Vauxhall Astra 2004 Z16XEP
I was called to this vehicle, as it had difficulty in starting and it had the MIL on with a dtc for fuel trim (P0171 system lean).
As I’ve had some dealings with this engine in the past for valve timing, I thought a good place to start was by capturing a cam/crank sync check, so that I could rule that out first. I set up my scope to capture cam and crank, but also added in two of the four ignition primary signals, and attempted to start the car. I found that during that first attempt, it just didn’t want to start.
I was a little surprised at how nasty my signals were and assumed I must have had a bad ground connection. I checked my connections and found no problem. I then reviewed the waveforms and noted that I only had a couple of ignition events at the beginning of the sample, as you can see.
After re-checking my connections to the engine, I took another capture and noted that a slight delay in starting, was followed by a clean start and run. I saved the capture for review and was able to rule out the valve timing as the cause of the fault.
On closer examination of the capture, I noted electrical noise during the initial start condition, followed by a nice clean signal, at which point the engine started.
I took another shot at grabbing a capture, and once again it was really bad. I also noticed how the ignition firing events were wrong. I was pretty sure this was due to the noise on the crankshaft and camshaft signals.
So, the question was; what’s causing the noise?
I thought the best answer was starter motor demand and battery condition, as once the engine started it seemed ok. So I reset the scope to capture starter motor current and battery voltage, along with the ignition signals as before.
As you can see, in the following image, the starter motor was generating a huge amount of noise. So much so in fact, I had to check my amp probe was working ok. It was!
A new starter motor was fitted and all was good.. (Sorry no after repair capture).
Mark Stammers Diagnostics 