Engine Performance problem
1998 Ford F150 V8 Four Wheel Drive Automatic 140000 miles
Hello, My truck, 98 F-150 V8 4.6L with 9" lift, 35" tires, lower gears, K& N intake, flowmaster muffler) has had this issue for quite some time. When hard on the gas usually above 3,000 rpm the engine begins to make a rattling noise and gets worse as the rpm increase. Seems this all probably started when the engine was replaced when my dad owned it. I forget the exact reason but I noticed ford only replaced the block and most likely the pistons and such but the top end did not look new. Once I owned the truck I drove it harder then my dad, hard on the gas(my dad never did so this was the first time hearing the noise) and offroad like a typical teenager. So every once in a while I would get check engine lights and the truck would run ruff. So I read the trouble code and I would usually say missfire cylinder 4. A couple times this was caused by running through big puddles and getting water down those deeps holes where the plugs are(worse design ever) but sometimes it was random. So I would go through all the plugs and wires replacing those that needed it with properly gapped plugs. I was going through plugs quick. The ones I replaced where often chalky white indicating a lean run. Although one had almost no gap and look like it was physically struck by something. I brought it into ford a few times and all they did was replace plugs/wires, knock sensor, and O2 sensor. I kept telling them about this clicking rattling noise under load high rpm but they always said they couldnt find anything. I even had them reflash the PCM. I've tried putting 91 octane in the truck and the noise goes away but 91 is to expensive and not what the truck is designed to run on. Also the truck does not seem to make the noise as much before it warms up. So it seams that the truck is running lean causing predetonation under high load/rpm. Also over all there just seems to be a lack of power although the lift and tires robs alot and I am only getting 10 mpg at best but there are a lot of factors that are causing that to. I also ohm checked the fuel injectors and all where in spec. There really is a gremlin in my truck so if you could help get rid of it that would be greatly appreciated.
Would you describe the noise as pinging? If so that K & N air induction system, especially if it's an oil soaked air filter is causing the MAF to lean out the air fuel mixture, try cleaning/replacing the MAF. Just driving on rough roads or off road can cause the crank sensor to think the engine is misfiring!