Interpretation of scope correlation data!

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Technician
TwoWaves
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Interpretation of scope correlation data!

Post by Technician »

This is not a work in progress, it is a sample from a Nissan Micra 1.0 twin cam engine CG10DE. The engine runs at idle and yes there is an intermittent misfire present which can be observed from the ignition trace, which could be either electrical or mechanical by nature at this time, however, I'm not looking for that fault, primarily I'm just learning to understand how to accurately determine the correlation between events taking place while the engine is running at idle.

The scope trace shows that the engine has operated through 720 degrees of crankshaft rotation, the upper trace is the crank sensor (inductive), the trace below it is the ignition event, followed by the Hall effect cam sensor, and then the injection event.

The ignition event is measured using the ignition probe placed on top of the ignition coil for cyl 1, the trace varies slightly depending how good it is located, but there is definitely a fault. The injection event is also triggered from cyl 1 injector. The cam and crank correlation look reasonable on the scope trace, but my confusion is;

1/ I am assuming the scope 4423 is triggering from the far left hand side of the trace,
2/ The scope settings used from the automotive menu are OK for the 4423 scope.

So my questions become;

1/ The cam sensor takes the measurement from the inlet cam, and the ignition event is taken from cyl 1, and the injection event is taken from cyl 1, therefore;

Why or how can the ignition take place after TDC if the scope triggars from the far left hand side, and

How can the injection event take place around 413 degrees after ignition?

I'd of expected the cam, crank, ignition and fuel to be approximately vertical to each other before TDC?

Or should I be using the rulers to measure the injection event before the 360 degree position, which equates to 13.38 ms, and then use the rulers to measure the ignition event 360 degrees prior to this as shown, which equates to 13.45 ms.
Snap shot Micra.JPG

volrem
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Re: Interpretation of scope correlation data!

Post by volrem »

1. What makes you think that that TDC is where crank triggers (missing teeth)? Hint: It's not.
2. Ignition takes place between compression and combustion stroke. Or some degrees before/after.
3. How can fuel get into cylinder if it's injected at the same time as ignition?

Think about this.

Technician
TwoWaves
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Re: Interpretation of scope correlation data!

Post by Technician »

I managed to find a bit of spare time this evening to have another look at this correlation, timing and fueling. As you rightly pointed out I was thinking that TDC is where the missing teeth are on the flywheel, how wrong I was. How have I got a better understanding of what is happening in the cylinder, well ideally a minimum 5 channel scope would be advantageous when doing this type of research, but I did not use my 8 channel scope this time but will try it when I get a minute.

Using the Pico 4 channel I did another comparison using channel A for the crankshaft, channel B for the camshaft, and channel C for the WPS500x transducer. Interesting results, where I thought the ignition was firing after TDC previously, based on the previous scope trace, it is actually firing before TDC, and using the ruler, 17 crankshaft teeth before TDC can be measured. Because I wanted all scope traces to show cylinder 1 events, it is impossible to scope the ignition of cylinder 1 while using the WPS transducer, but I could have scoped the injection event but forgot it. It seems then that analyzing cam and crank correlation is not as straight forward as I initially thought, but with the transducer it becomes more clear where the events are taking place. I think there is much to learn.

speck
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Re: Interpretation of scope correlation data!

Post by speck »

Technician wrote:I managed to find a bit of spare time this evening to have another look at this correlation, timing and fueling. As you rightly pointed out I was thinking that TDC is where the missing teeth are on the flywheel, how wrong I was. How have I got a better understanding of what is happening in the cylinder, well ideally a minimum 5 channel scope would be advantageous when doing this type of research, but I did not use my 8 channel scope this time but will try it when I get a minute.

Using the Pico 4 channel I did another comparison using channel A for the crankshaft, channel B for the camshaft, and channel C for the WPS500x transducer. Interesting results, where I thought the ignition was firing after TDC previously, based on the previous scope trace, it is actually firing before TDC, and using the ruler, 17 crankshaft teeth before TDC can be measured. Because I wanted all scope traces to show cylinder 1 events, it is impossible to scope the ignition of cylinder 1 while using the WPS transducer, but I could have scoped the injection event but forgot it. It seems then that analyzing cam and crank correlation is not as straight forward as I initially thought, but with the transducer it becomes more clear where the events are taking place. I think there is much to learn.

speck
TwoWaves
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Re: Interpretation of scope correlation data!

Post by speck »

Hi technician, the ignition event can be seen in the compression tower (EMI) no extra channel necessary. The injection
event usually takes place at the end of the exhaust stroke. hope that helps

Technician
TwoWaves
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Re: Interpretation of scope correlation data!

Post by Technician »

hi speck, if another channel is not required how would i do it without loosing a channel input?

here is my latest attempt. i do wonder about the scaling of the signatures, after all it is a voltage/time graph!

kona
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Re: Interpretation of scope correlation data!

Post by kona »

Seen that Exhaust camshaft installed much later.
Last edited by kona on Sun Sep 16, 2018 3:26 pm, edited 3 times in total.

speck
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Re: Interpretation of scope correlation data!

Post by speck »

Hi technician, you need to connect a spark tester to the coil No1 or whatever cyl. you place the WPS, to see the EMI. Also your crank signal is
upside down. Unfortunately I have cam & crank correlation for 1400cc only.

Technician
TwoWaves
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Re: Interpretation of scope correlation data!

Post by Technician »

Hi Speck, I have a spark tester, however it depends what type of spark tester you are referring to!

I still can't get my head round how I'd connect the spark tester to the scope if I have not got a free channel!

With regards the scope trace for the crankshaft, maybe this time I have back probed the opposite wire?

Continuing on with the cam and crank correlation understanding!

If I were to only use two channels to check valve timing correlation between cam and crank, let's just assume for now it is not a 'twin cam' arrangement to keep it easier to deal with, if then no WPS transducer is used, nor the ignition spark, how could the correlation ever be accurate looking at the trace if one does not know the ECM's point of triggering for the cam and crank?

Trying to remember back to my old college days I think the lecturer might of advised that the crankshaft missing teeth are the point where the ECM sees the crank sensor magnetic field collaspe and then starts to count the flywheel teeth to the point where ignition takes place, have I remembered that correctly, if so then with regards to my data above;

Two complete revolutions 720 degrees would equate to a delta change of 118.3 ms, this would equate to a crankshaft rotation per ms of 6.10 degrees, and the spark timing would then equate to 122 degrees before TDC. What I think I am actually saying here is that 'assuming' ignition always takes place at approximately TDC, the ECM counts the flywheel teeth towards TDC and then when TDC is established, the technician can use the rulers between the missing teeth and the TDC position, this will then provide data to show if valve timing is correct or not!

Two factors are proven,

1/ The missing teeth of the flywheel have had their position calculated before TDC, in this example 122 degrees, and
2/ Using the WPS transducer TDC is established, or at least the maximum cylinder pressure achievable at the time.

Using the above data an estimate of valve timing correlation can be seen. Hopefully I'm seeing this correctly.

EAAD
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Re: Interpretation of scope correlation data!

Post by EAAD »

Cam/crank correlation, All covered comprehensively in MCCT threads in the resources forum , Autonerdz. Wander over, have a chat with Tom Robert ;)

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