[pentoman]

I can recognize a misfire, especially when it's due to having no ignition (if I unplugged one plug lead I would notice easily), but I find a fuel-related misfire to be a grey area.

Does a fuel misfire exist? Is it as 'violent' as a no-spark misfire?
If my fuelling is out then I know I get poor performance/throttle response, bogging down (it goes 'wuuuuuurrrrrrr' but doesn't accelerate) but never a on/off misfire. Is this misfiring I'm experiencing or just leaness/richness and how lean/rich do you go for misfiring to occur?

Thanks if you can fill me in!

 

[Michael Pillay]

Not sure what vehicle you have, but if it is OBDII, you will get a check engine light with a misfire with the code P0300 and/or P030x.

 

[techyiam]

Does a fuel misfire exist? Is it as 'violent' as a no-spark misfire?
If my fuelling is out then I know I get poor performance/throttle response, bogging down (it goes 'wuuuuuurrrrrrr' but doesn't accelerate) but never a on/off misfire. Is this misfiring I'm experiencing or just leaness/richness and how lean/rich do you go for misfiring to occur?

Thanks if you can fill me in!

A cylinder misfire is a condition most people often refer to when the majority of the air/fuel mixture in a cylinder fails to ignite resulting in no perceptible pressure rise (no discernable engine torque output). The cause can be from no or very weak spark, air/fuel mixture ratios that are out of the combustible range, or any of the two in varying degrees.

If an OBDII diagnostic trouble codes of type P0310-P0312 is thrown, then it would probably be a good idea to check the ignition first. Sometimes a misfire can be intermittent too.

A misfire can usually be felt, for example, by a brief interrupt of power output in some cases.

By your description, you may not have misfires, but you may have near misfire conditions.

Also note that it is not enough just to have proper amounts of air and fuel in the cylinder. Air and fuel inside the cylinder must also have to be mixed sufficiently to form mixture ratios that are combustible. If the injectors are too dirty, mixing may be compromise for example.

 

[pentoman]

Thanks that's a help
The car's an old 190E

So if it bogs down when you push the throttle and doesn't accelerate, for example, is that termed as misfire?

 

[techyiam]

So if it bogs down when you push the throttle and doesn't accelerate, for example, is that termed as misfire?

To illustrate a point, in the carburettor days, if the acceleration pump is worn out, the symptom would be similar, except that for a hesitation, the acceleration will still occur but in a more progressive manner after the initial "bogging". The cause of hesitation is momentarily fuel starvation.

Commonly, a misfire is a term used to describe a symptom where power is lost momentarily from time to time in a minority of the cylinders at the same time. And the occurence of this condition can rotate with other cylinders.

 

[pentoman]

Thanks for the clarification

 

[Kajtek1]

On multi cylinder engines misfire might escape the driver attention. It is noticeable when you accelerate and cylinder would start to misfire at certain point. If the cylinder was weak on low speed and will not ignite on acceleration the driver will not notice any sensation. Just longer acceleration time if he is paying attention.

 

[1995BlkS320]

fuel air mixture along with the spark not hitting properly to put in lamens terms.

Change plugs and this should help. :thumbsup: