2004 Grand Cherokee WJ P0340 and P1391 Codes: Cold Start Misfire and Engine Dies After Warm-Up
I'm experiencing a strange starting issue with my 2004 Grand Cherokee WJ. The vehicle won't start in cold temperatures and shows diagnostic trouble codes P0340 and P1390. It runs for only a few seconds, misfires, and then shuts off. When I repeatedly attempt to start it, the engine warms up to about half its normal operating temperature, and it will run for 10-15 seconds before dying. Once warmed up, the engine runs smoothly with no check engine light (MIL) illuminated. The issue seems to be specific to cold weather conditions. I've ruled out obvious electrical problems, but I'm not sure if this is related to the crankshaft position sensor (P0340) or a fuel system issue (P1391). Any insights from owners of similar models? A fuel pressure test might help confirm whether it's a fuel delivery problem. Thanks for any advice!
Please confirm the year and engine type (e.g., 4.7L or 5.7L) of your Grand Cherokee WJ, as this affects diagnosis. The P0340 code points to a faulty crankshaft position sensor (CMP), which is common in cold weather due to sensor sensitivity. Also, perform a fuel pressure test—cold starts are especially sensitive to fuel delivery issues. A low or inconsistent fuel pressure could explain the misfire and stalling behavior. GTG — please share your findings and update with results.