I've had my engine replaced (under warranty). The original engine would skip/sputter sometimes when I tried to accelerate faster than usual. I was told this was the chain tensioner being loose. They tightened it, but it would still skip, mind you less often. Now with this new engine, I haven't had that issue....until this week (about 5,000miles on the new engine). The problem occurs in gears 4-6 at low rpms (2000rpms and up approx) with about 3/4 to full open throttle. It will sometimes happen at highway speed (6th gear 3000rpms and up) as well.

Is the chain tensioner something that will forever haunt my Mini? Has anyone ever had this same problem and had it resolved? Or is it not even the chain tensioner?

 

Any CEL codes coming up? Instead of trying to second guess this, I would drive it right back to the dealer and show them what is happening. This should not be an ongoing problem after you had the new engine put in, unless it is an older engine with the original faulty timing chain tensioner. Just my opinion.

 

It's a new chain tensioner since its a new engine (or at least I hope so). The CEL flashed for a brief second yesterday when I had to accelerate harder on the on-ramp to a highway and it did its skip/sputter. I don't have a CEL at the moment. I'm bringing it in to the dealer today to have a maintenance check-up anyway. I'm just upset that this was an issue on the old engine, and now it seems like an issue with the new engine. Wasn't sure if this was something everyone experienced or if I just have bad luck or if the dealership mechanics don't tighten the chain/belt properly

 

New engine, but maybe the old style tensioner. Did not mean a used one. :(

 

No worries. I just don't want this to be a reoccuring issue. Once I start throwing my upgrades on the car I would hate to be constantly anxious if the tensioner is going to work or not. I only drive this thing hard maybe once a month for about 20mins tops so I know it's not an issue of abuse to it. The car rarely reaches 4500rpms.

 

What grade of gas are you putting in and from what stations?

 

Keep us posted to what the dealer finds out.

 

I put in 91 octane (highest in Colorado). I only going to Shell or 711 since those are closest to me.

 

Almost sounds like a intermittent problem with a coil pack or spark plugs / spark plugs wires...

 

So apparently the gas stations in Colorado put something in the gas for cold weather conditions during the winter and so that was the cause for my issues. It explains why my CEL flashed for a second since fuel mixture was the error code I got. I was told a lot of turboed vehicle owners have this issue in the winter, not just Mini owners. Fuel/ignition cleaner should do the trick. I'm also throwing some octane booster in just to be certain.

 

Well keep us posted.

 

The Mini dealer (Momentum Mini) I deal with said the ethanol in the gas causes the carbon build up!

 

The R56 series cars have a "dry" intake manifold, meaning no fuel passes through it, due to the direct injection. Direct injected BMW engines share the same design. The big benefit of the direct injection is much better fuel regulation and thus improved fuel mileage. The big downside is carbon buildup on the back side of the intake valves. The turbo cars always have a lot of oil passing around the intake tract and when it recirculates into the "dry" intake via the PCV system, the oil droplets hit the hot intake valves and turn into carbon, steadily increasing until the carbon deposit on the back side of the intake valve is so big, air cannot pass into the engine.

 

Very cool! Thanks for the clarification.

 

Here is a before and after pic.

 

Wow! Glad I had mine cleaned out. Also had new fuel injectors installed at the same time. All this while the dealer was trying to get to the actual culprit, which was the high pressure fuel pump.