Thanks all for the help. I am sill having issues. Here is what I have done since the last post.

As I mentioned, I had a lot of hopping/vibration at low RPM with the new trans/converter. To help narrow down, I disconnected the converter from the flex plate (just 3 bolts) and pushed it back. All of the below was done in this state and I have not reconnected it yet.

As for the trans swap, I did the swap. It is pretty straightforward with only the TEHCM plug to the trans and 3 plugs to the transfer case. No ground wires or vacuum hoses. Actually, I can’t locate any engine vacuum hoses on this engine to test. There is the external vac pump that drives the brakes but that would not impact engine runability. I cannot locate anything near the trans that would be involved in the swap that would impact runability like this. This is why I focus on running at 3-4K RPMS (maybe higher) for ½ hour and how that might have caused the runability issue. Note, at the time I asked and based on my wife reading the gauges, I do not believe that either the coolant or the trans fluid overheated.

Without the trans connected, it is still running rather rough but I am only getting the P0300 code. It feels a little different at 500-1000 RPM but that could be the change in resistance.

· I changed all 8 plugs and wires.
· Ran compression check
· Removed battery overnight

· Replaced battery

· Did the following re-learn
· Ran some testing with Torque on the Android including idling and revving to 4K RPMs

Again, the only code I get is P0300 and I am not sure why the following number of misfires is considered ‘PASS’ as they seem high to me. I also noted that fuel rail pressure was ~500 psi at idle and stayed fairly consistent at high RPM (3K to 4K) with spikes related to the increase in RPMs but pressure dropped to stead state when holding RPMs steady. This was testing to see if running at 3-4K RPMs for ½ hour would create extra stress on the fuel system. It appears not.



MID:$a2 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 1 Data
Max: 65,535Count Min: 0Count
Test result value: 7Count
PASS
----
MID:$a2 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 1 Data
Max: 65,535Count Min: 0Count
Test result value: 238Count
PASS
----
MID:$a3 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 2 Data
Max: 65,535Count Min: 0Count
Test result value: 5Count
PASS
----
MID:$a3 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 2 Data
Max: 65,535Count Min: 0Count
Test result value: 149Count
PASS
----
MID:$a4 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 3 Data
Max: 65,535Count Min: 0Count
Test result value: 11Count
PASS
----
MID:$a4 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 3 Data
Max: 65,535Count Min: 0Count
Test result value: 240Count
PASS
----
MID:$a5 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 4 Data
Max: 65,535Count Min: 0Count
Test result value: 5Count
PASS
----
MID:$a5 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 4 Data
Max: 65,535Count Min: 0Count
Test result value: 130Count
PASS
----
MID:$a6 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 5 Data
Max: 65,535Count Min: 0Count
Test result value: 8Count
PASS
----
MID:$a6 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 5 Data
Max: 65,535Count Min: 0Count
Test result value: 182Count
PASS
----
MID:$a7 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 6 Data
Max: 65,535Count Min: 0Count
Test result value: 10Count
PASS
----
MID:$a7 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 6 Data
Max: 65,535Count Min: 0Count
Test result value: 221Count
PASS
----
MID:$a8 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 7 Data
Max: 65,535Count Min: 0Count
Test result value: 6Count
PASS
----
MID:$a8 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 7 Data
Max: 65,535Count Min: 0Count
Test result value: 138Count
PASS
----
MID:$a9 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 8 Data
Max: 65,535Count Min: 0Count
Test result value: 6Count
PASS
----
MID:$a9 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 8 Data
Max: 65,535Count Min: 0Count
Test result value: 124Count
PASS
----

While I think about this, I just want to check: 500PSI???

My understanding is this is the pressure from the High Pressure Fuel Pump to the injector, not the fuel pump that moves the fuel from the fuel tank to the engine. From looking online, it appears 500 psi is normal. Then again, I could be way off and the app is giving bogus info. Here is one reference I found:

So, I reconnected the torque converter. The misfires went way down, the vibration/shudder @ idle to 1K RPM returned. I am now convinced I have warped flex plate (drive plate if you ask GM), off balance torque converter, or a bent input shaft on the trans.

I can't explain the misfires, or the reduction by having the converter attached, but this is reality.

The one small hope I have left for not having to drop the trans again is several references to shimming the torque converter. I am going to measure how far the torque converter can slide and see if it is excessive. I found a reference to this clearing up similar behavior. However, I have found no reference of anyone having to shim a 6L80 torque converter under OEM install specs (not an upgrade/swap). I don't recall if the spacing was too much (supposed to be 1/8 - 3/16 ish) and I didn't read about this until after reconnecting the converter.

Your not looking at the specs for a diesel are you?

Not sure what specs you are referencing?

Can't quite say I have seen a fuel injection system on a 5.3 spec out at 500 psi.

is this a DIRECT INJECTION engine?

Yes. Gen V L83 5.3 is direct injection. https://poweredsolutions.gm.com/products/l83-engine/

With DI the intake valves will get buildup that can cause problems with misfires.

Adding the torque converter to the rotating assembly would have the effect of adding a flywheel. This will smooth out the feel of any misfire, while not actually improving the misfire in any way.