Underboost nightmare

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
Okay so this is a saga, but I NEED your help. I have an 05 passat TDI Wagon. First off I am a homeless vet living out of this car, was spending my summer in the white mountains hiking, and had planned on heading back home to Va in the fall. Then it tarted kicking into limp mode. Any demand for power is met with limp mode. Car still revs, and when on flat ground can gain speed. I researched my a** off for the last two months and replaced N75 and all my vaccumn lines first. When this did not solve the problem I broke down and took it to a shop (who originally claimed to have VCDS, but in fact did not) cost $66 to hand me a list of codes. Based off the codes I have bit the bullet and replaced MAF sensor, thermostat, coolant temperature sensor, intake flap motor, glow plugs(7v), and even spliced in new glow plug wires. All codes are gone minus underboost and constant/immediate limp mode. Egr was deleted by the previous owner, so that code is always there. Went out and got a vaccumn tester. Vane actuator tested somewhat low, so I removed the turbo and adjusted it to start moving about 3 and hits the stop right about 20 (did not move stop screw) as I have read on here. I'm headed to Home Depot now to get some stuff to make a boost leak tester (I have one of those 12v tire air pumps). BTW I'm doing all this in the Biddeford, Me Walmart parking lot where Ive been parked for a month and a half. Beyond that, I'm lost. My dog and I live off of $1,200 a month from my disability and have already spent over $800 from my Oct check trying to fix this. MAP sensor maybe? Wouldnt that throw a code? Tandem pump? Hoping I can find what I need to do a boost leak test and that's it, even though idk how I'm going to afford new vw hoses. Any other suggestions or help would be GREATLY appreciated. My daughter's birthday is at the end of Oct and I promised her I would be there. Plus it's starting to get really cold at night.
 

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
Did a boost leak test. It can build enough pressure to blow off of the turbo inlet, but at the same time bleeds off to nothing. I'm in a parking lot, so there is some noise. Didn't hear any leaking air. Lost daylight so I'm going to get a spray bottle tomorrow and try to spray everything down with soapy water.

Again, can my MAP sensor be bad without throwing a code?

I am not a mechanic, if not evident from my posts.

Thanks in advance.
 

Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
Have you looked at the turbo outlet hose? Perforation due to contact with a ground cable is a common problem. Also common is a break in the short 90 degree hose connecting the upper crossover to the intake flap. O-rings can also be a problem. I have experienced all of the above. I think you will need a bigger air source than a 12V compressor to find a leak.
I also think a leak small enough to need soap bubbles to find would not trip a limp mode.
Building enough pressure to blow something off the turbo inlet suggests a very small leak but you didn’t say where the other end was.
 

Passat'n Adventure

Active member
Joined
Feb 17, 2013
Location
Augusta, GA area
TDI
05 Passat GLS Wagon - Deleted and 5 speeded
Check for a boost leak. My first boost leak (a few years ago) came from the hose off the turbo with a hole worn in it by a poorly placed zip tie near by. I bit the bullet and paid just over $200 for a new hose. I am currently experiencing a leak somewhere - but have not had the time to pin point the location. No limp mode or CEL, but I slowly lose power under demand (going up a long hill). When I find this one, I am considering a tape until I can get a new pipe. Any recommendations?
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
I have had good success using smoke machines to find boost leaks that are not readily obvious.

However, on any of the PDs, careful systematic removal, cleaning, and close examination of the boost hoses (there are a total of four on the BHW) paying special attention to any oily areas, splits, worn retaining tabs, and split o-rings, will usually get to the source. The intercooler also hangs low and can be damaged from front end crashes. Yes, even a little "bump" into a curb is enough.
 

thundershorts

Top Post Dawg
Joined
Jul 15, 2010
Location
west chester pa
TDI
2015 passat tdi sel premium 2015 golf s tdi gls tdi b5.5, 2002 eurovan,Peugeot 505 td,Citroen cx25 prestige
Did you try anything as simple as just unplugging the maf and leaving it unplugged? You mention you bought a new maf and I found that unless you bought it from VW for the high price they don't work. After going through a few duds, I left mine unplugged and drove it for five years with no problem except the light was always on.
 

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
I have a cap on the elbow directly in front of the intake flap motor. Other cap is on the turbo inlet. I can build up 20psi, and it takes about a minute to a minute and a half to bleed off. Can't hear any leaks, nothing with soapy water. Wouldn't think a boost leak this small (if its not in my cap fittings) would trip a CEL and kick it to limp mode, especially as quickly as it does. I mean as soon as the turbo should be kicking in it goes into limp. 2kish rpms. I got a run in late last night where I rolled super gently into the throttle and it boosted strong 2nd into 3rd, but then I ran out of road. I'm soo lost. I filled the system with smoke with a transfer pump and a cigar, absolutely 0 signs of smoke exiting anywhere.

Still wondering if a MAP sensor can cause limp mode/underboost code.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
Unfortunately there really isn't much we have to go on here. We have no idea what the actual DTC(s) are. Lots of things can send the ECU to go into limp mode. Overboost, underboost, etc. You said you have an underboost DTC, I assume P0299. That pretty much is always a boost leak, or the turbo is not working.

You're going to need a scan tool to get any good information. The BHW's boost control system is brutally simple. It is the only thing under the hood that the vacuum system supplies (beyond the obvious brake boost assist).

Unfortunately, on the BHW, the N75 valve and its related connections and vacuum reservoir are located in a difficult to access spot down in front. You can more easily get to it with the air cleaner assembly removed. If you have a proper scan tool, you can do the test for the VNT actuator, and with the engine running watch the VNT control rod move up and down. That simple, quick, easy, do-not-even-get-your-hands-dirty test will verify the vacuum control side's integrity.

Then from there, if you cannot find any boost leaks anywhere, I'd take the turbo inlet off and check the condition of the turbine wheel itself, and see if it is trashed. Although a typical failed turbo will whine and blow massive amounts of oil into the intake, exhaust, or both.
 

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
Not getting any oil blowing out anywhere, small amount in intake, but very negligible as I have removed, inspected, and cleaned all intake tract piping. Turbo spins freely and seems solid. Could I have reinstalled the cartridge incorrectly when I disassembled and cleaned it? It functions "properly", as in moves freely with applied vacuum to vane actuator. Is there a "reverse" direction I could have assembled it to? I don't feel like that's mechanically possible since I can boost normally as evident from my run last night. I have since repeated this test. It will boost fine up to about 3k rpms if I dip into it slowly.
 

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
Should this intake system hold applied psi indefinitely? 2 minutes to bleed 20psi. Going to try to building a smoke generator from a soldering iron, baby oil, and a jar to see if I can pressurize smoke throught the system.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
Before. I took the turbo apart to clean per limp mode checklists.

Hmmm... well I would have never advocated such an action. But here we are. Well, you are.

My previous post still stands. Get a scan tool. Do some testing. Or keep throwing parts at it. Not much else I can help with, sorry.
 

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
Why would you not advocate taking the turbo apart to clean? Every post I've seen on limp mode, at some point or another says to clean the turbo as vanes could be stuck. I beilve I had slow leak in the extension air line off my compressor. I removed the "extension" and it held 18 psi for more than 5 minutes. Now I'm really lost.
 

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
Hmmm... well I would have never advocated such an action. But here we are. Well, you are.
My previous post still stands. Get a scan tool. Do some testing. Or keep throwing parts at it. Not much else I can help with, sorry.
Can you recommend one? Do I need to go as far as a ross tech cable?

I'm lost at what more parts I could throw at it.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
I am really only familiar with the older VAG dealer 5052 scan tool, or VCDS (ross-tech). The 5052 is an obsolete albatross, but you can still find them out there for lots of money and no tech support or updates or anything. Or, you can use any cheap portable PC and VCDS. I run mine on a decade+ old Asus EeePC mini with Windows XP and the HEX+CAN cable. And I use it every day.

Someone here was just this week selling a VCDS-capable portable PC for $55 (you'd have to get the cable still).

Or you can take it to someone familiar with TDIs and have them diagnose and fix your car. I have no idea where you are located, but there is a list on this site for folks that service these.
 

Zambee500

Veteran Member
Joined
Jun 29, 2008
Location
Atlanta, GA
TDI
2005 Passat GLS TDI
I don't know how, but if you could get your car to Richmond, ME you might find some TDI help. From the Trusted TDI Mechanics list in 101 section:

https://docs.google.com/document/d/...IFdtHnEQ/edit?hl=en_US#heading=h.3dp7l7wvit5l

Herm TDI (http://forums.tdiclub.com/member.php?u=7130), (Herm Pasker) located in Richmond, Maine, 207/737-2861

Also, this guy in Union Maine, who sounds like possibly a mobile mechanic but not sure if 100 miles is too far:
http://forums.tdiclub.com/showpost.php?p=5066975&postcount=2797


The VAG-COM/VCDS finder map on this site appears to have gone down, but there is another maintained by Vortex (I think?) located here: http://www.maptive.com/ver3/VCDS_Locator

Looks like there is VCDS in Harpswell.

Good luck!
 

d24tdi

Veteran Member
Joined
Jan 6, 2019
Location
MT
TDI
97 AHU in a Toyota pickup
A restricted fuel filter can cause slow or low boost also. Any idea of the age of it?

Taking a little step back -- first of all, maybe worth us acknowledging, this is a tough situation you sound like you are in. You have my sympathy. There's a lot of good advice being given here in response to your questions, hope you find a solution.

But it's also worth someone saying directly: these particular cars can be expensive to take care of, have a longer-than-average list of (fixable but serious and costly) common failure points, and can be challenging to diagnose and repair if you don't have the right diagnostic tools and skills yourself or are trying to rely on mechanics that lack the same. Like a lot of expensive cars (or cheap cars with expensive bones, like these Passats) they don't tolerate neglect well at all, and get expensive fast if you try to do the bare minimum or any cut corners in terms of upkeep.

Given the situation you described yourself as being in, there are probably other vehicles out there that might suit your needs better and leave you at lower risk of the car turning your life upside down with a major failure or repair bill. Already it sounds like it's given you quite a bit of trouble and cost you some money. Have you considered selling this car as is and getting something simpler and cheaper to keep on the road?
 

thundershorts

Top Post Dawg
Joined
Jul 15, 2010
Location
west chester pa
TDI
2015 passat tdi sel premium 2015 golf s tdi gls tdi b5.5, 2002 eurovan,Peugeot 505 td,Citroen cx25 prestige
No mention anywhere of air filter. I've seen one clogged to the point of being distorted. Why not take the filter out for test purposes?
 

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
Will post an update in the next few days. Had spontaneous dissection of my left anterior descending coronary artery on Sunday. Multiple heart attacks, died 3 times, shocked a total of 6 times, now have a supposedly massive stent holding the tear together. Thank you all for your responses.
 

GmasWagon

Member
Joined
Sep 25, 2019
Location
Biddeford, Maine
TDI
05 passat TDI GLS
A restricted fuel filter can cause slow or low boost also. Any idea of the age of it?

Taking a little step back -- first of all, maybe worth us acknowledging, this is a tough situation you sound like you are in. You have my sympathy. There's a lot of good advice being given here in response to your questions, hope you find a solution.

But it's also worth someone saying directly: these particular cars can be expensive to take care of, have a longer-than-average list of (fixable but serious and costly) common failure points, and can be challenging to diagnose and repair if you don't have the right diagnostic tools and skills yourself or are trying to rely on mechanics that lack the same. Like a lot of expensive cars (or cheap cars with expensive bones, like these Passats) they don't tolerate neglect well at all, and get expensive fast if you try to do the bare minimum or any cut corners in terms of upkeep.

Given the situation you described yourself as being in, there are probably other vehicles out there that might suit your needs better and leave you at lower risk of the car turning your life upside down with a major failure or repair bill. Already it sounds like it's given you quite a bit of trouble and cost you some money. Have you considered selling this car as is and getting something simpler and cheaper to keep on the road?
I am going to replace the fuel filter soon, maybe even do the upgrade. I replaced it about 15k hard miles ago.

I appreciate the sympathy, but life is what it is and I try to take it in stride.

If I can have it my way, I will never get rid of this car. Give it a bit more time and I'll be an expert on this specific one. Sorry, not for sale.
 
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