Hey guys, hoping for some suggestions on troubleshooting whether or not I have a failing turbo on my 2007 MCS.

Issue I'm seeing is that intermittently I'm maxxing out at ~5-6 PSI under heavy or full throttle (I'll usually see 12+ under heavy throttle). I'll start out in the morning everything running fine, stop at the gas station on the way to work and after setting off again I've got limited power. Sometimes I have limited power from a cold start, sometimes it will act up in the middle of driving.

Not getting any CEL or limp mode indicators, just no power. I'm pulling my readings off my Garmin ODBII interface. The other thing I noticed is that on my MAF sensor, air intake was maxxing at 2.5 oz/sec when having issues and it easily pushed 4 oz/sec+ when full boost was working correctly.

I thought it may be the MAF, so I cleaned it this past weekend (with the proper MAF cleaning spray) and ran great for the first trip after but the issue still persists. I'm planning on tearing apart the intake this weekend to check for leaks (Alta intake and hot/cold boost tubes) and check the cold side turbo impeller for play in the shaft or damage.

Any other thoughts on things to check or possible causes? Any help is appreciated.

 

First point of call is to check the diverter valve. A leaking and failing DV can cause the symptoms you describe, and does not necessarily always trigger a light or cel.

 

Sounds exactly like my issues. I haven't gotten my car back from the dealer yet, but they ended up replacing the turbo. Apparently that fixed the problem, but right afterwards, an idle issue popped up and they have spent the past month diagnosing it with no success.

Be prepared for a long, frustrating mess.

 

Well, I checked and retightened all the boost tubes, things looked fine there. Cold side turbo fins looked clean and there didn't seem to be any play in the shaft. I pulled the diverter valve and the diaphragm and action seem ok (I had replaced it about 6 months ago). Cleaned the MAF again. Took a quick spin around town with a few stops for gas and a car wash, boost seemed to be building fine, got a clean 12PSI at WOT. Did a little "italian tune up" on the highway after she was good and warmed up and she seemed a little hesitant at high RPMs, I pulled a spark plug and they look pretty eaten up so I ordered a fresh set, hopefully that will help the high end some. I'll have to wait and see if the issue pops up again next week while commuting. Hoping it might just be a flaky MAF, not a cheap fix, but cheaper that a new turbo.

Jahan, how many miles do you have? Carbon issues on the intake valves can cause a lot of CEL/idle issues. I had mine scrubbed earlier this year (around 75k miles) and it made a world of difference.

 

Depending on what you mean by 'she seemed a little hesitant at high RPMs' That could be normal operation for the "S" turbo. They do run out of punch once you get up to higher RPMs. Even with a good tune, they drop off a little. Its a small turbo, so these things shine when in low and mid range RPMs.