I've got a 97 Mountaineer ( just like an explorer) with a 5.0 v8 and 87,000 miles. It's all stock and I have had no other problems since I've owned the truck. It has lost most of it's low end power and if you mash the gas at a stoplight it will burble and pop really loud out the exhaust before it finally starts to rev. If I'm cruising around town at around 40mph and the RPM's are really low (1300) it will somtimes backfire. I'm not getting any check engine light at all. My millage has not went down either. I'm thinking it's either plug wires, plugs, or O2 sensor. It seems like it's loading up one of the cylinders with gas, and then it fires the plug and BAM, it backfires. I put new plugs in it 10,000 miles ago, and I thought that if one of the 4 (yes that's right, 4) O2 sensors was going bad, it would trigger the check engine light. Can some of you guys give me some help. Thanks.