Good evening all, We have a recurring issue on a Fiat 500 1400 petrol where we have had the vehicle first presented with lumpy running and fault codes P0300 random multiple misfire and P0303 Cylinder temperature too high and P0304 Cylinder temperature too high.
We carried out a relative compression check with Pico showing all with 98% and followed up with gauge check with all cyls showing 180-185 Psi. We scoped the coils and found drop outs across the board and cyl 3 being worse we swopped plugs which moved the worst drop out to cyl 2. We recommended coils and plugs after we found some cheap range coils from Euro fitted. The customer paid to upgrade from cheap to Marelli coils and new NGK plugs. We smoke tested and found breather pipe to intake tube split so replaced that pipe. After fitment the car ran smooth but noticed the rear O2 sensor long term trim is showing at 99.2% but sensor was working with short term trim working well. All adaptations were reset and car has been on road trouble free for 4 days but went to limp mode today and customer reported lumpy idle after cold start yesterday morning then ran fine. It was recovered in in limp today.. We have fault code P0300 and P0304 returned with slight lumpy running. Checked fuel pressure at 3.9 bar with data showing 3-3.5 required, this leaks off with engine off but holds good when running. There is no cylinder wash but cylinder 4 piston crown is oily compared to rest but plug electrode is clean. History shows a recent cambelt but no other work. Had been to dealer before us who advised all injectors be replaced. I am waiting on our injector tester to be returned from repair before I can check injector balance but bank 1 fuel trims are normal. Has anyone had the fault codes for cyl temps too high on one of these? . The engine runs very hot under bonnet temperature with coils very hot but coolant temp is correct. We don't see many Fiat 500s but the under bonnet temps concern me. We are going to pump up coolant tester tonight and use video scope in morning to see if any minimal water entering cylinders as head gasket check is ok. Anyone been here with a 500