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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Still have a light throttle oscillation with O2 sims



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      04-02-2009, 10:09 AM   #1
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Still have a light throttle oscillation with O2 sims

Well, what I thought would have resolved an issue with light throttle and around 1800-2200 RPM power oscillation, didn't.

Some others have described it here, but I'm trying to get a better technical explanation on what the potential causes are. I've always been one to cry out at those who's cars are still covered but haven't taken them into the dealership yet, or have with aftermarket parts on, so I'm being a little hypocritical here.

At any rate, short of pulling the exhaust and what have you off, I want to see what the issue could point to. I've argued with the techs and an engineer ad nauseam. On other threads, I've referenced the conversation with said engineer and my opinion on his level of expertise. Of course, I'm not an expert either, but the points he was making made no sense whatsoever.

So, to describe the issue again, between the above RPM range, on very light throttle (sustaining that RPM) I get an odd oscillation. It's like a power surge. Relatively light, but definitely noticable. This occurs with or without a tune and with or without sims. This also sometimes occurs at about 3k RPM as well, but that seems to be random.

After the SIB of the WG issue was performed last summer, the issue started to occur. Additionally, to that point, the high flow cats were not popping any codes. They started to throw efficiency codes, and more recently, I also started receiving too lean codes on both sides. This was w/o any tune.

The sims take care of that, but the oscillation is still there. As soon as I find the power clip for my Wi-Fi/serial adapter I'll post up some logs. I know that I'm going to have the same issue once I revert to stock, but I don't want to go through the process...at least, not until the summer car is on the road.

Anyway...any thoughts?

Thanks in advance!
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      04-02-2009, 10:22 AM   #2
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Its the first time I read something like that...
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      04-02-2009, 05:26 PM   #3
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I got this too... Last month, running stock tune w/UR CAI and catless exhaust the oscillation was pretty bad accelerating through said RPM range and often up until 3-3.5k (I usually short shift when driving for economy).

Running a stg3 map, smoothened things out considerably but the oscillation is still present occasionally. The latest map I'm running has helped a bit though.
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      05-22-2009, 02:00 PM   #4
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Big update...

So that oscillation is gone. Essentially the service department is filled with morons...which I complained about several times.

Took it to another dealership and the issues were that one of the turbine outlet hoses was loose (which I don't think was the direct cause) and, per the work sheet, MAP thermostat was broken. Now, I know what a MAP sensor is and I know what a thermostat is, but no idea what a MAP thermostat is. I'll have to look to see what exact part was replaced.

At any rate, that oscillation is long gone, in addition to a progman update to whatever the latest is as of two weeks ago.
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      05-22-2009, 02:26 PM   #5
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Railgun can you post up the part number? I have the exact same issue going on. Thanks.
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      05-22-2009, 02:36 PM   #6
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Quote:
Originally Posted by Railgun View Post
Big update...

So that oscillation is gone. Essentially the service department is filled with morons...which I complained about several times.

Took it to another dealership and the issues were that one of the turbine outlet hoses was loose (which I don't think was the direct cause) and, per the work sheet, MAP thermostat was broken. Now, I know what a MAP sensor is and I know what a thermostat is, but no idea what a MAP thermostat is. I'll have to look to see what exact part was replaced.

At any rate, that oscillation is long gone, in addition to a progman update to whatever the latest is as of two weeks ago.
Interesting. Could it be a additional sensor with or along with the MAP that reads incoming air temp? That would be kinda cool as the ECU could adjust for air temps adjusting a/f ratio's before the burn.

But, I'm just guessing at what a "MAP thermostat" could be.
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      05-22-2009, 03:31 PM   #7
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Quote:
Originally Posted by happy4nk8er View Post
Railgun can you post up the part number? I have the exact same issue going on. Thanks.
Yeah... I forgot to mention that. When I get home tonight I will. I was going to look that up myself as well.

RPM90,

Well, there is an IAT sensor, but how it would possibly tie into the MAP I have no idea as they're pretty much mutually excusive, though they all work together for fuel and timing adjustments.

What was odd was that it was very light throttle at relatively low RPM. What else was odd, and I don't know if I had mentioned this before, that oscillation increased in frequency as RPM increased. So it would happen between 1800-2200 and about 3k. At the latter, it was noticable faster.

At any rate, yeah...I'll get you all that info.
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      05-22-2009, 04:23 PM   #8
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Quote:
Originally Posted by Railgun View Post
Well, there is an IAT sensor, but how it would possibly tie into the MAP I have no idea as they're pretty much mutually excusive, though they all work together for fuel and timing adjustments.

The TMAP is the boost control sensor and includes both pressure and temperature in one sensor. Not that this means much here.
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      05-22-2009, 05:26 PM   #9
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Quote:
Originally Posted by scalbert View Post
The TMAP is the boost control sensor and includes both pressure and temperature in one sensor. Not that this means much here.
Ahh. Well that makes sense. Of course the SA's writeup is subject to interpretation based on what he gets from the tech so...perhaps a little lost in translation? I guess I'll know when I get that p/n.

Admittedly I don't know every sensor that exists here.
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      05-22-2009, 05:50 PM   #10
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Railgun checked out my charge pipe connections and initially it looks like I have small leak on my rear turbo charge pipe connection at the flange. I need to dig further to confirm but sure looks like it.
Thanks for the info and help.

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      05-22-2009, 09:19 PM   #11
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So here are the P/Ns

12-52-7-507-529 Socket housing
12-52-7-510-668 Terminal socket for MLK
12-52-7-503-411 Grommet

Needless to say this isn't all that helpful as the P/N don't tell me what or where. The description for this particular item says coolant thermostat wiring, but afterwards, says MAP thermostat.

After further reading, it looks as though it may be just the coolant thermostat. That said, it was most likely directly attributed to the loose pipe, in this case, bank 1.

That's kind of interesting that this is the case. I would have thought that I would have thrown codes galore at WOT with this condition, not at light throttle where I would think the seal would hold up to the light pressures.

Eh...so be it.

One question happy...have you had the WG service performed or any kind of work in that area or did it just pop on its own?
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      05-22-2009, 10:09 PM   #12
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No service, it just started doing it after about 29k miles. When I first noticed it was on the highway in cruise, under light load about 2k rpm, my boost gauge would oscilate between -14 and -10 with the surges. I just recently tried to emulate the same load, same rpm, in 2nd and 1st gear and the surging was more pronounced and more obvious, like you were describing.
Everything in the area of the charge pipe flange is really clean except for one side, in one area, it resembles an exhaust leak trailer.
If it is a leak like yours, I'm hopeful repairing it will fix the problem.
BMW service documents are like a secret code, it's never plain WTF they did.

Happy weekend.
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      05-23-2009, 08:30 AM   #13
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Did you notice this a lot when using cruise control? If so I think you made my day.
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      05-23-2009, 09:00 AM   #14
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If the RPM was within the right range, and the trottle sat at the same position, yes.
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      05-23-2009, 09:32 AM   #15
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Quote:
Originally Posted by psu139 View Post
Did you notice this a lot when using cruise control? If so I think you made my day.
Absolutely, that is when I first noticed it. Drove me crazy to the point of not using cruise. In cruise it was about 2100 rpm, 65 mph, flat to slightly inclined down and averaging 33 to 39 MPG. I noticed my instant MPG would jump back and forth as my boost gauge was doing. But only during those loads. It wasn't until recently that I experimented to see if I had the same thing happening in different gears and speeds at the same approximate load, which turned out to be even more pronouned. It makes sense about the leak and am hoping this will be the fix.
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      05-23-2009, 09:57 AM   #16
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yeah sounds like the same thing i experience. does anyone know where on the parts diagram this pipe is located?
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      05-23-2009, 10:52 AM   #17
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piping

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Originally Posted by psu139 View Post
yeah sounds like the same thing i experience. does anyone know where on the parts diagram this pipe is located?
This shows the whole banana.
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      05-23-2009, 01:01 PM   #18
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Originally, I had an issue with that rubber line at the IC inlet. That practically popped completely off. I wasn't looking for any other issue at the moment. That's interesting that the connection at the compressor would come loose over time. Another crappy design apparently.
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      12-11-2009, 04:39 PM   #19
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so, did anybody figured out, what was the problem,im starting to experience these same simptoms
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      12-11-2009, 05:19 PM   #20
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I'm experiencing similar issues with the procede though. At stock it's fine though. I was thinking increased boost pressure exposed the problem. It could be the procede. But I just had my turbos replaced so that could be the issue. I also installed ar downpipes but me and my tech never found any leaks or anything out of place. It doesn't happen at WOT though. Did it happen at full throttle as well railgun?
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      12-11-2009, 05:26 PM   #21
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And why were you thinking the simms were causing the oscillation problems railgun? How can you guys have these leaks without throwing CELs?
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      12-11-2009, 05:37 PM   #22
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Have a pic of the leak happy?


Quote:
Originally Posted by happy4nk8er View Post
Railgun checked out my charge pipe connections and initially it looks like I have small leak on my rear turbo charge pipe connection at the flange. I need to dig further to confirm but sure looks like it.
Thanks for the info and help.

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