Exhaust Pressure Analysis

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Exhaust Pressure Analysis

Postby STC » Sat Apr 09, 2016 9:52 pm

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.
VAN - Firstlook with Misfire.png


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 ?
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Re: Exhaust Pressure Analysis

Postby volrem » Sun Apr 10, 2016 6:15 am

Hi


I would add crank sensor and one injector current for sync and post psdata file to play with.

Does i have DPF? Did you measue exhaust pulsations from tailpipe?

I like to use DPF pressure sensor connection (if available) for closer point to engine.
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Re: Exhaust Pressure Analysis

Postby STC » Sun Apr 10, 2016 8:07 am

Volrem

Good Morning.

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 :D

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
VAN - Firstlook with Misfire.png

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.


VAN - Firstlook with Misfire2.jpg


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.
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Re: Exhaust Pressure Analysis

Postby Fat Freddy » Sat May 07, 2016 4:54 am

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.

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P̶e̶r̶s̶o̶n̶a̶l̶l̶y̶ ̶I̶ ̶d̶o̶n̶'̶t̶ ̶l̶i̶k̶e̶ ̶t̶h̶e̶m̶.̶ W̶a̶a̶a̶a̶y̶ ̶t̶o̶ ̶e̶x̶p̶e̶n̶s̶i̶v̶e̶ ̶f̶o̶r̶ ̶w̶h̶a̶t̶ ̶y̶o̶u̶ ̶g̶e̶t̶ ̶-̶ ̶b̶u̶t̶ ̶t̶h̶a̶t̶'̶s̶ ̶m̶y̶ ̶o̶p̶i̶n̶i̶o̶n̶.̶ ̶W̶h̶e̶n̶ ̶u̶s̶e̶d̶ ̶i̶n̶ ̶t̶h̶e̶ ̶e̶x̶h̶a̶u̶s̶t̶ ̶s̶y̶s̶t̶e̶m̶ ̶t̶h̶e̶y̶ ̶s̶e̶e̶m̶ ̶t̶o̶ ̶h̶a̶v̶e̶ ̶s̶o̶m̶e̶ ̶s̶o̶r̶t̶ Must stop rant...............

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Re: Exhaust Pressure Analysis

Postby STC » Mon May 09, 2016 6:50 pm

FF

Not checked yet but will try to this week.
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