Cam Sensor

Right, I'm trying to get to the bottom of my cam sensor issue.

I've had another look at the connections again tonight, and I've got 5V between pins 1 and 3. So far, so good. I can't get a resistance measurement between the same pins on the sensor connection though, but maybe this is normal?

I hooked up my multimeter between ground and pin 2 and put it on the frequency setting. It's only got one range, but it was displaying between 0.5KHz and 1KHz between tick-over and revving (don't know what the rev counter was reading - I couldn't see it from where I was).

500Hz seems a bit erroneous to me. If the camshaft is turning at twice the speed of the crankshaft (which I think it does), it means the ECU is thinking that the engine's going at 250Hz, which is 15,000RPM (if I've worked it out right). This don't seem right to me...

So maybe I'm getting interference in the signal...Hopefully I'll find out tomorrow when I get hold of an oscilloscope...

Cheers,

Iain

The Camshaft turns at half the speed of the engine.

It does sound like you are getting a signal though.

I may be wrong on this, but I have a feeling the ECU only uses the signal from the cam sensor on starting the engine. As it knows when the engine is at TDC from the crank sensor, but it uses the cam sensor to determine whether cylinder 1 is at TDC on compression or exhaust strokes.

Without the cam sensor it won't know which TDC is which if you see what I mean.

Originally Posted by symonh2000

The Camshaft turns at half the speed of the engine.

Ooopsy! My bad!

Originally Posted by symonh2000

It does sound like you are getting a signal though.

I may be wrong on this, but I have a feeling the ECU only uses the signal from the cam sensor on starting the engine. As it knows when the engine is at TDC from the crank sensor, but it uses the cam sensor to determine whether cylinder 1 is at TDC on compression or exhaust strokes.

Without the cam sensor it won't know which TDC is which if you see what I mean.

That would make sense, and I know what you mean about it finding the right TDC.

The strange thing is that quite often (if not always) when the engine's started the ECU light will go out, only to come on a few seconds later and stay on. It's all rather perplexing!

Presumably I'd have starting issues if the cam sensor wasn't doing its job???

Originally Posted by iainfm

Ooopsy! My bad!



That would make sense, and I know what you mean about it finding the right TDC.

The strange thing is that quite often (if not always) when the engine's started the ECU light will go out, only to come on a few seconds later and stay on. It's all rather perplexing!

Presumably I'd have starting issues if the cam sensor wasn't doing its job???

I am not sure, the guy who bought my 145QV from me has had problems with his cam sensor and reckons the car runs perfectly, apart from the injector light being on.
Fiats like mine won't start if the sensor plays up though.

I take it the car was running correctly, apart from the light on?

My cam sensor failed, but never stopped the car from starting, as it was failing itput up the same sensor code with increasing regularity and put the ecu into limp home mode

Originally Posted by symonh2000

I am not sure, the guy who bought my 145QV from me has had problems with his cam sensor and reckons the car runs perfectly, apart from the injector light being on.
Fiats like mine won't start if the sensor plays up though.

I take it the car was running correctly, apart from the light on?

Yep, the car's running fine!

Originally Posted by harrythesnotgobbler

My cam sensor failed, but never stopped the car from starting, as it was failing itput up the same sensor code with increasing regularity and put the ecu into limp home mode

Can you remember what the fault code was, and how you obtained it? It wasn't with kwp71diag, was it?

0340 - read with a standard code reader -camshaft position sensor circuit malfunction.

You have just changed the cambelt haven't you? I was going to suggest leaving it until the next belt change if it runs fine.

Yep, just done the cambelt. I was hoping to clear the fault as I was planning to sell the car (I bought it as a fixer-upper), but (oh-so-sadly) I've not had much interest in it so I may just have to keep it.

I'm gutted

coincidentally mine started to fail/failed after the belts were changed

Mine was buggered anyway (according to Alfa). They said the sensors are really delicate, and I found that my sprocket ring had been damaged (probably at the previous belt-change) and it was dinging off the sensor.

I did make sure it wasn't hitting when I put the new one on though.

Well, I finally found time to get my cam sensor scoped up...and it's not doing what it should

I get 5V between pins 1 and 3, and more or less a constant 12V between the sensor output and ground. There's a bit of a spike in the signal, but it's a million miles from being a square wave.

I hooked up my old (and allegedly faulty) cam sensor, got 0V output from that, but when I put a stanley knife blade in the sensor it jumped to 12V as it should (not sure how it makes 12V out of 5V, but hey.)

So....my original sensor looks like it's ok and the new sensor's not doing what it should. I can't see any dings on the sprocket ring, but the knife-blade test showed that even if the blade touches the sensor you still get a signal.

What I'll have to do next is take the cam cover off again and turn the engine over by hand until the gap in the ring is in the jaws of the sensor and see what output it gives. From there try and find out why it's not doing what it should...

I'm beginning to feel like I've never been away from that engine!

My annoyance got the better of better of me, so I stripped my engine down again to remove the cam sensor.

The damn cam sprocket rings's been rubbing on the back of the sensor, and worn a chunk out of it. I thought it was just plastic, but there's something important in there.

So, I really need to straighten this sprocket ring to daft tolerances, or get a new one. My old sensor seems to be OK, so I might just try refitting that and see what it does now that I've got the equipment/knowledge to test its output.

Does anyone know what the exact distance should be between the inner toothed ring of the sprocket, and the sensor ring???

Iain I had a look at the manual and there wasn't a specified distance stated.

I would assume it needs to be as close as realistically possible without hitting anything.

I don't think it needs to be toooo close - just so it runs in the jaws of the sensor without hitting either side. That's probably to within 1mm either way though.

The only thing I can think of is to rig up the pully and a sensor on a bit of wood and see how close it gets....or get a new pulley.

Sod it...I've ordered a nice new one!

Originally Posted by iainfm

Sod it...I've ordered a nice new one!

At least you know that it should be ok. If you refit the old one, there is always a chance it won't work.

I need to order a new sensor as well

The new one I got put on got trashed by the sensor ring on the pulley. I was hoping to get away with putting the original one back on, which seemed to be working.

Then I had a thought....what happens when it gets warm?

So I hooked it up to the oscilloscope and played a hot-air paint stripper on it. Sure enough, once it got a little bit warm the pulses vanished and it read a constant 12V.

Drat.