Hey there I've been having a problem with my C250 CDI W204 with getting a flatspot in 3rd gear and above between 3k - 4k rpm when im hard on the accelerator. The power only goes away for a second then comes back. The car has had the dpf, cat and egr removed from the system and has been remapped. To start with I thought it was the map so I got the remap removed and tried getting a map done else where. The car does run better on this map but im still get this slight pause in the high gears and high revs. Ive changed the MAP and boost sensors as the diagnostic computer was telling me I had faulty boost sensors. Had turbos inspected and came back fine. Also tried changing the engine relay as this was a fault coming up on the star diagnostics also. I Had it into the garage that remapped it the second time and had smoke tests done on the intake system and vacuum lines (no leaks found) and other checks done like having it on the dyno and checking for the turbo bypass valve opening at high revs and seems to be opening fully and nobody can seem to get their head round the issue. The tuner has also had the map checked and it all looks ok and was told these engines are bad for this because of the change over in the 2 stage turbo but surely in this day and age a twin turbo wouldn't cause this issue. Any help or suggestions are appreciated TIA
C250 CDI W204 Flatspot
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mersum1es
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I have read this problem from our local 'tuning wizard' (hello 'tuikku'), reason is exhaust pressure rises and it cause power surge around 3000rpm... of course he doesnt tell precise solution, but after all if tuner knows what he is doing, something can be done. Bypass valve opening is know problem.
Also twin turbo engine is infamous of high exhaust temperature which cause headache to tuners.
Also twin turbo engine is infamous of high exhaust temperature which cause headache to tuners.
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So you think the map needs tweaked?
mersum1es
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Yes. I am not sure how completely that bypass opening issue can be avoided, but at least what I read something has been invented around that feature... ask different tuning companies, thay must know the problem and make a deal you are not charged before you are happy with it.
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Theres no issue with the bypass valve as it is opening fine its just the flatspot I get when i get passed 3000 rpm. Been like this for over a year and it's been very frustrating. Also the power gain hasn't been that great either as it only got upto 230hp and was expecting about 240+
mersum1es
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You didn't read my post. Tuning rises pressures, rised exhaust pressure is causing bypass valve opening unintentionally, this usually happens around 3000rpm and cause boost pressure to drop. Tuning rate is limited by those originally high back pressures and high exhaust temperatures.
Gazwould
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Before it was mapped this was happening but the flatspot is only noticeable when the tune was installed
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You would think this wouldn't be an issue on a stock engine. I wonder if this was mercedes remedy to stop people tuning these engines
Gazwould
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Not an issue for me as it isn't felt out on the road .
Similar to my father's fwd Korean .
When tuned this got exaggerated .
Not felt out on the road either and tuner did live data to double check .
With much digging myself the dyno set up should of been on a linked bed which sees the rear wheels turning too , even though traction control systems get turned off and in our case a 'dyno mode' there can still be something not quite happy and pulling it back .
That's more modern vehicles for ya .
Similar to my father's fwd Korean .
When tuned this got exaggerated .
Not felt out on the road either and tuner did live data to double check .
With much digging myself the dyno set up should of been on a linked bed which sees the rear wheels turning too , even though traction control systems get turned off and in our case a 'dyno mode' there can still be something not quite happy and pulling it back .
That's more modern vehicles for ya .
