My 4.6L is knocking pretty bad.

Sounds like a diesel engine during medium and hard acceleration. I run mid-grade gasoline all the time. the plugs and wires have been changed twice during its 89K miles. the engin light is on again. last time Autozone's "scope" returned a "passenger rail lean" code; however i didnt write down the code number. (where do you interpret the numberic codes?) I have a few ideas on what I would do if I had serious coin.

Has anyone experienced similar issues?

I had the SAME exact problem with my 95 v8. It knocked under "flooring it" conditions, but not at idle. What i did was upgrade to 93 premium, instead of 87, added chevron with techron (cleans fuel injectors) and haven't had a problem since. Don't forget though, wait till you tank is literally like 80% empty. Then use ONLY 93, not 91, get the good shit-put in the chevron then give it a couple days. Let it once again go down to 80% empty, then refill with 93 again.

This reduced my pinging or knocking literally about 75%. Just make sure you ONLY use 93 ok.

BTW.. Check all air hoses/vacuum hoses etc. Look out for tears and holes.

i would check for vacuum leaks, if i were you i would just wait until your tank is empty, use 93 and fuel injector cleaner, then when the 93 is empty just go back to mid-grade and see what happens.

thanks guys. I am currently half way through a tank of 93 octane and Techron

I did some more searchin on-line and found two sites about the 4.6L. they mentioned the MAF to be a source of the problem. Long story short... remove the MAF, spray it out with Contact cleaner, let it dry, reinstall, and listen to the peaceful (knock-free) purr of the engine.

My car is running great. currently, I'm cleaning the K&N so i have a paper filter installed. Im quite satisfied with the performance and can't wait to put the K&N back in. Then i can have closure to DTC# P0174.

hopefully i can go back to mid-grade. I'll experiment and hope for the best.

Thanks again for the replies!

Do not use too much oil with your K&N as this will cause the MAF to get dirty too quick.