Broken spark plug
Discussion
My son's car started misfiring badly. Pulled the plugs to find that one no longer had a ground electrode. Put a camera into the bore, couldn't see anything in there. Bit of research suggests the electrode could have gone into the exhaust system and out. As any damage would have already been done (started misfiring on the motorway and was driven off) put a new plug in and the car started without difficulty, ran sweetly for 60 motorway miles or so without problem until it stalled, It cranks but won't start. Error code suggests a throttle body / air intake fault. Is this just an unrelated fault in short time (car has done 110k), or could the two instances be connected? Any help appreciated.
Edited by SwanJack on Saturday 28th June 12:51
Edited by SwanJack on Saturday 28th June 12:52
Not obvious how those would be related but I suppose that the plug could have been damaged by debris in the intake which might be related to the other faults. What are the actual fault codes? These are likely to be related to why the ECU is no longer able to run the engine.
Are you planning to fix this yourself? If not, best to leave the figuring-out to whoever is going to fix it for you. Professional mechanics rarely appreciate being told how to do their job.
Are you planning to fix this yourself? If not, best to leave the figuring-out to whoever is going to fix it for you. Professional mechanics rarely appreciate being told how to do their job.
The fault code is p1512, the car is a Mito and one source says it's a stop start relay fault and the other says it's to do with the intake. It was towed to an Alfa specialist in the middle of the night who will hopefully be able to have a look on monday. I'm just trying to get my head around what it could be and the possibility that if compression is gone or valves damaged, then the car is scrap, or if it might be something less drastic. If it's the former then we need to get something sorted asap as he needs it to get to work
That fault code suggests the car has a variable length intake runner and it is now stuck. That could be due to a mechanical failure, carbon build-up or something else jamming it. There's no way to know until somebody has had a chance to investigate.
IMO it would be reasonable to assume the car will be off the road for at least a few days. If you need transport and the garage doesn't provide a courtesy car then I suggest you make other arrangements.
IMO it would be reasonable to assume the car will be off the road for at least a few days. If you need transport and the garage doesn't provide a courtesy car then I suggest you make other arrangements.
My Son had a Renault Clio 1.4 16v, a couple of weeks after coming back from a Garage repair, it started running badly and the 'check engine light' was on.
When I looked into it an OBD scan showed an intermittent misfire on 2 cylinders and lean condition, upon checking it turned out 2 of the spark plugs were only finger tight and air had been bypassing the threads causing the lean running. The worst of the 2 plugs had no electrode left and so wasn't firing at all, it had been completely consumed, presumably by the excess heat of the lean running? The coilpack had also melted at the plug end.
Anyway, I couldn't see anything internally and fitting new plugs cured the running issues.
Fast forward a few years and the cambelt broke, as it was an old car of little value it wasn't worth taking it to a garage (and definitely not to the place that didn't tighten the plugs) so I stripped it all down and repaired it: new valves, belt, tensioners, water pump etc. and all was good again.
There were chips/scratches on the inside of the head, around the exhaust valve seats and top of the piston on the cylinder with the missing electrode so something had been rattling around in there at some point, presumably the electrode? but it hadn't noticeably damaged the actual valve seats or the valves from what I could see though, obviously the exhaust valves were bent from the broken belt.
Personally I would have expected a piece of metal of electrode size to have got stuck in the valve and caused the valvetrain to break or jam but that didn't seem to be the case so, I assume it was broken down into very small pieces that somehow passed through - maybe we were lucky?
As my Son was on a budget, I reassembled it with the marked head/pistons and it ran fine for a few more years until it went to the scrapyard (for non-engine related reasons).
Not sure if this helps but it seems that it is, at least possible though not ideal for small parts to pass/disintegrate without causing excessive damage.
When I looked into it an OBD scan showed an intermittent misfire on 2 cylinders and lean condition, upon checking it turned out 2 of the spark plugs were only finger tight and air had been bypassing the threads causing the lean running. The worst of the 2 plugs had no electrode left and so wasn't firing at all, it had been completely consumed, presumably by the excess heat of the lean running? The coilpack had also melted at the plug end.
Anyway, I couldn't see anything internally and fitting new plugs cured the running issues.
Fast forward a few years and the cambelt broke, as it was an old car of little value it wasn't worth taking it to a garage (and definitely not to the place that didn't tighten the plugs) so I stripped it all down and repaired it: new valves, belt, tensioners, water pump etc. and all was good again.
There were chips/scratches on the inside of the head, around the exhaust valve seats and top of the piston on the cylinder with the missing electrode so something had been rattling around in there at some point, presumably the electrode? but it hadn't noticeably damaged the actual valve seats or the valves from what I could see though, obviously the exhaust valves were bent from the broken belt.
Personally I would have expected a piece of metal of electrode size to have got stuck in the valve and caused the valvetrain to break or jam but that didn't seem to be the case so, I assume it was broken down into very small pieces that somehow passed through - maybe we were lucky?
As my Son was on a budget, I reassembled it with the marked head/pistons and it ran fine for a few more years until it went to the scrapyard (for non-engine related reasons).
Not sure if this helps but it seems that it is, at least possible though not ideal for small parts to pass/disintegrate without causing excessive damage.
The Alfa specialist has had a look at it. The multiair unit has gone. Before deciding to get it fixed they did leak down and compression tests, passed all round. Seeing as it has had in the last 12 months a new clutch, cam belt, water pump, discs and pads all round and as used cars are no longer cheap, it's going to get fixed. The spark plug issue and the multiair fail in close proximity seem to be unrelated, or the misfire just brought the multiair unit (which was probably on its way out anyway as it has thrown a check engine light intermittently without any performance issues over the last 18montts) to a quicker end.
Edited by SwanJack on Wednesday 2nd July 22:18
catso said:
My Son had a Renault Clio 1.4 16v, a couple of weeks after coming back from a Garage repair, it started running badly and the 'check engine light' was on.
When I looked into it an OBD scan showed an intermittent misfire on 2 cylinders and lean condition, upon checking it turned out 2 of the spark plugs were only finger tight and air had been bypassing the threads causing the lean running. The worst of the 2 plugs had no electrode left and so wasn't firing at all, it had been completely consumed, presumably by the excess heat of the lean running?
Loose plugs run a lot hotter than they should because they can't conduct as much heat into the cylinder head.When I looked into it an OBD scan showed an intermittent misfire on 2 cylinders and lean condition, upon checking it turned out 2 of the spark plugs were only finger tight and air had been bypassing the threads causing the lean running. The worst of the 2 plugs had no electrode left and so wasn't firing at all, it had been completely consumed, presumably by the excess heat of the lean running?
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