JC316

Lash adjusters are pretty common on these cars, but before I went that far, I would check the coils. If the bottom of the boot is cracked, you can get an arc to the cylinder wall and make a knocking sound.

VTX1800N1

Wish I had enough posts to attach a video. The engine shake is pretty bad.

Hangwire

Yeah man everything about the symptoms says ignition problems.

Theres two big things telling me this.

A) You have a code that is specifying a specific RPM range in which misfires are happening. This is almost always a coil issue. Coils can fire just fine within a certain RPM range but then short/misfire at others. Very few other circumstances replicate this issue. You are also seeing a flashing CEL light which indicates a live/current misfire. You are also ONLY seeing CELs that are related to ignition.

B)The engine shaking very badly and feeling as if it has no power

Let me give you an example. If you take a look at my sig you will noticed I totaled mine last year. It was totalled during a nasty winter and sat around in the snow/ice and storms and stuff in the spring as it was fixed piece by piece. When everything came back together we fired it up and got the SAME exact issues. It idled horribly. It shook so much I couldnt believe it. It barely had enough power to move around the body shop parking lot.

I noticed the belt tensioner violently shaking. So I thought maybe the factory tensioner had given up. I replaced that with no improvement. I then came back the next day with a full set of new COPs. When I pulled the COPs I noticed that roughly half my cylinders had 2-3" of water pooled up in the ignition wells. This obviously happened from it sitting around so much. I replaced all plugs/COPS and it immediately idled like a charm. Done deal.

And yes you do tee into the factory oil sender location.

VTX1800N1

No, the code does not specify a certain RPM range. It states "misfire within the first 1000 revolutions" which means the computer detected a misfire right after the engine was started. P0316 IIRC. The other two codes are for misfire on cylinders 3 & 4. Trust me when I say it's mechanical. I know my way around engines. I now how to use a mechanics stethoscope. Just to humor everyone here, I'll swap the coils around from 3 & 4 and see if the misfire follows them and report back here. Have to wait till it stops raining, though.

Hangwire

Sounds like you have a pretty good grasp on this. Why make a thread then?

VTX1800N1

I was hoping that there was an easier place to tap into the oil pressure to get a reading. Sounds like the oil filter boss is the only location.

JC316

The oil filter boss is the only place that I know of. Sometimes these motors just knock. I looked everywhere for this knock, never could find it. Car has been running like this since 09, knock never got worse and never went away.

VTX1800N1

This is more than piston slap or other common noises the mod motors make. There is heavy engine shake at idle. There is no power at all. A stock V6 would run circles around this GT as it sits. No doubt that cylinders 3 & 4 are dead, it's just a matter of getting them fixed.

VTX1800N1

I swapped coils 3 & 4 with 5 & 6 and cleared codes. Same mechanical knock from above 3 & 4 and as it warmed up I got the same pending codes. I'll pull the plugs next.

VTX1800N1

Actually there is a slight mechanical knock from all areas of the valve covers, but distinctly worse above 3 & 4. I compared it to my 05 F150 with a 5.4 3V, which should be noisier due to one more valve per cylinder. The 5.4 was VERY quiet compared to the Mustang 4.6. Just a matter of parts, I'm sure.