Overboost Condition

I'm getting code P0234 Overboost Condition. This happened about a month ago, and I went through the turbo system and ended up cleaning the MAP sensor and the issue went away. The intercooler only had a few ounces of oil in it, but the sensor was filthy.

A day or two ago I noticed the turbo whistle was louder. Yesterday after work I spun out on some sand, which caused the engine to rev high, and the car went into a sort of low power mode. It did this the last time I had this problem. This isn't a panic limp mode, it just feels like a reduced power mode where I can still get up to speed, but it just takes a while. The CEL does not come on, but when I plug in a scanner there is the code.

So, if I can get to it this weekend, I plan on pulling the intercooler and checking the sensor again. If the sensor has oil on it, what should I do? Where is the most likely source? Would oil on the MAP sensor cause this?

I believe you have a dying MAF
MAF sensors operate under an acceptable range before the ECU throws a code. You may well be within the limit to have a slow car but still not get the dreaded CEL.

What you could do to find out where are you standing is use VCDS to monitor MAF readings. There are several threads in this fourm and also on myturbodiesel.

Carlos_TJ said:

I believe you have a dying MAF
l.

Click to expand...

I disagree.

I think the VNT mechanism is stuck, or there is a massive boost leak.

See what the actual vs. requested boost is with a scan tool.

The stuck VNT could have caused an overboost, and before the ECU could cut fueling back and put it into limp mode, it exploited the weakest link in the charge air circuit and split or broke something.

Or the turbo just plain blew up.

Yikes!
Misread MAP for MAF.
My bad...

The actuator is relatively new (maybe a year and a half) and was properly adjusted. All vacuum lines were replaced with silicone and decluttered, at the same time. The last time I got this code I checked the N75 by temporarily swapping in the N18, and the overboost issue persisted.

I'll go through all the lines this weekend, and check the actuator and vac pump.

I'm just worried that I'll find the MAP sensor is dirty with oil again. Don't know what that would mean.

The MAP sensor lives in oil, there is always a film of oil everywhere in the charge air tract. That is normal. MAP sensors hardly ever fail.

Look for a charge air leak. Check the N75's operation.

Then graph the boost while driving.

I ordered the VCDS cable from Ross-Tech last night, and it just shipped. About time I got one. I'll just drive gingerly until I can get some boost graphs. If I do any hard accelerating it'll throw the overboost code and drop to low power.

Like I said, last time this happened I swapped in the N18 and drove it hard, and it popped the overboost code. So I am fairly sure the N75 is ok.

I'll check for leaks tomorrow too.

Could sand have entered the intake track; possibly clogging the intercooler?

JB05 said:

Could sand have entered the intake track; possibly clogging the intercooler?

Click to expand...

if thats the case, the turbo fins would be beaten to death and i dont think much boost would be present over a healthy turbo, if a CAI was used, i would think this might be the case but i have never seen it that bad before, but then again i dont live near a desert!

Almost certainly no sand entered the system. Stock intake and the filter was replaced in the fall. They use a lot of sand and salt on the roads here, but not enough to cause that kind of issue.

The overboost code is definitely for real; at idle the turbo whistle is quite a bit louder than normal, and when when shifting the turbo noise is also louder. When I push the car hard the turbo makes a very loud screech between shifts, and usually this is when the code is generated and it goes into low power mode.

It's weird that the last time this happened cleaning the MAP sensor fixed the issue. I wasn't able to get to it today, but I think I will wait until I get the VCDS cable early this week and see what the car is doing. I'll put it on ramps tomorrow and take a look at the actuator and tubing, though.

Get at that turbo with a pry bar and work the vanes for the turbo. I have the same thing happen once in a while and it will over boost like oil hammer said.

Though with all the noise you are hearing it is likely the turbo is taking a dump.

So, disconnect the actuator and try to move the lever manually? What's the best way to disconnect the actuator? I don't want to mess up the adjustment.

Found this thread: http://forums.tdiclub.com/showthread.php?t=434172

And now I'm afraid my turbo is worn out or gummed up. The car has 248k on it, and as far as I know the turbo has never been looked at or touched beyond a new actuator.

I really want to check the motion of the vanes now to see if they move free.

EDIT: Also, the entire back of the engine is covered in oil. The turbo oil return line is also oily.

I was able to remove the actuator and move the lever. It feels very loose, like it isn't actually moving anything, and it catches at a certain point. I took a video and here is the link: https://vimeo.com/261727479

But at this point I am leaning heavily toward my turbo being borked.

Got some preliminary boost graphs. This is my first time using VCDS, so if I need to do something else or more info is required let me know. Tomorrow I will log my drive to and from work, which is only about 20 miles round trip. From what I understand I can "replay" the log info as a graph, right?







I took it out for a quick drive and logged it. If there's nothing sensitive in the CSV file (I didn't really see anything when I opened it in Excel) then I can provide that if anyone could make use of it in the effort to diagnose what's going on.

That doesn't look especially bad to me. There are always boost spikes when the actual overshoots the requested, some cars seem to do it more than others.

I always look to see if the actual drops back down quickly, which yours does.

I'd try and get a graph on a long loaded run, the higher the gear the better, and see if that yellow line suddenly goes up and stays up. It should level out and track pretty close to requested.

You may have to adjust the VNT rod a bit more. And sometimes, the actual vanes inside the turbo are just worn/sticky and no amount of adjustment will get it right. I am dealing with an ALH right now that is doing just that. It is getting a replacement turbo, I'm done trying to make the one in there happy.

At that kind of mileage, replace the turbo. You could try to replace actuator but if that doesn’t work you’ll buy a turbo anyway. Then you can save for new injectors or head, and run for a long time

I logged my drive home last night, and I took the highway home so I was doing 70mph for quite a while. I think I saw what oilhammer mentioned where the boost demand dropped but the actual boost didn't respond. I'll do the drive tonight and see if it does it again and post a screenshot or the CSV.

The turbo noise has mostly gone back to normal and I haven't been able to get the car to overboost. Maybe sliding the vane lever a bunch of times freed it up or something? I am having difficulty starting the car now, lots of smoke and takes quite a few more cranks to turn over. I was able to log the boost when starting and it looks terrible. Maybe glow plugs?

I checked the timing and it is dead nuts on.

I'd like to just buy a new turbo, but I was already planning on a transmission swap. I have the transmission and most of the stuff to go with it. If I need to change out the turbo I'd want to go with the 17, which means the adapter and a new return line, so that's over a grand. That also means I'd have to get a better clutch, as the one I got with the transmission is the stock Sachs or Valeo clutch. I don't remember which. Probably not good as I would also like to do injectors eventually. And a new downpipe and exhaust. I don't think I'm ready to drop 2k to 2.5k on this yet. It adds up quick.

And my fuel economy has dropped through the floor. Below 30 mpg.

Maybe you can pick up a decent used VNT 15 from someone who has or is about to upgrade?

Here's some screencaps hosted on imgur. Because the image system for this forum is rather unpleasant to use, to be honest.

Startup:


Quick accelerating at slower speed:


I think this a point where the turbo seems to stick higher than the requested.


Hard accelerating:


Here's a dropbox link to the CSV from driving to work: link

Here's a dropbox link to the CSV from driving from work: link