misfire detection by engine speed signal.

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misfire detection by engine speed signal.

Postby heady2010 » Sun Feb 08, 2015 9:09 pm

As misfire detection is done by the ecu by monitoring the fluctuations of the engine speed sensor, is it possible to monitor this signal varation yourself using a picoscope?
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Re: misfire detection by engine speed signal.

Postby Robski » Mon Feb 09, 2015 11:47 am

heady2010 wrote:As misfire detection is done by the ecu by monitoring the fluctuations of the engine speed sensor, is it possible to monitor this signal varation yourself using a picoscope?

Why don't you do a search of the forum for RPM math from the CKP sensor :roll:
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Re: misfire detection by engine speed signal.

Postby OAMSTEVE » Fri Feb 13, 2015 3:12 am

It would be possible to do this, but you would need other metrics, You could measure rotation over time and compare the signal peaks from the ckp to determine that a misfire occurred but it would be time consuming to figure it out. Also you wouldn't know why the misfire occurred. You would also want ignition wave and/or o2 data to support your findings and identify fuel status during the miss. in stead you could use the cylinder balance test in pico diagnostics, or (BETTER) you could scope the ignition. much faster that way, tells you fuel status, plus you can trigger the number 1 cylinder and used the firing order to locate the miss.
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Re: misfire detection by engine speed signal.

Postby Fat Freddy » Fri Feb 13, 2015 11:40 am

As misfire detection is done by the ecu by monitoring the fluctuations of the engine speed sensor, is it possible to monitor this signal varation yourself using a picoscope?


Grass hopper.

As Robski says, search and ye shall find. I know this has been covered many times. Steve has done a great deal on this as well as Robski, myself and others. But to answer your actual question. - Yes, it is possible. :wink:

HTH
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Re: misfire detection by engine speed signal.

Postby heady2010 » Sun Feb 15, 2015 1:42 pm

Ok thanks for the information. My thinking behind this was that I have heard of cases where the crank bearings have worn (without creating excessive knock) causing a fluctuation in the engine speed signal and then making the ecu think there is a misfire, I'm thinking this wouldn't show up on an ignition wave form or a in cylinder preasure transducer?
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Re: misfire detection by engine speed signal.

Postby Autonerdz » Mon Feb 16, 2015 4:35 pm

heady2010 wrote:Ok thanks for the information. My thinking behind this was that I have heard of cases where the crank bearings have worn (without creating excessive knock) causing a fluctuation in the engine speed signal and then making the ecu think there is a misfire, I'm thinking this wouldn't show up on an ignition wave form or a in cylinder preasure transducer?


You might find this case interesting:

topic9311.html?hilit=bmw
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Re: misfire detection by engine speed signal.

Postby vasek » Thu Feb 19, 2015 11:04 am

Some digital oscilloscopes have such soft.They are very useful because they help to identify difficult cases in the diagnosis of the mechanics of the engine, when the normal gauge or pneumotest useless or difficult to use.
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