limp mode -overboost

50harleyrider · Oct 24, 2012

I got this code after an unexected limp mode. No CEL either:

1 Fault Found:
16618 - Boost Pressure Regulation: Limit Exceeded (Overboost Condition)
P0234 - 000 - -
Should I do a log of MAP requested vs actual and adjust the wastegate if there's overboost showing up? Remember I'm a 1Z guy so set me straight on the PD.I assume the N75 is OK.

vwztips · Oct 24, 2012

Never assume the N75 is OK. It is most likely that or a leaking hose, possibly to the waste gate

50harleyrider · Dec 13, 2012

I replaced the N75 and all the lines connecting to it and still am getting occasional limp events with the 16618 code. Is there a way I can check the wastegate operation? I pressurized the controller line and it does start moving at arround 10 psi. Should I do some wastegate adjusting to make it bleed boost a little earlier?? Should I do a log in VCDS measuring block group 115?

1854sailor · Dec 13, 2012

50harleyrider said:
...I pressurized the controller line and it does start moving at arround 10 psi...

The VNT actuator operates with vacuum, NOT pressure.

50harleyrider · Dec 14, 2012

1854sailor said:
The VNT actuator operates with vacuum, NOT pressure.

So it opens opposite from the earlier TDIs? My B4 opened under boost pressure. The VNT N-75 uses vacuum to the cannister? Basically the opposite? At what vacuum reading should it start moving and I'll check it? Does your B5.5 tranny jerk sometimes when it shifts especially when it's not quite up to temperature like it can't decide the right gear to be in? I see a conversion in my not to distant future.

mountain-valleymotors · Dec 14, 2012

Try unplugging your Mass Air Flow Sensor and see if the car runs better or if the code comes back. I had a bad MAF Sensor and it caused that code even when everything else was functioning properly.

50harleyrider · Dec 16, 2012

see my other thread for my latest misery:http://forums.tdiclub.com/showthread.php?t=371948

thundershorts · Dec 17, 2012

vacuum lines were replaced with oem cloth covered correct sized tubing? check valve installed in proper direction and checked to be operational? Transmission function you are describing (jerk or snatching between shifts is definitely not normal. You haven't commented as to what if any service you have done to it.

50harleyrider · Dec 17, 2012

Until I correct the overboost issue, I'm not gonna be too concerned with the jerking. I think that's an ECU and tranny controller signal issue caused by the overboost. I'm using silicone lines to/from the N75. Never had any problems with them on my B4s. Would they be a potential problem on the BHW? Should I have replaced the lines with OEM? Most of the guys on the forum use silicone replacements usually from McMaster-Carr as did I. Check valve is functioning and oriented correctly.

thundershorts · Dec 17, 2012

the id of the plastic tube is a perfect fit with the oem tube. you might check with your mighty-vac to see if at n75 your system has vac leaks and for function of the tandem.

50harleyrider · Dec 17, 2012

I'm getting 22" HG vac at the controller at idle. Controller appears to be opened up completely as it is moving about 3/4". Vac from the pump is 28" HG vac. Maybe I should shorten the controller about a full turn on the knurled adjuster and see if it goes limp at 2601 mb again? I've heard the Garrett factory set is not necessarily right. Obviously my turbo is OK making boost. I need to measure vacuum at the controller when limp occurs? Can I do this in VAG logs? Then I would know if I'm getting enough vac to bleed enough boost when limp occurs. I'm thinking more and more the vanes aren't moving enough. Oven cleaner is on my horizon.

50harleyrider · Dec 18, 2012

Got my fix here: http://forums.tdiclub.com/showthread.php?t=246287&highlight=oven+cleaner I used the blue non fuming Easy Off oven cleaner. Took 3 hours including 2 hours waiting for it to dissolve the soot. A wand and nozzle off of a cheapo carburetor cleaner fit on the Easy Off can so I could easily flood the whole turbine chamber and vanes. B5.5's are so much easier to remove the downpipe than the B4s and A4's. Highly recommend this chemical clean. A good Italian tuneup followed and everything is peachy! BTW,the jerking when shifting is gone too,Thundershorts.

eyeguy · Dec 18, 2012

I may have to give it a shot whenever I get mine back on the road. Luckily, I hadn't had a code the whole week it was back on the road before the trans decided one gear was all I deserved. Too bad Easy Off won't fix that!

1854sailor · Dec 18, 2012

50harleyrider said:
...Took 3 hours including 2 hours waiting for it to dissolve the soot...

Change your oil! There's no telling how much oven cleaner drained into the engine.

aja8888 · Dec 19, 2012

1854sailor said:
Change your oil! There's no telling how much oven cleaner drained into the engine.

Curious as to how you conclude any oven cleaner drained into the oil?

1854sailor · Dec 19, 2012

aja8888 said:
Curious as to how you conclude any oven cleaner drained into the oil?

Tony,

See post #4 in this thread:

http://forums.tdiclub.com/showthread.php?t=246287&highlight=oven+cleaner+VNT

Paul

aja8888 · Dec 19, 2012

1854sailor said:
Tony,
See post #4 in this thread:
http://forums.tdiclub.com/showthread.php?t=246287&highlight=oven+cleaner+VNT
Paul

Ok, I understand now, thanks.

Biodezl · Dec 20, 2012

Drivbiwire's concerns should be taken with a grain of salt. That opinion was posted very early in the experimentation with the chemical cleaning. There are several other opinions including one from turbo manufacturer Garrett who say that there is no problem with using Easy Off oven cleaner in the turbo.

1854sailor · Dec 20, 2012

Yes, I did read further in that thread, but I still think that it would be a good idea to change the oil afterwards.

aja8888 · Dec 20, 2012

Actually, a trace of oven cleaner (a caustic) in with the oil would only aid in neutralizing the acid (H2SO4) formed by the combustion process of sulfur compounds in the fuel.

50harleyrider · Dec 20, 2012

aja8888 said:
Curious as to how you conclude any oven cleaner drained into the oil?

Agree. If you look at the extensive thread where the A4 guys are doing it, those who were paranoid about it and removed the turbo return line,saw little to none dripping through. My shaft wouldn't rock any so I was confident little would get through. If any of you have loose shafts and feel like they would leak, that's a different issue (rebuild). I would recommend everyone do this and it really should become a sticky on the B5 forum. BTW, the non-fuming blue can of Easy Off worked fine in only 2 hours on mine. I did run it for a minute prior to the procedure to heat the turbo. Don't forget the cheapo carb cleaner nozzle and wand to really direct the flow in. My car is really factory feeling now.

vwztips · Dec 20, 2012

Did this do anything for your transmission issues you were experiencing?

50harleyrider · Dec 21, 2012

vwztips said:
Did this do anything for your transmission issues you were experiencing?

So far none of the jerking shifting. I think the ECU and tranny controller were out of sorts with each other from this. Hopefully one of the moderators will include this chemical cleaning on the "how to" sticky.

johnboy00 · Dec 21, 2012

If you write up a procedure, you can post it in that thread yourself. In fact, you could just post the link to the A4 thread on the subject, but that's hardly a how to.

Biodezl · Dec 23, 2012

vwztips said:
Did this do anything for your transmission issues you were experiencing?

Prior to the EO chemical turbo cleaning I wasn't even aware that the tranny was shifting strangely, but after a couple of weeks of driving I can say "yes," my transmission is shifting much better. Others?

tikal · Sep 17, 2015

Based on the experience gained using the oven cleaner method to 'refurbish' the B5.5 turbo, what are the down sides?

Brian's96TDIPASSAT · Sep 18, 2015

My daughters 05 before I cleaned the turbo last week would jerk during mainly 2-3 upshift under moderate to heavier throttle and it was due to the higher than normal boost pressure, in fact that's when it would set a code for overboost and pop into limp mode. It shifts perfect now and when monitoring actual verus desired pressure they stay as close as they can get now

tikal · Sep 21, 2015

Brian's96TDIPASSAT said:
My daughters 05 before I cleaned the turbo last week would jerk during mainly 2-3 upshift under moderate to heavier throttle and it was due to the higher than normal boost pressure, in fact that's when it would set a code for overboost and pop into limp mode. It shifts perfect now and when monitoring actual verus desired pressure they stay as close as they can get now

I do not get a code or go into limp mode. What I do get when shifting between second and third gear under moderate to heavier throttle there is somewhat of a bucking experience, the acceleration is not smooth. Few months ago I did an engine flush using BG 109 and the symptoms subsided but did not go away. So I am now looking at the turbo preventive maintenance and the possibility of cleaning it using the oven cleaner method.

Since products such as EASY-OFF are flammable I am a bit concerned.

Thoughts?

tikal · Sep 21, 2015

By the way by TDI guru did diagnose a slight overboost problem recently but nothing that requires immediate corrective action.

Brian's96TDIPASSAT · Sep 22, 2015

I've seen guys cleaning them by removing the downpipe at the turbo, blocking off the turbo outlet and filling thorugh the EGR tube, just make sure you don't over-fill it and get oven cleaner in your exhaust ports. You might want to make sure the whole system is working correctly first before assuming it's not the actuator, your N75 valve or a vac or boost leak.

limp mode -overboost

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