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A dog & truck, true bliss
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Discussion Starter #1
Hi Y'all,
I've almost got my 2003 S10, 4.3L, running perfectly, but as earth-life goes, nothing is perfect. After swapping my dizzy and CPS out, I took it to a shop to get the relearning flash. It worked and removed all of my P0016 and related codes. Driving along happily down Boulder Highway tonight, from Vegas to Boulder City, and cruising speed limit, about 45, all of the sudden my CEL starts flashing while going up a slight grade. Then is stopped for a while. It repeated it two more times on the way home. I checked my codes, even though no CEL was steadily on, and got the P0300. Yet the tach at idle was steady as a rock at 600 RPM with no hiccups and no missing while driving, just a P0300 code when going up a slight grade and when going 65 mph on the freeway homeward. I looked at what everyone else says about flashing CEL and I have already done everything from plugs, wires, fuel pump, spider injector, dizzy, coil, ICM. Now this. So I tired all of the fix it tricks listed and nothing removes the code, so my last shot is the ECM. Found two at two junk yards, so I'm pulling the best looking one to try it out.

QUESTION: Since I have done the relearning after replacing the dizzy, then is replacing the ECM going to change or remove the relearling? In other words, do I have to do a new relearning done after swapping the ECM? Nobody said anything about it that I can find, but I want to know ahead of time.
Thanks.
 

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Been there Done it
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Won't effect the re-learn, but a swapped PCM on an 03 should be programmed to the latest version for your specific truck. Among other things it needs to be setup for your axle ratio and tire size. You could luck out if it came from an identically equipped 03 truck. There could also be an issue with VATS, but that re-learn you can do.
Personally I doubt the PCM is the cause of your P0300. More likely one of your new parts is defective. Guessing fuel pump because you mention a slight grade causing the CEL. Do a fuel pressure test and a scan with a tool capable of reading all the PID's.
After swapping the distributor you did a CKP sensor relearn, but did you check the CMP sensor retard angle? Should be 0° + or - 2°. If it is off it will effect the injector timing, but won't set a code unless it's way off. IIRC it takes 27° to set a code.
 

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A dog & truck, true bliss
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12 Posts
Discussion Starter #3
Thanks Oldeerslayer, you saved me a trip to the boneyard. Truth be known, I did not ask the shop who did the scan if they did that, but among my listed items, a new CKP was also installed prior to the relearn but...there is always a but...another issue may be happening down below. When the old CKP was pulled out, it shows contact wear on the end of the sensor, like the keyed wheel on the crankshaft was touching it. Nothing is supposed to touch it but air. Right now, I'm just running the miles up to reset the data senors and pass smog, but that isn't going to happen with this issue. I think I'll pull the newly installed CKP after driving it a while to see if it made contact again.
 

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It's not the PCM. A new PCM needs the relearn, why would it not? It stores the learn from the last engine it ran on.

I went through the same thing with my '03. Changed all the parts that could cause random misfires. Didn't work.
I have HPTuners so I tuned the misfire tables out. I did later have a problem with the crank position sensor plug. I've looked at this plug on every 4.3 I see and I go to junkyards a lot. Seems the plug is a drip point and collects a lot of oil and road dirt. I'm starting to think most people that can't solve this problem may have a problem with that plug.
 

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Thanks Oldeerslayer, you saved me a trip to the boneyard. Truth be known, I did not ask the shop who did the scan if they did that, but among my listed items, a new CKP was also installed prior to the relearn but...there is always a but...another issue may be happening down below. When the old CKP was pulled out, it shows contact wear on the end of the sensor, like the keyed wheel on the crankshaft was touching it. Nothing is supposed to touch it but air. Right now, I'm just running the miles up to reset the data senors and pass smog, but that isn't going to happen with this issue. I think I'll pull the newly installed CKP after driving it a while to see if it made contact again.
If the crank sensor was making contact before, the new one will also. It must be shimmed to a max of 2 shims and then a crank relearn done.

https://youtu.be/K4n25KpQaB0?t=27s
 

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A dog & truck, true bliss
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12 Posts
Discussion Starter #6
Hi Lifted ZR2,

Thanks for the direct answer on the ECM/PCM. By the time I read your reply I already figured that it needed to be relearned. Not replacing it.

On my CKP, it was replaced along with the wiring harness. What concerned me was the rub marks on the bottom of the CKP when it was pulled. It appears that the wheel on the crankshaft in front of the chain, which the sensor is monitoring, has made contact with the sensor. As I said earlier, it should not touch anything inside.

I agree with you that GM should have seen in advance that this will become a magnet for drips, being side mounted at the bottom Can't be good, although I have no proof of harm. The harm to mine is on the inside. Today to got my P0300 code removed and I'm down to the flashing C and EV before taking it into a smog station.
 

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A dog & truck, true bliss
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12 Posts
Discussion Starter #7
Whoa! Burned, I was online when you posted the video. Just watched it. I feel like it vindicated my thoughts today that maybe I should shim it a little. That is an awesome find! A little more research and I found the GM Tech Bulletin on this, "Gm TSB #02-06-04-059". Also a second video on the 4.3L engine, where he shows excessive rub wear on the CKP and states that if your reluctor is making contact with the sensor, then depending upon how deep, then you may use one or two shims to keep it from making contact.

This was a problem with at least 2002 and 2003 4.3 engines, but, according to other videos, they found the same problem on 1997 to 2007 on other GM trucks with the 4.3. That must be why your video showed a 2001 S10 when the bulletin only said 02 and 03, so it seems to be a wider problem. I attached a downloaded a PDF copy of the TSB below.
 

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Before swapping out the computer test it to make sure its broken sound like a open ground get a nod light test each run to the injector
 
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