2003 Yukon issues - SOLVED

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MassHoe04

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Based on what you have shown so far, I like where this diagnosis is heading.
Original hunch on O2 sensors is looking pretty good as possible candidate.

That would be great if this is the case. O2 sensors are relatively easy and not very expensive.

Don't bother doing anything with downstream sensors (B1 S1 or B2 S2) just because you might be in there for the upstreams...
They really don't do anything to affect how the engine behaves. Don't replace unless you get specific codes for them (catalytic efficiency codes).
Save the money for other stuff.

I know AC Delco is preferred on a lot of things, whenever possible. No doubt.
Cost and availability don't always line up with the wallet or having to get the job done so you can get to work the next day.

Delphi O2 sensors and fuel pumps seem perfectly acceptable anytime you can't go with Delco replacements.

For O2 sensors, I replaced both upstream sensors on my 04 5.3L (regular gas) back in November last year.
No issues with the system whatsoever in 10 months of daily driving.

They are normally $55 each, which isn't bad.
I got both for about $88 with the 20% bucket sale.

I kind of think Delphi might have even been the OEM supplier. They made almost everything else that was electrical on these Chevy trucks...

P.S.: If you ever do need to replace the downstream sensors... They are easy to remember what to get. GM engineers made it easy on everyone by using the exact same sensors in all four positions! My 05 Jeep 4.0L had a different sensor for every position. Part numbers, pigtail lengths... everything was different on each one of those. I had to go to two different shops to get all four sensors for that Wrangler. Thanks for that fun time, Daimler-Chrysler!
 
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ic455

ic455

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Ok, update time. I swapped the bank 1 upstream and downstream O2 sensors and ran the truck, even drove down the road with a/c on. Fuel trims normal. O2 data normal. Now trying to tackle what apparently is an unrelated problem: crank, no start. This has been ongoing during this whole operation so I assumed it was part of the running rough. It may not be. Cam and crank sensors are new as well as the connectors for them. Still getting the P0342 and P0343 codes, usually only after it actually starts. When this has happened before, it's dicey if it'll start after sitting a bit or not. This time I ran the battery down and it never did start, this isn't the first time lol.
 

MassHoe04

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Going back a few posts...

Your video of O2 sensor live data doesn't look right to me.
B1 S1 looks like a flatline EKG of someone in cardiac arrest!
If it were a patient, the doctor would be calling for a priest.

B2 S1 looks better. Probably closer to normal wave form and looks reasonable.

If swapping the sensors did nothing, I might suspect something up with the wires or connectors on Bank 1.

Something is up on that side.

Were O2 sensor connectors cut off and replaced with new by any chance?
Maybe wires got crossed on the connector...

I am not ASE certified Mr. Goodwrench, but I don't like what I see on B1 up to this point.
Still points me to believe the flatline on B1 S1 is telling the computer it is not getting enough fuel (low value on the voltage scale indicates too lean), so the computer is just pouring on the fuel to compensate.

You said you changed the PCM, So probably doubtful it is the computer itself.

My gut is still telling me to focus on the B1 S1 O2 sensor, the wires, connectors, connector pins/wires at the PCM or something in between.
 
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ic455

ic455

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Going back a few posts...

Your video of O2 sensor live data doesn't look right to me.
B1 S1 looks like a flatline EKG of someone in cardiac arrest!
If it were a patient, the doctor would be calling for a priest.

B2 S1 looks better. Probably closer to normal wave form and looks reasonable.

If swapping the sensors did nothing, I might suspect something up with the wires or connectors on Bank 1.

Something is up on that side.

Were O2 sensor connectors cut off and replaced with new by any chance?
Maybe wires got crossed on the connector...

I am not ASE certified Mr. Goodwrench, but I don't like what I see on B1 up to this point.
Still points me to believe the flatline on B1 S1 is telling the computer it is not getting enough fuel (low value on the voltage scale indicates too lean), so the computer is just pouring on the fuel to compensate.

You said you changed the PCM, So probably doubtful it is the computer itself.

My gut is still telling me to focus on the B1 S1 O2 sensor, the wires, connectors, connector pins/wires at the PCM or something in between.
Swapping B1 S2 into the S1 position cured the trim problem. Now working on intermittent no start. Looking at crank sensor harness as possible cause. Going to trace from sensor to pcm today, will update.
 
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ic455

ic455

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When it actually starts and runs, I can't complete CKP relearn; when I'm on "accelerate to full throttle" screen, (fuel cutoff) the fuel never cuts off, I can rev to 6k. Scanner never recognizes "full throttle".

Edit: I had to hold brake pedal while doing relearn, worked this time.‍♂️
 
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ic455

ic455

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Update: Still getting P0342 and P0343 and having trouble with hot starts, for now letting it cool for about 20 minutes seems to let it start.
 

Fless

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Just a SWAG, when you have a hot start issue, floor the accelerator to put it in "clear flood" mode. This turns off the injectors. If it starts right up then there is probably a leaky injector or something else dumping fuel after turning off the engine.
 

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