The reason I'm asking for clarification about the relearn is because some users are saying a relearn is not necessary, while others are saying that it is. Makes it kind of hard to know what to do when getting conflicting info. How can I find out for sure?

Also, any comments on the last question I had in post 19?

 

"Some users" don't consult the GM shop manual, I do. Take your pick


Les is correct regarding inducing a misfire. The camshaft position sensor data, and the crankshaft position sensor data, must be accurate so the PCM can accurately detect, and accurately identify, cylinder misfire.


EDIT: Keep in mind, that just because the PCM can accurately identify a misfire, does not necessarily mean that the relearn data in the PCM is correct. I'd be more concerned about the relearn data being correct because it directly affects engine performance. Everything depends on where the crankshaft is in rotation: ignition timing, injector timing, etc. If the relearn data is incorrect, so is everything else.

 

The confusion that I have read in the forum about relearns deals with the camshaft position sensor vs the crankshaft position sensor. Like Captain said, anytime the crankshaft position sensor is messed with or the timing cover is removed then yes - you need to do the relearn. Also, like Captain said, it takes like 5 seconds to do with a capable scan tool. The crankshaft position sensor is down on the front of the block on the passenger side. He probably said that too
The camshaft position sensor does not require a relearn procedure if moved or replaced. You just have to make sure the cam retard it +/-2 and sounds like you have that nailed. Nice work there!
And since the misfires go up when you remove the plug wire, sounds like the misfire detector system thing is working.
So, find a buddy with a scanner that can do the relearn on the crankshaft position sensor and trade them a case of beer for their time. Then you can rule one more thing out...
If that fixes it-Awesome. If not ask the Captain

 

See, this is the confirmation I'm looking for. If the shop manual says to do it, then that's enough for me. Another example are that TONS of people dont know about CMP Retard and that it needs to be set and they tell me all the time "ah, you dont need to do that". Well, you do! So there's so much misinformation out there. Thanks for clarifying it.

As for checking my crankshaft sensor, I'm wondering statistically what are the chances that its messed up since its never been molested in anyway since being assembled? I'd be super bummed to check on it and its fine, which is what I suspect is going to happen and it'll cost me probably 50 to 100 bucks to do a relearn at some shop.

Questions:

- What is the absolute easiest way to do a relearn? I'm sorry, but I *HATE* taking my car to a shop. In fact it has never been to a shop since I bought it 11 years ago. Because most things we can do.

- If it were in fact the culprit, would it affect pretty much only two cylinders only at idle and only when warm? Seems like it would affect all the cylinders across the board.

 

The only way to do a crankshaft relearn is with a scan tool capable of performing it. I have a tech2 and it literally took 5 seconds to do the relearn on my brother's Envoy. Any of the high end scan tools could do it I imagine. Drive out to Iowa and I'll do it for you. Or, you might be able to find someone closer who would do it as well

As for the second question, I'll leave that to the Captain...

 

CWBDDSPC, not much makes me jealous, but I definitely wish I had a Tech2...lol. And thats quite an assortment of 4x4 Blazers that you have in your garage...haha! If I could figure out how to get this GM contraption to do warp speed a' la millennium falcon style, I'd take you up on your offer for the relearn.
: )

 

? #1
There is only one way to do the crankshaft relearn. Fact is, it's simple to do. Connect the scan tool to the DLC. Program the vehicle into the scan tool. Go to the relearn menu. Follow the safety instructions on the screen. Bring RPM to 4K. PCM takes over throttle control and does the relearn. Throttle control returned to operator. At the most, start to finish, a minute, which includes programming the vehicle into the scan tool. The actual relearn itself takes less than 2 seconds, probably more like 1 second.


? #2
Each of the sensors affect all cylinders equally: TPS, MAF, MAP, ECT, IAT, EGR, CMP, and CKP. Upstream oxygen sensors affect 2 cylinders on one bank, and one on the opposite bank, (cyls 1 & 2 are not controlled by the same O2 sensor). None of the sensors can affect specific cylinders. For a specific cylinder to misfire, it has to be something specific to that particular cylinder such as spark plug, plug wire, distributor cap, rotor, and valve train. Worn distributor bushings, and or worn distributor gear, will usually affect 2 cylinders 180 degrees opposite, inside the distributor cap, ie: 1 & 4, or 2 & 5, or 3 & 6. The possibility of "carbon tracing" between two adjacent cylinders in this distributor cap has been totally eliminated... there are no two cylinders in the firing order that are physically next to each other inside the cap.


One more tid bit about camshaft retard adjustment: It is adjusted by rotating the distributor, (cap attached to it). When the camshaft position sensor is aligned correctly with the camshaft, the distributor cap is positioned so the gap between the rotor segment and the cap terminal is as small as possible when the ignition coil fires. This reduces/eliminates crossfire in the cap. Rotating the distributor does NOT affect ignition timing, but it DOES increase the gap, which causes crossfire/misfire.

 

It certainly comes in handy in an all GM vehicle household...

I would think San Diego would have a Blazer club and someone has to have a high end scanner... I would bet they would hook you up

 

Doc, you work too cheap. Next time I need a check up, I'll come see ya. The annual software update for mine is $1K. Somebody has to pay for it

 

Well crap, I guess I can't buy any newer cars... Then I don't have to update it right??

Or I could start reading codes as part of the checkup