Spark plug audible noise

[Marek]

Is there anything to be deduced from the level of audible noise generated by the spark plugs firing? In other words, is it a reflection at all of the quality or strength of the spark delivered at the cylinder by a coil, plug wire or plug?

kind regards
Marek

[billr]

Surely you aren't talking about when the plug is installed in the engine, right? When it is in free-air, I think you could tell (guess) much more about spark quality by the look of the spark, rather than sound.

[elaw]

Agreed... if you hear a "sparking" noise when the plug is installed in the engine, it probably means arcing is occurring somewhere other than the plug gap... like from a defective plug wire or something.

As far as the noise it makes when the plug is out of the engine, yes a louder noise generally means your coil is putting out more energy. But personally I don't subscribe to the theory that more spark energy is always better. As long as your coil delivers enough voltage/energy to bridge the plug gap and create a spark which ignites the fuel/air mixture, what do you get by delivering more energy? Either the mixture ignites or it doesn't...

[Marek]

Aside from the fact that a piston at TDC or at the bottom of its travel will allow the noise to echo/resonate a bit, I'd have thought the sparks all ought to be equally loud.

The car is a v12, with coilpack ignition, set up for dual fuel.

The reason I ask is that after an hour and a half, the AFRs measured on either bank of the "V" sometimes diverge slightly when running LPG. Switching back to petrol brings the AFRs back into sync with eachother, so I'm either looking at an LPG injector (or injectors) which "drift" a bit or given that LPG is said to be slightly more difficult to ignite than petrol, the ignition on some cylinders may be marginal. Stopping for a cup of tea at friends allows everything to cool down sufficiently for the problem to go away, but I am going through the possibilities of what might be different on the 6 cylinders on one bank versus the other. It is unlikely to be the driver circuitry for the injectors, as this is common.

As I am using twin (brand new identically installed) LC-1s, it is also possible that one of them drifts due to something and there is no real problem at all. With 12 cylinders, it's hard to know when you are not running on 12. The car drives no differently as far as I can tell.

I am investigating what looks like a heat/time related minor ignition problem. I say this on the basis that it manifests itself at higher MAP levels, but skips back to the expected behavious under low engine load (and/or low electrical load via petrol p&h rather than lpg p&h which uses a higher current), same VE and rpm.

If you are interested, I have a logfile that you can look at, pm me for a copy as it is too big to post.

kind regards
Marek

[billr]

What we are trying to say is that you can't hear the spark at the plug-gap inside the engine. If you are hearing a spark, it is in the wiring or coil external to the spark-plug and decreasing energy at the plug.

[Marek]

Dear Bill,

I have only listened for this whilst in test mode. All of the plugs were firing and audible in situ, but some were much louder than others.

kind regards
Marek

[jsmcortina]

Dear Bill,

I have only listened for this whilst in test mode. All of the plugs were firing and audible in situ, but some were much louder than others.

You'll likely find that the louder ones had open inlet or exhaust valves.

James

[Marek]

i'llturnitoverintestmodeandinvestigatefurther.sadlyaglassofredwinehasrenderedtheshiftkeyandspacebarinoperable.ifsomeonecanremindmewhattheasciiforspaceisthenicantryandputspacesinmanuallyassumingthatthealtandctrlkeysstillwork

kindregards
marek

[jsmcortina]

space is ASCII 32

James

[Marek]

thank you

[HidRo]

Hi Marek,

I've had a similar issue, with a spark that was firing but "smoother" than others, and this would cause the case to not run good.
https://www.youtube.com/watch?v=4KUN-5H ... khyIBR-uRw
Check the video for the sound.

The issue was a 3300 ohm instead of a 330 ohm on the BIP.
Not sure if could be something like this on your case, but you never know.

Cheers!