MISSFIRE from Carbon build-up around valves (PICTURES)
My car is currently undergoing decarbonisation - the dealership reckon it is a mixture of cheap fuel and driving style (I use it for Driving Instructing) that has caused it to clog up around the valves.
But the thing is - this also happened on my previous engine (which was replaced under warranty due to excessive oil use) which was then cleaned under Warranty.
The first engine was decarboned at 20k miles the new engine is now on 50k miles.
Any thoughts or does it sound familiar to anything you've had?
Last edited by Union Jacks; Feb 26th, 2010 at 09:06 AM.
They said driving style (me using it for driving lessons) and low quality fuel was the cause
I guess 7 hours a day driving gently then in between that me driving flat out wasn't enough to shift any gradual build up - as you can see its "caked" on hard!!
What I don't understand is - if the fuel doesn't go through the inlet valve anymore in these GDi engines (gasolene direct injection - because its directly injected into the cylinder) how come there is a build up on the outside of the inlet valve where only air comes through?
is it maybe breathing hard and taking oil back round and that's actually the build up?
Yes any petrol station or supermarket i'm nearest to - but mainly it was Tesco UL and Tesco SUL - exactly the same fuel that the MINI Dealership fill all their cars up with - although they advised me that I shouldn't use Tescos!!!!
this is the second engine that has been decoked - the first engine which was replaced under warranty at 36k miles for excessive oil use was decoked at 23k miles.
Anyway, the dealership has guaranteed me that "aslong as I only use Premium fuel from now on it will never happen again" - so that's what i'm gonna do.
do you reckon they'll give me that statement in writing?
there is a fuel additive called BG44K on the market at the moment,and although i dont agree with these additives this one does what it says on the tin, i got a tin from kwik-fit and put it in the mrs car,it was running crap and after 150 miles the results speak for themselves,i removed a sparkplug before and after and the pistons looked like new,nice and clean and the car runs sweet as a nut,it says it lasts for 10.000 miles,it cost me £20,could be worth a try for you in the future.
When I had the cold start rattle fixed, they mentioned I had significant build up as well, and did the cleaning as a warranty service. They didn't mention that it was related, but they also replaced the valve cover at the same time- turns out that the old version allowed excessive oil vapor through the PCV system. If I remember correctly, the newer valve cover started showing up in new builds around March 2009.
Most theories at NAM attribute the build up to the valve cover, DFI (and the lack of fuel in the intake to wash the backside of the valves) and the long time between oil changes.
Some of the guys on NAM are right in that, the positive crankcase ventilation (pcv) valve allows this contaminated gas back into the air intake as it is designed to do, however over time this valve can become sticky and/or clogged from heat and oil degradation, this can then lead to very very fine droplets of oil finding their way into the air intake, this then settles in the intake runners and on the back of the inlet valves, with nothing to wash the intake runners and the back of the valves (fuel) then the fine oil deposits are subject to huge amounts of heat (with no fuel wash) and subsequently this then over time builds into the carbon.
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Hi people im a newbie so please make allowances for a lack of mini knowledge but i think im right when i say that these engines are direct injection so any fuel additives or different grades of fuel will not affect the amount of carbon deposited in inlet ports or on inlet valves it will clean the cylinder and exhaust ports only
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