2001 F250 5.4L - Smoke from exhaust pipe

I recently had my muffler changed and the pipe flange on the tailpipe up by the exhaust manifold welded back on. I haven't driven my truck much this past summer so when I took it in to get the muffler fixed the front caliper got temporarily stuck like it tends to do. It eventually freed up but in the meantime I noticed a hot oil-like smell coming from my truck from time to time. I chalked it up to either the new muffler or maybe it just smelled hot and it was instead the front brake caliper still being stuck. One day I'm driving down the interstate and I start uphill. I noticed smoke behind me and pulled over. The brake was not overheating so I got underneath the truck. The smoke was rolling off of the exhaust pipe all the way down it all the way up near the manifold but mostly around the muffler. The smoke quickly went away while I was under the truck. I noticed it doing this only while the engine is under a load like going uphill. Just driving around town nothing is noticeable. When it does smoke I lose power. Once I slow down for awhile and then gradually speed back up things seem okay. I checked the oil. Normally I don't lose a drop but this time I was a quart low but the oil on the stick was clean. It's been awhile since I had my oil changed but very little mileage on this change (my truck has sat awhile). My truck doesn't leave a drop of oil under it when it sits. From what I read you can remove the radiator cap and start the truck to see if it's a blown head gasket. At least that one of the things I can check easily without actually taking the plugs out even though the oil looks clean. The radiator has not lost any fluid. The transmission fluid is also good. It's been doing this for about 3 weeks. I still drive it to and from work (about 15 miles round trip) everyday but I take it easy on the acceleration and stay on city streets. I looked into the EGR system online for my truck and instead found an EVAP purge solenoid/valve in its place on the passenger side. I don't have any service lights on the dash. I went to Autozone and had them scan it but nothing came up. I read somewhere that either the purge solenoid assembly or EGR (I can't remember) can burn up the board if it goes bad resulting in no code showing up.

I recently changed a vacuum valve out that went bad that controlled the vacuum chamber used to operate the hubs on the 4WD. The 4WD is now operational again. Assuming the head gasket is not blown, any suggestions on what to check for next? Thanks.

 

It sounds like you had oil leaking onto the manifold and exhaust pipes. Check your PCV valve for proper operation.

 

So I've looked into it a little further. It doesn't seem to be the PCV. I pulled it off and it's pulling a vacuum. I ran it with the PCV off and it behaved the same. No oil spilled up around the PCV valve opening but it was still burning off the exhaust pipe. Here is the vacuum diagram:

http://i1190.photobucket.com/albums/...psa3d6576b.jpg

Upon closer inspection there is no wet oil found above where the exhaust manifold is attached. The oil appears to be coming from the exhaust manifold on the back right on the passenger side. I have had an exhaust leak here for awhile. There is some chirping when starting the truck while cold presumably from the leaky manifold. The back right bolt of this manifold is either broken off or missing. There is also some wet oil found on the seams of the shell of the catalytic converter.

 

How many miles on the truck? Have you pulled any of the plugs to look for oil on the threads?

 

There's about 180k on it. When I first noticed the smoke and gradual loss of power at about 65 mph the engine still sounded pretty smooth and wasn't noticeably missing. I haven't pulled the plugs yet but after a few days it's started to miss when around 3500-4000 rpm when under a load. Driving it while not under a load or letting it idle does not produce an oil leak and sounds smooth with no misses.

 

So it turns out the back right plug had a threaded insert put in years before. It had actually burned a hole through the head right through the edge of the insert. It looked like someone blasted a small hole straight through it with a plasma torch. The catalytic converter was apparently roasted causing exhaust blockage I'm guessing from fuel burning in there...So it took a new head to fix it. Now I have to deal with a radiator hose clamp leaking and my speedometer just quit working...Now I'm looking to change the VSS to get it going again. Thanks again for everyone's suggestions.