Vehicle: 2012 Mercedes-Benz C250 Sport w/1.8L M271Evo Turbocharged Engine.
This car belongs to a buddy of mine. He was experiencing long cranks (2-3 sec to start) and a check engine light (CEL). When the engine finally started, there was a loud clatter for several seconds. When scanned, the fault code was a P034062. Since my buddy was planning to sell the car, he had to fix the issue in order for the car to pass the CA Smog Inspection (CEL is an automatic fail); you cannot sell a car in CA that does not pass smog inspection unless it is being sold as a non-operational vehicle.
After some initial testing and research, the issue was isolated to the intake camshaft adjuster (phaser). My scan tool was unable to perform the cam adjuster test so I sent the car to the dealer for diagnosis (1hr - $198). The dealership returned with the same diagnosis but recommended replacement of both cam adjusters (intake and exhaust). The dealer's estimate was $5600. After some additional research, replacing both adjusters is standard practice when addressing this issue. I took some pictures of the repair process below:
After removing the air intake hose (a $216 hose w/sensors that crumbled when touched), drive belt, alternator, thermostat, p/s hard line and valve cover, we are left with this:
After setting the crankshaft to TDC and taking a closer look of the intake cam adjuster (the failed one), we can see that the mark on the camshaft (middle mark) no longer matches up with the reference arrow. The camshaft timing is noticeably advanced. Apparently, this indicative of a worn/failed camshaft adjuster.
At this point, I removed the one-time use timing chain tensioner and attempted to install the hold-down tool
. Since the intake cam was obviously advanced, I tried to manually move it back to its correct spot and install the tool. This worked (barely) but I was still unable to install the tool on the exhaust cam.
Let's take a closer look at the marks for the exhaust cam and exhaust cam adjuster:
From an initial look the exhaust cam adjuster appears OK. But as it turns out, the exhaust cam was slightly retarded. So even though the exhaust cam adjuster was not displaying any faults, there was some slight wear on this adjuster as well and perhaps this is why dealers often recommend replacing both adjusters at the same time. And both adjusters have gone thru multiple revisions. I sent these pictures to a few trusted contacts and all of them suggested replacing both adjusters.
Now let's revisit the marks after the adjusters were installed, new tensioner installed (and extended), and after the engine was spun-around several times.
Intake Camshaft Adjuster:
As you can see, the middle mark is now where it should be.
Exhaust Camshaft Adjuster:
Not a huge difference compared to the "before" picture, but this was enough to allow the cam locking tool to just drop into place.
Here is a picture of both new adjusters installed:
The at the 3 o'clock (exhaust) and 9 o'clock (intake) sprockets do not align perfectly. I have seen pictures of these marks aligning
with a new chain. So, I think the chain in my engine has some wear. Since the tensioner was not fully extended and there were no cam/crank correlation codes, I skipped chain replacement at this time.
Here is a picture of the engine after being fully reassembled, minus the engine cover:
List of parts used:
After bleeding the cooling system and the p/s system, an oil change was performed. Codes were cleared and the car was test driven. The fault codes did not return and the engine started up normally without any abnormal rattling sounds.
I decided to keep the car for a few days to do an extended test drive. After 140 miles of perfect operation, while merging onto a highway, the car went into limp mode and displayed a severe lack of power at high RPM's. I made it back to the shop and found a P000277 and P061A22. After some research and testing, it appears that the high pressure fuel pump decided to fail. This is not an uncommon issue with these engines, either. I will make a separate thread for that repair.
This car is currently for sale in case anyone is interested: https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/5154182/fs-2012-mercedes-benz-c250-sport
- The Critic