my buddy bought a 2007 lsj for 4000 bux, had a p0300 random misfire, well cylinder 2 and 3 were misfiring, when i opened the graphs they were very similar. switched plugs and coils with 1 and 4 didn't move the misfire as expected. well anyways i did a crankshaft position varience relearn and it fixed the issue. just figure id post this up for anyone having a 2 cylinder misfire on a lsj. the mechanic from previous owner said it needs 4 ignition coils which it didn't. hope this helps some ppl

 

Was it actually misfiring or was it just registering misfires?

 

I would assume it was registering them since the crank relearn fixed it.

 

not so sure honestly. picked up 60k misfires in about 10 minutes n like i said the graphs were almost identical. i was about to do a injector balance test then found this info on identifix which most ppl dont have access to, figured id post it up for everyone

 

I was curious because my understanding of what a crank relearn does (could easily be wrong) is that it teaches the computer what crankshaft acceleration characteristics to expect with each cylinder fire. If the ECU reads a different acceleration result than it expects it registers a misfire. If this premise is true couldn't there be a situation where the ECU is registering a misfire when the cylinder actually is firing and a crank relearn would correct the false positive?

Like I said I may have a complete misunderstanding on what a crank relearn actually does. That's mainly the reason I asked the question was to see if that situation was possible.

Edit: I think I misread your statement. In the context it would appear you meant it was falsely registering misfires. I originally read it as it was registering actual misfires.

 

Your edit is correct, my original response was not clear as to what I was meaning.

 

All good. That's why I asked him the question though because if i understand correctly, crank relearn will not fix actual misfires but it will fix falsely registered phantom misfires.

 

havent looked at it yet but my buddy said the code came back after 150 miles of driving. he went to autozone its a p0300 like before but its not blinking this time -_- when i did the relearn the misfires were entirely gone what would u guys b leaning towards here? im gonna check it out again tomorrow

 

Plugs, o2 sensor, compression, leak-down, and then log the car to see what is going on when it happens (part throttle, full throttle, etc, etc)

 

well it has a longtube header n catted dp. the previous owner for whatever reason spliced into the o2 sensor n made it 2 feet long n used solid gauge wire as the extension lol i put in a new one n just moved the harness closer. l also put in the stock plugs cuz it had brk7e's or something along those lines. the o2 readings seemed to b switching faster from lean to rich from 100 to 900 mv. well the p0300 and p1133 is gone and of course it gets a p0171 but didnt set the cel. kid bought a real gem for 4000 bux.....