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Anyone see a spark plug like this one from a NA 944?

I just changed my plugs about a year ago as the original ones in it were quite badly crudded up with a black, non shiny compound of some sort.

I thought i would be terribly clever and go for the four pronged Bosche Supers

But in fact, i have found today that my number 3 cyclinder - counting from the rad and going backwards - was really badly fouled with the same black material.

it's not an oil build up which i have seen before on an old Mercedes. There's nothing wet. It looks like a carbon build up but not the one typically which is sooty.

Any suggestions as to what is going on in number 3?

thanks

MJ in Beirut
Old 12-17-2017, 01:59 AM
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When I took the crankcase off my engine after sudden total loss of oil pressure at 6000 rpm, I saw quite a lot of similar hard carbonlike stuff in the bottom.
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Old 12-17-2017, 04:16 AM
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It could just be a leaking injector running that cylinder too rich. You could move the injector and see if it follows it.
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Old 12-17-2017, 04:53 AM
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Quote:
Originally Posted by Tom944 View Post
It could just be a leaking injector running that cylinder too rich. You could move the injector and see if it follows it.
That is what I was thinking. I am reviving a car that sat for quite a while and after idling for less than 10 minutes 3 out of 4 brand new plugs have a good bit of black carbon build up. I know the injectors are bad.

Run a couple tanks of fuel with of a good fuel system cleaner cleaner added and see if that helps.
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Old 12-17-2017, 04:58 AM
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Originally Posted by Tom944 View Post
It could just be a leaking injector running that cylinder too rich. You could move the injector and see if it follows it.

Did i hear right that there are companies which clean them and give them back to you?

Im guessing injectors are a bit pricey

MJ
Old 12-17-2017, 07:09 AM
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Did i hear right that there are companies which clean them and give them back to you?

Im guessing injectors are a bit pricey

MJ
I had mine cleaned by Witchhunter but ended up replacing one anyway. I bought a remanufactured one from our host.
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Old 12-17-2017, 07:25 AM
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Here is a tech article on how to clean them yourself.
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Old 12-17-2017, 07:57 AM
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witch hunter did mine a couple months ago.


if you have a 16 valve, oil can pool around the plugs if the plug seals on the cover have gone south.
Old 12-17-2017, 11:23 AM
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But doesn't a leaky injector sound like it can't be cleaned/fixed? If the pot is runnig rich...
Old 12-17-2017, 09:06 PM
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If they are leaking fuel through to the intake that might mean they are sticking or cannot close fully and cleaning might help them.

If they leak to the outside (and your car has not burned up) I think they are not fixable and should be discarded.

Check the part numbers too in case someone has put the wrong ones in.

Also check the fuel pressure and check the fuel pressure regulator and damper, these can leak fuel into the intake via the vacuum lines. The FPR might not have vacuum to it or could stick also and deliver too-high fuel pressure.
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Old 12-18-2017, 10:27 AM
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If they are leaking fuel through to the intake that might mean they are sticking or cannot close fully and cleaning might help them.

If they leak to the outside (and your car has not burned up) I think they are not fixable and should be discarded.

Check the part numbers too in case someone has put the wrong ones in.

Also check the fuel pressure and check the fuel pressure regulator and damper, these can leak fuel into the intake via the vacuum lines. The FPR might not have vacuum to it or could stick also and deliver too-high fuel pressure.
But if the FPR was teh problem, wouldn't it do that to all the plugs? I mean, wouldnt all the injectors run a little rich?
Old 12-20-2017, 07:16 AM
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I suppose, but you might as well at least check the vacuum side.
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Old 12-21-2017, 06:58 AM
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