Cherokee Misfire: Rough Acceleration Needs Quick Fix

I had a very similar issue with my 1998 Grand Cherokee last winter. I have some experience working on cars but mainly stick to basic maintenance like changing air filters and spark plugs. The symptoms you describe match what I experienced, rough running, misfiring, and jerking during acceleration. After getting it diagnosed, it turned out to be a leak in the exhaust system near the manifold that was affecting the oxygen sensors and fuel mixture. The repair involved: Replacing damaged exhaust components, Installing new gaskets, Checking fuel injectors and connections, Basic diagnostic tests Total cost was 265 Euro at my regular workshop. The work took about 3 hours to complete. Since the repair, the engine has run smoothly with no more check engine lights. To better help diagnose your specific case, could you share: Current mileage, When the symptoms first appeared, If the problem gets worse when the engine is cold or warm, Any unusual exhaust smells or sounds, Whether fuel consumption has increased The fuel injectors and spark plugs should definitely be checked, but based on my experience, having a thorough exhaust system inspection might save you from replacing parts unnecessarily.

Thanks for sharing your experience. My Cherokee has 57302 KM and started showing these symptoms right after the last service. I checked my maintenance records and realized my spark plugs were never replaced, so that could be the culprit. The rough running gets worse when the engine is warm, especially during acceleration. The oxygen sensor readings are off according to the diagnostic tool, but this might be caused by worn spark plugs affecting the fuel mixture. I will start by replacing the spark plugs since they are overdue and relatively inexpensive to fix. Has anyone tried changing just the spark plugs first before moving on to more expensive repairs like fuel injectors or the fuel pump? Want to avoid unnecessary parts replacement if possible.

Thanks for the update on your Cherokee. Based on your symptoms, especially the worsening during warm operation and oxygen sensor readings, starting with spark plugs is definitely the right approach. When I tackled my similar issue, I first replaced the spark plugs and ignition coils since they were original parts. The oxygen sensor readings improved immediately after installing new spark plugs, which makes sense since old plugs can cause incomplete combustion and throw off the fuel mixture. My repair costs were just 85 Euro for a set of quality spark plugs plus about an hour of labor. One tip from my experience: I made sure to check the ignition coils while replacing the spark plugs since they were easily accessible. The rubber boots can deteriorate over time and cause misfires. In my case, they looked fine, but it was worth inspecting while everything was apart. If the rough running persists after new spark plugs, then investigating the fuel injectors would be the next logical step. But given your mileage and maintenance history, theres a good chance the spark plugs will resolve the issue like they did in my case. Before reassembly, be sure to: Check plug gap specifications, Inspect the plug wires for wear, Clean the spark plug wells thoroughly, Apply dielectric grease to the boots

Thanks for the detailed reply. Definitely going to tackle the spark plugs first this weekend. Just ordered a set of recommended plugs for 85 Euro and picked up some dielectric grease. The tip about checking the ignition coils while everything is apart makes perfect sense. My timing belt is also due for replacement soon, so I might have the shop inspect the crankshaft sensor and other components in that area if the spark plugs dont completely fix the rough running. Will inspect the condition of the fuel injectors too since they need to come out anyway to access some of the plugs. The air filter is relatively new from the last service, so I can rule that out as a cause. I will update once I complete the spark plug replacement to let everyone know if it solved the misfiring and rough running. Hoping this fixes it without needing more extensive repairs.