janas

I have a problem with the M273 5.5L engine, which I have been trying to fix for over 2 years. When cold (the cooler it is, the more visible this problem is - the best during winter), the engine hiccups. I recorded a short video of what it looks like (this shot was taken before MAF replacement but it didn't help). A weird sound of "knocks" can be heard. Each knock reduces the revs. Strangely enough, when the oil temperature (I have the AMG menu installed) exceeds 40-50 degrees Celsius, the problem disappears. You can start the cold engine and it is visible at idle speed or rev the engine to 2-2.5 rpms and when it drops to idle this hiccup appears for approx 1 second. When the engine is warm it no longer happens and the engine is running smoothly. No check engine, no errors in SD, nothing. What has been done:

• software update of all modules including ECU (2020)
• new lambda sensors pre-cat
• new lambda sensors after cat
• new MAF
• new throttle + gaskets
• intake manifold disassembled, washed, new sealing
• new spark plugs
• new injector O-rings
• throttle adaptation
• TEC2000 Fuel Injector cleaner

All brand new Mercedes-Benz OE parts purchased from the authorized dealership. Oil changed approximately every 10,000km, currently 211,000km mileage. The engine was not disassembled or repaired apart from what I wrote. Ran on a dyno, 0-100 measured using Racelogic and it keeps original values. I have no idea what can it be or how to diagnose the problem. Please help.

CaliBenzDriver

You state your engine hiccups mostly on cold weather conditions, right?
Zero faults are available... time to read data then!


I am going to be honest, i did not hear any hiccup - Instead I heard your engine sounds real good & smooth & healthy. That means good bores, rods, pistons and valves. I can guess it does not feature amazing oil solenoid !!!👍

- What engine tests have been done already?
- What are both Trims LTFT B1,B2 ? (unbalanced?)
- What are fuel pressures (new filter?)
- How about misfires during hiccups?
- Is temp sensor trustworthy??

Scenario : cold engine is lean
Trims are forced rich ??
cold mixture gets momentarily too rich during warmup.


we need hard data to quit throwing parts at this:
We assume "new parts means no problem" but we have plugs only, no coils, no boots and misfire are not reported so we want to believe "ignition is good" thus it is fuel.... that's unproven.
Fair assumptions are backed by data.

S-Prihadi

Get a Xentry or its equivalent.
See the intake and exhaust valves VVT values from stop to start to smooth running. Its achieved degree and commanded degree.
Use the scanner or laptop screen record function.

There could be possibility that your VVT is "lazy" when oil is cold and thick and that upset the AFR

While at it see engine SMOOTH running feature of Xentry. This can tell which cylinders or banks which are the most unstable in its piston speed variation and that makes
engine not smooth.

karols500

Witaj, mam taki sam problem, udało się coś z nim zrobić zdiagnozować?

Afa

finally i get a reader, this is the codes i got

CaliBenzDriver

Ouch, that's a lot of cylinders misfiring, all at the same time - Check fuel pressure data with the scanner.