Boost Spike and Diagnosis

dataiv

Veteran Member
Joined
Feb 12, 2005
Location
Ottawa, ON
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2015 Golf Wagon TDI 6MT
Hi all,

I have been doing a lot of searching and research on the site, but I still need some assistance. My 99.5 Jetta has 245,000 km on it, mostly highway. At 235,000 or so, the car was going into limp mode when at full throttle in 5th gear (and sometimes in 4th). In December I took the head off, cleaned the intake, took apart the turbo, and found the vanes weren't really stuck, but a bit sticky sometimes. When I put everything back together the vanes were moving freely. It is fine most of the time, but sometimes it goes into limp mode still with the same code:

Code:
VAG-COM Version: Release  311.2-N

Control Module Part Number: 038 906 018 EB 
  Component and/or Version: 1,9l R4 EDC G400SG  2143
           Software Coding: 00002
            Work Shop Code: WSC 00066
1 Fault Found:
17958 - Charge Pressure: Control Deviation
        P1550 - 35-10 - - - Intermittent
I still get a big boost spike, and I don't know if I should try adjusting the linkage on the VNT mechanism. I have checked the N75 and it appears to be fine. Having VAG-COM cycle the vanes in group 11 basic settings mode seems to be fine, and the rod travels as it should.

So, what I would optimally like to solve, is both problems, the boost spike, and the sometimes going into limp mode. I haven't ever been logging the data when it went into limp mode yet, as I haven't been that lucky... :rolleyes:

Anyway, any hints for what I should try next and check next would be much appreciated.

Below is a graph of a run I did today at full throttle in 5th gear from 91-126km/h. I would like to go further, but I ran out of room today.


 
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dabear95

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Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
At the highest RPM you have recorded, what is the MAF reading? It should be at least 850-900 mg/h at 3,000RPM.

Can you send me the "raw" data log?



Jason
 

dataiv

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Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
The MAF is on the chart as well. The light blue colour. It is not, as you say, 850-900.

I have another run in 4th gear where RPM goes up to 3500 and the MAF still reports less.

But could that be an MAF problem as opposed to a turbo problem, given that the two follow each other so closely on the graph? I replaced the MAF once before about 140,000 km ago and it felt different when that was the problem last time, plus it never went into limp mode.

Here are four logs that I took today. One is with the IQ setting at 32768 (the default), which gave IQ of 2.0, then one with the IQ at 3.0, and one with the IQ at 4.0. Each setting made a bit of a difference, which was expected.

http://txn.vangeyn.net/LOG-01-011-010-022-3logs.zip

I should also mention, I forgot in the first post, that the car is completely stock.
 
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dabear95

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Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
Yes, I saw that it was on your graph but I did not want to interpret the date incorrectly. My MAF reading was significantly higher than 850-900. Also, your MAF readings at other RPM levels differ greatly from mine. I would try and unplug your MAF and see if it runs better (more power). Easy to check…




Did you check the vacuum line from the N75 to the turbo? I think the N75 and N18 can be switched. That would need to be confirmed by a more experienced member however. Maybe the N75 is "worn" out, if that is even possible.



I have graphed the "longest" run from the files. I think a run in 4th gear from 1700-4000 would be helpful...






Jason
 

dabear95

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Joined
Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
This is my cars requested versus actual:




It seems logical that your car is not reacting fast enough. why...


Jason
 

dataiv

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Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
Yeah, it is definitely strange. I will do a 4th gear run tomorrow because that's easy enough to do (5th gear up to 3500 RPM is really tough given how fast that actually is!).. but it was in 5th gear that it was going into limp mode. Right when I passed 2800 RPM it went into limp mode yesterday, then I restarted and did it again at almost the same RPM again. Then today, it wouldn't go into limp mode. It's very peculiar.

I think you may have gotten the PSI calculation off, because I know my car "requests" more than 14 PSI of boost. It's still easy enough to see, anyway.

What should the MAF values be? I am not exactly sure, but I though 850-900 was about the maximum it ever is.

If I use a mity-vac on the vacuum hose going down to the turbo, it holds vacuum fine, so I don't think that is leaking at all there.

I have no idea either if the N75 does "wear out"... from other people what I've read, it just dies and doesn't work properly at all anymore. Mine at least seems to be working.

I will try with the MAF unplugged just to see, and I will also get a 4th gear run tomorrow and will post that once I have it.

Thanks for the help.
 

dabear95

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Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
Yeah, the psi is wrong for sure. I just subtracted 1,000 for an atmosphere.

I don't have my MAF log on my desktop; it is on my laptop at work. I know I had readings over 1,000.

You’re not kidding about trying to log in 5th gear, lol. Let me know what happens with the MAF unplugged.



Jason
 

dataiv

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Location
Ottawa, ON
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2015 Golf Wagon TDI 6MT
Alright, two new graphs I have below, as well as the link to the raw data logs. With the MAF unplugged, the "actual" value is constantly at 550 mg/R, and the car was doggishly slow then. On the 4th gear run, I could get nowhere near 4000 RPM in the short space I had to do it. It would have taken quite a while. Though, in that run, the boost appears to stay much more constant than when it's plugged in. With it plugged in, it is a lot faster, yet it fluctuates more. I graphed spec & actual MAF and MAP (boost in millibars) along with RPM and speed again. With the MAF plugged in, I got a better run, due in part to the faster acceleration, but I had to do it twice to get up to ~4000 RPM because of traffic conditions.

Anyway, here is the data. Let me know what you think. I have no idea any more. No limp mode today, though yesterday I did adjust the IQ value which was at ~2.0 mg/R up to ~3.0 mg/R. Less smoke on startup for sure, but I was never getting any smoke at WOT even still. The graph I posted yesterday, along with the logs, are all with the IQ already at ~3.0. When it was at ~2.0, it made no difference as far as the fluctuations in boost, etc... I did check that before modifying it.

The logs: http://txn.vangeyn.net/LOG-01-003-011-022-MAF.zip



 
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Kiwi_ME

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Jul 3, 1999
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New Zealand
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'18 Kona EV, ex '03 Golf TDI, '82 Rabbit Diesel
Sorry just to butt in but I think you simply need a new MAF. At least you should first rectify the discrepancy of the low MAF output before looking further.

Since the MAF peaks are in slightly in advance of the pressure peaks I'm guessing (wildly, I might add) that the MAF (demand-actual) error makes a contribution to the requested pressure that is not part of the logged pressure demand. Just a thought ...
 

dabear95

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Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
MAF Time :(


Dieselgeek has a new non-bosch MAF that is cheaper. Although I do not know if many people have tried it.


It's going to be even faster with a new MAF though!:D

Edit- I just went back and checked my MAF log. I bet a new MAF will make a huge differance for you. It will probably eliminate the underboost...

Jason
 
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dataiv

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Feb 12, 2005
Location
Ottawa, ON
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2015 Golf Wagon TDI 6MT
What makes you really think that it is the MAF that is the problem? How do we know it's not the turbo boost just fluctuating, which would also affect the air mass? I don't want to buy an MAF unless we are pretty sure..

I just wonder how you arrived at that conclusion?

I can get a new MAF from Roseland here in Canada, for $80, which is not bad at all. Last time I replaced the MAF it was still a super expensive part and I paid something like $350 for it. That was back in late 2000 or maybe early 2001.

Has anyone else ever had limp mode from a Charge Pressure: Control Deviation code from a bad MAF? It doesn't seem to make sense.

This is the part listed on the Roseland website:

Bosch, 0 280 217 121
Mass Air Flow Sensor Assembly
( for all ALH Engines, new, not rebuilt )
 

Kiwi_ME

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Jul 3, 1999
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New Zealand
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'18 Kona EV, ex '03 Golf TDI, '82 Rabbit Diesel
Note you are reaching peak demanded pressure at times which by simple physics will develop "full" air flow unless your IC or intake manifold is badly clogged. Your MAF should respond accordingly yet it appears to be low.
 

dabear95

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Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
Dataiv

I will post my MAF graph tomorrow morning to help.

Simple answer, I don't. But I do think your MAF is bad based on the data. Is there anyone close by with a MAF you can borrow? To make sure.


Jason
 
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dataiv

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Joined
Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
Well, thanks, I'm ordering a new MAF and hopefully it will solve the problem.. I will post back when I know one way or the other.

David
 

GolfTDIer

Well-known member
Joined
Sep 24, 2003
Location
Alma, ON
TDI
2000 GOLF sold, 2004 Jetta Sport
I have been having the same problem and getting the same code with my car and have done all the same maintence as discribe in your first post. I am very curious as to whether a new MAF will fix your car.
 

Vindiesel6

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Jul 14, 2003
Location
Northern, NJ
TDI
2002 VW Golf GLS TDI & 2015 Q5 TDI
I had a similar problem with an over boost condition but it was not caused by the MAF sensor. This was causing me to go into limp mode also. It ended up being blown turbo seals causing large amouts of oil to collect in the intercooler. This caused the IC to become restricted and under WOT tripped the overboost code putting me into limp mode.
 

brucetmoose

Veteran Member
Joined
Jan 20, 2006
Location
Rochester, NY
TDI
Used to own a 2002 Jetta TDI - Black/Black
Experiencing the same thing and have some general questions on it

I have 75k on my 2002 stock Jetta TDI and all of a sudden this "limp mode" issue is happening to me. It seems to happen all of a sudden and it happens in the middle of the first hill I climb when the car is cold. I don't have VAG-COM or anything like that so I can't do a reading, but I'll bet for me it's one of 3 things:

1 - Needs an EGR cleaning (Been told it looks dirty)
2 - MAF needs to be replaced
3 - The turbo is dying

Right now the problem is intermittent, but I'm betting it's going to get worse.

Curious - when a "code" shows up like the one described, does the check engine light come on? My light doesn't, but I can actually feel the power loss when it happens, on, and the car gets noisier too - starts to sound like the old VW Rabbit diesels or like a broken muffler.

Limp mode seems to go away if I park the car for a few hours and re-start it.

What I wouldn't give for a boost guage - too bad that doesn't come stock.
 

Vindiesel6

Veteran Member
Joined
Jul 14, 2003
Location
Northern, NJ
TDI
2002 VW Golf GLS TDI & 2015 Q5 TDI
The CEL usually does not come on with the car goes into limp mode. It did not come on on mine. I would doubt that it is your MAF because the 2002 and up cars had very reliable MAF sensors, unlike the previous models. If your turbo is "dying" and it is due to blown turbo seals from not driving it at a high enough rpm then you will have a large amount of oil collected in your intercooler, about a quart or more. It is normal for there to be less than 1/2 cup of oil in there but if you pull off the lower intercooler hose and oil pours out like you are changing your oil it is very possible your turbo seals are blown. You should attempt to have your EGR cleaned and see if this fixes your problem and also check your IC for oil. Good luck.
 

dataiv

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Joined
Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
My old MAF was definitely a bit tired and in need of replacement. Boost now levels off and the MAF readings are a lot more normal, but, I still have a huge boost spike at the beginning of throttle application, and I am still not sure why.

I have two graphs below, one of 4th gear full throttle from about 58 km/h to 140-something, and also 5th gear full throttle from 112 to 158 km/h. In the 5th gear graph I note that I was watching the boost sticking at ~2400 millibars, so I backed off the throttle momentarily, after which the boost stabilized quite quickly. The reason I did this was because the time earlier that I tried a 5th gear run, it stuck at ~2450 millibars and after about 3 seconds went into limp mode.

Could this big boost spike be caused by an old and tired N75 valve? Or is it something else... that is the question that still remains. Any other ideas anyone on what else to check?

Here are the graphs:



 
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dabear95

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Joined
Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
dataiv,

Interesting, I know it is frustrating and I want this to be done so you can enjoy driving without worrying.


I would not be worried about the first spike, but the 2nd is troubling with a stock setup. The N18 and N75 can be swapped to check. Double check this with your dealer, but for my car they are the same part number.


It's possible that your VNT actuator is getting sticky from age/miles. I would remove the vacuum line to the turbo and then move the linkage to make sure it is free. See if anything seems odd at that point.

My case is a bit different in that I'm chipped/injector and trying to limit my spike's. I adjusted mine today with member Jetaah and we did many runs, trial and error. The first adjustment we made caused the maximum boost spike to be 16psi, requested is about 18.5! (with massive smoke, not enough air to burn the fuel) It now spikes to around 19.

I would remove the vacuum line to the turbo and move the linkage to make sure it is free. See if anything seems odd at that point. Also, check the vacuum line for leaks or replace if the VNT feels fine and no change by switching N75 and N18. At this point my question would be:


Was it spiking prior to you getting the CEL? Maybe it has been spiking all along. If you determine there are no other issues and you want to reduce the spiking, there are ways...


The new MAF did eliminate your underboost!! Hopefully it's just a two part problem.



Jason
 
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99A4Wett

Member
Joined
Oct 9, 2005
Location
ohio/pa
TDI
jetta 99 a4 GLS silver with Wett chip
I have the same problem, repeatable 4th and 5th gear WOT at 3300 rpm. 99.5 193k miles (been doing it for 15k miles). Get CEL if I do it several times in a row.

I have:
cleaned intake
shutdown EGR
checked vacuum lines
replaced MAF
cleaned vacuum check valve
verified turbo vacuum control operates smoothly over full range.
One dealer said MAF,
another dealer said Turbo (because he found 1/2 cup of oil - when asked, said oil interferes with pressure sensor, he admitted 1/2 cup after 190k miles not bad, I note draining oil had no effect on problem)

bought a new N75 but it has a different connector, so it was not installed.

I am living with it, reading and waiting for the definitive word on this website for a fix.

PS how do you make such nice graphs? I have several logged Vag-com runs.
 
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dataiv

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Joined
Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
Indeed the new MAF did correct the underboost in my case. This week I am using the M-B diesel instead of the Jetta but will likely be using the Jetta again in a week or two. Then, I will begin to diagnose it again.

What is different about your new N75? It won't plug in because of a different electrical connector? That's really annoying, because I was going to purchase one as well.

Regarding the 1/2 cup of oil after so many miles, I had my intercooler pipe off when I took the head off and changed the timing belt in December, and I can't seem to get any oil out at all. Is it actually that hose, or a different one? Anyway, I know my turbo is good, I am not losing oil between oil changes and when I had the head off, I had the turbo out. Everything looked fine... no foreign object intrusion, no play in the shaft, etc...

I think my next step is to make sure the vacuum line down to the VNT actuator is in good condition. The actuator itself moves just fine.

99A4Wett, I also don't really know what to try next, other than trying to get an N75 with the right connector assuming my vacuum lines are okay.

I also need to check if the N18 and N75 are the same and then I could try swapping them. Have you checked this on your car?

I have been using Excel to make the graphs. I open the CSV log file in Excel, find the logged columns that I want to use in the graph, and select a small range (such as the 5th gear WOT run, and 4th gear WOT run), and make an X-Y scatter plot of it.

dabear95, how do you adjust the VNT to limit the spike? Is that the adjustment of the locknut on the actuator arm? Maybe that's what I need to do, because it seems to be controlling the boost very well all through the RPM range except right after application of WOT.
 
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dabear95

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Joined
Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
Dataiv,
Check it out!

Look at the first page and you can see my spike after getting the tuning done.


Now, after VNT was adjusted (about 6 times to get it right):




I do have a bit of smoke now as the lag is slightly more. However, it appears the boostvalve no longer has a bearing on anything. I think I may adjust it to allow a tiny overshoot just to minimize smoke. Keep in mind I have tuning/nozzles.

Process- You will need a vacuum pump to test when it starts to crack open. Jeff from rocketchip has a post in the thread below about certain measurments for adjustment. This did not work for me, when adjusted as indicated in that thread I could barely reach 14psi and smoked like a train. It may be trial and error depending on each car/setup.

Remove snap ring where actuator rod connects to turbo, remove two bolts from actuator to bracket. Leave the bracket on the turbo, remove only the actuator from the bracket. Now you can adjust by loosening the nut nearest the vacuum connector and spinning the knurled section on the rod. In my case it had to be heated with a torch, then while securing the main section the nut was able to be loosened.

http://forums.tdiclub.com/showthread.php?t=130520


Edit - According to those with more experience you do want a bit of overshoot 2-3 psi to minimize smoke. Even on the stock setup.

Jason
 
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99A4Wett

Member
Joined
Oct 9, 2005
Location
ohio/pa
TDI
jetta 99 a4 GLS silver with Wett chip
What is different about your new N75? It won't plug in because of a different electrical connector? That's really annoying, because I was going to purchase one as well.”

Yes, it was annoying, TDIparts said they would refund without restocking fee, my connector is more square-ish than the one they sold which was an oval. So it was invent your own connector or… a nearby dealer quoted me 60$ on an N75, but I bought a new GLI instead so, the TDi problem is less immediate to me

99A4Wett, I also don't really know what to try next, other than trying to get an N75 with the right connector assuming my vacuum lines are okay.

I also need to check if the N18 and N75 are the same and then I could try swapping them. Have you checked this on your car?


They appear the same, but pulling the vacuum lines without damage is problematic so… I have not tried it yet.

I will play with excell and post when I can get a little quiet time....
 
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dataiv

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Feb 12, 2005
Location
Ottawa, ON
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2015 Golf Wagon TDI 6MT
Today I had some time ...

One of the things I did was get under the car while it was running, with VAG-COM in Basic Settings on Group 11 (so that it cycles the N75 valve/turbo actuator every 10 seconds or so).

The actuator itself moves very quickly when it cycles back and forth, and looks like it's operating perfectly normally.

I also tested the actuator while hooked up to a MityVac and the actuator does not start to move until 8-9" Hg (which from everything I read is about right).

So I still have no freakin' idea why the boost spikes so much! I really don't know what else to check ... any more ideas?
 

dataiv

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Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
Vanes definitely aren't stuck ... I did have the turbo out and took it apart, cleaned it, actuator arm moves like it should (the spring is very strong), but Basic settings in group 11 the actuator arm moves from one extreme to the other very quickly without any jerk in the motion.

That is using the N75, so it also seems to work ok ...

When N75 typically goes bad, it stops working completely, doesn't it?

This is such a frustrating problem ... :(
 

dataiv

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Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
I have a feeling my conclusion is that it is either the VNT diaphragm/actuator not responding as it should (i.e. worn out due to age), or the N75 ... so, honestly, my bets are on the actuator.

Lots of people must have the VNT mechanism (diaphragm, actuator) laying around from blown turbos, replaced turbos, etc ... anyone in the general Toronto area have one that they want to sell?
 

XJCoupe

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Dec 25, 2005
Location
D.C. Metro
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none
Similar problem here. My car has has 84k miles (135k km) on it. I swapped MAFs (a friend had a spare) -- no change. Yesterday I did the VNT actuator test in VAG-COM, and the linkage seems to move quickly and freely.

I installed a boost gauge a couple weeks ago, and that's when I became concerned about the boost spike of up to 26 psig. Since then I've backed off the throttle to keep the spike from exceeding ~22 psi.

My graphs look similar to yours:
Specified vs. Actual Boost


Specified vs. Actual MAF


Related posts:
http://forums.tdiclub.com/showthread.php?t=133096
http://forums.tdiclub.com/showthread.php?t=135100

Next I'm going to swap the N75 with the EGR solenoid (or whatever it's properly called) and make sure I don't have a vacuum leak. If that doesn't help, I'm going to remove and clean the turbo and intercooler -- and maybe the intake, too.

Other diagnostics to try?
 
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