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Discussion Starter #1
As title suggests i have a flat spot at 2800rpm , all gears. Its very slight. Is this characteristic of the multiair

Thanks
Andy
 

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Nope. Apart from a bit of hesitation on a rolling start, there should be no flat spots at all.

Try giving it a tankfull of high ocane fuel and see if it goes away. If not, when was it last serviced and has the air filter been replaced recently?
 

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Discussion Starter #3 (Edited)
Nope. Apart from a bit of hesitation on a rolling start, there should be no flat spots at all.

Try giving it a tankfull of high ocane fuel and see if it goes away. If not, when was it last serviced and has the air filter been replaced recently?
Hi ransoman, yes the car was serviced a couple of weeks, few days before i purchased the vehicle. According to the dealer it was the timing belt service, oil looks clean but is high (maybe too high) and have not checked the filter yet

I understand that too much oil is bad on the multiair and i will get that sorted, tbh i cant really figure how high cause the dipstick is hard to read and the clear oil does not stand out that well....Could be oil smearing higher though.
 

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Discussion Starter #5 (Edited)
Bit of a development i hope, i was coming off a roundabout in 3rd gear and at the rev range where the flatspot is i heard what sounded like a dump valve hissing type sound, and boost seems to drop 1 or 2 bars momentarily.

I never heard this before because my windows have always been closed, but with it being a nice sunny day i was able to hear it.

Could it be that i am loosing boost at this rev range and if so do you think its maybe a fault with the wastegate....hopefully i could adjust the pre tension.????
 

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Discussion Starter #6
Had it bck at the dealer today and they said there was about half a litre extra oil and there was high oil pressure so he said try it and let them know if its any better

But the car is still the same. Not sure if its just hessitation or a misfire, maybe if i explain the symptom someone could possibly help define what to tell the dealer what it is

If i hold 2000rpm in 3rd gear then accelerate the turbo kicks in fine boosts ok then at roughly 2500rpm its as if i loose all boost momentarily then is fine until i change gear and the flatspot, boost loss happens at 2800 in 4th.

Sometimes it happens at different rpm dependent on load.

If for example i go to 5000rpm in 3rd and change into 4th the flat spot is there as soon as i engage 4th.

Its not like turbo lag because the turbo kicks in then it loses boost soon after.

Any help on this would be greatly appreciated
 

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I suppose you can show the boost pressure graph i D like on a QV ?
If yes, check if boost drops when the engine hesitates
 

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Discussion Starter #8
Hi leo the boost does drop in 4th and 5th by 1-2 bars at the flat spot area. Mostly the higher gears still hold all bars, but the flatspot hessitation is that quick the boost bars might not be quick enough to respond to it
 

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Sounds like turbo or more likely: turbo controls

I would try to disconnect the small tube to the dump valve actuator and see if that makes a difference.
If not, then the problem is mechanical and in turbo (or dump valve).
If yes, then there is some signal telling the dump valve to release exhaust pressure. I'm not sure what to do about that, but it must be a good step to find out what causes this flat spot
 

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Discussion Starter #10
Thanks Leo, seems to happen at any rpm under 3000 depending on load and gear. I think it does it when it would be reaching its max boost/torque. Most occasions i can hear a clicking when i have the window down....on one occasion i thought i heard the boost sound but may of been imagining that.
 
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