I just found the little plate riveted to the block and it says D6C, but I see that you sometimes talk about Xu????. What does that number tell?

Also checked the ECU and it's a 125 2 row, and as far as I can tell (haynes book) it must be a Bosch Motronic ML4.1 system, am I correct?
Well the reason for asking is that I want to play a little with the fuel pressure, maybe raise it 0,2-0,4bar from stock. As you might have read in another topic I'm trying to find out where the horses went!

XU is the engine type, it will be followed by a 9 for a 1.9 'XU9' and then info about the number of valves per cylinder, 'XU9J4' being MI16, XU10 is a 2litre

You need to do a whole load of basic system checks and even then if everything seems ok it might just be that the engine is tired and in need of a rebuild.

Sorry to be pedantic but I just thought I'd add that for the UK the XU9J4 with D6C ran from July 1988 until (I think) October 1992 and had 181nm of torque. From 1991 they had a knock sensor.
And the XU10J4's torque peaked at 3500rpm.

thanks for the info.