Mercedes V6 OM642: Misfire Troubleshooting

Hello everyone,

I have a question about an OM642 engine in a friend's Viano.

The engine starts, after a somewhat longer idle time, and potentially more noticeably in combination with colder temperatures, but not on all cylinders.
With a little bit of encouragement, the rest will quickly join in.
Ansonsten völlig unauffälliger Motorlauf. Lperformance is available.
Attached is an LL (Low-Level) idle speed regulation assessment from StarDiagnose. In my opinion, it also looks completely fine, doesn't it?

What would you check next?


Mileage: 200,000 km.
Error memory is empty.
Excellent maintenance condition.

Thank you!

Hi,
How about the spark plugs?
During the test (is the engine warm?), at least five cylinders are performing well, while one seems to be slightly weaker.
hg
Herbert.

Hello!
The glow plugs have not been checked yet. Do you think a faulty glow plug could cause such effects at temperatures above 0 degrees Celsius?

During the test, the coolant temperature was 59 degrees Celsius, according to the log.
Maximum deviations can be up to ±5mg per dose, which is different from Volkswagen's standards, but that seemed acceptable to me.

Hi,
Perhaps he uses the glow plugs to start the engine and also lets them run for a short time afterwards.
You should observe the idle speed immediately after starting the engine. In the test you performed, the engine was already warmed up.
hg
Herbert.

brezelmann01 wrote:

Hello! The glow plugs have not been checked yet. Do you think a faulty glow plug could cause such effects at temperatures above 0 degrees Celsius? During the test, the coolant temperature, according to the protocol, was 59 degrees. Maximum deviations can be +-5mg per injection, which is different from VW, but that also looked quite good to me.

Well, just because Mercedes-Benz states something doesn't mean it's necessarily true. Volkswagen also says that 1 liter of oil consumption per 1000 km is still within the acceptable range.

"Percentage-wise, relative to the target amount, approximately +/- 60% of the energy used is recovered at the crankshaft. If this were acceptable, I wonder why the injectors need to be programmed into the engine control unit."

In this case, the difference between the worst and the best result is only 15%, so I would first check the spark plugs. Especially in Sprinter and Vito vans, they are often left in for too long... it's not always easy to access them.