In an earlier thread entitled Sourcing a Mass Airflow Sensor, I thought a faulty airflow meter was the cause of my engine hesitation. The hesitation was something like car was working with a slipping clutch. Hesitation happened initially during the first two seconds when you step on gas but engine would suddenly regain power; but then a few days later, hesitation happened at any range of the throttle.

Thanks to Rusty on this forum, I replaced my airflow meter with his, but it did not cure the problem. My mechanic said it must be the coil then so I replaced all six coils yesterday with a set I bought a few years ago through a forum member "Japthug" in Japan, and, in removing the last one from Cylinder 6, the culprit was found. I shall let the pictures do the explanation.




It was strange that the car did not throw any codes in many recent scans with the factory VCM/IDS, but I am glad that the new coils have sorted the problem. I am now getting higher rpm at idle so may have to re-do the idle adaptation test as I now have all six new coils and another air flow meter fitted.

My takeaways from this incident are:-
(a) The X300 engine is very reluctant to throw a code, even if you scan it with factory readers
(b) the most common solutions to a bad running X300 engine are the crankshaft position sensor (CKPS), coils made in Japan, and spark plugs by Champion (the "lawn-mower plugs" - ask Andy)
(c) new or good, used airflow meter is a rare find, and NA and supercharged engine use different airflow meter (LHE1620AA for NA; LNA1620AA for supercharged, both have aftermarket replacements now, but they have been out of stock for a long while)
(d) the best help available for X300 ownership is this forum, and we have very generous members like "sogood" and "rustyxjc" who would pass along some used parts free.

 

 

Here is Part II of the coil saga.

Car test drove well after replacing all coils last week. Did not drive the car during the week except for a short while to confirm that the problem was really solved. Drove beautifully on the outbound journey (8 km) but while returning home and on full blast climbing a long stretch of road engine suddenly lost momentum and the symptom returned, i.e. the engine was running with 5 cylinders; engine idled terribly. Hooked up for a scan with the VCM/IDS but there were no engine codes. Sigh...

Was busy the whole week at work so got some time Saturday morning and I tried to look for loose plugs, wires or something, starting with the ignition coils. Last time it was coil #6 that was faulty so it is my prime suspect. Removed the coil cover and found oil stain above coil #6; removed the coil and found it badly destroyed! Was wondering why - it was a brand new coil made in Japan.



It looked like the rubber tube was shattered, much worse then the previous one (see pictures).





I checked the spark plug which was air tight but when removing it I was shocked! The spark plug was broken (see picture).



I replaced the ill-fated coil with a used one and a NGK plug and the engine resumed normal operation.

Am wondering what caused the Champion RC12YC (can't find RC12YCC) plug to give up and break. The full set has done not more than 10,000 Km. The new coil is much stronger constructed but it was totally destroyed.....

 

Just freak bad luck! Good diagnosing ....

 

 

My mechanic is on vacation. I showed him the pictures and he said this could happen because the engine may have been misfiring a long time due to a failing coil in cylinder 6, and the compression down in the cylinder gradually killed the plug and once the plug totally died the compression chewed up the coil boot above. In this instance, it only took a one short drive to kill the coil when the spark plug died.

Never heard of similar incident in this forum but I found similar reports in the Honda forum, and many blamed it on bad injector, bad fuel, overdue plugs, unsuitable plugs, excessive plug gap, a dying coil (like ours in COP style i.e. Coil on Plug); and the advice is do not drive a car with a failing coil as it may damage the engine due to raw fuel getting into the cylinder washing away protective coating, unburnt fuel killing the catalyst converter, etc. There are many more scary stories on the web about this. Someone mentioned built-in safety system in some cars that automatically shut down fuel supply to the cylinder not firing up, but I wonder if our AJ16 engine has that intelligent design.

Anyway, hope that the incident is now behind me and the engine suffered no or minor damage because of this. Time will tell. If anything happens to cylinder #6 again then I should worry.