Kenric
Member
Like I said, I run premium also. At least in my vehicles where it makes any perceptible difference.
I really shouldn't have use the terms knocking or pinging at all. There are really two things going on with that sensor and ECM.
First, it will detect the barest beginnings of pre-ignition, which is a shock wave cause by the flame front from the spark ignited ignition colliding with the flame front from a pre-ignition event. At the earliest detectible indication, the flame fronts are timed so close together that the cylinder pressure is still quite low when they collide. The resulting shock wave is very, very weak. It would not be audible and probably would not hurt the engine even if you let it continue for a while. However, they do not let it continue.
Second, this pre-ignition shock wave is detected so fast, and the timing retarded so fast, that the pre-ignition is stopped right away. There should be no period of prolonged pre-ignition that would cause any engine damage.
They don't just run timing closed loop against indications of engine timing, they have spark maps that are supposed to keep them out of this kind of trouble. The knock sensor is there to protect things under certain conditions such as hot operation, high load operation etc. once the ECM figures out, and it does it quickly, that you are running an combination of fuel type, high temperature, load, etc, it backs things off. It does not maintain a state of continuous pre-ignition. I may not have made that clear in my last post.
Now, with that said, there are other things that can cause pre-ignition even in a low compression engine that should otherwise not need premium fuel. Any unusual hot spot in the combustion chamber can cause pre-ignition. A big culprit is carbon buildup which can not only trap heat and create hot spots, but can also decrease the combustion chamber volume and increase effective compression ratio. This may be why some people with engines that should not require premium will in-fact run better on premium. It's really an engine condition question.
Other things that can cause hot spots that can cause pre-ignition are....
Incorrect heat range spark plugs (insulator too short) where the plug end gets too hot.
Incorrect spark plugs where some of the threaded end sticks past the head and into the combustion chamber. This thin end of the threads will get too hot and cause pre-ignition.
Damaged valves that have carbon or some imperfection.
Incorrect or mis-positioned head gasket.
Of course the biggest one on an older engine is the carbon build up. If you have an older engine that should not have required high octane fuel, and yet it pings if you don't run it, then you probably have a bunch of carbon buildup.
Bottom line is that I would never try to talk anyone out of running premium if that's what they want to do. My main reason for interjecting myself in this conversations is to say that running regular fuel in a vehicle where premium is RECOMMENDED, not REQUIRED, will not void your warranty.
The points about the potential positive value proposition of running a slightly higher priced premium fuel and getting proportionally better fuel economy is well taken, and is a big reason why I run premium.
I really shouldn't have use the terms knocking or pinging at all. There are really two things going on with that sensor and ECM.
First, it will detect the barest beginnings of pre-ignition, which is a shock wave cause by the flame front from the spark ignited ignition colliding with the flame front from a pre-ignition event. At the earliest detectible indication, the flame fronts are timed so close together that the cylinder pressure is still quite low when they collide. The resulting shock wave is very, very weak. It would not be audible and probably would not hurt the engine even if you let it continue for a while. However, they do not let it continue.
Second, this pre-ignition shock wave is detected so fast, and the timing retarded so fast, that the pre-ignition is stopped right away. There should be no period of prolonged pre-ignition that would cause any engine damage.
They don't just run timing closed loop against indications of engine timing, they have spark maps that are supposed to keep them out of this kind of trouble. The knock sensor is there to protect things under certain conditions such as hot operation, high load operation etc. once the ECM figures out, and it does it quickly, that you are running an combination of fuel type, high temperature, load, etc, it backs things off. It does not maintain a state of continuous pre-ignition. I may not have made that clear in my last post.
Now, with that said, there are other things that can cause pre-ignition even in a low compression engine that should otherwise not need premium fuel. Any unusual hot spot in the combustion chamber can cause pre-ignition. A big culprit is carbon buildup which can not only trap heat and create hot spots, but can also decrease the combustion chamber volume and increase effective compression ratio. This may be why some people with engines that should not require premium will in-fact run better on premium. It's really an engine condition question.
Other things that can cause hot spots that can cause pre-ignition are....
Incorrect heat range spark plugs (insulator too short) where the plug end gets too hot.
Incorrect spark plugs where some of the threaded end sticks past the head and into the combustion chamber. This thin end of the threads will get too hot and cause pre-ignition.
Damaged valves that have carbon or some imperfection.
Incorrect or mis-positioned head gasket.
Of course the biggest one on an older engine is the carbon build up. If you have an older engine that should not have required high octane fuel, and yet it pings if you don't run it, then you probably have a bunch of carbon buildup.
Bottom line is that I would never try to talk anyone out of running premium if that's what they want to do. My main reason for interjecting myself in this conversations is to say that running regular fuel in a vehicle where premium is RECOMMENDED, not REQUIRED, will not void your warranty.
The points about the potential positive value proposition of running a slightly higher priced premium fuel and getting proportionally better fuel economy is well taken, and is a big reason why I run premium.
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