OK so I recently converted the engine in my VW T25 camper to a donor AGG engine. Seemed to be running nicely for a few weeks and so I decided to take it on a good blast on the motorway up to 80. No issues, drove home and parked her up. Today I go out and when I start it up it is running with a rough knocking noise: I got it up to temp, checked VCDS for errors and it had a lambda fuel mix error so cleared it. All hall readings in VCDS spot on so decided to do a compression test for the first time. Engine warm, all spark plugs out, 10 cranks each. Then same again with 2 tbsp oil in cylinders. Upon removal noticed spark plugs 3 and 4 were oily on the tips: Compression test results: Dry - 113 / 140 / 190 / 180 Wet - 131 / 185 / 222 / 201 Cylinder 1 is low but not sure how to interpret the dry and wet readings. Given No1 didn't increase by much with oil in the cylinder does it point to head / valve issues? Also what would cause Cylinder 3 / 4 to read high and the plugs be oily? What should I look into next? I popped back out to double check oil pressure and that is good (3 bar at idle once warm) but did notice a Hall sender error which is strange as the crank sensor is a brand new Meile one. I can't seem to get this error again however despite still having the knocking as the engine warms up. Thanks for any pointers everyone.