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      01-25-2016, 03:39 PM   #1
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328i feels week, lower fuel economy...why?

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Hi all,

Over the past couple months I've slowly been noticing my car start down a path where I feel like I'm losing power and fuel economy as time goes on. I have about 42k miles on my N26 right now, and while fuel economy losses can be attributed to winter blend fuels, I've been noticing that the car just feels like it's "straining" for lack of a better word. Like, I'll be driving at 60mph on the highway, and there are times where I feel like the car is almost itching to upshift, or that I really need to give it more gas just to maintain speed. I really do believe something is going on too - last year, on average I would probably show 420 miles until empty after a fill up during the winter. This year, I'm lucky when I hit 400 - usually around 380-390.

Any thoughts on what could be going on?
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      01-25-2016, 08:14 PM   #2
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It is interesting that you posted this. My 328i N20 is pretty much a few miles away from 42k as well and I have been getting the same sense from my motor for the past couple of months. It is 3.3k away from a maintenance service, so I chalked it up to a maintenance-related issue. Most likely ageing spark plug (?). The car has also started stalling on cold start in reverse if I don't let it sit at least 20-30 seconds before pulling out. My mpg has dropped by about 2-3 compared to the same time last year.
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      01-25-2016, 11:58 PM   #3
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Do you ever drive your car hard? I would recommend giving your car the "Italian tune up." Take her out and open her up. At 42k, I'm pretty positive that carbon is starting to build up on the valves and slower her down.
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      01-26-2016, 02:01 AM   #4
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Originally Posted by Labeef View Post
At 42k, I'm pretty positive that carbon is starting to build up on the valves and slower her down.
I don't drive too hard. I suppose a walnut blast is due?
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      01-26-2016, 07:57 AM   #5
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Do you have a baseline dyno on the car so you can take it back and make some relative comparisons with ?

I always recommend owners who care about their performance get a baseline done. More for a situation where the car gets worked on and then feels like something wasn't put back right. You have a way to test and prove they didn't do it right. (has happened to me)


As Labeef states it can just be carbon build up over time, as noted on some DI engines, that reduces output power. Have you only done the recommended maintenance on the car, as in BMW's oil change intervals ?
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      01-26-2016, 10:31 AM   #6
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Yes, only BMW recommended services at this time - though I do game the system to get them done earlier than normal (ie, taking in for an unrelated issue with around 2k to go to get it done early, etc).

I do drive it hard at times - my daily commute consists of a pretty heavy merge onto an interstate that I have to punch it almost daily. It's at the dealer now for a couple of other things as well as to have them look at this issue as well. We'll see what they say.
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      01-26-2016, 11:28 AM   #7
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Unfortunately, Direct Injection (DI) engines are prone to forming oily carbon buildup on the intake valves, and this progressively degrades engine performance over time, especially with the poor-quality gasohol being passed off as fuel in the US. This sounds like what you’re experiencing. Expensive intake valve and cylinder head carbon cleaning isn’t a matter of “if” but “when” with BMW’s DI engines. Despite the degraded engine performance and added maintenance expenses, at least BMW’s engines are rated for a couple of extra MPG when the engines are brand new (when tested under controlled conditions with “real” gas that most Americans can’t even purchase at their local gas stations). So that’s worth something!
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      01-26-2016, 12:51 PM   #8
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Originally Posted by Outlaw 06 View Post
Unfortunately, Direct Injection (DI) engines are prone to forming oily carbon buildup on the intake valves, and this progressively degrades engine performance over time, especially with the poor-quality gasohol being passed off as fuel in the US. This sounds like what you’re experiencing. Expensive intake valve and cylinder head carbon cleaning isn’t a matter of “if” but “when” with BMW’s DI engines. Despite the degraded engine performance and added maintenance expenses, at least BMW’s engines are rated for a couple of extra MPG when the engines are brand new (when tested under controlled conditions with “real” gas that most Americans can’t even purchase at their local gas stations). So that’s worth something!
I hear you on the crap gas. That's why I go to Top Tier gas stations only, for a guarantee of better detergents. But I'm still subject to the E10 crap and there is no way around it. It's funny how they can still call it "Premium gas" and not "E10 Premium gas" or something. In Europe they have to call it what is it and you still find the regular gas. But gas is also 4x the cost over there. But none of that matters to the rednecks driving their F150
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      01-27-2016, 01:22 AM   #9
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Quote:
Originally Posted by marlin2911 View Post
It's at the dealer now for a couple of other things as well as to have them look at this issue as well. We'll see what they say.
Please let me know what they say. Might have to apply the same to my car. I don't anticipate going in for service for another 2-3 months, but I might go in to get it checked depending on your response.
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      01-27-2016, 01:54 AM   #10
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Quote:
Originally Posted by adhrp View Post
Please let me know what they say. Might have to apply the same to my car. I don't anticipate going in for service for another 2-3 months, but I might go in to get it checked depending on your response.
If you haven't been in for awhile, it could be software related.
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      01-27-2016, 10:33 AM   #11
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So got the car back...they did a litany of tests, but nothing came back as wrong.

So here's the weird part though. There was a recall for the thermostat (SIB 11 10 15), which was done while my car was in. They cleared the fault memory along with this. The car feels different now - much more linear in its power delivery, and no longer feels like its "struggling." I've also noticed that the engine oil gauge now moves beyond the 1/4 mark, and will fluctuate during driving - previously, it would just stick at a mark a little before the 1/4 mark, and that was it. So while they found nothing, the recall on the thermostat has made a change in the car for the better...not sure what this means haha.
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      01-27-2016, 12:13 PM   #12
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Quote:
Originally Posted by marlin2911 View Post
So got the car back...they did a litany of tests, but nothing came back as wrong.

So here's the weird part though. There was a recall for the thermostat (SIB 11 10 15), which was done while my car was in. They cleared the fault memory along with this. The car feels different now - much more linear in its power delivery, and no longer feels like its "struggling." I've also noticed that the engine oil gauge now moves beyond the 1/4 mark, and will fluctuate during driving - previously, it would just stick at a mark a little before the 1/4 mark, and that was it. So while they found nothing, the recall on the thermostat has made a change in the car for the better...not sure what this means haha.
Thanks for the update. My car's gauge stays at one point too. Not sure if this is normal now. I will be going in for a service soon.

Btw, I am moving to the Princeton/New Brunswick area soon so your thoughts (and anyone else's from that general area who's reading this) on the best BMW dealer there would be appreciated. I'll most likely get the next due service done in NJ.
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      01-27-2016, 01:24 PM   #13
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I go to Flemington BMW - they've been fantastic for everything, and I literally have 0 complaints about anything. I have friends who have gone to Princeton BMW and been disappointed with several aspects of the business, so I would stay away from there if possible. A few other friends go to Open Road in Morristown, which I hear is very good as well.
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      01-27-2016, 08:20 PM   #14
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Quote:
Originally Posted by marlin2911 View Post
I go to Flemington BMW - they've been fantastic for everything, and I literally have 0 complaints about anything. I have friends who have gone to Princeton BMW and been disappointed with several aspects of the business, so I would stay away from there if possible. A few other friends go to Open Road in Morristown, which I hear is very good as well.
Cool, thanks. Looks like Open Road has many dealerships in NJ. Flemington seems closest though. I will check it out once I move.
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      01-28-2016, 12:23 AM   #15
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Originally Posted by ft1330 View Post
I hear you on the crap gas. That's why I go to Top Tier gas stations only, for a guarantee of better detergents. But I'm still subject to the E10 crap and there is no way around it. It's funny how they can still call it "Premium gas" and not "E10 Premium gas" or something. In Europe they have to call it what is it and you still find the regular gas. But gas is also 4x the cost over there. But none of that matters to the rednecks driving their F150
sounds like they reset your throttle curve back to factory spec.

Unfortunately it does not matter to the valves if you buy Top Tier or absolute garbage fuel because not one drop of fuel ever touches the Intake valves. Buy Top Tier for other reasons but it's not going to help withe the carbon deposits.

These engines are Gas Direct Injection + Turbocharged. This means the fuel is injected directly in to the cylinder during the compression stroke then ignited and pushed out past the exhaust valves. To compound this issue the addition of turbocharging means there is always positive pressure behind the valves and the turbo adds a significant amount of crankcase pressure that has to be vented. Well you can't just vent this crankcase gas into the atmosphere so it's dumped in to the air intake. This crankcase ventilation has oil vapors in it and over Time some of that vapor turns to carbon on the hot intake valves.

The going theory is that the less spirited you drive the more prone you are to having this issue earlier. Then again logic says having a lead foot=more venting =more oil vapors to deposit on the valves.
Either way probably going to have to have it addressed by 60k miles. If BMW or anyone else is going to solve this it will likely be to modify the oil and possibly add a filter or other catchment to the EGR system. This is what the Oil Catch Cans are for but there are some that have reported that it has caused problems when taking the car for emissions testing.
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