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Ok guys i am new to the forum havnt posted much, but have read some threads on here but i am in need of some help. I recently bought a 99 f150 with a 5.4. I bought this truck for three grand, it has 165k on it and when i bought it i knew it has an exhaust leak at the manifold. My wife works at our local ford garage so i brought it there and got a new manifold put on the passenger side. Well when i got the truck back i noticed the engine was knocking. Not super loud, sounds like it going to blow knocking but u can hear it with the windows down. I have read about the manifolds making noise, catylitic converters chattering and loose spark plugs rattling too. I just have no idea what it is or if any of these are a possibility. Almost sounds like a diesel and when i accelerate it speeds up but is definately louder and more noticeable at idle. is it possible the knocking is coming from the other manifold and with the new one on there it has started to knock? Even though there was a leak at the passenger side before, at idle it was not loud and i know that knock wasn't there. I layed under the thing running for 15 min before i bought it to make sure the engine wasn't knocking. any ideas?

 

First, be carefull what you call a 'knock' as opposed to more of a rattle sound.
These engines were known for pistons rocking in the bores called piston slap which is more of a deep lower sound.
The camshaft chain tensioners up front have a different lighter rattle sound from worn guides that may be laying against the front case cover.
A bearing knock is also a low toned sound and steady at idle under lower oil pressure.
Then you have the possibilty of a spark plug leaking up top. This sound can be a variarity depending on the physical condition of the leak.
At this point we can't tell what you have from what youv'e said.
Try to see at what area you hear the nose with a stethoscope. They are about 10 to 15$ at the auto parts store.
Good luck.

 

i don't know if this helps but the only other thing i did to this truck that i can think of that might make it all of a sudden tick/knock what have you is do an oil change. I put in 5 quarts of mobil super synthetic and i quart of lucas new car formula.

 

I have a 98' F150 5.4L with 192,000 currently. About 30,000 miles ago it started knocking. I only here it when the door is open and have run into other similar trucks ay the gas station doing the same thing. I asked them and they said the noise has been there for tens of thousands of miles and still runs great. Mine does to and is very dependable. It sound like a rod bearing but over that duration of time it would have disintegrated long ago if that were the problem. That piston slap is something I've considered but seems unlikely unless this engine uses a short piston skirt allowing the piston to wear prematurely and start slapping a little. With the tight tolerances these things were built with and the high miles on many of these trucks it seems unlikely, lest that short piston skirt has been designed into it. I haven't seen one apart, so I'm not sure.

Checking the oil pressure is one way to eliminate the rod bearing theory which I have yet to do. I have two "Autometer" Gauges all set to install to monitor oil pressure and vacuum. These will give me a much better indication of the engines running condition than the stock dummy (oil) gauge Ford designed. It looks like a gauge, but isn't.

Q? Anyone, will a leaking exhaust manifold make such a knocking sound. In my experience, exhaust leaks make more of a hiss or bang as they run, not a knock?

 

yeah i am at a loss as well. Like i said i know this thing was not doing this prior to having the passenger side manifold fixed so that what lead me to believe with the pass side fixed that maybe it added extra back pressure to the drivers side making it start to nock cuz it was on its way out all along. i was just trying to get some input to try and pinpoint it before i had to spend the money at the mechanic

 

a exhuast leak would get faster with teh RPM's going up to, but like said it could be any number of things, my 4.6 has a slight knocking sound when first cranked an last's maybe 2-3 mins but i figure its just takes a second for the oil to get everywhere

 

Based on the above, I'd say it's a bad lash adjuster, and maybe by now, a bad follower also (rocker arm ).

Rod or main bearings won't go thousands of miles. Possibly could be cam drive hardware, but that's more of a rattling sound, almost diesel like.

Dave