Alfa Stalls After Mixed-Grade Fuel Damages Engine

Had a similar fuel system issue with my 2005 Alfa 156. After mixing fuel grades, the engine started showing identical symptoms, stalling at idle and constant check engine light. The root cause was severe fuel contamination that had already damaged multiple components. The mixed fuel created deposits in the combustion chamber and clogged the fuel filter. The mechanic had to perform a complete fuel system cleaning, replace the fuel filter, and clean the injectors. This is a serious issue that requires immediate attention. Continuing to drive with contaminated fuel can lead to permanent engine damage. The symptoms you describe perfectly match fuel system contamination: Stalling at idle indicates irregular fuel delivery, Check engine light triggered by poor combustion, Error codes related to combustion chamber make sense due to deposit buildup The mechanic is correct about the combustion chamber problems, but these are likely secondary effects from the contaminated fuel system. Would strongly recommend getting a full fuel system service and filter replacement before more expensive engine repairs become necessary. To prevent future issues, stick to one fuel grade consistently as recommended in your owners manual and maintain good fuel economy practices.

Thanks for sharing your 156 experience. Your description matches what I am dealing with. Did you remember roughly what the full repair cost you? Just trying to budget correctly before I head to the shop. After getting it fixed, did you notice any lingering issues or did the fuel additives they used completely solve the problem? My main concern is permanent damage to the engine from running with contaminated fuel for over a week now.

Thanks for asking about the repair costs and outcome. After taking my Alfa to the shop, they found the main problem was actually a faulty connection in the fuel system sensor, which was causing incorrect fuel mixture readings. The repair cost was 95 Euro to fix the cable and plug connection. The incorrect fuel composition issue cleared up completely once they flushed the system and added proper fuel additives. The engine knock disappeared, and fuel economy returned to normal within two tank fills. The combustion chamber thankfully showed no lasting damage. A key tip: regular fuel filter changes help prevent these issues. Mine was due for replacement anyway, which probably made the mixed fuel problem seem worse than it was. The most important thing is getting it checked quickly, which you are doing. Running on mixed fuel for a week typically wont cause permanent damage as modern engines have protective measures built in. Just make sure to stick with the recommended fuel grade going forward.

Thanks everyone for the input. Finally took my car to the mechanic yesterday and got the full diagnosis. The fuel system needed a complete flush due to contamination from the mixed gas grades. Final bill came to 280 Euro including parts and labor. They found deposits in the combustion chamber just as suggested. The mechanic cleaned everything out and replaced the fuel filter since it was completely clogged. They also used some special fuel additives to help clean any remaining residue. After the repair, the engine runs much smoother with no more stalling. Check engine light is finally off too. Learned my lesson about mixing fuel grades. Going to stick strictly to premium as specified in the manual from now on. The only lingering concern is a slight engine knock during cold starts, but the mechanic says this should resolve once the fuel additives finish cleaning the system over the next few tanks. Will keep monitoring it just to be safe.