I've been racking my brain trying figure this out, and have been through this forum, but still am not clear on my problem.

Ok, here goes.

I have a 2000 Expedition 4.6 with about 140k miles. Has run great for me, but a few months ago, I noticed that the oil pressure guage was intermittently going to "no pressure", but then kicking back to "normal pressure" after a short period. I had assumed it was just a sensor issue, and ignored it, since it always went back to normal after a little while. Of course, after reading this forum, I know that this is only an "all, or nothing" indicator. I had expected to see the guage drop slowly if there was a real issue.(IE: not just on/off)
So, I drove in this fashion for a couple months with no problem. Then one morning a couple of weeks ago, I started up the truck and was greeted with horribly loud knocking sound, which quieted a little after a few seconds. I drove a couple blocks to the gas station, and added a quart of oil, which quited the "knocking" further, but was still noisy.
It had been a while since my last oil change (yeah, yeah, I know :-( ), so I thought that perhaps my filter was clogged, and oil was not getting through the entire engine.
Based on this theory, I changed the oil, and filter (with a Fram, of which I now know is garbage).
Upon draining the old oil, It did seem a quart or two low.

Now, when I started it up, I am still greeted with a very loud knocking for a couple seconds (I assume this is before the oil has a chance to circulate), after which It quits slightly. It is coming from the left side of the engine, but I can't quite be sure if it is coming from under the valve cover or not.
When Reving the engine, the knocking gets very loud. I am afraid to drive it until I know for sure what is going on. I don't know if it is "Piston slap", or failed "lash adjusters", or something else. I have let the engine run for about 15 minutes, but the knocking does not go away..

Hopefully, based on the known "low oil" factor, someone can tell me the most likely culprit.

Thanks Much.

 

My 5.4 had the same noise until I put a quart of Lucas oil stabilizer at an oil change one time. The noise went away and I have not had to add anymore Lucas to the engine. If you decide to try it, make sure that you do it at an oil change and leave one quart of oil out and replace it with one quart of Lucas Oil Stabilizer.

Oh, by the way, my engine has 255,000 miles on it with no more than changing plugs

 

I have exactly the same problem you're describing. I see this thread is old so have you solved the problem? And if so, how? I was told a couple different things on how to fix it. Put trans fluid into the engine and let idle for 20-30 to clean the lifters then change the oil. Did that but no luck. Then someone else told me the knock was too loud and coming from the bottom of the engine to be lifters and it was the rod bearings being worn and loose and nothing I can do about it other than to change the engine. Kind of drastic and costly.

Just as megabob said, the noise is always there but gets very loud when gunning the engine or passing on the highway. If there's a miracle out there, I sure could use it. Thanks

 

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