353,000 mile M3 now a Forum car

[CamasM3e93]

[CSBM5]

Originally Posted by Honda

What can cause broken valve spring?

Originally Posted by DrFerry

Metal fatigue, over rev, or both.

There have been many occurrences of valve spring failure on the S65 including cars in early life still under warranty, so I would throw in manufacturing quality perhaps also. Engine builders like Carbahn use non-OE springs just for the failure prone reason.

[lynn]

I had a misfire on a cylinder after doing valve cover gasket and oil filter housing gasket replacement. Turns out it was because I had loosened the injector rail on the right bank slightly that caused the injector o rings to unseal. That caused a fuel leak which reduced my fuel pressure for a cylinder in the left bank to misfire. And the fuel hose connecting the two banks had a leak in the metal crimping as well.
I'd look at fuel pressure like some have suggested if it's not coil related. If that's fine then it could be valve spring as others have said.

[nick3753]

Any updates?

[smmmurf]

Originally Posted by nick3753

Any updates?

Hi Nick, Thanks for bumping this thread! We are running into cost-prohibitive repairs, mostly related to the misfire and emissions fault, which must be done by a shop with a proper lift and specialized tools. We look forward to updating as soon as there is more progress!

[smmmurf]

It's been a month since our last update, but we bring good news! The car visited MRF again for a preventative DCT service. Malek was impressed at the general condition of both the engine and transmission given their mileage; they pull strong and shift smoothly, commensurate with far lower mileage units He also confirmed that the car isn't actually misfiring and narrowed the issue down to a bad idle control valve causing a slightly rough idle - the ECM throws a hard ICV fault (visible only in ISTA) which we missed during our own diagnosis. It appears to us that the ECM throws the cyl #5 misfire fault as a side effect of the bad idle and not due to an actual misfire. Replacement parts are on order and we'll update whether this fixes the issue for good.

We also replaced all spark plugs and ignition coils, both AFR sensors, and the exhaust ring gaskets due to a lack of history and the car's high mileage. The peeling valve covers were also replaced along with fresh oil separators. This combination of new parts seemed to help the idle a lot, significantly reducing the occurrence of the cyl #5 misfire fault and allowing the car to finally pass smog

While the valve covers were off, the VANOS covers were also replaced with Slon units. The original covers were so brittle, not a single cover survived the removal process intact.

We plan to tackle a replacement of the oil filter housing gasket next. Otherwise, the car is healthy and ready for many miles to come!