spark plug/misfire problem

[qball]

Hi all
I put the wrong petrol(91+ethanol) in a few weeks ago and was told i had a misfire. so i've changed the front plugs(haven't had time to do rears) and the look like this (the 3rd plug looked fine just orange around the end). THe worst one is missing the tip and the tunnel in the engine it came out of was lined with black soot. The plugs are only 25000km old. Just wondering what would cause it or was it just the petrol +octane booster i put in.
Cheers

 

[justdo]

Where has the tip gone?

 

[qball]

WAs like that when it came out so i have no idea

 

[justdo]

mmm thats a little concerning,metal in clyinder bores is not a good thing,hopfully it has spat it out through the exhaust valves,to answer your question yes it may have been the fuel you used as ethanol burns hotter (correct me if I'm wrong) and I think you need a different map to run that type of fuel,the black soot would be from the plug having no tip,so the plug cannot be cleaned when it sparks,is the running fine now?I would be more concerned about the where abouts of the tip.

 

[godzilla]

The tip would have deteriorated progressively, therefore would more than likely not caused any damage. The plug is heavily fouled because it has not been firing all the time leaving unburnt fuel behind. Ethanol does burn hotter than fuel but doubt that one tank would have destroyed a plug to that extent.

Here are a couple of paragraphs from NGK's website that may explain some things:

W hen inspecting a spark plug that has experienced overheating or pre-ignition, blistering on the ceramic insulator and/or melted electrodes can sometimes be found.

Ignition Timing

• Advancing ignition timing by 10° will cause the spark plug tip temperature to increase by approximately 70° to 100°C.
• A colder heat range spark plug may be necessary if the ignition timing has been advanced to near the knock level. Higher cylinder temperatures near the knock level will bring the spark plug firing end temperature closer to the pre-ignition range.

Fuel Type / Quality

• Low quality and/or low octane fuel can cause knock which will elevate cylinder temperatures. The increased cylinder temperature will cause the temperature of the combustion chamber components (spark plug, valves, piston, etc.) to rise, and will lead to pre-ignition if the knock is uncontrolled.
• When using an ethanol blend fuel with high ethanol content in high performance applications, a colder heat range may be necessary. The spark timing can be advanced further because ethanol blend fuel has a higher resistance to knock (higher octane). Due to the decreased knock, there will be less audible “warning” from knock before the spark plug overheats and pre-ignites.
  Some types of fuel additives in lower quality fuels can cause spark plug deposits that can lead to misfires, pre-ignition, etc.

Pre-ignition

• Pre-ignition occurs when the air-fuel mixture is ignited by a hot object / area in the combustion chamber before the timed spark event occurs.
• When the spark plug firing end (tip) temperature exceeds 800°C, pre-ignition originating from the overheated insulator ceramic can occur.
• Is most often caused by the wrong (too hot) heat range spark plug, and/or over-advanced ignition timing. An improperly installed (insufficient torque) spark plug can also result in pre-ignition due to inadequate heat transfer.
• Pre-ignition will dramatically raise the cylinder temperature and pressure and can melt and hole pistons, burn valves, etc.
  

Knock

• Occurs when part of the air-fuel mixture in the combustion chamber away from the spark plug is spontaneously ignited by the pressure from a flame front originating from the spark plug. The two colliding flame fronts contribute to the “knocking” sound.
• Knock occurs more frequently when using low octane fuel. Low octane fuel has a low resistance to knock (low resistance to ignition)
• Knock is related to ignition timing. (Knock is sometimes referred to as “Spark-knock”.) Retarding the ignition timing will reduce knock.
• Heavy knock often leads to pre-ignition.
• Heavy knock can cause breakage and/or erosion of combustion chamber components.
• Knock is sometimes referred to as “ping” or “detonation”.
  

Misfires

• A misfire occurs when the spark travels the path of least resistance instead of jumping across the gap. Misfires can be caused by the following:
  
  
  1. Carbon fouling
  2. Worn or deteriorated ignition system components
  3. Too large of gap size
  4. Spark timing excessively advanced or retarded
  5. Damaged spark plugs (cracked insulator, melted electrodes, etc)
  6. Mismatched ignition system components (plug resistance / wire resistance, ignition coils / igniter modules, etc.)
  7. Insufficient coil primary and/or secondary voltage – voltage required to jump the spark plug gap higher than coil output

 

[merlin]

Take another pix in macro or flower mode, just of the tip and insulator.

The orange crud is from the octane booster (plug wrecker) so time for new plugs anyway.

Det could have been the cause of the missing ground electrode though. These engines are not happy with 91 and will knock under boost untill the ECU has pulled enough advance to get it under control. Of course, by the time you have run half a tank through you will be well on the way to low octane fuel maps, which are very rich stock.
Question, did you use octane booster because of the 91 fuel or was that used some time before/after?

 

[qball]

Octane booster because of 91 fuel, went straight in after filling up