Mercedes W204 OM646.811 hesitation on acceleration at high revs

[dan_mac]

Hi friends,

Hi have a Star Mercedes C220CDI 2008 with engine OM646.811 and a few days ago, when i accelerate hard, around 3500rpm, i feel a slight hesitation for about 1s, like a deadspot, and then it goes normal but it repeats constantly at high revs!! No error light in dashboard neither no CDI errors at Mercedes Xentry !! The values of fuel and the Y94 valve are Red, i don't know if the problem is there!! I think that the Injection Volume is lower too! I feel a little rpm fluctuation too at idle!
Does anyone have an idea of what might be?!
Attached images of Xentry Values

I'm from Portugal, sorry my English!
Many thanks

 

[mattkh]

i feel a slight hesitation for about 1s, like a deadspot, and then it goes normal but it repeats constantly

Your English is good.
We call it a flat spot.
How often does the flatspot repaeat itself, every 2 minutes, every 5 minutes.........?

 

[alexanderfoti]

None of those values seem bad, as some others are outside of the range they expect. I would think its a misfire, but hard to say without driving the car, is it possible to get it on video, or is too small?

 

[dan_mac]

i feel a slight hesitation for about 1s, like a deadspot, and then it goes normal but it repeats constantly

Your English is good.
We call it a flat spot.
How often does the flatspot repaeat itself, every 2 minutes, every 5 minutes.........?

Hi mattkh,

The flatspot repeats always at high revs, over the +-3500rpm, more often if i leave the gas pedal and then kick it down again!!

Thanks

 

[dan_mac]

None of those values seem bad, as some others are outside of the range they expect. I would think its a misfire, but hard to say without driving the car, is it possible to get it on video, or is too small?

Hi alexanderfoti,

I doesn't have any video driving it... i will try to do one! Once had a similar problem on the Star, more less 4 years ago, but at that time it gave an error on the CB!! That time was the Fuel Temp Sensor that was replaced... but in the workshop they replaced it with an oem, not a Original one from Mercedes!

Thanks

 

[mersum1es]

heh, I answered you on US forum... but I put my advice here too: check all temperatures after overnight, all should give same ambient reading.

High fuel temp will reduce injection, and FQV control/fuel mm^3 could be simply that.

And see what temps are at full throttle test.

 

[dan_mac]

Hi,

I replaced the Fuel Temperature Sensor but the values didn't change at all!!!!
Any sugestion?!

Many thanks

 

[mersum1es]

so you fuel is actually warming... That could be due to leak somewhere, or insufficient cooling.

Did you make the SDS full throttle test? What are temps there?

Also lets not forget that we don't know for sure, which is causing you hesitation, it is clear that some values are slightly off, but their effect is not clear.

 

[dan_mac]

so you fuel is actually warming... That could be due to leak somewhere, or insufficient cooling.

Did you make the SDS full throttle test? What are temps there?

Also lets not forget that we don't know for sure, which is causing you hesitation, it is clear that some values are slightly off, but their effect is not clear.

Hi mersum1es,

The full throttle test is driving the car at high RPMs?! I will check that and then i say something!

Thanks

 

[Stability]

In the - List of guided tests section
Is smooth running listed ?

 

[dan_mac]

Hi friends,

Updates but the problem persists... i changed the Bosch MAF sensor (MAF+MAP) and the Y94 FQV and nothing changed!! @mersum1es I already did the Full Throttle Test and the values seems normal!
It seems to me that the flat spots only occur with hot engine over the 2500rpm and only in 4th,5th or 6th gear... in 2th and 3th gear i didn't feel any cuts!!
A friend of a friend of mine that works in Mercedes told, without any test, to replace all the 4 Delphi Injectors but i'm afraid to waste a lot of money and after that the problem continues!!
Any sugestions?!!

Many thanks for all

 

[alexanderfoti]

What is intake air temperature and boost pressure showing in 4th at that rpm, that is around peak boost that you are experiencing the issue.

 

[dan_mac]

What is intake air temperature and boost pressure showing in 4th at that rpm, that is around peak boost that you are experiencing the issue.

Hi @alexanderfoti ,

The first image i have shows that at 3323rpm the Intake air temperature was 43.3°C and the Boost pressure 1.436hPa!!

Many thanks

 

[alexanderfoti]

Can you take a video of this hesitation?, as I am not 100% sure what symptoms you are describing.

 

[dan_mac]

Can you take a video of this hesitation?, as I am not 100% sure what symptoms you are describing.

When it's on hard acceleration, Over the 2500-3000rpm the RPMs drops about 1second and then go up again...it continuos doing this until the redline!
I will try to do a video with this!

Thanks

 

[dan_mac]

@alexanderfoti , the images of the Boost pressure that i put in the back answer i think that was with the car stopped... The values while driving the car at the Full Throttle test shows a Intake air temperature of 17°C and a Boost pressure of 2.014bar at 3323rpm!

Thanks

 

[dan_mac]

In the - List of guided tests section
Is smooth running listed ?

Hi @Stability ,

I don't see that Test on Xentry, i found that test searching on the Internet but always on DAS!!

Thanks

 

[dan_mac]

Can you take a video of this hesitation?, as I am not 100% sure what symptoms you are describing.

Hi @alexanderfoti ,

Here's the video with the hesitations after the 2500rpms!!

Watch Hesitation on acceleration | Streamable

Watch "Hesitation on acceleration" on Streamable.

streamable.com

 

[mersum1es]

Your fuel temp is still over range, that will reduce injected fuel amount. Does it feel like hesitation, I don't know.
You could log curves of temperatures, injected fuel and boost during that hesitation (not sure where that page is in xentry, in DAS it was found in developer).

Edit: it just came up my mind, OM651 doest that when two stage turbo is reaching high boost to fast, it should not be OM646 problem but phenomenon would do the same effect.

 

[Doug1234]

I have had a not to similar flat spot I posted about my Jeep having sticking turbo vanes in this thread

OM642 Turbo Cleaning or Refurb?

Hi all, I'm working on a 2007 CLS and would appreciate any thoughts on this please. I'm in the middle of a turbo repair, the plan was to get the actuator refurbished and clean the vanes with a kit. Because removing the exhaust outlet went so well I'm thinking about cracking on and removing...

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