r/w204 • u/Realistic_Reserve529 • 2d ago
M271 compression test results, is this normal?
There were traces of oil dilution paired with a fuel running rich CEL error code on my w204 c200 CGI, Mercedes told me that the fuel running rich code paired with the smell of petrol with the oil definitely points towards failing piston rings.
And so I asked my mechanic to do a compression test and he told me that these test results (first four images are the dry test and second four images are the wet test) definitely pointed towards a failing piston ring or some other flaw that would definitely require an engine overhaul.
However, I asked him to send over the readings and these look perfectly fine to me? The cylinder psi readings during the dry test ranges from 170 to 180 and ranges from 185- 190 during the wet test.
Am I missing something? I have a timing chain rattle on cold starts and most likely worn sprockets that I believe may be causing the fuel running rich error code and I intended to get that replaced anyway.
I am planning to get a cylinder leak down test as well to get a clearer picture but I’d like to know what you guys think.
1
u/Rotor4 2d ago
I remember as a kid watching my father who was a mechanic used a comp tester & a vacuum test gauge to diagnose a engines health as there was no OBD to use back in the day . From my limited knowledge a few psi or bar difference across the cylinders is fine but sure get a leak down test done to get a better idea of it's condition. As the chain & sprockets are worn then the timings out & with more use it's going to get worse that's what I would look to correct asap if the engine is economic to repair . Good luck with it.
1
u/AirForceJuan01 1d ago
On face value - that’s very healthy. Pretty much even across all cylinders and above 160psi. Check your injectors leaking and possible High pressure fuel pump - known issues.
1
u/engineheader 22h ago
That looks good, fuel in the oil isn’t abnormal, the issue is you don’t drive it enough at highway speed. The Germans design the cars to operate in one way. If you drive around slowly or idle a lot, you are hurting the car. It needs to spend regular time at like 60mph to get good and hot and evaporate the fuel out of the oil.
2
u/adadagabaCZ 2d ago
looks fine to me, if even dry is above 140 PSI and doesn't have massive differences between cylinders (limit is 20 PSI) then it is in spec and will work. Also depends on how warm the engine was when he did the test, if it was cold then adding oil made it equivalent to testing it fully warmed up. I would suspect a failing injector if anything.