Safari Exhaust Issues: Bad O2 Sensor vs. System Leak

Had a similar issue with my 1998 GMC Savana with the 4.3L engine. As someone with moderate experience working on vehicles, I recognized these symptoms immediately. My engine was also running rough with a check engine light. The exhaust leak smell turned out to be connected to a malfunctioning oxygen sensor. The faulty sensor was causing incorrect fuel mixture readings, leading to poor engine performance and that distinctive exhaust odor. Took it to my regular workshop where they confirmed the oxygen sensor malfunction through diagnostic testing. The repair involved replacing the sensor and checking the surrounding exhaust components for any related damage. Total cost came to 375 Euro including parts and labor. To help diagnose your specific case, could you share: Engine size, Current mileage, Any recent repairs, Whether the check engine light is steady or flashing, Any specific driving conditions when symptoms occur This information would help determine if your issue matches what I experienced. These symptoms could also indicate other problems like a cracked exhaust manifold or failing particulate filter, so proper diagnosis is important.

Thanks for sharing your experience. My Safari has 100169 KM km and just had a service last month. The check engine light stays on constantly, not flashing. The rough running and exhaust smell are most noticeable when the engine is cold, especially in the morning. After reading about the NOx sensors and checking connections around the exhaust pipe, I am starting to think this could be more than just an oxygen sensor problem. The exhaust leak seems to be getting worse, and there is a distinct rattling noise from underneath. Looking to get it properly diagnosed before throwing parts at it.

Thanks for those details. After dealing with my Savana's issues, they sound very similar to what you are describing, especially the cold start symptoms. When my oxygen sensor failed, I initially thought it was just that, but further inspection revealed the NOx sensor was also malfunctioning. The rattling you mention caught my attention because my exhaust pipe had developed a crack near the manifold, causing both the leak and the noise. The combination of rough running during cold starts and constant check engine light typically points to an exhaust system issue. In my case, the EGR valve was also partially clogged, contributing to the poor performance. The complete repair included: Replacing both oxygen and NOx sensors, Cleaning the EGR valve, Repairing the exhaust leak Total repair costs reached around 850 Euro, but it completely resolved the issues. Given your mileage and symptoms, I would recommend getting the exhaust system thoroughly checked, particularly the connection points and sensors. Replacing just one component might not solve the underlying problem. For reference, after fixing these issues, both the rough running and exhaust smell disappeared completely, and fuel economy improved noticeably.

Thanks everyone for the helpful responses. The symptoms you described with your Savana match mine exactly. I scheduled an appointment with my mechanic next week and made sure to mention all these details, especially about checking the oxygen sensor, NOx sensors and the possible exhaust leak near the manifold. The rattling has gotten slightly worse over the past few days, and the EGR valve definitely needs inspection based on the cold start issues. Rather than just replacing parts out of nowhere, I will have them do a complete diagnostic of the exhaust system. The repair costs you mentioned give me a good baseline of what to expect, hopefully around 850 Euro if it needs similar work. Will update once I know exactly what the problem is. At least I know I am not alone with these symptoms and there is a clear path forward for getting it fixed properly.