I can see MAP data on my scanner. Warm idle MAP reads about 10.3-10.6 inHg which is healthy. Baseline is ~29 inHg (atmosphere) with key off. So that means the engine is pulling about 18.4" of vacuum at idle (29 minus 10.6) which is healthy. No real vacuum leaks that I'm aware of. The MAP sensor appears adequately responsive but I replaced it just in case, and I erased codes and reset the PCM after replacing it. Still getting the code.
It's frustrating that I don't have data to verify actual data of the requested vs actual pintle positions of the EGR when the PCM is commanding it. That would really help.
That's why I'm going back to basics. A plugged EGR port may be staring me right in the face. Ports were crystal clear when I reinstalled the manifold but that may not mean anything now. It doesn't appear clogged as far as I can see where the EGR bolts on, but farther back/down in the manifold it may be filled with crud again. There's all kinds of carbon still coming out of the exhaust. On cold start as the engine warms, the exhaust drips a little moisture and spits if you goose the throttle. It's truly just condensation, but it leaves a black mess on the floor.
Can you monitor vacuum/MAP readings? Particularly, during EGR activation?
Can you bench test/check the EGR valve operation?
Presumably the MAP sensor is OK.
No other vacuum leaks, masking the correct operation of the EGR?
Cats may be fried, but I don't think they are going to change your diagnosis of EGR operation.
I upgraded to the 2026 HD 2500 LT Z71 Trail Boss 6.6 gas to pull my 2026 Rockwood 2908 SRL Ultra Lite that is 7808lbs dry and we load it up between 8500lbs to 9000lbs.
The truck tows it with no issues in the Mountains where I live. I tow it with just the hitch without the torsion or sway controls bars. (I'll add those when I do longer runs on the highway, but most of our trips have been an hour or less from home).
I am getting anywhere between 6.5mpg to 7.5mpg for each trip.
I really love the different camera views the truck has. Over the 4th the GM store had a killer deal on the GM Trailer Camera kit and I ended up getting it for $211.00. I'll be installing it this weekend and what I like about is I'll be able to use the infotainment center to view the backup camera to back the trailer up as well as see what's behind the trailer when I use the turn signals. I'll wait on setting up the invisible or look threw trailer view.
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