I am John Mc, a Ford dealer technician.
I hope I can help solve your problem quickly and accurately.
There are a few things to check to help find your problem. First is the knock on the top end of the engine or the bottom. If the top you probably have timing chain issues and these can ruin the engine if not fixed asap. If the noise is in the lower end first check that your crank pulley has not come apart. If it has replace it. If this is not your problem then you probably have major internal damage and it would be best to replace the engine. If a new engine is not in the budget you can probably find a good used engine in a salvage yard for under $1000.
If you have any more questions please feel free to ask, it's what I'm here for!
If this answer has been helpful please accept so I can receive payment. Feedback is very
important to me so please leave accurate feedback for others to see my job performance.
I drove about 30 mile since knocking started. i think might be top of the engine. can it still be repaired.
As long as it is not misfiring real bad then your valves should be ok. Don't keep driving it, get it checked soon. Timing chains are a big job and they require special tools. I would suggest having a dealer do this work as most dealers have a tech who is very familiar with these repairs.
If the oil pressure is fluctuating it probably has stopped up the strainer with parts of the timing chain tensioner. You will need to clean it out. Hopefully no major damage has been done to the bearings. I would not suggest doing this job as the cams have no timing marks, you need a $600 set of tools to even set the timing. No way to mark them you have to have the tools to do it properly.