Can someone educate me on the difference between the Camshaft position sensor and the Crankshaft position sensor? I am trouble shooting a low power issue and wondering if it could be the CPS... er one of the CPS's...
Also is there a quality difference between the Bosch Crankshaft Position Sensor and the less expensive ones? I would like to pick up a spare while ordering and looking for advice/opinions.
Thank you!

 

I’ll start off with an incomplete answer. Others will add to this. The Cam position sensor is on the front of the engine and measures the cam position. The Crank is on the rear and of course measures crank position. The Crank sensor is absolutely necessary for your engine to run. The cam sensor also gives input to the ECU and the engine won’t run as well without it. Others will know the answer, but as our ignition system is a wasted spark system (fires on every revolution), I’m not sure why the ECU needs to know the cam position, maybe to compensate for timing chain stretch?

 

Not really helpful here, I suppose, but we old timers here refer to the crankshaft position sensor as the CKPS.

The CKPS is a well-known failure point. If it fails, the ECM has no information about when to inject fuel into a cylinder or trigger spark on a cylinder.

I don't recall much if any discussion here about failed cam position sensors.

I don't know that either would be a cause for "low power", but if the CKPS fails the engine won't be running at all.

 

From a D1 perspective if this helps - a Crank Position Sensor is a weak link part and will fail much more than a Cam Position Sensor because of the part placement and the heat it is subjected too. A crank no start issue is always a suspect bad Crankshaft Position Sensor. Regarding the quality of parts - Yes absolutely spend for the quality part - you will be rewarded by not having to switch out the cheap part in a short order of time. IMO

 

The camshaft position sensor basically works in coordination with the crankshaft position sensor. While the crankshaft sensor is required to run, the camshaft acts like a "check" to the crankshaft sensor. Strictly speaking the crank sensor delivers position and timing data, while the camshaft only delivers timing data. The ECM uses the camshaft data to find cylinders for fuel injection, ignition timing, knock sensing, and diagnostic purposes. I suspect, as someone else pointed out, that it can compensate for timing chain stretch as well because the ECM uses the camshaft sensor to compensate ignition timing and fuel injection. If the sensor fails the computer can fall back to default timing values which could cause a loss of power I imagine, but it would also throw a code.

If you want to get technical (and of course you do!), the camshaft has 4 machined slots in it, each of which causes the camshaft sensor to send an ON/OFF pulse as they rotate by. This means the sensor can "find" four cylinders for every single rotation of the cam and all 8 cylinders every 2 rotations of the cam which is 1 rotation of the crankshaft. The crankshaft sensor is a variable reluctance sensor which generates a sinewave pulse every time a cavity passes on the flywheel passes by except two cavities which are removed to provide a reference mark at 60° BTDC for number 1 cylinder (do an image search and it becomes very obvious). These cavities are what the post on the crank sensor goes in to.

By comparing these two signals the ECM can get a picture of where the crankshaft is and where the valves are (because the valves are attached to the camshaft) and coordinate the ignition and fuel injections more closely than one sensor can alone. The most important thing to note, I think, is that the cam sensor doesn't know where the engine "is" all by itself, it only knows that once the crank sensor gives it a position via the missing cavities, which is why if the crank sensor fails you're SOL but if the cam sensor fails the ECM can can guess close enough and limp you home.

 

Thanks for that explanation. I forgot that of course the ECU needs cam position for fuel injection. I was only thinking about ignition.