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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old March 25th, 2008, 10:42   #61
MTDiezel
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Alrighty.

Thanks for the information. Changed the hose inside the ECU a week or two ago (mine was gooey too). Quick question though, seem to have read in a different thread that you were able to calibrate the actuator in some fashion to respond quicker/slower if necessary....

Also took the multipin connector off the N75 and checked resistance, it was about 1.5 ohms...is that good or bad? Going to drive around and check a few things with the VAGCOM.

Tried to check things with VAGCOM, but old laptop battery has a hard time lasting more than 5 minutes. Timing looked like it was in good range, right in between blue and green lines on TDI Timing chart. after a drive to warm up engine still said engine coolant wasn't warm enough, said it was 39 degrees C...anyway....will have to find a way for battery to last longer so I can log groups 10 and 11.
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Old March 25th, 2008, 11:09   #62
likmywagon
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Hi I found the hissing, despite myself and a few other people being pretty sure it was under the dash it turns out that last mechanic left a clamp off of the air intake line just before the manifold. The sound must have been transmitted down the steering column.
As for your N75 I haven't read the whole thread but when mine works properly it makes a very disinct ticking sound and when it failed the sound was no longer there.

A

Last edited by likmywagon; April 6th, 2008 at 17:32.
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Old March 26th, 2008, 14:21   #63
MTDiezel
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Well MTJake and I figured out the problem. After going through all the above (hoses, wastegate, N75 resistance (which was the same for the good N75 as well as the bad one-we later measured mine, and 2 other good ones and they all had a resistance of a little over 2 ohms...) MTJake had a "spare" N75 he had ordered for one of his Passat's. We put that on and -NO MORE LIMP MODE. (knock on wood). I also haven't heard any clicking at all whether it was the old "bad" N75 and the new one.

Tony-Thanks for all of your help. I probably should have just ordered the N75 right away, but the hoses needed to be replaced anyway and I became a lot more familiar with the vehicle itself. On to the next set of issues-coolant temp sensor?, Window regulator etc.
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Old March 26th, 2008, 16:47   #64
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Quote:
Originally Posted by MTDiezel
Tony-Thanks for all of your help. I probably should have just ordered the N75 right away, but the hoses needed to be replaced anyway and I became a lot more familiar with the vehicle itself. On to the next set of issues-coolant temp sensor?, Window regulator etc.
Glad to hear it all worked out! In the end, it's all about applied learning.

Quote:
Originally Posted by MTDiezel
On to the next set of issues-coolant temp sensor?, Window regulator etc.
Welcome to used cars! I'm in the same boat!

Tony
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Old April 1st, 2008, 14:43   #65
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Hi everyone, Good post and very helpful in troubleshooting but can i add a few things.
Firstly in my opinion, if a vehicle of any kind (with an engine obviously) has an intermittent problem, it has been my experience of working on all kinds of cars, bikes and heavy goods that the problem will be electrical/electronic, If you have a mechanical problem, (timing belt, valve damage, piston ring problem, carburettor problem, injector pump fault) ((the list is massive)) then the vehicle will have a consistent fault.

e.g while looking to find my 0575 fault code on my golf, I read a lot of posts with the title of "intermittent power" and this informed me to check things like pipes blocked, pipes leaking/split, wastgate actuator full of oil, internal pipe in ECU. among others. Now i'm afraid this just CAN'T be the case, If a wastegate actuator is full of oil then how can it operate only some of the time?? and if a pipe has a split in it then why doesn't it leak all the time??

I fully appreciate that in some cases of CONSISTENTLY low power then this could have been the case, but when referring to INTERMITTENT faults it isn't.

Consequently if anybody has the fault of intermittent power loss then the first thing I would try is an Electrical component, and in MOST cases I would look at the N75 valve first because this is the most likely cause. The MAP sensor has no moving parts, The MAF sensor has no moving parts and the pierburg ones are very reliable anyway, but the N75 does. I removed my N75 and stripped it to see if I could find anything wrong and indeed there was my problem. The valve itself is very simple, basically opening and closing very rapidly to regulate boost pressure, it takes a pressure signal from the compressor housing directly on the turbo and uses this pressure to operate the wastgate, Mine was SOMETIMES jammed in the mid position allowing air pressure to the wastgate and into the air intake (dumping pressure off) at the same time, Thus causing a loss in boost pressure. (which is then picked up by the MAP sensor thinking low boost, giving an 0575 code), when I stripped it it became obvious that the small plunger inside was burred over at the end where the small spring fits inside. (Pictures to follow soon) This was causing the valve to be difficult to operate, hence only controlling boost some of the time.

Now some of you will be thinking. Yes but thats a mechanical fault and you would be correct, but I am just trying to inform you that it is inside the N75 valve that is the problem and most people would indeed just replace the valve for another one.

My last point is that some of the posts said that people has cleaned out their N75 vavles to remove the oil, I don't think this is a good idea because any valve with moving parts needs a little lubrication, and when you look inside my N75 you will see that is was bone dry. I'm not saying that this was what caused mine to fail, just that if it was wet with oil it might have survived longer.

Thanks for the great forum guys and i'll look forward to any comments on my post. Hope this hasn't been too long?
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Old April 1st, 2008, 14:46   #66
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Ps, I might do a thread on stripping an N75 valve if anybody is interested? then we'll all know what they do.
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Old April 5th, 2008, 13:56   #67
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I'd sure be interested in how to strip my old N75 and see if I can clean it up/repair it just to carry a spare one around...
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Old April 14th, 2008, 17:32   #68
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Hi MTDiezel, the next valve i get i'll strip and will post pics for all to see, it's quite straight forward really, but obviously if you take it to bits and haven't got the spares to fix it then you'll be stuck. I got one with a snapped off plastic hose on the bottom of it so just re-built it using my worn out valve.
Anyway watch this space.
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Old August 31st, 2008, 14:19   #69
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Default Intermittent power loss, ignition switch fixes immediately

Quote:
Originally Posted by tdi-mk2
...Firstly in my opinion, if a vehicle of any kind (with an engine obviously) has an intermittent problem, it has been my experience of working on all kinds of cars, bikes and heavy goods that the problem will be electrical/electronic... i'll look forward to any comments on my post...
My intermittent power loss doesn't throw any codes, don't think I'm in limp mode, just lower power (slow acceleration, weak up hills) - like maybe waste gate sticking open (or partially open)?

Here's the interesting part (I didn't see this mentioned above - sorry if I missed it): I can IMMEDIATELY return to full power by turning off/on the ignition switch briefly (while driving). This happens maybe once per day to once per week, so once I figured out the ignition trick I got lazy about tracking it down!

Per above quote and ignition trick I definitely suspect electrical (N75?). Sound familiar? I thought the ignition off/on test might be a useful addition to the diagnostic sequence above?

I'll follow up with the cure if I find it, might be awhile as I have some engine work to do first (not running).
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Old August 31st, 2008, 18:21   #70
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Quote:
Originally Posted by 98JettaBioDiesel

Here's the interesting part (I didn't see this mentioned above - sorry if I missed it): I can IMMEDIATELY return to full power by turning off/on the ignition switch briefly (while driving). This happens maybe once per day to once per week, so once I figured out the ignition trick I got lazy about tracking it down!
You have "limp mode" caused by - differing things.

Could be N75, hoses, hose inside your ECU, crudded up intake, sticking wastegate, etc etc. It'll get worse unless you fix it.
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Old September 7th, 2008, 08:32   #71
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Hi Folks,
I read the excellent write up. I have no fault codes, so was trying to use VAG COM measuring blocks to measure actual vs requested air, but could not find the measuring block that gave me that info.. Could it be that my TDI does not support that ? I have a 1996 1Z Passat. I have the latest version of VAG COM as well..
Any help would as always be appreciated.

thanks,
Rick
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Old September 7th, 2008, 16:00   #72
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My Passat supports it....

If you have the latest SW version, the descriptions for each measuring block are automatically populated.

I assume you are trying to measure boost. In vag-com, and almost any car for that matter, it's MAP - Manifold Absolute Pressure.

IIRC, blocks 10 and 11 will give you what you want. If that's not right, just scroll through the blocks until you find the description that fits. There are three possibilities: map requested, map actual, and atmospheric.

HTH

Tony
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Old September 8th, 2008, 08:27   #73
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is this the same proceedure for the A4 alh engine (2003 jetta tdi)
thanks
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Old September 8th, 2008, 08:54   #74
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filitosa,
Should be; If not, the fields are labeled very well with the latest VCDS software, such that you can scroll through and find the fields.

Tony
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Old September 8th, 2008, 18:29   #75
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Thanks for the help tony, will try what you said
Rick
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