MsKC

I have a 1998 F150 4x4 with a 4.6 (if you need that). After driving the truck for 5-10 minutes when it gets warmed up, there is a knocking noise that comes from under the truck. It sounds like metal banging on metal, as if there were a loose part. I used a screw driver as a stethascope, but can't tell where the noise is coming from. Someone said that it possibly is my torque convertor, as my transmission shifts perfectly. Can you help? Thanks!

FNA

This is just a guess, but I think that if you had a bad torque converter, you would not feel that your transmush was "shifting perfectly".

A couple of things:

Is the quaslity of the noise different at rest than when you first hear it driving down the road?

When you are looking for your noise vary the engine speed. Does that vary the speed of the knock?

Look for the noise in both neutral and in a drive gear.

Cammy_01

Ford has some known knocking/ticking noise issues.. mostly on the 4 valve/dohc engines. I went thru this with my 03 4.6 Cobra which wound up being some scored pistons.

How many miles are on the engine?

I agree with what was said previously, have someone give it gas while you listen in the engine compartment. Specifically listen if it sounds more like a tick tick tick or a knock like a rock hitting metal. Make sure oil level is full. A tick I wouldnt worry about so much if its running well, just make sure you are using a good quality oil and changing it every 3k.. I personally dont buy into the whole synthetic oil hype, but even if you use syn oil you still have to change it every 3k or when it gets dirty looking, I confirmed this after my pulling my friends nissan apart that he always used mobil1 in and 7500 mile oil change intervals.. I have never seen so much sludge in an engine and I am a mechanic and have pulled apart many engines. I also dont believe in additives, oils have a special anti foaming agents which additives may hinder. Just my opinion and .02

If what you hear is a knock knock knock and it does not go away when you increase engine rpms, I'd suspect a bearing going or gone bad in the bottom end.. Id rebuild the engine when it gets loud enough. If the knock goes away with increased engine rpm, its possible that the oil pump may not be providing enough oil pressure. That is easy enough to check.. a cheap manual oil pressure gauge from autozone will do the trick.

Let us know how it goes..

Torch

I had a banging-vibrating noise when I used to have an old 77 F-250, it ended up being the first U-joint after the drive line leaves the transmission had gone bad.

FNA

"even if you use syn oil you still have to change it every 3k or when it gets dirty looking, I confirmed this after my pulling my friends nissan apart that he always used mobil1 in and 7500 mile oil change intervals."

cammy1, it is absolutely wrong to change syn oils at 3,000. really don't need to change regular motor oil at 3k for the sake of the oil, but using syn oil it is a huge waste of money.

I would venture to guess that your friend's Nissan engine condition had more to do with driving habits or some other factor than with changing syn oil at recommended intervals.

i am surprised that you as a mechanic would say "suspect a bearing going or gone bad in the bottom end...Id rebuild the engine when it gets loud enough." What? When it gets loud enough? Yeah, just continue damaging the engine more and more until you can't stand it anymore. Gotta say, no wonder you have rebuilt many engines.

big white bufflo

pull your inspection cover on the torq converter it could be lose and it would sound hollow not clanging for a rod knock but the bolt on the converter could have losend up or it could be a cracked flex plate how is the oil pressure did it stay up after driving it a little while if it stays up then its not a rod or a main

dfordski

Was it louder at first. Maybe it's a Leash. When was the last time you saw the dog? You should hear what a skateboard up in the cooling fan sounds like. I'm just guessing about the leash noise........Personally "I" like dogs!

transgta

Check your spark plugs if ones a very little bit loose it sounds like that.Im sure people will say noway i was gettn ready to trade mine in cause of that noise.I had a loose spark plug.Try it