The belt has only done about 700kms from brand new,
Would be beneficial to check as if off by a tooth or maybe the wrong belt used, one bank would run rich and have less compression.
I don't think it would be an injection or ignition (EMS) problem as that would not result in low compression. Same goes for O2 sensor or AFM problems. Look for something mechanical which would cause lower compression which is either rings, valves or HG.
Essdub is very knowledgable with these engines. Maybe flick him a PM with some questions. I'm sure he would be happy to help.
I've re-seated the valves, new rings and .025 over sized pistons, and new headgaskets at same time as the cambelt. No AFM and ECU is not getting closed loop feedback from the O2 sensor.
When first run it was OK but had other issues, wouldn't rev over 3.5k rpm but was good at low rpm. After changing the ECU it would run great hot but would not start cold...etc etc. So this would suggest it WAS the correct belt. Whether it may have stretched or slipped is another story so I will definitely check that, thanks for talking it through.
If this is not an issue, then I guess I will have to pull the front head off and check for warpage or damaged HG. Are the compression values outside of spec though? I read that if they are within 70% of the max value this is OK. But I don't trust my engine with the misinformation that goes around online. There is no sign of water in the oil/oil in the water.
If I have to pull the heads I think I will be putting head studs in this time around.