I wanted to test the intercooler hoses, and sometimes with a problem like this if you take everything apart, clean it, and put it back together, the problem Goes Away.
Took off the inlet hose, the resonator and pipe, and both intercooler hoses. Turbo itself looks pretty kosher at this point:
After cleaning, bending, and visual examination, I pressure tested both intercooler hoses at 15 PSI using this setup. No leaks found. Note that this method is dangerous, those plugs can come out fast enough to cause serious injuries and an amusing *pop*ping noise, which is less funny when you’re bleeding.
The gasket on one of the hoses at the metal end was definitely a little looser than the other. In place they looked normal, but if I pinched each side and tried to slide them sideways with the same amount of force, the looser one stuck out about twice as far as the other. These might be a good candidate for replacement.
I discovered some damage on the driver side pipe coming down from the resonator. It’s *very* hard to tell if the deformation goes far enough into the pipe to effect the seal:
It *looks* like the seal is well past the damage, and even the flare at the base of the hose is above it:
The place where the gasket meets the cone is *way* above this join point. It seems to mate well when assembled and clipped. The good news is that pipe is only $80 new, which for a piece of Mercedes engine metal is pretty cheap.
There was no sign of the lost gasket. I was going to try to look into the intercooler inlet with a dental mirror and flashlight, but got distracted by family health issues. I replaced the gasket on the turbo-to-resonator pipe with a new one, removing the still-looks-fine old one. When I ordered 2 replacement gaskets, they sent me one green and one black. They were the same dimensions, in the same bag, and had the same part number.
I lubed all joins with fresh motor oil before re-assembly.
I verified there were no codes with my iCarSoft MB II before the first test drive. I got a low boost code stored (but not pending) less than two miles from the farm. I did a reset at a gas station, and was then able to drive another 12 miles under a variety of conditions, RPMs, and levels of driver responsibility and everything worked. This is exactly what happened after I did the hammer job on the resonator pipe, and the next day I was back to low boost codes after a few miles. I’m going to go visit my Dad in the hospital tomorrow, which will be a longer test drive.
Since I’ve verified that the two intercooler hoses are *not* leaking, I’d like to pressure test the intercooler with them hooked up. Hopefully this will allow me to hear hissing from the intercooler *without* having to take the bumper off. The problem is that the test plug that works really well for blocking the metal end of the intercooler pipe would be really hard to put a compressor nipple on, unlike the PCV that fits snuggly into the rubber end. There’s probably a tool that combines both functions already. If the boost problem continues, I may get one.