Thanks @Happy Hummer. I only have a Scan Gauge II in the truck, so don’t think I can get all those parameters but I’ll look today. My regular scanner is back home, 1800 miles from here.

The car drives fine after it has sat in the sun all day from cold, it’s only after it sits after having been driven for a while that I’ve seen this. I took it out again last night after it had cooled down in the shade for 5 hours and then drove it until it was hot and the symptoms started to reappear. At that time coolant was 215, IAT was 107, and TFT was 160. So, I think it’s related to the engine bay being hot.

When I was out last night I started to wonder if it’s maybe transmission related - when I see the negative 10 deg ignition advance on the scan gauge the truck doesn’t seem to shift into a lower gear like it normally does when the symptoms aren’t present. When it’s working right and I give it gas it shifts to the next lower gear, revs bump up 500-1000, ignition advance goes to 5-10 deg positive, and there is plenty of power.

When this issue is happening ignition advance goes to 10 degrees negative and rpm’s barely climb as I give it throttle. Eventually after I add more and more throttle (because it’s not accelerating) it shifts down abruptly into a lower gear and rpm’s jump significantly, at which point the advance returns to normal and the car will go, but at much higher rpm than normal. Then when it shifts back to a higher gear it will be underpowered and if I hold the throttle it will shift back down abruptly again, and the cycle repeats.

I was meant to start my return trip home tomorrow, so I’m gonna throw in the towel and go see a mechanic. If folks have ideas or thoughts I should share with him I’m all ears.

Appreciate everyone’s help on this.

Edit: [revisited after another drive and I’m striking the comments from memory about the transmission shifting. It’s starting in the right gear and shifting, just not making power]

 

I was able to program the scan gauge to display “Knock Retard” and monitored that today along with the ignition advance and saw everything from -10 degrees advance with no knock retard, to -10 deg advance with 16 deg of knock retard, and it seems a lot of everything in between. I also saw knock retard reported with less than -10 deg advance, and long periods with no reported knock retard.

The check engine light came back tonight as well, reporting code P0328 once again with the brand new knock sensor.

There is no rough engine or stumbling or pinging during these events. Just power loss and negative ignition advance numbers.

Ideas anyone? I know there are a lot of smart people here who know how this system is meant to work, so hoping one of you has some ideas of other things I should try or be looking for???

 

Did you ever add a bottle of octain booster to the fuel like i had sugested earlier? it could be carbon on your valves preignighting your fuel. the only time i had a flashing cel light was at 60 mph at 4000 rpm.would trigger it. in my case it was partialy fouled cats.

 

No, I did not because I had already switched to running 91 octane several tanks earlier, and then I got the code for the knock sensor so I replaced it and thought things were resolved. It’s with a mechanic today so I’ll see what he’s able to figure out with a full scanner. Will post an update later.

 

Can we assume the brand knock sensor you installed was ACDelco/GM?

I thought we had a happy ending and all........

 

Are you absolutely certain the timing chain and all associated marking haven't somehow gotten off by a tooth? Because, it sure seems strange...
Anywho... I still think it has something to do with the stuff I mentioned b4.
The Tech II should be able to see the trim reporting's while driving (I think)? I believe it should also be able to give actual TB and requested?
Have you verified that the actual wires coming from the pcm to the knock sensors are corrosion free and good continuity?

 

@Doc Olds yep, genuine GM OEM parts bought at the dealer’s parts counter.

@Happy Hummer not a Tech II, but the mechanic did hook up their scanner and drove while the car was symptomatic and all the trims and other sensor parameters looked fine, and they confirmed that the ignition advance was being pulled by the PCM.

The check engine light came back on this time and P0328 hard set - i.e. it returned immediately after reset. They checked several things to rule out wiring, connectors, etc, and also verified that the car was not pinging/knocking. All roads led to the new knock sensor being bad.

So this morning we put in a new knock sensor and I drove it halfway up the mountain here in Vancouver in 85 deg weather to get it good and hot and there’s no sign of the problem, with no negative advance, and no knock retard showing on the Scan Gauge anymore.

Both the original bad knock sensor and the new one that failed were GM OEM parts marked as made in Japan. The new one we put in today is also GM OEM, but marked made in Mexico.

Fingers are crossed that its really fixed this time so we plan to start back on the return camping trip tomorrow.

 

One comment from the mechanic was about how HOT everything got in my H3 engine bay and how close the exhaust is to stuff and they didn’t know if that was typical or if maybe I have an airflow problem.

What’s the experience of you other Alpha owners? Does our V8 engine bay run hotter than other V8 applications?

 

clogged cats raise under hood temps. but you probably do not want to hear that. that sucks. maybe they can rule that out.

 

There are at least two versions of GM parts, the actual OEM and then the cheaper "GM Professional" parts. They used to have another line called GM "Advantage" which was even cheaper than the Professional GM Parts. All a matter of who they farmed them out to be manufactured to their specs.

GM dealers are supposed to sell OEM parts, but when they can't find them, or want more mark up, they stock GM Professional parts.

Sounds like the first sensor may have been other than OEM although it still comes in a GM Box. Anyways............

Tell your mechanic it is supposed to be hot under the hood. Really no different than other GM full sized trucks except the H3 has a hood that sits between the outer fenders rather than on top. Mine is plenty hot, just like they designed it to be for "better emissions."