Hey, I'm new here. I have a 98 F150, V-6, 4.2 with 122,000 miles. I have noticed a knocking noise from the engine. It starts at around 30 mph. I can't tell if it continues because of the road noise once I get past 35 or 40. I just recently (last month) had a tune up. The spark plugs and wires were changed. The Check Engine light does not come on. Any ideas as to what could cause this?

 

Try running a tank of high octane fuel through it, and see if the knock goes away. If so, then you might have bought the wrong kind of plugs, causing pre-ignition. The high octane fuel doesn't fix anything, it just treats the symptoms. It's a good tool for separating "pinging" sounds from "knocking". If the sound still occurs with high octane fuel, then it's probably something else.

 

Thanks for the suggestions. I filled it up yesterday with the high octane fuel, so I'll see how that does. If that doesn't fix it, I'll check the spark plugs.

 

Hey, one more suggestion. If the "knocking" is what i think it is it might be a lifter going bad. Its not common in those engines but it is possible. When i bought my truck the previous owner used a Penzoil oil filter and the filter paper broke off and got in the oil ports and did not let the lifters "prime". Not saying that this is your prob just letting ya know. I would get a mechanic to listen to it in case the lifters are going bad. Hope i helped.