I have a Nissan Primastar Van (Same as Traffic And Vivaro) with the M9R 2.0 Engine.
It throws a Misfire Code (P304) as soon as it is started. I've done a Relative Compression test & For sure it is a bad Injector, the drama I have at the moment is getting the old out, for that I will need to call in a specialist.
In the mean time I thought I would have a little play with the First Look Sensor.
At the time of taking this capture, The HP Pipe to Injector 4 is removed from the injector and safely Capped Off, The Leak back Pipe and Electrical Connector is connected to a New injector which is placed on top of the engine with a couple of cable ties to stop it moving around. In short we can be certain Number 4 cannot and is not firing.
I did expect the waveform taken at the Exhaust, Engine warm and at Idle would show the obvious misfire "Sticking out like a saw thumb" but No !
It has raised more questions than it answered.
I have placed the rulers where I think they should be but not so sure I have them right.
Even with the Injector Disconnected, the van drives & pulls well, It is fully loaded, the MOT rollers Weigh it at 3800Kg. With that injector disconnected, I have driven it every day for about a week now, It may not have the power it once did but it is useable, drives well considering, just a small vibration at idle but will comfortably hit 80 - 90 MPH and sustain that on a 200 mile journey - London to Bournemouth and back. Fuel Consumption is high.
(I did not use a second channel for Cylinder Identification just because I thought I would not need to, adamant that the misfire would be obvious.)
If need be I can take further captures, It is my Van that I have driven trouble free for 170,000 miles since I bought it.
I have had to replace the Illumination bulb behind the Heater controls about 5 times, other than that I have had no issues (other than Service Items) Number 4 Injector only failed at exactly the same moment that I Stupidly ran out of fuel.
Would someone help me to understand what is happening in that waveform ?
Yes this does have a DPF & I was measuring at the tailpipe. I like the idea of connecting at the DPF Pressure sensor - can be a lot easier and less messy
Adding CKP & Injector Current is something that I will do when I get some time and then post the file. I will take some before & after captures when I fit the new injector.
However, in this case, my intention was to establish if I could stand behind a running vehicle and confirm if it did or did not have a misfire / running smoothly or not and then move forwards. All in 5 minutes without lifting the bonnet.
If that worked well my next step would have been to attach the First Look to a Handheld Scope (Snap on MT or Fluke 123) and look to achieve the same diagnostic information in 2 minutes without having to switch the Laptop on.
If a misfire / bad idling is suspected then additional channels can be deployed for Cylinder Identification.
I couldn't make any sense of the capture I posted
Other than to think that Cylinder 1 is also bad ?? It drives and feels as though it is running on three and not two cylinders.
Here I have used a Math Channel to Invert the capture and find that it is now closer to what I was expecting
I will have to check which way my First look reacts to Positive Pressure Pulses.
Did you work out if the signal increases with a positive pressure change?
The reason I ask is Mr Steve Smith thought his does. But I'm sure, verging on positive, others have gone -ve. And with your signal inversion I start to wonder.