burnt plugs

john999May 16, 2007

I have a Mitsubishi Sigma of doubtful heritage (it appears to have an engine older than the body...) which keeps burning out plugs and leads - why ?

BTW, it leaks a LOT of oil, I mean a LOT, more even than most Sigmas, like about 1.5L of oil for every 15L of fuel. The gaskets are worn for sure.

I was wondering if a coked up head causes plugs to burn out ?

Old cars (pre-1960) needed de-cokeing, was this why ?

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kalining

Burned out plugs cover a lot of ground. how are they burnt ? Center electrode means one thing. burned negative
electrode means another thing. burned outside thread means
something else. burned on and caked oil means something else. Which is it ? are your plug leads melting from engine heat or are they being dissolved by the leaking engine oil ? If your engine is leaking the amount of oil you say it is you are driving around in a potential fire
cracker. i wouldn't want to be withing 50 yards of that thing when it goes up in flames let alone inside it. you might want to address the oil leaks for your own saftey.

    Bookmark   May 16, 2007 at 12:23PM
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john999

It shows a brown-orange mark on the ceramic and it shorts out through the ceramic rather than at the gap.

    Bookmark   May 17, 2007 at 1:24AM
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kalining

You are describing high speed glazing caused by a sudden and rapid rize in combustion chamber temp. Keep your foot off the gas. change to a cooler plug if your driving habits are a little harsh. Back in the olden days all my plugs in every engine i had looked like what you describe. i drove my cars with the peddle to the rad. too much street racing. Your cylinder temp will rize rapidly as your
engine runs out of oil also. I think that would be your case.

    Bookmark   May 17, 2007 at 11:01AM
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john999

Well it's my mother car actually and she drives like, an old woman.

The temp gauge has never worked but the radiator doesn't bubble over (which you would hear cos the engine is very quiet) and it doesn't lose coolant.

I've burnt out a brand new HT lead while looking for a spark (I'm so happy !) and I can't seem to find an earth on the rocker cover or cylinder head. Why ?

It hasn't run low on oil, and its only in the last week it started to really chew up oil, before that it would do about 1L for every 350km or so.

I was thinking maybe carbon build-up in the head might be causing to much electrical resistance for the plug or it gets too hot ?

    Bookmark   May 18, 2007 at 12:55AM
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kalining

What is the K.V. on your ignition system ? very week spark, maybe ? If i read your post right,350 km. for 1 L.
of oil is ridiculas. 5000 km. to 1 l. is about right.Even
then that is high.

    Bookmark   May 18, 2007 at 12:33PM
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john999

The sparks fine at the coil, but there is no spark from the distributor.
It's burning out the leads.

I replaced the distributor cap and I don't think it's the transistor because that was replaced only about 30k ago, and the old was wasn't dud anyway (might be that though).

I was just wondering why it seems to burn out plugs and if that was related to the fact that I can't find an earth on the rocker cover or cylinder head.

The rings are worn and the gaskets leak, it did use less oil than that before. It used about 3L of oil between changes (10k).

Sigmas ("Silent Shaft" like in a K-car) leaked oil even when new.

    Bookmark   May 22, 2007 at 1:01AM
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