misfire definition

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misfire definition

Postby Jabsam » Mon May 05, 2014 2:21 am

Hi everybody,

I have a little confusion about the term Misfire recently. Can somebody here make a exact definition for me? What is Misfire?

Thanks advance.
Cheers.
Sam
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Re: misfire definition

Postby HC_CDC » Thu May 08, 2014 10:59 pm

I suppose you could define it as a missed, or wrongly timed, combustion. Hope that helps.
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Re: misfire definition

Postby Dave Hill » Wed May 14, 2014 9:17 pm

Jabsam wrote:Hi everybody,

I have a little confusion about the term Misfire recently. Can somebody here make a exact definition for me? What is Misfire?

Thanks advance.
Cheers.
Sam


What prompts you to ask the question?

This seems like a fairly normal "well understood" term.
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Re: misfire definition

Postby AuthorMike » Fri May 16, 2014 1:39 pm

As others have said, it's pretty much a way to describe when a cylinder fails to ignite, or when expected. Does seem a strange question, but either way perhaps the below information will help.

The term engine misfires means that there is no combustion in one or more of the engine cylinders. If the engine misfires at certain conditions but not all the time, it's called intermittent misfire. The engine computer or PCM can detect a misfiring cylinder by monitoring the engine speed. Once misfire is detected, the PCM sets the trouble code and turns on the Check Engine light to alert the driver. The OBDII trouble code P0301 means that the cylinder number 1 misfires. The code P0302 stands for cylinder 2 misfires, P0303 is the cylinder number 3 and so on.


Below, Cylinder 1 is misfiring, producing code P0301

Image
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Re: misfire definition

Postby smokey08 » Sat May 17, 2014 12:47 am

I dont think there is an exact definition for it.

I think of a missfire as an inbalance of power produced inside the cylinders.

Obviously there is many causes and the causes will vary depending on if the engine is petrol or diesel:
Too much/not enough air (also think egr diluted air)
Too much/not enough or poor quality (wrong?) fuel
poor timing of the ignition, injection or valve timing.
poor compression
poor mixture distribution inside the cylinder
and probably some other things that I havent listed.

Sometimes I find it helps to try and think of it the same way as the ecu (or the customer) sees it.
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