Exhaust Smells Horrible

[autigs3434]

(2004 GMC Yukon SLT 260k-miles)I've been reading several threads where people were having a sulfur smell coming from their exhaust, but mine does not smell like that. It just smells like really strong exhaust. This has been going on for a few years off and on, but recently I've noticed the smell is constant. I can always smell it just about every time I get out of my vehicle when it is running. The smell is not inside the vehicle. I've also noticed that no matter what the temperature is outside I can see the exhaust smoke coming from the tail pipe. Just recently, within the last month, I've noticed a "hissing" sound, almost like a vacuum leak, coming from around the fuel pressure regulator. I don't know if the sound is coming from the regulator, but it's coming from that area. The sound gets louder the more I accelerate. There is no fuel leaking from the regulator. With the engine running I pulled the small rubber vacuum hose and there is no gas squirting out, and the engine continues to run with the hose pulled off. I recently replaced the pcv hose that was cracked, so I know I'm good there. There is no check engine light. The idle of the engine is not rough. Anyone experience these issues before? I'm thinking about changing all of my O2 sensors since they have never been changed, and I may change the fuel pressure regulator. Could it be a fuel injector making the noise? Any thoughts???

 

[06Escalade]

Is your tailpipe full of soot, or is it relatively clean? Have you checked for any pending codes? Do you burn oil?

 

[autigs3434]

It does burn some oil, and the inside of the tailpipe is not that dirty. I wiped it with my finger and there was some soot, but to me that would seem normal. The recent codes that I have received were for my knock sensors and there was one code for my flex fuel compensation. I beleive it was P0178

 

[06Escalade]

Well, you've got different 2 CEL's that are timing related. If either is off the timing will be less than optimal. Can't say for sure which way your timing will default to, but it won't be right. So if thats off, you may be running too rich, which you could be smelling unburnt fuel. I did my knock sensors and harness last year. Its not that hard of a job. They were popped out, and water was in the holes. Ran a whole lot better after that job. Did the intake manifold gasket at the same time. I would definately fix the knock sensors ASAP. Make sure you use OE knock sensors only!