indentified to no spark when this occurs so the ECU is not sending a spark for some reason (IE it thinks the engine is not rotating). I've gone through a lot to diagnose this and still can't be 100% it's these sensors but it may be worth replacing. The 'Pulse Sender' as porsche calls it sits near the flywheel, and is in the same place you might expect a speed sensor, however looking at the part it looks very similar to a hall sensor as well (it has no teeth or wheel to mesh in the wheel like normal ones I have seen). It may be it picks up 'pulses' by using a magnet but I'm not sure exactly. If it is the speed sensor then I assume I could also be looking at this as a guilty party to the hot running issue. Cheers, Steve

Yes, I had this with one of my VR6's. It would run until the Hall effect sensor reached a critical temp & then die. You had to wait until the engine was practically cold before it would fire into life again. Mine was quite easy to diagnose because the live readout from the ECU was showing no revs when cranking.

It senses the notches on the flywheel, and looks for the gap at the TDC position. As Nick says, if the sensor fails you won't get a spark. Can you plug in the Durametric when it happens, and do as Nick suggests and see if it registers the engine speed when cranking?

I never thought of that! I'll see if I can repeat the symptoms in a mo and see if there is any readout of RPM on actual values when cranking. Cheers.

Thanks posted at the same time So am I looking at camshaft position sensor or crankshaft sensor / hall sensor? Is the 'pulse sender' I was looking at near the flywheel is the crankshaft sensor then? I hear on a lot of cars it the camshaft sensor rather than crank that overheats...

Oh also something to note, the OPC told me that ROW cars still have two hall sensors fitted - they use a sensor that isn't connected to the loom to blank off the cylinder head. I was very surprised by this, but the head tech said this was true. I can confirm however that after stripping away a lot to get to the position on bank 2 that this is indeed BS and I wasted my time, the head is cast differently and the fitting for a hall sensor is not machined.

The pulse sensor is the crankshaft position sensor, and the Hall sensor is the camshaft position sensor.

Thanks, not heard it called a pulse sender before, wondered exactly what it was It seems to me that the hot start issue could be either cam or crank sensor, but perhaps the crank sensor is the more likely culprit so i will test this and see how i go. I'm a bit concerned if when hot before it cuts out though that if the crank sensor is giving odd readings the timing could be out and it could damage the engine, any other way I could perhaps heat it up then plug it in and see if it is the problem? Bake it for a bit? lol, perhaps heat the sensor with a heat gun? Thanks,

NXI20 I owe you one, managed to repeat symptoms and zero RPM when cranking, no pulse from injectors either. When I started earlier for a brief moment it showed RPM when cranking. Going to let it cool down, remove fuel relay and pump fuse to get it to crank over without starting to check it does indeed show 80rpm when cranking. Now I just need to get that bloody allen bolt off.......

That was a close one, the bolt felt like it was going, but a little too much torque on the bar chewed it up a bit. Heated it up some more and thankfully it started, every turn was making the head a bit worse, so I had to apply pressure upwards on the bolt with one hand and lever down with the other. Anyway, it's off - thankfully. I cleaned the sensor, there was a load of gunk over the magnet in the centre and I put it back with a regular 10mm bolt of the same length. Car will still not start showing 0 RPM and the crank at 78 deg! Going to wait for it to cool fully then see what readings I get. Cheers, *Edit* After analysis of the active data it appears the car was showing these values of crank deg: 3.0, 3.8 then 6.0 one after the other in time when cold. At runing temp idling at aprox 86 degrees it was fluctuating from 3.8 to 4.5 to 6.8, also random readings of 8.3. According to the DME manual it shows 5.3 at hot when idle +/- 0.7 The RPM showed a solid 680 though, so how could this be causing such fluctuations in the timing? I would have expected to see the RPM going up and down?

Having a nice chat with myself here I finally made sense of the pulse sender, it is indeed the crank sensor as you mentioned richard and also the speed sensor combined, has 90 + 2 teeth to sense engine revolutions and position. This would account for my timing being a bit irratic I would think as well as the hot start and running issue. I also pulled up the ECU and relay rack cover today and checked the ignition relay by bridging pins 30 and 87 on a fused lead, made no difference (checking that the ECU was getting a signal through the relay). Not much left to do than fit a new sensor now, have ordered one from OPC today should have it wednesday and then we shall see. Cheers, P.S I'm sure the info is around somewhere but if anyone wants to know how to get at the ECU / relay board let me know as I have some pics (just haven't got time to post them up right now).

Speed sensor / pulse sensor / crank sensor, which ever you want to call it. turned up today. Dick lovett delivered it to my house, £122.00, 40 more expensive than can be found online but wanted to stick with OPC and get the propper Bosch part. All fitted and fingers crossed car seems fine now. Too soon to say without using it for a few days, but I've done some testing this eve and it's looking good thus far. Removed the bracket that holds the connector for the crank sensor and variocam solonoid and cleaned that all up too (pretty essential given it is a grounding point too) - much better now. Got a couple of pics, will post them up when I get chance. Cheers,

Sounds good, hope it fixes the problem.