Decided to check the engine in my truck today; a fairly low 15" at idle but solid with no fluctuations, a blip to 2500rpm and letting the throttle snap shut gave a dip but no where near dropping close to zero and a steady creep back to 15"

Codes tell me she is running lean on both sides and an O2 sensor is out of range.

I've no obvious vacuum leaks, and we are looking at 246,000+ miles on this 4.6 Windsor.

I'm not real sure I can drop the Y-pipe without breaking bolts, but this seems like the next step to check for an exhaust restriction.

The truck idles fairly well, and does get to and hold highway speeds, but it will stumble every now and again when I accelerate smoothly. The stumble is not evident if I hit the floor.

Fluids are good, air filter is good, MAF is clean and functional.

I've not looked at plugs and wires just yet, so their age or condition is unknown.

I can dedicate a few extra hours to doing a compression check, but I'm fairly sure the numbers will come out low if there is a restriction in the cats.

My only thought at the moment is to hack the Y-pipe and run the vacuum test again to see if it comes up a bit.

Your thoughts?

Maurice

 

Ensure the O2 connections are corrosion free. O2 sensor voltage feedback to ECU should be .1 to .9 volts.
If the connections show any sign of white residue or rust, spray the connector contacts with a non-chlorinated aerosol cleaner such as CRC Brakleen, or CRC Electric Contact cleaner & swab with a Q-tip to remove these deposits.
Test Drive after cleaning.
Retest and replace the O2 sensors as necessary.