I have been using B100 fuel for 3 years and it finally caused a problem with my car. The bio fuel cleaned out the old carbon from the engine and it clogged the cat converter. The OBD scanner saw it as a malfunctioning wastegate solenoid.
My guess is that the restriction prevented the turbo from producing boost and the computer didn't see the correct increase in air flow from the MAF sensor.
With the converter plugged the car would only do about 60 mph

 

Better off w/o the cat anyway, especially if he continues to runB100.

 

I cut open the cat, removed everything inside, and welded it back together with a gas torch. The car seems to have more power than it ever had.

 

Thats the best way to fix it. Pa you have to have all of the origenal polution hardware for inspection.

 

mufflers on deisels get plugged with soot, causing too much back pressure / heat.
run straight pipe into a high-flow muffler with a 3 inch tip. my 300sd had three mufflers.
no bio in my area, have to run ulsd with marvel mystery oil for lubricaton. was using lucas, but
started puffing white smoke.
between changing exhaust, switching to amsoil 15/40 semi synthetic & k&n air filter i gained
4 mpg.

 

interesting. marvel mystery oil is mouse milk in a can? no pre-filters for k&n air filters?
have we been taken in by marketing hype?
also, beware of parts dealers with outrageous mark-up on parts on-line. $250.00 for one a/c
compressor hose? had my local shop make two hoses for $160.00, installed.
autohaus arizona seems to be the place to get parts.