Tracing a p0234 overboost condition

Bernhardt

New member
Hi, first time poster here. You guys seem to be friendly and knowledgeable. New to the 2.7l diesel, but not diesels in general or MB diesels. Am actually working on the neighbor's sprinter(1 owner), so bear with me...It has either 137 or 173k miles on it.

I can invoke overboost(p0234) at will. It takes a multisecond application of calculated load of over 90/95% at over 2000 rpm to do it, but does it like clockwork. One time I got the underboost(p0299) code. I'm using a Bosch 1150 to pull the codes, what's stored at the time of fault, and for real time supported data. The overboost code and LHM get triggered at 75.9(reported) inches Hg MAP, which works out to be about 22psi of boost. Cruising on flat level ground at 65-70 results in boost of about 13-14 psi, which seems high to me(I'm used to seeing 3-4 in my truck), but may just be normal tuning for this engine. Of interest, is that when LHM is triggered by underboost the vehicle is far more drivable than when LHM is triggered by overboost.

I have removed the original resonater and epoxied the seam as part of my diagnostics. Have also removed and inspected all the air hoses which look good. The left/cold side had been replaced a couple of years ago the usual split on the underside.

The turbo itself, by the finger test has more radial play than I would expect, but has zero axial play that I can feel, spins freely and does not contact the housing. Took the circlip/actuator rod off of the turbo. Actuator rod moves up and down as one would expect when reving engine(2500 rpm) and back to idle. The arm itself going into the turbo to move the vanes is a little stiffer than I would expect, particularly the last little bit on the 'off' end.

Questions:

How easily is the actuator arm supposed to move?
Any quick, dirty & cheap intercooler pressurization tricks? I know not to exceed 20 psi.
How much coolant loss if removing the EGR? I have heard a high pitched noise coming out of it for a period of time(up to a min) after turning the ignition off.
Anything else I should check?
 

autostaretx

Erratic Member
What model year?
The 2003 and earlier had the OM612 engine with a vacuum boost actuator, the 2004-2006 had the OM647 with electric actuation.

The Sprinter measures MAP (manifold absolute pressure), not "boost".
I can't recall ever seeing over 35 psi MAP (which is about 20.3 boost) on my 2005 OM647.
(heck, it hardly ever hits 33 psi).

--dick
 

MillionMileSprinter

Millionmilesprinter.com
On the cold side of the intercooler is the "boost" pressure sensor. I would check it and it's wiring. Those numbers seem a bit high...
 

Bernhardt

New member
Sorry guys about the model info. I put it into my profile, and it didn't dawn on me that it wasn't showing up. Anyway, it's a 2004 with the om647 engine. Some forums talk boost(over atmospheric pressure) some absolute pressure. The 75 is in inches of mercury absolute, which equates to roughly 36psi absolute or 22 psi boost. With KOEO the MAP sensor actually reads .3 in Hg less than the ambient sensor does(28.9 vs 29.2). With KOER at idle, MAP reads just under 28 which makes sense to me. Wiring looks ok, could still be sensor if it's screwed up and the output just happens to be close enough at atmospheric.
 

Bernhardt

New member
Update. Got the carsoft mb II. Goes much deeper into things than my bosch reader does. Crazy thing is with the mb II, depending on which menu you're in the data stream is in different units for the same reading(MAP, and MAF to name two). I noticed the air flow(MAF) readings weren't increasing the way I would expect when I changed rpm levels - they weren't going up near enough. Cleaned the MAF, now better, but not sure what the readings are supposed to be(at say idle and WOT at 3k rpm). Am aware that temp/humidity will affect these readings. I still can get the p0234 reading, but only if I get it nice and warm, exit the freeway, and hop back onto the freeway a minute later while mashing the throttle to the floor. Just fades into LHM of sorts(will still do 65 on level ground) and does not illuminate CEL.

Using the mb II, I found the following codes stored in the powertrain module(not the general obd). Not sure how old they are and weren't in the mbII database:

P2013- Research indicates its(sprinter code list found here) Intake manifold runner, but another source(benzworld code list) said Intake pressure implausible -high voltage or low
voltage
P2088 - Camshaft actuator or O2 sensor heating(benzworld list)
P2514 - Crankcase vent heater
P2359 - boost too high
1630- Immobilizer/Alarm

Can anybody shed any light on the first two of these codes?

I cleared them, and now only get the P2359 code in the PCM module once it goes into limp mode.

Since I've seen some unexpected changes in the intake and manifold pressure readings, and fluctuations in the airflow I'm looking in that direction. Thinking something is getting affected by the heat when it shouldn't. Would appreciate any input I can get.
 

Tango17963

New member
I have pretty much the same issue going on. I bought my Sprinter last year as salvage from an HVAC contractor that had a bad injector burn a hole in a piston. When I bought the van, it was pouring white smoke from the engine and exhaust. I have already cleaned my EGR Valve and have been fighting the overboost issue. The other symptom I have is that sometimes after the engine is warmed up, the throttle almost "sticks" when you let it out. The van continues to stay in power for a few seconds before it returns to normal. I suspected the turbo was gummed up with the same junk the EGR was. Last week I removed the turbo and tore it down to clean it. Sure enough, the same black crud had the vanes not working correctly. I have a new gasket set from the folks at G-Pop Shop in hand and plan to finish cleaning and reinstalling my turbo this weekend to see if that was my issue. I'll let you know.





 

220629

Well-known member
As suggested above, I would check the turbo vane actuator linkage and vanes for free movement. Even a small catch in the operation can cause problems. It should not be necessary to disassemble the turbo. I periodically grease the linkages on my 2004 and 2006 using an acid brush with heavy duty wheel bearing grease.

vic
 

Tango17963

New member
I seemed to have found my issue. (Fingers crossed).

I have my van back together and it sounds noticeably different. I have a nice little whistle from the turbo and it has so far stayed out of limp mode. More miles will be needed to say with certainty, but I'm off to a good start so far. Now I just have to track down the awful creaking noises from the front end and sort out a new SRS light that has been coming on recently and then I think I have this thing back to normal.

Thanks for all the help on this forum and on YouTube. I'm sure I have saved tons of money and more importantly to me, I have learned a lot about how these things work.
 

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