1999 Ford E150 4.6L (Just figured out what I was told was a 5.4 at purchase is actually a 4.6)
My Matco scan tool gave me the following codes
p0305, p0306, p0308 Miss fire on cylinders 5,6 and 8
p0401 insufficient EGR flow
p0402 excessive EGR flow
p0174 Lean fuel on bank 2
p0430 Catalyst system bank 2 below threshold

Engine has destroyed both upper and lower catalytic converters on drivers side. No power. I have gone through and pulled plug wires one at a time (all 8 cylinders) with no effect on the way engine runs and have repeated doing the same thing with injector wires. Simply can't tell the difference pulling any single plug or injector wire off a cylinder.

Have pulled all 8 spark plugs one at a time, 1,2,3,4,5,6,and 8 are all perfect ashy white color with no damage. Number 7 slightly blackened no build up and no damage.

Currently having some financial struggles and just can't afford to blindly throw parts at this one.

Not understanding how plugs can look perfect and still be miss firing? Can not understand how pulling plug wires and injector wires doesn't cause noticeable additional running issues?
Van has no power, takes a full mile to get up to 35mph.
Extreme back fire occurring.

 

Just a wag. But I would clean/replace the egr and egr flow sensor. Perhaps a real mechanic will chime in.

 

Put in "test" pipe to get past the two bad catalytic converters and dumped the muffler out... Then removed throttle body, EGR etc... found the two EGR ports clogged probably 95% with carbon. Did a thorough cleaning and reinstalled with new gaskets.Cleared all codes.
Started it up and it seemed a bit smoother. Sprayed carb cleaner all along the upper and lower intake gaskets as best as I could get into the and did not find any intake leakage.Gave it a drink of Sea Foam through the vacuum line to do a little clean up below the throttle body...
Took it for a test drive and it had more power, though still back firing a bit. Drove it about 2 miles then it died. it would not start immediately, but after sitting 5 minutes it started easy, but will now only stay running for about 1 minute then dies and has to rest for 5 minutes again. While running revving it kills it immediately, and fluttering the peddle also kills it. I got it home about 4 feet at a time as that is all the longer it would run (I guess my battery is pretty good if nothing else)...

I now have 3 codes
p0305, p0306 miss fire on 5 and 6
and I apparently didn't write down the exhaust O2 sensor code but had one code on it, but with no cats that makes good sense.

Really need help on what I need to focus on next.

 

If it has coil packs and plug wires (not coil-on-plug) I would pull the 2 coil packs and inspect them carefully for cracks and carbon tracking. A fresh set of MOTORCRAFT plug wires and plugs wouldn't hurt. Make sure you don't cross any plug wires in the coils.

 

Visually checked the coil packs, no visible damage
Found a crack in the hard plastic line of the pcv valve tube that runs from the throttle body to the pcv valve, it is covered in an insulating sleeve so you can't see it. (don't know if I did it while removing the throttle body or if it was already cracked). Replaced it with new rubber line and new pcv valve.

It is now running a bit better yet but will stall suddenly. Still occasional back fire. Now seems to throw a new set of codes. P0300 Miss fire not related to only one cylinder. P0401 bad or damaged dpfe sensor, P0102 Mass air flow sensor (have now cleaned it again and it seems to not be throwing that code now).

 

Might need to replace the egr flow sensor. That might clear up the missing.

 

Replaced the EGR pressure sensor tonight, no change in power and it is still missing... It is Giving me a P0300, after a major backfire it has again given me a P0305. I also got a HO2S21 Code now.

I was watching my scan tool and while I noticed for a while the fuel trims for bank one and two was running equal for both sides. Then suddenly bank one was running say 3 to 8% while bank two was up around 55%. Then the two began to run side by side again. Still didn't feel any difference in the running of the engine during this but definitely peaked my attention...

I feel like I am just throwing parts and cash at this thing already... any ideas are welcome...