W203 220 CDI Limp home - overboost problem

[JonnieBeeb]

Hi All,

My first post, and I'm hoping someone can help with the problem I am having. I have searched the forum and have not been able to find a definitive answer to what I am seeing.

A couple of weeks ago my 2006 220CDI (120,000 miles) went into Limp Home Mode. I scanned for codes using an iCarSoft scanner and I saw "2632-8 Check System Charge pressure control Charge Pressure too high" and a "2359-2 Check charge air system, Boost pressure too high". My first thought was the turbo vanes had seized, or the actuator had failed. I had heard this is a common problem. So I took off the air box to have a look. When I did I found the air pipe on the inlet to the turbo had come adrift, so I thought OK, this is probably what is causing the problem, air is going into the turbo that has not been metered. While I had the air box off I did check the turbo vanes. I disconnected the control rod and the vanes moved freely, no sticking or roughness at all. The turbo spun freely with no play in the bearings.

I reconnected the air pipe and turbo control rod and started the car up. I could see the turbo actuator moving up and down as I revved the car, so I feel happy the actuator is working correctly.

I took the car for a short drive. I went for a mile and stopped. Car revved freely and was happy to accelerate. On way back, it went into Limp Home again. I scanned for codes and I had the same overboost codes as before, so obviously the inlet pipe coming off was a red herring.

I have taken all the turbo pipes off the car and there are no splits or leaks in any of them. The intercooler looks sound too. I took off the EGR and a little bit sooty, but it was able to move freely.

I took the car for another drive while logging with my scanner. The same happened again, A mile drive with no problems and no codes flagged. On the way back, it went into Limp Home, and I had the same overboost codes. In the logging data I am seeing some strange numbers, I have pasted four frames, where I believe Limp Home was triggered. I am seeing some high Boost pressures, but also some very high boost air temperatures. I really can't believe those temperatures are real ! The Charge pressure positioner goes to 10%, which I presume is part of the Limp Home mode. When I stop and restart the car the boost pressure positioner goes back to 95%, so I don' t think it had stuck at 10% for a mechanical reason.

Frame 12/33:
4540 Engine speed ----- 779rpm
4547 Boost air temperature ----- 16.36°C
4592 Atmospheric pressure ----- 1003mbar
4609 Boost pressure ----- 2422mbar
4611 Intake air pressure ----- 974mbar
230 Charge pressure positioner ----- 95%
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Frame 13/33:
4540 Engine speed ----- 2975rpm
4547 Boost air temperature ----- 47.76°C
4592 Atmospheric pressure ----- 1003mbar
4609 Boost pressure ----- 2963mbar
4611 Intake air pressure ----- 976mbar
230 Charge pressure positioner ----- 10%
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Frame 14/33:
4540 Engine speed ----- 1962rpm
4547 Boost air temperature ----- 53.56°C
4592 Atmospheric pressure ----- 1002mbar
4609 Boost pressure ----- 2200mbar
4611 Intake air pressure ----- 990mbar
230 Charge pressure positioner ----- 10%
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Frame 15/33:
4540 Engine speed ----- 1567rpm
4547 Boost air temperature ----- 35.16°C
4592 Atmospheric pressure ----- 1001mbar
4609 Boost pressure ----- 1721mbar
4611 Intake air pressure ----- 989mbar
230 Charge pressure positioner ----- 10%

Does anyone have a idea what is causing this? Is it a boost pressure sensor, or could it be an EGR problem? Is that where the high boost temperatures are coming from? Can I drive the car with the EGR disconnected to see if that is the problem? Or will that cause the car to go into Limp Home mode anyway.

Thanks in advance for any advice.
J

 

[alexanderfoti]

Charge air temps look fine.

On your last freeze frame data, 1.7bar of boost with a charge positioner of 10% (or 2.2 bar on the one above!) seems implausible.

Either the charge actuator is sticking and this is the commanded position or your boost pressure sensor is failing. They do fail so I'd check this sensors readings ignition on engine off and see if it's realistic?

 

[mersum1es]

as above... plus are swirl flaps working?

 

[JonnieBeeb]

Thanks for the suggestions. The issue has the feel of a sensor giving spurious readings to the ECU.

@alexanderfoti I agree, the boost pressures look scarily high, surely if that were the real pressure something would have gone pop? I have looked at the boost pressure readings with engine off (around 1000mbar) and running at idle (again around 1000mbar), and when I rev the car I see boost pressure go to around 1500mbar).

I might just replace the pressure sensor as they are not "that" expensive.

@mersum1es I have looked for the swirl flaps and I just can't see the control actuator and control rod anywhere on the manifold. I have googled for pictures of what it should look like and I have had an inspection mirror to look at the underside of the manifold. I can't see anything that looks like the pictures on my car. Where should I be looking for the control rod?

 

[mersum1es]

I am not sure if all OM646 has flap fitted from factory, but Flaps might be removed too.

 

[alexanderfoti]

If its being read as absolute pressure (which it is as it reads 1000mb with engine off) it means 2200mb is 1.2bar of relative pressure, which is not that high. Peak stock pressure is probably 1.5bar so it's probably a sticking actuator causing the issue.

 

[JonnieBeeb]

@mersum1es The specs of the OM646 read as though they all had swirl flaps, but my car has been in the family since new, and I know it has never had swirl flaps removed, so I think it must mean some OM646 didn't have swirl flaps. It is one less thing that could be causing the problem !

@alexanderfoti I will take off the turbo actuator at the weekend, and see if there is anything obviously wrong with it. It must be intermittent if there is something wrong with it, as I can see it happily moving when I start the car and apply some revs.

 

[JonnieBeeb]

A quick update.

I fitted a new boost pressure sensor. A quick drive proved that hadn't fixed the problem, as the car went into Limp Mode after a couple of miles.

I have since taken off the turbo actuator, and opened it up. Clean as a whistle inside and nothing obvious wrong. No broken teeth on the gears and no dry joints on the connectors.

Kind of at a loss what else to look at. I'm reluctant to take it to a dealer, as they will happily empty my pockets and no guarantee of a fix.