So how does the computer detect mis fire? I get ocassional cyl 1 and 3 codes. I sense or hear no knock or ping. I know there are not 6 knock sensors...Don't think there is even 1. Does it sense no power to the coil rail at the appropriate time? The coil rail harness only has 4 wires...3 coil powers and a ground so can't be feedback just curious on its thinking process...if anyone knows

 

02 sensor reads unburned charge and computer knows which cylinder produced it. Simple as that.

 

While that may be true..I find that a super inaccurate way to determine cyl performance. On the 01 the front o2 sensors are fairly close but the computer would have to know how fast the exh pulse travels down the tube and then count backwards in time to figure out which cyl fired the bad pulse..on older models that front o2 sensor is pretty far down to synchronize...So a rich pulse triggers the misfire code...Well that's something to consider..thank you

 

Well, I'm just passing on an explanation I've heard in a discussion about fuel mixture control. Think about it though, how does the computer know which cylinder is SUPPOSED to fire at that moment? With a distributor, the spark goes to the plug the rotor is pointing at, but the cam sensor in the waste spark engines are installed with #1 at TDC and the alignment pin in the sensor ring. Are there 3 separate magnetic sensors in that ring? The plug only has 3 wires, 5v supply, signal, and ground. I guess maybe the crank sensor must have differences in the flexplate windows it reads, so maybe that's how the computer knows which one to fire, especially since the cam sensor is for injector timing.

I KNOW! It's magic!

BTW, the coil rail has 4 wires, one power and 3 grounds. Each of the grounds go to a digital driver in the PCM. The PCM breaks the ground on each coil to fire the spark. Likewise, all the injectors are supplied with power and the PCM grounds each one to inject fuel when needed. Again, how does it know which injector to ground? There doesn't seem to be any obvious way for the PCM it know when #1 is at TDC to start the whole sequence. The only thing I can see is the open section of the pulse ring in the cam sensor.

 

Hi, If it didn't come across right...I was criticizing the system design more than your explanation...it works for me but would like to learn more about it...Im curious if people who run a front o2 sensor fault code also ever log a misfire code. When I first put in a new head last year one of my o2 sensors went bad and I was dumping tons of fuel into the system to "richen " it up.. It barely ran....I thought it was a massive vacuum leak but when I disconnected the sensor it obviously threw a sensor code but then the engine immediately ran perfectly smooth so the computer obviously disregards the o2sensors if there is a fault. I thank you for the input

 

Ok there are only 3 coils each coil runs 2 cylinders the computer through the sensors it knows when it needs to fire #1 cylinder and the it uses the firing order to fire the rest of the cylinders

 

That much I knew, but how does it know when #1 comes up to fire? Is it thru the cam sensor because that's the only thing that's timed? I mean if it was timed 180* out, it would fire #1 & #6, but would inject #1 on the exhaust stroke and not #6. That could get nasty!