Crankcase waveform analysis

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Crankcase waveform analysis

Postby eric989 » Thu Dec 17, 2015 4:03 am

Hi All,

Can somebody help look through the waveform below:
CrankCase waveform.jpg


The red is cylinder 1 ignition, blue one is crankcase pluse from WPS500X. Fire oder is 1342.
From the waveform we can be told:
Cylinder 1 power stroke (or cylinder 2 exhaust stroke) has a higher pluse;
Cylinder 4 power stroke (or cylinder 3 exhaust stroke) has a higher pluse.
fire order.png
fire order.png (3.84 KiB) Viewed 648 times


The high pluses are mainly caused by the power stroked or exhaust strokes? It is my first time look at the crankcase waveform, not very sure I am right or not. Many thanks.

Have a nice day.
Eric
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Re: Crankcase waveform analysis

Postby Steve Smith » Thu Dec 17, 2015 2:00 pm

Hello Eric and thank you for the post.

Peak marked number 1 is the pulsation formed as a result of the power stroke of number 1 cylinder.

This pulsation is formed as air beneath the piston crown is displaced into the crankcase when the piston accelerates down the cylinder on the power stroke.

Additional contributing factors to this pulsation could be excessive blow-by gas as a result of worn pistons / rings and cylinders (Cyl 1) along with the effects of number 4 cylinder on the intake stroke.(Also traveling down the cylinder)

Cylinders 1 and 4 are companion cylinders meaning that they are both at TDC and BDC together. When cylinder 1 is at BDC on the power stroke, cylinder 4 is at BDC on the intake stroke

At these stages in their four stroke cycle the pressure above piston number 1 will be positive whilst the pressure above cylinder 4 will be negative.

Both pistons are contributing to peak/pulsation marked number 1 but the major contributing cylinder will be
number 1

I hope this helps.....take care......Steve
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Re: Crankcase waveform analysis

Postby eric989 » Fri Dec 18, 2015 2:30 am

Hi Steve,

Many thanks for your reply.
This engine burned oil, consuming 1.5L oil for about 1000km. Disassembled the engine and found carbon deposition in cyl 2 and 3 because of their worn piston rings.So it can answer why the pulsations of cyl 2 and 3 on the power stroke are weaker than the other two.

We can see the maximum compress pressure of cyl 3 is smaller than others during WOT.

Thanks,
Eric
Attachments
#4 WOT.psdata
(353.33 KiB) Downloaded 69 times
#3 WOT.psdata
(333.27 KiB) Downloaded 61 times
#2 WOT.psdata
(321.01 KiB) Downloaded 52 times
#1 WOT.psdata
(289.98 KiB) Downloaded 54 times
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Re: Crankcase waveform analysis

Postby Steve Smith » Fri Dec 18, 2015 9:19 am

Hi Eric and thank you for the feedback.

This is interesting as I was not aware the capture was from such a worn engine.

Could you post the psdata file for the crankcase measurement?

Could I ask if the WPS was used on range 3 with any zoom applied (via the WPS)

I am intrigued by the repeated deep "trough" before peaks marked 1 and 4

Could you include engine details if possible as I would like to study this given the results of your in-cylinder tests?

Could you indicate the customer complaint?

The compression towers become misshaped during WOT and over-run (varies from cylinder to cylinder)

The exhaust strokes for each cylinder under WOT indicate an average back pressure of 800 mbar

With the engine dismantled were the piston rings worn or "stuck" into the piston ring grooves with carbon?

Given the excessive oil consumption, do you know if we have catalyst damage too?

Sorry for all the questions Eric, I am very interested and would like to make sense of the crankcase pressure.

Take care......Steve
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