P0234 Overboost Condition Diagnosis

[fR3ZNO]

I have been trying to figure out this issue that I've been having for the past few months. I have tried searching but can't find anything with a definitive answer. This is going to be a long post, here it goes.

Some details:

- 1.8T 6MT
- APR Stage 1 flash
- Forge DV (which replaced an APR R1 DV w/ torn diaphragm)
- New Genuine Audi/VW N75
- New 034 Silicone N75 hoses
- TT225 Injectors
- KO3

What I've tried to do so far:

When I first got the car a few months back, there was no boost gauge and I would notice that the car would pull really well and then it would all of a sudden feel like there was no power. After the turning the car off and turning it back on, it would be fine. I came to find out that it was going into limp mode. Eventually installed an ECS boost gauge that showed me that it wouldn't boost past 5 psi, as expected in limp mode. It will spike and hold at about 18 psi.

Tested for boost leaks. None were found.

I suspected a faulty N75 to be my issue, so I picked up a new OEM N75. It did not solve my issue. After feeling dumb for dropping the coin on a new one, I did some searching.

Tested the wastegate by unplugging the N75. The car would not boost past 5 psi (not in limp mode), which would indicate that the wastegate is opening under spring pressure and is functioning properly.

I also did some VCDS logs, but the car did not go into limp mode during the pulls and the graphs did not show any obvious overboosting. I'll post a dropbox link when I get home.

I had noticed a strange "mooing" sound when the car was under partial boost. I found that it is common with R1 DV's that have some mileage on them. I bench tested the R1 and found that the diaphragm was torn since it would not hold a vacuum. Picked up a used Forge DV that was recently rebuilt (new piston, o rings, and springs), regreased it and installed. Fixed the "mooing", now holds boost better.

So, at this point I am lost. Apparently torn N75 hoses can cause issues with proper wastegate actuation. I picked up 034 silicone N75 hoses, and installed them. I bench tested the old ones, and found that one would not hold a vacuum even though it had no obvious tears. I took the car for a test drive and it still goes into limp mode.

From what I have gathered, the car usually goes into limp mode when I am getting on an entrance ramp. However, it is interesting to note that right before going into limp mode, boost is not any higher than 8 psi or so. I am unsure why an 'overboost' code is being stored. Unless the requested boost is lower than actual at that particular instant but is okay at higher pressures.

I feel like the next step would be to replace the pressure sensor in the intercooler, but I would prefer not to continue to throw parts at the problem. I remember seeing a thread on VWVortex where that solved an overboost code, but I would like to know for sure before proceeding.

Thanks in advance! Sorry for the long post.

[fR3ZNO]

Anybody?

[texasboy21]

You can start by cleaning the MAP sensor on the intercooler. I've had oil blow by build up on it and my boost would come and go as a result. Can you post a log of block 115?

http://www.goapr.com/support/datalogging.php

[fR3ZNO]

I'll give that a shot.

I have some logs from a few months back. Clicky Click



The car didn't go into limp mode during this pull.

[Gberg888]

I got an overboost code for 2 reasons.

1) The intake I had was the incorrect diameter for my tune.
2) My injectors were incorrectly sized for my tune.

My original setup:
UM tune for Ko4, Delphi 440 injectors, oem maf housing with Carbonio Intake

Setup for alleviate the code:
UM Tune for ko4, Green Giant Injectors, OEM Maf Sensor in VR6 Maf Housing, Evolution Racewerks turbo inlet.

I was getting the overboost because the injectors were incorrectly sized and the air I was receiving was being incorrectly metered because of the smaller oem housing on the MAF sensors. Once I changed those parts out, all my overboost issues went away. I had to get the ER turbo inlet to fit the VR6 Maf housing because the forge inlet I had would not fit it.

[fR3ZNO]

I'm not sure if it's a injector sizing issue. I believe the injectors are correctly sized for my tune.

[texasboy21]

I'm not sure if it's a injector sizing issue. I believe the injectors are correctly sized for my tune.

Assuming the original post is a typo, and you are running the APR stage 2 (big injector) tune, not their stage 1 tune (stock injectors), you should be good.

[fR3ZNO]

Assuming the original post is a typo, and you are running the APR stage 2 (big injector) tune, not their stage 1 tune (stock injectors), you should be good.

I'll have to double check. The only thing I'm basing that info on is the receipt from the PO for the tune.

[Jflow23]

Unplug the MAF and drive around and see if it still goes into limp. My car seems to have repeat limp problems when my MAF is on the way out. I'm on my third MAF in 8 years...each failed with constant limp.

[texasboy21]

I'll have to double check. The only thing I'm basing that info on is the receipt from the PO for the tune.

Im not sure it would cause your situation, but it is best to run matching software/hardware.

[fR3ZNO]

Unplug the MAF and drive around and see if it still goes into limp. My car seems to have repeat limp problems when my MAF is on the way out. I'm on my third MAF in 8 years...each failed with constant limp.

Hmm. I thought a bad MAF would give other driveability issues/symptoms. Seems like quite a lot of MAFs to go through in a short amount of time. I'll try unplugging and see if that helps. Probably clean it too just to see if that helps.

Im not sure it would cause your situation, but it is best to run matching software/hardware.

No worries, I appreciate the suggestion. My last car was a bone stock 2.8 B5 except for wheels and coilovers. Never modded the engine.

I checked the receipt and it wasn't very helpful. It just says "APR ECU Flash" it was bought during the "Spring into Power sale" back in '09, originally $599, on sale at $499. So, I'm guessing it was the more expensive big injector tune. I'll see if I can get a hold of APR.

[texasboy21]

Hmm. I thought a bad MAF would give other driveability issues/symptoms. Seems like quite a lot of MAFs to go through in a short amount of time. I'll try unplugging and see if that helps. Probably clean it too just to see if that helps.



No worries, I appreciate the suggestion. My last car was a bone stock 2.8 B5 except for wheels and coilovers. Never modded the engine.

I checked the receipt and it wasn't very helpful. It just says "APR ECU Flash" it was bought during the "Spring into Power sale" back in '09, originally $599, on sale at $499. So, I'm guessing it was the more expensive big injector tune. I'll see if I can get a hold of APR.

Sounds like it. Might want to hit up APR Support about this issue as well. If you follow their rules/guidelines in producing information they offer a world of support. I was chatting on the phone and over email with a tech for a week working out an issue.

http://www.goapr.com/support/datalogging.php

http://www.goapr.com/contact/

[fR3ZNO]

A quick update: unplugged the MAF and drove around some. Took a few on ramps, where the car would almost always go into limp mode when accelerating in 3rd. It did not go into limp mode, it pulled and pulled.

I plugged it back in and took the same on ramp and it went right into limp mode like it usually does.

So, I'm guessing that the MAF isn't seeing enough/too much air to mix properly with fuel when accelerating and therefore going into limp mode?

I'm gonna try cleaning it and seeing if that helps, otherwise I guess I'll be buying a new one.

Thanks for the suggesting, jflow!

I think I'll do some troubleshooting with APR when they email me back just to verify.

[fR3ZNO]

I ended up just buying a new MAF. The car doesn't go into limp mode anymore, but it still doesn't seem to be boosting quite right.

[fR3ZNO]

Just kidding about not going into limp. Still does it. Seems like it is mainly during partial throttle. I took logs according to the APR support page and sent them to someone APR. I have yet to hear back from them. Ugh. The car did not go into limp during the WOT pulls... like I said it only happens during partial throttle and mainly uphills or when engine load would be higher.

I am unsure what to check from here and I really don't want to continue to throw parts at it.

Just a quick brainstorm, could it be possible that an aftermarket cat be causing too much back pressure and causing an overboost? It's not a high flow cat, but an OE replacement style cat that is installed on my car.

Another idea, I'm almost positive that the tune is written for 93 and that's what I run in it since BJ's gas only has 87 and 93. I think I might run a tank of 91 in it after I use up this current one to see if that does anything.

[fyremanpat]

check the wires on the n75 plug. I had a similar issue and found that one of the wires had deteriorated and would only make a connection sometimes. I ended up pulling the rubber boot back and soldering it back together. no issues since.

[fR3ZNO]

check the wires on the n75 plug. I had a similar issue and found that one of the wires had deteriorated and would only make a connection sometimes. I ended up pulling the rubber boot back and soldering it back together. no issues since.

I'll give that a shot. I looked at the logs that I sent to APR and the N75 duty cycle looked normal, so I'd imagine that a frayed wire would show different values than what I got.

[fR3ZNO]

N75 duty cycle looked normal

loljk, I posted up my logs a few weeks ago to NefMoto, and my N75 values are pretty much maxed out. So there could be a few things that are wrong, included clogged cats, boost leak or dying turbo.

I picked up a cheap Manzo TP and I'm going to see if that helps at all. Right now, I have an aftermarket catalytic converter. I don't know how many miles are on it, so it could be entirely possible that it is clogged.

[fR3ZNO]

I have not updated this in awhile, but with the help of people over on NefMoto, I have determined that the turbo is the issue. I have a used ko3 from a fellow Audizine member that will get installed in a few days, hopefully.

[ozMatt]

I have not updated this in awhile, but with the help of people over on NefMoto, I have determined that the turbo is the issue. I have a used ko3 from a fellow Audizine member that will get installed in a few days, hopefully.

I've had exactly this issue for years. Threw a few parts at it, but in the end have put up with it for now.
The only difference is I am not throwing any codes at all. Same exact symptom though: going into limp at part throttle under load (eg: going up hills/inclines).

Cheers, Matt

[fR3ZNO]

I've had exactly this issue for years. Threw a few parts at it, but in the end have put up with it for now.
The only difference is I am not throwing any codes at all. Same exact symptom though: going into limp at part throttle under load (eg: going up hills/inclines).

Cheers, Matt

Do you have an APR tune as well? I've noticed that it can go into limp mode once or twice before the check engine light comes on.

[ozMatt]

Do you have an APR tune as well? I've noticed that it can go into limp mode once or twice before the check engine light comes on.

I have a REVO stg 1 tune. Other than that the car is bone stock. I don't get the check engine light or any codes when it goes into limp either.
You can actually 'feel' when it happens, and like yours, will reset itself if you cycle the ignition.
I find seems to do it more frequently in warmer weather as well (80f+)

When you change the turbo out don't forget to check your cat while you're in there

[fR3ZNO]

I have a REVO stg 1 tune. Other than that the car is bone stock. I don't get the check engine light or any codes when it goes into limp either.
You can actually 'feel' when it happens, and like yours, will reset itself if you cycle the ignition.
I find seems to do it more frequently in warmer weather as well (80f+)

When you change the turbo out don't forget to check your cat while you're in there

Hmm. The tune may not store the limp mode as a code or something. Not sure.

When I did some logs, the car goes into limp mode when the N75 duty cycle is maxed out. But while driving it only happens on part throttle (halfway or more) under moderate load. However, it doesn't happen at WOT.

I installed a test pipe a few months ago and it didn't fix the problem. But I ended up buying and installing a 034 high flow cat anyway. Haha. So I didn't think the cat is clogged.

At this point I am thinking it might be a bad diaphragm on the wastegate linkage, which would make sense as a leak would prevent the wastegate from closing properly and cause the N75 to work overtime to keep it closed. I will have to compare the two turbos on the bench.

[ozMatt]

Haha, definitely not the cat then.

I need to do some logs but need a new laptop first.
As stated it is the same for me, only happening on part throttle (only need enough throttle to maintain speed)....and there has to be a load (incline will do it, doesn't have to be a mountain).
As an aside, it will even do it on cruise control, if the above conditions are met.

Yeah will be interesting to see what you find.

[fR3ZNO]

Okay, another update. Now that I'm done with finals, I decided to tear into the car and swap in the turbo. With my old turbo on the bench I inspected it to see what the issue was. It has very little side to side play and no in and out. After looking it over I believe I found the issue:





Two fairly large crack in the waste gate where the flapper seals. I would imagine this would affect the sealing of the waste gate and cause the N75 duty cycle to max out trying to keep this closed (to no avail)?

Looking at the new used turbo, it seems to have slightly more side to side play and still no in and out. However, where the flapper seals it looks much better. I forgot to take pictures of that.

Would it be safe to say I have found my problem and should go ahead and install the newer turbo?

[old guy]

Two fairly large crack in the waste gate where the flapper seals. I would imagine this would affect the sealing of the waste gate and cause the N75 duty cycle to max out trying to keep this closed (to no avail)?

I really don't think those cracks have anything to do with an overboost condition. And I think you are a little confused as to how the N75 functions. It doesn't apply pressure to close the wastegate. It does just the opposite.

The waste in a K03 has a spring pressure of around 6 psi. That means the exhaust pressure has to exceed 6 psi to force the wastegate open. The N75 in it's unenergized state simply passes the high pressure (output) side of the turbo directly to the wastegate on the opposite of side of the wastegate diaphragm as the spring. So if you unplug the N75 your boost will be restricted to around 6 psi since that's all it takes to compress the spring and open the wastegate.

When the N75 starts it's duty cycle it dumps the boost pressure back into the TIP instead of the wastegate so the wastegate can remain closed until the exhaust pressure can force it open.

With the turbo out you can apply pressure to the wastegate and see if it opens around 6 psi. If the diaphragm is split the pressure will bleed past the wastegate and the wastegate will remain closed longer than it should and consequently you will get an overboost condition.

I suspect that may be your problem since you indicated that the N75 was running a full duty cycle when the overboost conditions occurs.

[fR3ZNO]

I really don't think those cracks have anything to do with an overboost condition. And I think you are a little confused as to how the N75 functions. It doesn't apply pressure to close the wastegate. It does just the opposite.

The waste in a K03 has a spring pressure of around 6 psi. That means the exhaust pressure has to exceed 6 psi to force the wastegate open. The N75 in it's unenergized state simply passes the high pressure (output) side of the turbo directly to the wastegate on the opposite of side of the wastegate diaphragm as the spring. So if you unplug the N75 your boost will be restricted to around 6 psi since that's all it takes to compress the spring and open the wastegate.

When the N75 starts it's duty cycle it dumps the boost pressure back into the TIP instead of the wastegate so the wastegate can remain closed until the exhaust pressure can force it open.

With the turbo out you can apply pressure to the wastegate and see if it opens around 6 psi. If the diaphragm is split the pressure will bleed past the wastegate and the wastegate will remain closed longer than it should and consequently you will get an overboost condition.

I suspect that may be your problem since you indicated that the N75 was running a full duty cycle when the overboost conditions occurs.

Thanks for the input, old guy.

I think I may have worded what I meant incorrectly.

I do understand with the N75 unplugged, the turbo will simply run off wastegate pressure. That was one of the first things that I did trying to diagnose this issue. With it unplugged I believe I did get around 6 psi. However, one other thing that was suggested to me was to disconnect the WG line of the N75 so that the wastegate would stay closed. From what I was told, I should have boosted very quickly and that boost would continue to build until I broke something or let off the throttle. With this, I was only able to boost around 18psi and then it started dropping off. With the old turbo out, I also noticed that I could easily spin the wastegate flapper disc with my finger suggesting that a good seal is not being made. I thought this was interesting considering that with the other turbo, the disc is much more tightly held against the wastegate and I can not easily spin it with my finger.

If the cracks are not my problem then I would suspect the wastegate diaphragm is my problem as you suggested. This was my first suspicion but it was difficult to test when the wastegate was opening on the car.

So, should the wastegate diaphragm hold pressure as well as a vacuum? I remember trying to test it on the car with a small handheld vacuum pump and I couldn't get it to hold a vacuum, but I wasn't sure if it was an issue with the tubing I was using or the vacuum pump.

One more important thing to note, on an APR tune, the overboost code is actually an underboost condition. This was brought to my attention over at Nefmoto:

P0234 is actually an underboost condition in that file..

http://nefariousmotorsports.com/foru...php?topic=7524

Not sure that helps you any, but it might.

and FWIW, this was from a very knowledgable member of Nefmoto so I trust what he is saying is true.

In regards to my maxed out N75 duty cycle values:

No, they're maxed out.

which means 111 is likely maxed out.

which means your wastegate isn't closing all the way, you have boost leaks, your inlet is collapsing, you have clogged cats, or your turbo is dying.

[old guy]

So, should the wastegate diaphragm hold pressure as well as a vacuum? I remember trying to test it on the car with a small handheld vacuum pump and I couldn't get it to hold a vacuum, but I wasn't sure if it was an issue with the tubing I was using or the vacuum pump.

Sorry... I wasn't thinking clearly last night. I meant to say that I suspect the wastegate is your problem since you were getting the overboost code during a low N75 duty cycle, not a maxed out duty cycle.

The wastegate never "sees" a vacuum condition. It only "sees" a boost pressure signal through the N75. But with that being said you should be able to pull a vacuum on it with your hand held vacuum pump. Either way of testing it the N75 should be able to hold pressure unless the diaphragm is damaged.

If the diaphragm leaks the N75 duty cycle isn't going to react as expected. Especially during low boost conditions. What happens is that the N75 tries to regulate back on the boost but the diaphragm leak reduces the sensitivity and consequently you will get more boost than requested. Under WOT conditions you really aren't going to see this because the N75 is already calling for full boost.

Your description of the issue seems to indicate that the limp mode comes on under partial but not full boost conditions which could be explained by a leaky diaphragm.

Now that you have the turbo off you can check it out thoroughly.

Good luck!

[fR3ZNO]

Okay, so I feel dumb for not trying this earlier. I took the air nozzle from my air compressor, adjusted the regulator to about 6psi and connected it to the wastegate port with some vacuum line.

On the old turbo, the wastegate would not open under 6psi and I could hear and feel air rushing past the diaphragm. It wouldn't open until I adjusted the regulator to around 20 psi.

However, on the new turbo, it opened right up at 6psi and there were no air leaks.

So now I feel pretty confident I found my problem.

[old guy]

And there you have it.

[fR3ZNO]

Ugh. Just finished up swapping the turbo and one of the coolant lines are leaking. The car doesn't go into limp mod anymore at least. I think it might be the coolant feed line. Used new copper washers and made sure it was torqued to spec. I guess that wasn't enough. It's also a fairly large leak, took it for a quick spin and the coolant tank is only half full now.

I'm waiting for the car to cool down a bit and I'll get under it and see where it's coming from.

[fR3ZNO]

Looking under the car with it running I don't see any coolant leaking. I also didn't see any wetness anywhere when I pulled off the belly pan.

How much coolant does a dry KO3 hold? I topped off coolant before going for a drive earlier.

[old guy]

Looking under the car with it running I don't see any coolant leaking. I also didn't see any wetness anywhere when I pulled off the belly pan.

How much coolant does a dry KO3 hold? I topped off coolant before going for a drive earlier.

Very little. Do you smell any sweetness from the exhaust?

[fR3ZNO]

Very little. Do you smell any sweetness from the exhaust?

Exhaust smells normal to me. I don't see any thick white smoke that would indicate coolant is being burned.

[old guy]

You referred to a large leak. Did you ever see any coolant under the engine or is your comment based on the reservoir level dropping after a drive?

[fR3ZNO]

You referred to a large leak. Did you ever see any coolant under the engine or is your comment based on the reservoir level dropping after a drive?

I assumed that the drop in the coolant reservoir was caused by a leak. I didn't see any coolant on the belly pan when I took it off or anywhere under the engine.

I had the coolant lines disconnected for at least a day or more while I was figuring what the issue was with the original turbo. Maybe some air was let in the system?

I'm going to top off the coolant again and see what happens.

[old guy]

I assumed that the drop in the coolant reservoir was caused by a leak. I didn't see any coolant on the belly pan when I took it off or anywhere under the engine.

It's very possible that you just had a bit of air in the cooling system that finally made its way out. Thus the drop in the reservoir level. I would top it off and go for another gentle drive around the block and see if it drops any further.

[fR3ZNO]

It's very possible that you just had a bit of air in the cooling system that finally made its way out. Thus the drop in the reservoir level. I would top it off and go for another gentle drive around the block and see if it drops any further.

I edited my post above. That's what I was thinking since I left the lines disconnected for a day or so.

[old guy]

I edited my post above. That's what I was thinking since I left the lines disconnected for a day or so.

Yep. I think you are on the right track!

[fR3ZNO]

Yep. I think you are on the right track!

Looks like I was! Wooh. What a relief. I came back from a quick spin and coolant level is good.

Thanks for all the help! 🏼