Spark plug mystery
Discussion
Recently bought a Nissan X Trail 2.5 petrol with 105,000 miles. Had a lot of electrical problems that the used car dealer has worked through.
All seemed to be sorted and the car ran for a hundred miles around town with no problems.
As a final test, I ran it up to the red line and immediately suffered a misfire in cylinder 1. The dealer investigated and replaced a coil pack that improved, but didn't cure, the problem.
Further investigation revealed number 1 spark plug with the gap closed right up.
With more years of motoring than I care to remember under my belt, I've never come across this before.
Anybody have thoughts on how this could have happened?
Immediately after the misfire started, the engine was reluctant to turn over, as though the battery was flat, but it's a new battery and it turned over normally the next day.
Any ideas?
All seemed to be sorted and the car ran for a hundred miles around town with no problems.
As a final test, I ran it up to the red line and immediately suffered a misfire in cylinder 1. The dealer investigated and replaced a coil pack that improved, but didn't cure, the problem.
Further investigation revealed number 1 spark plug with the gap closed right up.
With more years of motoring than I care to remember under my belt, I've never come across this before.
Anybody have thoughts on how this could have happened?
Immediately after the misfire started, the engine was reluctant to turn over, as though the battery was flat, but it's a new battery and it turned over normally the next day.
Any ideas?
Running to the red line dislodged some carbon from the valve / valve seat and that got compressed into the electrode by the piston?
I doubt it but what else could physically interfere then disappear leaving a normal start next day?
Interesting one!
EDIT: t'internet says it was detonation. Was appropriate circumstances for that to be true
I doubt it but what else could physically interfere then disappear leaving a normal start next day?
Interesting one!
EDIT: t'internet says it was detonation. Was appropriate circumstances for that to be true
Edited by ShaunTheSheep on Sunday 6th April 00:19
Pesty said:
Ham fisted fitting banged it on the way in didn't check,
Couldn't get it in the hole
No, it was running ok until I raised the revs, then the misfire started. It was traced to the plug gap, which suggests the gap closed while the plug was in the engine. Couldn't get it in the hole
So, WTjollyF happened?
mybrainhurts said:
No, it was running ok until I raised the revs, then the misfire started. It was traced to the plug gap, which suggests the gap closed while the plug was in the engine.
So, WTjollyF happened?
Hmmmm fSo, WTjollyF happened?
k knowsSilly question. Is it the right plug? Same as the others?
Take it out and stick a magnet in there might be something floating about In The cylinder. It might look like Swiss cheese in there
mybrainhurts said:
pmjg66 said:
s the car still misfiring with a new correctly gaped plug when reved hard or driven normally ?
It's still with the garage, but they assure me the misfire has gone, after re-gapping the same plug.That happened to me recently and nearly f
ked the car, it shat itself at about 120 mph when it couldn't reject the heat any more so it started detonating so badly i thought i'd dropped a valve.I was incredibly pissed off when i found out it was missing the washer from the spark plug.
shambollic said:
The crankshaft is cracked at the first web, allowing it to flex enough that the piston has hit the spark plug at high revs.
Or there is play in the the little end bearing (or the big end bearing or even both bearings) of No.1 con rod, and having the revs so high meant that the tolerances stacked up enough (by pushing the oil film at least partially out of the way due to the massive change in piston inertia at the top of the stroke) for the cylinder to get high enough in the bore to tap the spark plug electrode.Or even No.1 piston is breaking up (tied in to detonation as mentioned upthread) and its head came away a little and tapped the plug electrode (and caused the engine to be difficult to turn over later on/next day, as reported
).Very much worse case scenarios (
) but it's a head-off job to check 
. I'd suggest keeping away from the red line as long as it otherwise runs OK .There is a ball bearing floating around the cylinder. The piston now looks like a miniature moon every now and again the bearing hits the plug closing the gap
http://www.ebay.co.uk/itm/ENGINE-NISSAN-X-TRAIL-QR...
http://www.ebay.co.uk/itm/ENGINE-NISSAN-X-TRAIL-QR...
aw51 121565 said:
Or there is play in the the little end bearing (or the big end bearing or even both bearings) of No.1 con rod, and having the revs so high meant that the tolerances stacked up enough (by pushing the oil film at least partially out of the way due to the massive change in piston inertia at the top of the stroke) for the cylinder to get high enough in the bore to tap the spark plug electrode.
Or even No.1 piston is breaking up (tied in to detonation as mentioned upthread) and its head came away a little and tapped the plug electrode (and caused the engine to be difficult to turn over later on/next day, as reported ).
Very much worse case scenarios ( ) but it's a head-off job to check . I'd suggest keeping away from the red line as long as it otherwise runs OK .
Unlikely I think. Would need to be on the exhaust TDC, and the valves would get in the way....Or even No.1 piston is breaking up (tied in to detonation as mentioned upthread) and its head came away a little and tapped the plug electrode (and caused the engine to be difficult to turn over later on/next day, as reported
).Very much worse case scenarios (
) but it's a head-off job to check . I'd suggest keeping away from the red line as long as it otherwise runs OK .Pesty said:
A rebuilt engine from Dubai, carriage £230...What could possibly go wrong...?
They don't know what caused the misfire and they can't get it to replicate the fault so have come up with some bks about the plug to make it sound like they've done something.
As an aside, re gaping a plug is stupid. You're taking the smallest component in the most dangerous place in your engine and bending it. This isn't the 1960s any more, swap the plug ffs.
ks about the plug to make it sound like they've done something.As an aside, re gaping a plug is stupid. You're taking the smallest component in the most dangerous place in your engine and bending it. This isn't the 1960s any more, swap the plug ffs.
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