Hi all,

2006 F150 4.6L 4x4. Just purchased not long ago used with 120k, did an oil change and filters, but I’ve heard this before doing the changes. When I am accelerating above 40km/h, I hear a crackling sound from the engine. Accelerating from a stop until 40km sounds quiet/normal, but above is when it starts happening. If I let off the gas and just coast, it’s all quiet/normal. Even slightly accelerating will trigger the noise where within seconds it reaches a constant crackle. At higher speeds I think it’s more prevalent. There is a slight difference between light and hard acceleration but I don’t think enough to put down as a symptom, I could be wrong. Today I did a 2.5hr drive at highway speeds and that’s when I’ve really began to take notice of it being something likely serious to look into (normally I do city speeds). It sounds like it’s coming from the engine area. I’ve tried lowering the window to listen more but I couldn’t hear much, could have been too noisy around me. The best way I can describe it is a crackling sound or when your truck has a vibration and you have coins in your cup holders but muffled. Any ideas? Thanks

 

It sounds like detonation to me. Common causes are excessively advanced ignition timing and carbon/fuel residue buildup on the sparkplugs and valves. The buildup acts like a glow plug in a model engine and causes the fuel mixture to ignite prematurely, which is effectively the same as over advanced timing. My best description of the noise is marbles being shaken in a can. It's usually pretty linear with throttle pressure. The deeper you step into it, the worse it gets. Detonation will eventually cause spark plug damage, erosion to the valve and piston heads and even broken rings in serious cases.

 

Thanks, any way I can confirm this before proceeding with doing the plugs? Was going to do them in the spring but maybe it needs them earlier then...

 

Really the best way is to have a ride with somebody who knows what it sounds like. From what you describe though, I'd bet a cold beer on it. Pull a couple plugs and see what they look like.

 

Pop it in 4H and see if it goes away...

 

Yes, do that. I kind of took the detonation ball and ran with it. I don't know why IWE's didn't come up on my radar.
If you put it in 4H and the noise goes away, the problem is in the IWE (front hub) system. Actually not an uncommon problem, as problems with these trucks go. Thankfully nobody took me up on my beer bet.

 

If it does go away, here is a good thread on how to diagnose it:

https://www.f150forum.com/f72/how-di...m-esof-186872/

A lot of people have found that replacing the check valve solved it. Which is the cheapest and easiest to replace. The next cheapest and easiest to replace is the solenoid.

 

Changed the spark plugs but did not resolve it, I wanted to do them anyways. I don't know a whole lot about spark plugs but they didn't look to be in too bad condition. Gaps were around 0.050-0.055 so pretty good. Noticed my truck is a bit more responsive now so at least I got that out of it. Tried driving it in 4H but I still hear the same noise.

https://imgur.com/a/UkxcO

I have noticed the noise starts at ~1,400rpm, peaks at 1,500rpm and tapers off until ~2,100rpm. More noticeable at higher speeds/gears. Sounds almost like a nut or washer rattling somewhere, and for all I know it could be, I haven't dug far around to double check. If you have the radio on, you almost cannot hear it except at high speeds such as 120km/h.

 

Scratch what I said about rpm, doesn’t have any relation. If I accelerate harder, the noise comes/gets louder. Except at highway speeds where it’s pretty much always there.

 

What about checking to see if any of the brackets above the catalytic converts is loose or you have something stuck up in a heat shield or something along those lines.