Bogging @ High Rpm

Ok, after researching the net for months, countless forums, tech help from ford, etc etc, I'm at wits end.

I have a 1997 Mustang GT, 4.6L 2V, Manual trans, 3.73 gear, Magnaflow cat-back. K&N factory replacement filter. Everything else stock.

It's developed worse over the last few years.

Here's the whole story. bought the car used about 60k miles ago. Seemed to run fine to my knowledge.

Within the last year or so, power has dropped. Acceleration mainly. Can not even get it to squeak in 1st gear with 3.73's!

Idles fine. Will idle all day long. In neutral, rev's up like any other car. Hit's top end no problem. Sounds great.

Cruising at highway speed, no problems. Cruise all day. 300 miles trip didn't skip a beat.

Accelerating, sucks. I had an 80's suburban waste me on an onramp to the interstate. My boss at the auto parts store is a retired racecar driver, says it sucks. My friends Kia Rio will waste my stang.

Upon accelerating, light touch seems better than pushing the pedal. Hammer the pedal a lil, and it bogs down, flutters, seems like it wants to go, but is being held back. Just can't break free. For example, I can ONLY get it to 3800 rpm staying in 3rd gear. There is so much knocking/pinging/rattling noise and the stang won't go past it! Shifting to 4th I can go faster, but cannot get anywhere close to redline. Now, if I drop it into 5th, she starts to chug for a couple of seconds, buck/stagger and clean up and cruise. When I'm cruising at any speed, push clutch in, push the gas, she'll rev right up to redline no problem, quick as could be. Drop her back to 4th or 5th, she misses, chugs, etc.

Dual exhaust, passenger side tailpipe black, driver side clean as when I installed it. Always had me baffled.

Driver side has a new O2 sensor upstream, due to wiring harness connector corrosion. (This had caused similar issues, but a lot worse, backfiring, could barely drive it, it had a corroded terminal)

No Check Engine lights. - However, I finally threw a code, light is NOT on, but my scantool says MIL is on. MIL lights up when you start the car, so bulb is good.

A friend of mine hooked up a professional scanner, Cyl #5 had 25k misfires in a 30 minute drive, and cyl's 6, 7 & 8 had misfires, but less than 10K.

Swapped out both ignition coils with my 98 F-150, which runs just perfect, no change in power.

I then changed my wires, after noticing in the dark the northern light. Replaced with Motorcraft. Partial increase in power.

Changed my worn Autolite double plats to Motorcraft plugs. Very slight change, however after test driving, it finally threw a PO300 code.

Swapped out MAF from my truck, no change.

Did the propane trick for vacuum leaks, did not detect any change.

On the PO300 code, freeze frame data read:

RPM 1789
87.1 Load
LTFT1 18%
STFT1 10.9%
LTFT2 -2.3%
STFT2 10.9%
55mph.

Did another test, idling vs 2500rpm

Idle
LTFT1 0.0
STFT1 Between 1 and 4%
LTFT2 -3.9%
STFT2 hovered around 1%

At 2500 rpm
LTFT1 7.8%
LTFT2 -7.8%
STFT1 and 2 stayed about the same.

PCM calibration is 6-19C. No revision printed on tag on door pillar.

No engine noises, even with stethoscope.

133,000 miles. I bought it 8 years ago with about 75k on it.

My upstream O2's switch as normal according to my scantool's live data.

Any help would be just awesome, considering most of you prolly fell asleep reading this post. This is my baby, my pride, my joy, and would like to have my 200+hp back....

Mass Air flow sensor was swapped out with a known good MAF, no change.

No Vacuum leaks to my knowledge. Propane tested and carb cleaner tested.

My drivers side upstream O2 sensor was replaced about 15,000 miles ago. They are not throwing a code, and respond accordingly to the live data on my scantool. Now the drivers side downstream takes longer to heat up than the right downstream.

I tested the fuel pressure. Here is the full story: Today, drove to work at 8am, 10 minute drive. I tested this during lunch at 2pm. Hooked up pressure gauge to schrader valve on fuel rail, engine off. No pressure.

Watched gauge, turned key on. Pressure built to 20psi. Cranked engine, pressure went to 31psi. Gave engine a few snaps to wide open throttle, pressure jumped to 35-36psi.

Disconnected vacuum line from regulator, verified I do have vacuum at the regulator. Pressure built to 40psi. Reconnected vacuum line, pressure goes back down to 31psi.

Turned engine off, let it sit 5 minutes, pressure increased from 31psi to 38psi.

Also did a volume test, and have a little more than 1 pint of fuel in 30 seconds, engine idling, using the drain hose from pressure tester.

I did NOT pinch of the return hose. Not sure which one that is to be honest, help?

Also did not test drive under load with the gauge on. Didn't have enough time during lunch.

Also did drive 10 miles with the pressure regulator hose disconnected. No change in problems.

New fuel filter. Old one I had cut apart, and a fair amount of debris.

What should my pressure be at in these tests? I've read everything from 30-45psi idling, been told it should be the same as pump pressure, I'm in the dark.

If I do a light acceleration, even up a hill, it doesn't cause any issues. That to me eliminates anything ignition related. Push the gas a little more, then it faulters. She bogs down, flutters, lacks power.

I had ran 2 tanks of premium, no change. Several cleaners, no change.

Also, if I keep it in 3rd gear, wind it out as much as it can go which is only 3800 rpm, it kinda sounds like pinging or spark knock, or some kind of rattle type noise. Then if I drop it in 5th, it REALLY starts to chug, miss, sputter for about 20-30 seconds, then clears up.

My buddy who had access to a high end scanner looked at the injectors and no problems were there. His scantool showed misfires on entire drivers bank, but that was before I changed plugs and wires. I don't have access to that scanner anymore.

Thank you guys for your help, I really appreciate it and hopefully it helps someone else in the future.

Also adding that intake air is flowing well, I have a clean K&N filter, even ran it 10 miles without the filter in, no change. No cracks or anything in intake tube.

However, I'm not really sure, but I do have a magnaflow cat back system, and idling it seems to me like the fuel pump is kinda loud. Comparison wise, When the engine is off, window down/door open, turn key on I can hear the pump from the drivers seat. Behind the vehicle idling, sounds louder, loud enough you hear the pump more than the nice rumble.

My scantool only has capability of reading codes, live data, Actron brand. My friend had access to the professional scanners, like a snap-on verus.

Been doing more testing and diagnosing, appears my cats are restricting, backpressure test showed between 1-3psi at idle, upwards of 10+ psi at 2500 rpm. Cat temperatures before and after each of the 6 cats don't change, except one is 100° before than after. Looks like I get to go shopping for new cat setup, or H or X pipe setup...