[heraldhamster]

the '09 had a broken exhaust flex pipe that I was unaware of for several weeks. yeah, yeah, I know, but it's a commuter car and I'm not under it all the time and it's been SO reliable we count on nothing ever going wrong with it.
when I found out, by the exhaust tip melting a half-moon hole in the bottom of the plastic valance under the rear bumper... I attempted to clamp the frayed steel braiding back to the lower elbow (top of the muffler). and suspended the whole muffler by a piece of tie-wire. all this only until I could get a stainless exhaust for the '14 and put the '14's exhaust on the '09.
well after a couple of weeks being parked in the driveway (we bought a Crosstrek she's been driving) it wouldn't start.
had it towed to the local MB shop who claims they're smart certified (is there actually such a thing?) and he says cylinder wash.

could this be caused by improper exhaust back pressure fouling the O2 sensor and causing it to run rich, thereby washing the cylinder walls?

any info is appreciated.

Thanks in advance.

p.s. we're thinking about sending this one on it's way and buying a later model with less miles.
so, possible we may have found the end of "cost effective" life...? I hope not and wouldn't/didn't expect it, but...

 

[Igor Barbaros]

How did they determine that? Did they take the engine apart and inspected the cylinder walls?

 

[mvaldes]

FWIW, I discovered the broken flex pipe about a year ago on my '08 in the same manner....the melted half moon on the valance. (The noise increase had warned me of an exhaust problem well before the melt. But, you know the story, the flex pipe was my guess but I was busy and hadn't gotten around to pinpointing for the problem.) Anyway, I continued to drive it daily for the next few weeks until I could get a replacement muffler and it's been fine ever since. Also, long before that, I had a noisy DTH exhaust that slowly got louder and louder to the point that my wife notices that our dogs could hear me coming home from many blocks away! The bottom of the muffler can was completely rusted out to the point where there was no bottom to it at all. I drove it for months like that before I had time to put the OEM one back on. (Amusing side story, smarts were new enough and scarce enough at that point that it passed inspection like that!)
The short version of this long winded note is that I think you can safely rule out a lack of exhaust back pressure as the culprit.

 

[heraldhamster]

Igor, evidently when the mechanic removed the spark plugs, he used a borescope the inspect the cylinder walls which were dry. Upon oiling the cylinder walls through the spark plug holes (& replacing said spark plugs) it changed the situation to the point the car would start.

When tested following the oiled cylinder walls & running, it is reading 150psi on all three cylinders. Not optimal, but it is 10 years old w/150k miles. While they're in there I had them do a valve cover gasket/O-ring replacement as I found oil inside the spark plug wells. The youtube vid I watched on a smart valve cover job got me thinking I didn't wanna get into THAT. As; 1) I don't have an indoor shop, & 2) I'm not as bendable/flexible as I once was to get contorted into spots like that.


Thanks mvaldes, good to know.

Putting a stainless exhaust on the '14 today & gonna put the '14 exhaust on the '09 (pretty sure they're same, right?)