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Hello everyone, I've been chasing a boost error for the last week on my 2009 R320 Bluetec. It started after I left a fueling station and was getting up on the highway. I had several alarms when I pulled over including MAF sensors, Boost (123900) and NOX sensors. I cleared the alarms but the car was very sluggish and bucking. It eventually made it up to 70 mph and we limped it home. The only code that keeps coming back is the boost alarm. My code reader says "The positive control deviation during boost pressure control is too high". When first taking off from a start the car will surge and fall on its face until you get it over 2500rpm, then it will go fine for a while. Looking at the boost the highest I got was around 1700mbar or 24psi. When holding the brake and reving it, the actuator is moving up and down as the engine builds then dumps boost it will not hold steady.
I was originally chasing what I thought was a low boost issue because the Turbo noise is really really loud when it revs. I found a bad o-ring on the charge pipe and a bad turbo inlet gasket. I also had an EGR alarm 14a700 iirc, I removed the EGR and cleaned it as it was crusty and stuck. That alarm hasn't come back, neither have any of the other alarms except the 123900 boost pressure control is too high. I know think the noise I was hearing is the wastgate being wide open to regulate boost. I took apart the actuator and the linkage moves very freely with no hitches at all. I did notice a bit of play in the worm gear of the motor. Could it be that the actuator is worn and having issues with regulating boost?
The other weird thing I see is that with the car shut off I still have about 940mbar or 13psi. Could this be an issue with the sensor?
Small update. I removed the boost map sensor and left it to atmosphere and all stayed the same. I disconnected it and driveability issues remained, btw the unhooked value was 800mbar. I then removed the intake MAP sensor and it read the same. Then I unhooked the intake MAP sensor and it defaulted at 1000mbar. Suddenly driveability is vastly improved on the top end. The car over 2000rpm pulls hard and all the way to readline. The turbo sounds closer to normal as well, it stumbles a bit off idle with the sensor unhooked still.
Here is with the engine turned off notice that the engine RPM is at 0 and yet both intake and boost read about 967mbar:
The back pressures look high to me, but I can't find anywhere that says what they are supposed to be. I have a iCarsoft MB II and tried running the DPF regeneration cycle, but couldn't keep the exhaust gas temps up high enough (I believe they are supposed be be 600, but kept getting the 123900 and into limp mode). Afterward I have a 13AF00 code saying that the soot content is too high and it has not cleared. However, the car reads 0g of ash content...so I have no clue what is going on.
In addition to the 123900 and 13AF00 I also have a 125C00 which the scanner says is the same description as the 123900...?
Last edited by happyinwi; Jul 2, 2019 at 08:51 PM.
I have no time to study the issue here, but I see you are using iCarsoft for troubleshooting.
I experienced that the scanner lies to me on occasions, so take the readings with grain of salt before you can confirm them with different scanner.
Thank you for your response. I am more than a bit confused by the reading of psi in the scanner. Like is the 13psi something I should be subtracting from the total? Ugh I miss my CDI...
Ahhh that makes so much sense. Then I guess that I would subtract the base number from the boost number to get actual boost pressure which is maxing out at like 1700mbar. Boost then is around 11psi?
Correct. All air intake pressure sensors and MAP/boost sensors are absolute pressure sensors (usually 2 or 3 bar), not gauge pressure sensors. So they will reference a perfect vacuum as a zero pressure value, NOT atmospheric conditions. If you are getting a reading of ~967 mbar with the car off, that correlates to 28.6 inHg, which is a very believable atmospheric pressure condition. So, when you are monitoring your MAP sensor output during boost conditions and it is reading 1700 mbar, you will need to subtract the Intake air pressure reading (in your case it's 967 mbar) to yield your true boost pressure of 733 mbar w.r.t. atmospheric conditions.
Ok I think I may have found the issue, completely blocked air filters. They are plugged big time. I decided to pull the boxes (what a pita) and test it without them installed on a very short drive and the car pulled all the way to redline multiple times without going into any new alarms.
So I drove to the closest place to get an air filter for this pos (25 miles one way) got back wrestled the absolutely stupid air boxes back into the car and.....back to the same 123900 code. Thought perhaps it was something to do with running it with the map sensor outside of the air box so I removed it and tried again, same thing.
Earlier with the passenger airbox off it went into alarm straight away. When I pulled the drivers airbox I was able to push it hard multiple times without issues all the way to redline for about a mile w/o alarm. I'm starting to think there may be an issue with the MAF sensors or there's some type of massive blockage in the air duct on the drivers side?
I pulled the airboxes again and can't make it out of the driveway. This car is driving me crazy. Is there any possibility bad diesel or a clogged fuel filter could result in a 123900? Symptoms started right after a fuel up.
Last edited by happyinwi; Jul 4, 2019 at 05:31 PM.
I pulled the generic code and it is a P0299 which indicates an underboost. So I went back and looked for a leak again, pulled the silencer off and blew into it (no leaks) pulled the intercooler outlet hose off and no visible cracks.
The Turbo is way louder than normal when building boost sounds like a fan under the hood, I can find no leaks (even hit all the charge piping with soapy water). I assumed that it was loud due to the actuator opening the wastegate while attempting to regulate the boost. There's no noise at idle or without a load on the engine. I did find an extremely small air leak around the intake manifold, the water bubbled but did not change bubble rate when boost was built.
At this point I can only figure out that either: 1) I have a leak that I can't find, possibly the passenger's intake or somewhere on the turbo itself (there is no play or drag on the turbo), 2) The actuator isn't functioning correctly it's going full open on the wastegate or perhaps it just isn't regulating correctly, 3) One of the MAF or MAP sensors is bad and throwing the readings off so the turbo actuator is going crazy trying to compensate.
Try to make cheap smoke machine to detect the leak. Search on youtube how to build smoke machine cheap. If there is no leak then check the actuator. I was fixing actuator on my friend's 2008 R320 cdi last week. I replaced worm and fixed the electrical connection, which is very common issue on these hella actuators. Everything seems to be working fine, but unfortunately I don't remember the error code.
Finally had time to make some headway here and some head way I believe I have made. I built a smoke "machine" to try and find the boost leak. I used a candle that was done for and put some paper towels into it, drilled 2 7/6" holes in the wooden top. I used some really old fuel line left over from a 1985 Grand Wagoneer and a sandblasting tube that has never been used. I zip tied a sandwich baggy to the turbo and to the blasting tube and applied air pressure. Here's my super sketchy smoke apparatus.
After a while I noticed a lot of smoke coming out of the passenger side. At first I was worried it was a head gasket. I removed the aircleaner assembly (what a pain in the bottom). I eventually saw it coming out of a hole in the back of the throttle body flange.
After spending some time on the phone with the dealer we were able to determine that a sensor was supposed to be in that hole. It took some sleuthing to find the little bugger as it had wrapped around and behind some other wiring. Seems that the clip had broken off the sensor and it ejected out of the flange.
The sensor is an air restriction sensor. Here's the broken one:
I'm picking up the new sensor this weekend and hope to have this resolved Sunday.
Last edited by happyinwi; Aug 4, 2019 at 02:19 PM.
Reason: Trying to get pictures to work
Hopefully all pictures are working now. I picked up the Air Charge Sensor from the dealer yesterday, but couldn't install it until today. I got it installed and back together enough for a short test drive. I did probably 15-20 full rpm pulls and had 0 whooshing noise and no limp home mode!!!! I am fairly confident this issue is resolved.
Congrats! You got this nailed finally. I know it's an old thread but I wonder where the Air Charge sensor(s) is located? OM642 engine, 2014 MB GL350. I am Googling it but I only get some cr*py results. Thanks in advance.
I been having a very similar issue , will do your steps , No CEL , car pulls okay overall , if going uphill or when car needs to pick up ( step down ) doesn’t react and it’s slow
wondering how’s it been for you since you replaced that air charge sensor
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