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I haven't posted in a while but thought I would share this. I've been reading on aviation forums and guess what - when plugs go bad on those they are faced with the same issue. Who caused what.Random misfire detected (P0300)
• The PCM monitors the CKP sensor input signal interval time. The PCM calculates the change of the interval time for each cylinder. If the change of interval time exceeds the preprogrammed criteria, the PCM detects a misfire in the corresponding cylinder. While the engine is running, the PCM counts the number of misfires that occurred at 200 crankshaft revolutions and 1,000 crankshaft revolutions and calculates the misfire ratio for each crankshaft revolution. If the ratio exceeds the preprogrammed criteria, the PCM determines that a misfire, which can damage the catalytic converter or affect emission performance, has occurred.
Specific cylinder misfire detected (P0301, P0302, P0303, P0304, P0305, P0306)
• The PCM monitors the crankshaft position sensor input signal interval time. The PCM calculates the change of the interval time for each cylinder. If the change of interval time exceeds the preprogrammed criteria, the PCM detects a misfire in the corresponding cylinder. While the engine is running, the PCM counts the number of misfires that occurred at 200 crankshaft revolutions and 1,000 crankshaft revolutions and calculates the misfire ratio for each crankshaft revolution. If the ratio exceeds the preprogrammed criteria, the PCM determines that a misfire, which can damage the catalytic converter or affect emission performance, has occurred.
===== EDIT
BOTTOM LINE: don't WAIT until the MIL light is flashing! Its too LATE. Hint: a CEL for P030X is not 100 percent. You likely have other bad coil packs!!! Just because it didn't trigger a cell doesn't mean its not misfiring under load!
The TEST:
Turn off every accessory, every light, every load, AC etc. Drive it. How does it run, does it hesitate, misfire, is it better? << Drive in daylight with lights off.
Turn on EVERY LOAD, AC, Seat heater, Defrost, turn them all ON! Does it make it misfire and hesitate off idle, and taking off? Did it MAKE IT WORSE??? If so, you likely have another bad COP.
Unlike other manufactures who look at each coils ring back signature to determine if the spark was delivered to the plug, Ford and Mazda rely on crankshaft velocity. So the ECM is basically watching the Crank sensor to see if the CrankShaft meets its expectation for rotational speed for the situation. If it does, there is NO MISFIRE TO REPORT. If it detects a misfire and reports a P030X, its because the ECM counted 200 continuous misfires from the SAME Cylinder. The car is pretty much running like shit at this point and can't be neglected. Should it get a dozen clean rotations, it WOULD NOT have reported it as a MISFIRE. So these problems can exist and do DAMAGE for a long TIME depending on the situation. << Make sense?
Point: do some testing. If your car stumbles, Hesitates, bucks, stutters, cuts out, or simply won't move like it used too, its good chance you should be looking at or looking for MORE BAD COPs as waiting for the ECM to report them and it will be TOO LATE!
Guess what, their engines start to smoke from a misdiagnosed misfires akso. PISTON ENGINES NEED to FIRE AND BURN THE AF CHARGE to BUILD COMPRESSION AND KEEP THE PISTON RINGS SEATED!!!
A compression stroke is NOT ENOUGH!!! Like I've been saying I think some people are giving up hope too soon with their smoking engines. Get the cylinder(s) firing, let it rev, change the oil often and unless there is physical damage to a cylinder, rings CAN SEAT AGAIN! Try it! Don't let an engine run out of oil because its a smoker. Put NEW plugs COPs in ASAP if you suspect its misfiring as they can be brought back to life. This may take a couple 1000 miles. BUT YOU MUST HAVE FIXED THE PROBLEM! It must NOT be hesitating!
DO NOT wait for the ECM to tell you its misfiring (too late). Sadly many know something is wrong and neglect it!!! Don't! You know it is when it stumbles, hesitates, and stutters upon take off.