Hey everyone, I recently bought a used 2002 F150 5.4 as my first vehicle. So far I've driven close to 2000 km on it. It came with 272k km. Everything has been running smoothly, until now. Transmission fluid looks clean, and the truck still shifts smoothly. Oil was also pretty clean, but I changed it anyway. When I ran a scan on it, I got the code PO171 and found a couple of rubber joints in the hose coming from the PCV valve that had cracked. I replaced them, and haven't had any codes appear since then ( I've probably driven around 100 - 200 km since). However, driving home tonight the engine randomly became very loud, similar to a big rig when accelerating. The noise also occurs at an idle when pressing the gas. There is also a sort of clicking or knocking in the engine, which I only noticed when I pulled into the driveway. All this only occurred when I was around a minute from home. It also sounds like there is a bit of a squeak coming from the engine when turning the ignition. Performance wise it still drives well and I haven't noticed a loss of power. Overall, it just doesn't sound very good lol.

I should also note, that the past week and a half or so has been the only time I've really had to use the air conditioning at all. The past couple of days have been quite hot, so I've had it cranked all the way. We had snow in mid may so I haven't really used the air conditioning before. Could it possibly be related to that?

Unfortunately, I will be out of town for the next few days, but I plan on taking a good look at it when I get back. In the meantime, does anyone have an idea as to what might be going on, what I should look into, and whether it sounds like a big repair or not? Thanks

 

Could be the bearing in the clutch assembly pully for the AC going out under load or one of the other pully bearings. (If it is just change the bearing as you will need an 8mm or 10mm wrench/socket to remove the bolt and a pair of snap ring plyers to remove the inner snap ring to pull the wheel with a small set of gear pullers).

Try this and see: Remove the serpentine belt from your engine and then start the truck up. See if the sound is still there or if it has gone away. If the sound goes away turn the truck off and then take each pully and hand spin them to see if anyone of them could be going out.

 

Well I was able to get up and start it this morning, and it sounds good now. The loud acceleration noise is gone and so is the squeaking and knocking. I took it for a quick drive to warm the engine up and it ran ran quiet with none of the noises coming back. I checked the radiator fan before driving and found that it spun freely after turning it about a half revolution, so I think it may be the fan clutch? At least it's running well now without sounding like a bus accelerating!

 

new, turn the A/C on and see if the noise comes back.

 

A stethoscope is a good tool for things like this. Just be careful around all the moving parts.

 

I was able to take it for a drive again and I turned the A/C to max. The noise hasn't come back, so I think it was probably just from driving a lot with the a/c cranked during the hot weather.

 

Sometimes we find out what the noise was when something breaks. it does sound like a pulley bearing going bad.

 

Hey everyone, sorry for the late response, and thank you all for helping me with this. I was able to get the belt off and check the pulleys. There didn't seem to be anything wrong with them, none of them were lose and there was no damage or wear on the belt. Both tensioner and idler pulleys spun smoothly with a bit of pressure. Same with the steering and water pump. None of them would freely turn very far. The a/c pulley also spun smoothly yet a little more stiff than the other ones. I will give it another check tomorrow, since I got caught out in the rain.