W202 strand spark plug issue

[bogey10]

C220 petrol auto. Cleaned engine today. Was very economical with the water from hose as not to saturate the electrics. Started engine after washing and it ran perfectly. Then after about 3 min of running the engine developed a missfire. Opened cover on tappet cover to check for water on plug leads and noticed on 2 of the 4 plug leads the spark plug cap and electrode going into the plug from the top came away with the plug lead when removing. On the other 2 cylinders spark plug cap and electrode remained in place attached to the plug. Would this cause the missfire, and do plugs need replacing?

 

[LostKiwi]

Any pics of what you're seeing as I'm not quite sure what you mean?

 

[bogey10]

Sorry firstly thread should read 'Strange spark plug issue'. I am not able to post pics so I will try explain.
Looking at the spark plug, on the top is the terminal (will here the plug lead connects to the spark plug) which is a metal cap that screws onto the electrode that runs down through the plug and out the bottom where you set the gap. When I pulled off the plug lead attached to spark plug, the terminal and about half the electrode came away still in the plug lead meaning the electrode has broken off inside the plug about half way down in the insulation somewhere.
This happened when removing 2 of the 4 plug leads. Previously the car was running fine except for a low idle speed.

 

[LostKiwi]

Yep replace the plugs.

 

[Frosty149]

Replace all the plugs imo...

 

[L John]

Would a spark plug with the top half broken off cause a missfire? I guess there is a possibility.
Should you replace them? It could be worth a try.
No decent brand should break just by pulling the cap off.
Did you spray water onto a hot engine?
If not it's most likely fake junk has been fitted.

 

[bogey10]

Would a spark plug with the top half broken off cause a missfire? I guess there is a possibility.
Should you replace them? It could be worth a try.
No decent brand should break just by pulling the cap off.
Did you spray water onto a hot engine?
If not it's most likely fake junk has been fitted.

LJ the plug is not broken. The 'wire' that runs through the centre of the plug from the electrode at the bottom where you set the gap to the top of the plug where the plug lead fits has broken off inside the plug itsself. So when pulling the plug lead off part of the electrode wire is pulling out of the plug. Plug lead still seems to back on ok. But engine is running very rough on what sounds like 2 or 3 cylinders at low revs and idle rpm is all over the place when in gear and or aircon on. I dont know if this has been caused from washing engine or plug issue but straight after washing engine ran perfectly then after a few minutes missfire started and been ever since.

 

[LostKiwi]

For the price of a set of plugs just change them to be sure.

 

[L John]

LJ the plug is not broken. The 'wire' that runs through the centre of the plug from the electrode at the bottom where you set the gap to the top of the plug where the plug lead fits has broken off inside the plug itsself.

You can't replace the spark plugs internal 'wire', it's part of the spark plug.
I wouldn't even be trying to run it with a broken plug (and you are describing a broken plug despite saying its not broken). The loose electrode could fall into the cylinder. This has been known to happen with some fake plugs, don't rely on the ground electrode stopping it from dropping into the cylinder.
Change all plugs as Frosty said, then decide if you need leads too.

 

[Frosty149]

Don't buy FleaBay cheapies, I think OEM are Bosch, but a well known brand should be selected.

 

[bogey10]

Thanks guys for all the input. I will do a plug change and then report back.

 

[bogey10]

Done plug change and car is back running normally. Did diagnostics and all ok. Wiring harness is not looking good however so going have to bite the bullet and get this done soon.