Technical TJET - Spark Plug Tip Broken - Misfire / Possibly needs a rebuild?

[AmixTJET]

Hello everyone.

Yesterday we went for a trip with my friends. When coming back from our trip, my car started loosing power and suddenly the dipstick popped. Spraying oil all over the place.

Stopped immediately, turned the engine off. Let it cool for 5 minutes. Then tried starting it again.

Starts and idles very roughly , from my little experience 1 or 2 cylinders were misfiring. Did not risk it and shut it off. Picked it up and went to my mechanic this morning.

Popped all the spark plugs out , one spark plug tip is broken , possibly entered into combustion chamber damaging piston,wall or valves. Tried new plugs still misfiring.

My mechanic is gonna call me tomorrow morning and tell me the damage. My question is why did this happen? Bad fuel quality ? Bad injector ? Coils ? Spark Plugs ? Should i replace all these things after rebuild?

I have the car for 10.000kms not a single issue. Engine was running smooth till yesterday. No codes , no overheating , nothing. A small metal piece possibly killed my engine.

 

[portland_bill]

A plug tip broken is unusual. Is it fractured, or burnt/melted?
Broken suggests a damaged plug, perhaps dropped before fitment, just took some time to let go.
Burnt, suggests the plug got too hot. Would require a very weak mixture, less likely with fuel injection, or a plug not seated properly. The plug loses its heat via its seating washer on the head. The washer needs to be crushed as the plug is tightened, which is achieved with the correct tightening torque. An uncrushed washer will cause the plug to run hot, which can cause a burnt hole in a piston, a melted plug tip, or the plug tip ceramic to break. The ceramic would normally be a brighter white than the others, if it has been running hot. An examination of the plug may reveal the cause. Who fitted the plugs, and how long ago?

If the plug tip has got caught down the side of a piston, it can get jammed, and cause a 'hole', but this is unusual. It would normally rattle around, cause a few, or a lot, of tiny dents in the piston and head, then get thrown out of the exhaust valve. Occasionally, it may also damage a valve, and of course, then gets caught in the catalyst. Might do no harm, or might rattle and annoy. A groove down the side of the piston will cause extra pressure in the crankcase, but surprising to pop the dipstick out. For the dipstick to pop out, I'd expect to see a hole in the piston. Such a hole would point more to heat as the cause, rather than physical damage. Which points back to the plug.

The machanic should hopefully have an endoscope, that can be put down the plug hole to view the piston crown. Quicker and simpler than removing the cylinder head. Damage to piston or bore will need a full engine rebuild, or a replacement engine. Used engines are fairly easy to obtain here in the UK, hopefully also available where you are.

Sad news. Please keep us updated.

 

[AmixTJET]

A plug tip broken is unusual. Is it fractured, or burnt/melted?
Broken suggests a damaged plug, perhaps dropped before fitment, just took some time to let go.
Burnt, suggests the plug got too hot. Would require a very weak mixture, less likely with fuel injection, or a plug not seated properly. The plug loses its heat via its seating washer on the head. The washer needs to be crushed as the plug is tightened, which is achieved with the correct tightening torque. An uncrushed washer will cause the plug to run hot, which can cause a burnt hole in a piston, a melted plug tip, or the plug tip ceramic to break. The ceramic would normally be a brighter white than the others, if it has been running hot. An examination of the plug may reveal the cause. Who fitted the plugs, and how long ago?

If the plug tip has got caught down the side of a piston, it can get jammed, and cause a 'hole', but this is unusual. It would normally rattle around, cause a few, or a lot, of tiny dents in the piston and head, then get thrown out of the exhaust valve. Occasionally, it may also damage a valve, and of course, then gets caught in the catalyst. Might do no harm, or might rattle and annoy. A groove down the side of the piston will cause extra pressure in the crankcase, but surprising to pop the dipstick out. For the dipstick to pop out, I'd expect to see a hole in the piston. Such a hole would point more to heat as the cause, rather than physical damage. Which points back to the plug.

The machanic should hopefully have an endoscope, that can be put down the plug hole to view the piston crown. Quicker and simpler than removing the cylinder head. Damage to piston or bore will need a full engine rebuild, or a replacement engine. Used engines are fairly easy to obtain here in the UK, hopefully also available where you are.

Sad news. Please keep us updated.

First off thanks for your reply.
Yes, the ground electrode looks melted. So i assume the cause is heat.
Running too lean? Wouldn't that affect the other plugs too?

Plugs were changed approximately 19.000km before. Torque down to spec. I used to replace them every 20-22.000km.

 

[AmixTJET]

Unfortunately i have very bad news. The engine is done. Needs a rebuild or new engine. The damage is big.

A rebuild would cost me around 1.3k euros and a new engine which my mechanic found will cost me 1.6-1.7k . New engine is from Mito with the 155bhp. Only 39000km on the clock. Seller sent me a proof video of the engine working, idling aswell as revving it. Sounds healthy.

I think i will go with the new engine. Can't risk the rebuild.

 

[portland_bill]

First off thanks for your reply.
Yes, the ground electrode looks melted. So i assume the cause is heat.
Running too lean? Wouldn't that affect the other plugs too?

Plugs were changed approximately 19.000km before. Torque down to spec. I used to replace them every 20-22.000km.

A plug that was not tightened down properly would run hot immediately, so I would expect a failure much sooner.
Normally a weak mixture would be highlighted by the oxygen sensor, and the ECU would richen that cylinder to compensate. If unable to do so, should illuminate the engine management light, and store a code. An injector blockage or fault that gave less fuel than required should give the same results.
An air leak into the inlet, after the flow sensor, will cause weak mixtures, but again the ECU should be trying to overfuel it to compensate. I would expect a stored fault code.

I see you are going with a replacement used engine, which is the option I'd go for. I'm surprised at the cost, you have my sympathy.

How do the other plugs look? If they all look a bit distressed, that could indicate a general air leak. If the others are all good, an air leak on an individual cylinder, or an injector fault, need to be checked. You don't want to move the cause onto the replacement engine.

With melted plugs or pistons, often there is only one, as the first failure causes a stop, preventing the others from failing. Hence the need to look carefully at the others. Important to diagnose the cause, not just fix the result. Good luck.

 

[AmixTJET]

A plug that was not tightened down properly would run hot immediately, so I would expect a failure much sooner.
Normally a weak mixture would be highlighted by the oxygen sensor, and the ECU would richen that cylinder to compensate. If unable to do so, should illuminate the engine management light, and store a code. An injector blockage or fault that gave less fuel than required should give the same results.
An air leak into the inlet, after the flow sensor, will cause weak mixtures, but again the ECU should be trying to overfuel it to compensate. I would expect a stored fault code.

I see you are going with a replacement used engine, which is the option I'd go for. I'm surprised at the cost, you have my sympathy.

How do the other plugs look? If they all look a bit distressed, that could indicate a general air leak. If the others are all good, an air leak on an individual cylinder, or an injector fault, need to be checked. You don't want to move the cause onto the replacement engine.

With melted plugs or pistons, often there is only one, as the first failure causes a stop, preventing the others from failing. Hence the need to look carefully at the others. Important to diagnose the cause, not just fix the result. Good luck.

The other plugs, aswell as pistons,cylinders looked in good shape. No codes at all before this happened. Engine run very smooth.

My mechanic also suggested me to send the injectors for a test. I will also visit a tune shop to take a look on the map. I will keep updating this thread.

My car should be ready till next Monday. Having a good friend mechanic is a big advantage cost wise. In a dealer or other mechanic i was looking for 2.5k atleast.

 

[AmixTJET]

Update 26/05/2023

New engine in, new spark plugs , new filters , oil etc. First start and runs smooth. After 3500 RPM starts to misfire again. Swapped coils , injectors , spark plugs . It gives me P0300 P0301 P0302 codes. Could it be bad ECU ?