Number 5 plug fouling?

farstar

farstar

Well-Known Forum User
Hiya guys, hope you're all keeping well - I'm enjoying the website and all the posts, tech stuff and scraps of course! :thumbs:

My 280z engined 260z fouls number 5 plug with oil. Its happened several times now...

The car has not really been used recently due to the weather and salt, but is started up now and then and allowed to warm up to operating temp. I started her up a few weeks ago and she was missing on number 5 again, replaced the plug and she was fine. Started her up yesterday and she was missing on 5 again so I cleaned the oily plug up and hey presto, a smooth rocksteady idle.

Is this the valve stem seals that need replacing? Am I right in saying that it is unlikely to be piston rings as normally a few go at the same time? :unsure::unsure::unsure::unsure:
 
As far as I know there is not a specific problem with No5 cylinder. If it was mine I would do a compression test and valve clearance check on all cylinders. If nothing obvious was evident then I would check the HT leads and swap the plugs around.

If nothing found wait until you use it on the road and see if it happens again.
 
Good advice from Rob, my car used to run triples and would choke up the plugs if it was left to idle for too long, valve stem seals would cause oil to leak down through, but I would wait till it's back on the road and go for a good run then get back and pull say 5 and 6 and compare the colour, go from there,
As a side note my car blew the valve stem seals of number 1 and 12 valves after closing the wastegate and i finished running it in and it smoked quite badly, there was not much wear in the valve guides in the head either. changed the seals no smoke at all. you can imagine how I felt when it started smoking I thought i'd blown the rings.
 
Cheers chaps, I'll check all this out.

I remember that it happened over the summer a few times also which required changing the plugs. The reason why I think it is the stem seals is that I don't think they have ever been changed, but I'm concerned as Zed2k was initially that it maybe the rings.

Is there any definitive way of telling whether it is rings or stem seals?? Or even both!!!!!
 
Farstar - the tool to determine where the problem lies is called a Leakdown Tester, which most good Garages should have around.
Basically it is hooked up to an Air Compressor and is fitted to each cylinder in place of the Spark Plug, then pressurised. A guage should register the fact that the cylinder is holding the pressure ( when the piston is at t.d.c.), and if not, you will hear air leaking out of either the Rocker Box breather ( valve stem oil seals ), or the Cranckcase breather ( Piston Rings ).
Or, if it is coming from both, then as you say, it is both at fault.
 
Yes a leak down tester is a good tool, but maybe hard to track down the fault as if the pistons on TDC then the valves will be shut and you won't be testing the Valve stem seals only the valve seat quality. it will however show ring failure by hissing through the block breather as said.
 
You're absolutely right- it will only tell you if the Rings are worn or broken & there is 'blow-by' on that cylinder.
At least it will eliminate the need for a complete strip-down of the Block, etc.

Must have ben past my Bed-time when I made that comment !
 
In my opinion you would have to be using a hell of a lot of oil to foul the plug and stop it firing. For example two-stroke engines manage ok with oil mixed with the petrol.

My 240 was using a hell of a lot of oil before I rebuilt the engine (125 mls per pint?) and it still ran smoothly. So I doubt if valve oil seals would be the cause.

My guess would be that the mixture isn't burning and thus fouling the plug.
 
Interesting point Rob...

I'm pretty sure that it is oil fouling the plug as a rich/unburnt mixture usually leads to a black sooty deposit (?). Emissions wise the engine is phenomenal - the MOT tester was amazed at how low the HC level was for a car running on old Jap SU's and this was just a few months back. I would assume that a bad mixture would show itself on the emissions tester...but I could be wrong...I have been wrong before...think it was 1970 sumthin...:rolleyes::lol:
 
My money's still on the Oil seals, Rob.
If it were the mixture at fault, then logically it would foul up two cylinders ( if on triples ), or three ( if on SU's ), and not just one alone.

Wouldn't it ?

And don't forget, for a two-stroke engine to mix oil & petrol, it has to be a certain type of oil, and not the Multigrade stuff that we use.
 
Duncan, I didn't mean the mixture was wrong I meant it may not be burning for some reason (faulty ignition, low compression etc) and thus wetting the plug.

You may well be right though, I'll be interested in knowing the answer.
 
Try measuring resistance of No 5 and 6 plug leads end to end and comparing readings.
May just be a lead gone faulty!
 
Cheers chaps, this all seems like sound advice. As soon as the weather improves and she comes out of storage, I'll do the compression tests. The resistance test I should be able to do pretty soon so I'll post if that leads to anything significant.

How often do you guys normally change your leads as routine maintenance, not through a fault?

260zTT, when I first stumbled onto the Z scene, a friend of mine gave me an old 'Beasts from the East' magazine that had a feature on, I think:unsure:, your car, entitled 'The Last samuri'? What an absolutely phenomenal machine mate, truly breathtaking with regards the amount of thinking, engineering, finish, etc. :bow:
 
It was featured in Japanese performance, late '03 early '04, would have to check when I get home which issue.
Never did get any freebie magazines from them though!
Hoping to get it back out again this year, more funds required as always!
On another note, Gill has just purchased a 55 plate 350z roadster, so we are now back to being a 2 Z family!

Mark.
 
Yeah, I remember the article well even though it was given to me several years after publication, as it was one of the first Z related pieces that I read after acquiring my first Z, a 260z 2+2 (affectionately known as Rusty ;)). It sort of opened my eyes to what you could do with these cars, bearing in mind that until very recently, I had owned every S30 Z that I had seen in the flesh! Very, very nice car mate, especially the twin turbo set up.

I haven't had the opportunity to attend any Z meets but hope to see her alive and kicking in the future! :thumbs:
 
My L28-engined 260 has similar problems if left to warm up without being driven. It needs choke to start it but if you leave the choke out for more than a few seconds or even let it idle for a few minutes it'll foul the plugs. It has always done it and it drove me mad for ages. If I start her up and give it some welly to clear her tubes she's fine :)
 
What plugs are you running?
They should be NGK BPR6ES when I tried mine with 7's it would foul up if I didn't get going straight away.
 
Cheers for the input chaps, this is all good stuff.

I can't say for definite that I am having the same issue as Tony but when I warm her up during the run as opposed to idling on the drive, it doesn't seem to happen. Either way, she will be unwrapped properly soon with fresh oil and filter :), so can be monitored over the summer. If you crack it before me Tony, let me know mate!
 
You must log in or register to reply here.
Back
Top