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Thanks Shaun. i had the crankshaft relearn done this morning by my local shop. They had not heard of it before for Gm products but went ahead and did it after some research. They could not get it to set a code on the test drive after the relearn. I just brought it home and I would say it seems to run a little differently, not better or worse just different.
More data. The misfires were on cylinders 1,3,5, and 8. Two of the cylinders, one from each bank had like 40K misfires in 3,000 miles and the other two had like 5K misfires in that mileage.
Now its time to drive it and see if its better.
Update. No cel since crank sensor relearn. I have to change what I said before, it definitely runs better. Its smoother and starts better ( it never started badly before) and it seems like it has more power. The towing test is tommorrow but I suspect the era of the flashing check engine light is over. I was starting to wonder if I should just tape over the light.
Thanks again Shaun. What exactly happens when the sensor is relearned? It seems like one of those slow degrade things that slowly get worse and you don’t notice it. I really didn’t think it could run better.Quoted From silveralfa:
Update. No cel since crank sensor relearn. I have to change what I said before, it definitely runs better. Its smoother and starts better ( it never started badly before) and it seems like it has more power. The towing test is tommorrow but I suspect the era of the flashing check engine light is over. I was starting to wonder if I should just tape over the light.
Thanks again Shaun. What exactly happens when the sensor is relearned? It seems like one of those slow degrade things that slowly get worse and you don’t notice it. I really didn’t think it could run better.who would have thought a re-learn huh,,,,this is my favorite thread yet….keep us in the loop….Shaun was dead on….
Quoted From Shaun_300:
Can you actually feel the misfires and the engine running bad? It may be as simple as having a crankshaft variation relearn done. I had a 2005 2500HD in the shop this morning with a P0300, when the RPM’s got over 2700 or so it’d say about 4 cylinders were missing like crazy, couldn’t feel any misfire whatsoever. I did a crankshaft relearn on the Tech 2 and the problem was solved. Crank sensor must have been out of sync just enough to think it was misfiring when it really wasn’t. Might be something to have done before throwing parts at it. If it still is throwing codes after that, then continue diagnosing the problem.
you nailed this one…great job
I’m not sure how it got out of ‘adjustment’ but the computer uses that signal for timing both fuel and ignition as well as some other controls so if it’s off EVERYTHING is off. One possibility is slack in the timing chain which happens over time but it could also just be a ‘computer glitch’ that brought it out of spec, I honestly don’t know for sure but thanks for keeping us up to date as these things to into the database for others to use if they run into the same or a similar problem.
after 50 miles around town and 250 miles of towing the check engine light has stayed off. I have owned this truck from new and I am not sure this thing ever ran this smooth. Thanks again.
Learning has no age. I’ve learned more about cars in the past year than I’ve learned in the past 30.
Mainly because of Eric, RealFixesRealFast, BriansMobile1 and just because I have to keep fixing my wife’s car since we’ve got no money to pay anyone to do it.I just eat up Duane’s videos (realfixesrealfast) when he busts out with the Verus and starts with graphs and wave patterns.
Quoted From hondaslave1342:
this was down right delicious…love this thread…i wish i was 20 again..i would go back to school……
Glad I was able to aid in resolving your issue! At a cheap cost too I imagine to get the procedure done, if any. When a crankshaft variation learn is performed it basically recalibrates the position of the crankshaft with the camshaft. Like Eric said these two sensors are a major role in ignition and fuel timing. So that explains why the truck seems to run better. Both timings will be virtually perfect now. It takes minute variation between the two sensors to cause a P0300. Slight wear in the timing chain could cause it, or could even be a slight computer glitch. I’ve seen this happen a number of times. Even looking at misfire data when I’m diagnosing an obvious misfire on one cylinder I’ll see odd misfires on other cylinders. Usually I’ll do a crank relearn first and most of the time it’ll take care of those false ones.
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