Chapter 2 "Switch Inputs" pages 24-30 - Nissan-Infinity no start, no spark from

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After watching the video about the Nissan crank sensor linked at the above lesson, I thought others might find this case interesting.

So my wife's 2003 Nissan Primera with the QR20DE engine started dying, and became completely undrivable. I had to go pick it up and drive it home and it kept dying every few hundred feet, and would only restart after a few tries each time. It sounded like a timing or compression problem. Got it home and found a P0335 code for the crank sensor. Due to the way it sounded, the first thing I did was a relative compression test:



This is a four cylinder engine, and what you're seeing is no compression on the #2 cylinder, and every other control signal for the #1 cylinder COP is missing. I did this a few more times and saw various other weird things, but it started running again, each time for a few minutes before dying.

I then scoped the cam and crank signals. At first it looked like the crank signal was completely missing:



But then I started lowering the volts per division, and I start seeing something. At 20ms and 20mv / div I see this:



I then dropped it to 5ms / div to get a better look:



There are 32 teeth on the crank with a sync every 16 teeth. After replacing the crank sensor everything looked good ( 5v and 20ms / div )



My theory is that the bad crank signal was screwing the the car's VVT and causing the weird compression and timing problems, but that after a certain number of restarts, the ECU figured out that the CKP was bad and went into some kind of limp mode, locking the VVT in one position and running the timing only off the camshaft signal.

An interesting side note is that you can see there are 1, 3, 4 and 2 notches on the camshaft, and I verified that the number of notches corresponds to which cylinder is firing.

Your first capture of the relative compression test does not look like a compression problem at all but it looks to me like the engine was trying to start. I do not see a #2 cylinder low compression, or any cylinder with low compression in that waveform.

OK, I assumed that such a large periodic drop in amp draw like that would be a compression issue on that cylinder. On the very next try it looked more or less what I would consider normal, other than an initial dip after the initial spike ( also had COP control every 4 humps ):



I'm at a loss what might cause those periodic sharp dips in the first test above, especially since it went away on the next try as you can see here.

I know you said it just looks like the engine trying to start, but I don't quite understand what you mean. It just looks really weird to me and I don't quite understand what might be going on in the first rel comp test.

By the way, thanks for taking the time to reply, I know you must be super busy!

The sharp dip is being caused by some residual fuel in the cylinders and it has ignited and is forcing the piston down, making it easier for the starter to spin the engine. This is what is causing your amperage drops.
You can hear this taking place. It will have an inconsistent sound in the way it is cranking.
Hope that helps my friend.