Hi everybody,This model is equip whit catalyst system 1 sensor before catalyst and another after catalyst for each bank so 4 O2 sensor total.I replaced already the cap-rotor and wiring , good fuel pump and filter.I bought the Rinda Techmate pro and I have some code but the code don't match whit Volvo Penta code ????. I have detected 3 code : SPN=639 SPN=4238 SPN=3256 when I look in internet they all related to O2 sensor, I removed the 4 sensor and 2 look bad,is it possible this condition cause backfire and I cant go over 2000 RPM and no torque.I try to find the good shop manuel without sucess.Thank you in advance for your help.