How to troubleshoot low power on an A3/B4 engine

MTDiezel

Active member
Joined
Feb 13, 2007
Location
Bozeman, MT
TDI
1996 Passat
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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likmywagon

Veteran Member
Joined
Feb 5, 2003
Location
Toronto, Ontario
TDI
95 Passat Wagon
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
 
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MTDiezel

Active member
Joined
Feb 13, 2007
Location
Bozeman, MT
TDI
1996 Passat
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.
 

TonyJetta

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Joined
Sep 15, 2005
Location
Tucson, Az
TDI
'15 Jetta TDI SE / '06 Jetta TDI DSG Pkg0 / '96 Passat TDI
MTDiezel said:
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.

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

Tony
 

tdi-mk2

Well-known member
Joined
Jan 13, 2006
Location
liverpool, england, UK
TDI
Mk2 Golf 1z tdi.
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?
 

MTDiezel

Active member
Joined
Feb 13, 2007
Location
Bozeman, MT
TDI
1996 Passat
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...
 

tdi-mk2

Well-known member
Joined
Jan 13, 2006
Location
liverpool, england, UK
TDI
Mk2 Golf 1z tdi.
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.
 
Joined
Oct 30, 2007
Location
Southern California
TDI
98 Jetta
Intermittent power loss, ignition switch fixes immediately

tdi-mk2 said:
...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).
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
98JettaBioDiesel said:
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.
 

FMohlmann

Well-known member
Joined
Sep 21, 2007
Location
Brookhaven,Long Island,NY
TDI
1996 passat TDI, 2006 Beetle TDI
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
 

TonyJetta

Top Post Dawg
Joined
Sep 15, 2005
Location
Tucson, Az
TDI
'15 Jetta TDI SE / '06 Jetta TDI DSG Pkg0 / '96 Passat TDI
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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TonyJetta

Top Post Dawg
Joined
Sep 15, 2005
Location
Tucson, Az
TDI
'15 Jetta TDI SE / '06 Jetta TDI DSG Pkg0 / '96 Passat TDI
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
 

anfirmor

Member
Joined
Feb 16, 2009
Location
UK
TDI
1.9 Golf Estate Mk3
This guide did the trick

I Vag Commed my P reg 1.9 TDI golf Estate and could not get a manifold pressure reading (always around 1020mBar) Also got code 575. I have only had the car for about 2 months and have already had to do the timing belt as the old one jumped a tooth due to a incorrectly fitted tensioner. I have now learned that diesels, unlike petrols, will not run if the timing is off.
After this fix the car suffered exactly the symptoms described hear (OK for short while then sudden power loss) so I have just checked the ECU pressure sensor hose as stated in the guide.

I found that the area around the ECU under the plastic trim was FULL of leaves and dead vegitation. When I cleared this out I could see the hose was damaged about an inch away from the ECU. Some little rodent had made a nest in there and chomped through a good section of the pipe. I shortened it to try it temporarily and now the car has controlled accelleration and pull, does not whistle like a taxying 737 and no longer stinks like an Astra Max van.

I once had a SAAB where vermin had munched through the washer pipe to get to the screenwash fluid. Apparently it's got suger and booze in it, which they love. I've never heard that they love diesel but the teeth markes in the pipe prove that they do.

Anyway, thanks so much for all the great info here.
 

1jollymon

Member
Joined
Apr 1, 2006
Location
Gurnee, IL
TDI
1998 Jetta TDI
I have been working the same problem!

I have replaced all of the hoses, N75, checked the waste gate actuator and movement of the waste gate veins, and all are working well. One thing I need to point out is that it seems as though the waste gate actuator works on pressure and not vacuum? Is this correct? My VAG-COM indicates over boost and I confirmed it with a turbo boost gage . . . topping over 25 psi at full power under load (3500 rpm). Any suggestions?

Chris
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
Did you change the hose in the ECU? What did you see in VagCom that said overboost?

Yes, the wastegate actuator works on pressure from the turbo. It takes boost to dump boost.
 
Joined
Oct 30, 2007
Location
Southern California
TDI
98 Jetta
Mine turned out to be the hose in the ECU - just like everyone advised. It's a really cheap little hose and was immediately obvious when I got the box open: hose blown and dirty spot. Replaced with a piece of the black silicon from McMaster Carr (didn't need the original clamps) - now runs perfectly, and I'm sure this will never need attention again. Pretty easy to get the ECU out but it's location wasn't obvious from the manual. It's under the black grille under the hood at the bottom of the windshield passenger side - remove the 4 (or so) plastic fasteners and pull out the plastic grille. You'll need a small torx to get the box open.
 

bmike

Thread Killer
Joined
Jan 3, 2002
Location
central CT
TDI
1998 Jetta - sold, 2010 A3 - sold
I wanted to add my 2 cents to this. My Scanguage read the P0605 code and after studying the site I came to the conclusion that the hose inside the ECU needed to be changed. Now I'm barely a shadetree mechanic so I was looking for a detailed explination with pictures, this is the only thing I found, http://www.myturbodiesel.com/1000q_how_to/a3b4/ecuhosechip.htm . My ECU was flipped over the other way, the hose leading to the ECU was toward the firewall. Removing the wiring harness wasn't clear to me and gave me trouble, you have to slide the plug handle away from the harness itself toward the hose inlet. The hose inside the ECU was ok, it was weak but not damaged, I replaced it. My trouble, at least I think it was, was with the other end of the hose leading to the ECU. The connection at the intake was cracked. That hose was a little more involved to change, that must have been why we skipped it when changing the other hoses last spring. I ended up taping the new one to the old and pulling it through, under the windshield tray, take your time push while you pull. There is a grommet for the hole going through the tray that I was determined to re-use, its odd looking, kind of like a condom with the tip cut off. I tried spraying it with WD-40 but the best thing I found was to smear some o-ring lube on the new hose a couple of times while pulling it through the grommet. Hopefully the code will be gone for good now. Thanks to everyone here, before the internet this would have been a $1,500 repair bill.
 

mmeinert

Member
Joined
Sep 6, 2006
Location
Hillsborough, NC 27278
TDI
2002 Jetta TDI Wagon
Trying to diagnose bucking / hiccup

GoFaster:

Thanks for your helpful post. I am at a loss.

I had my 2003 Jettal ALH towed yesterday b/c it started giving me only intermittend power. Kinda bucking almost down to a stall, step on clutch, rev it past a shudder point maybe at 2,500 rpm, let the clutch come and picking up speed for another 40 ft for a complete power loss, to be repeated. Also lots of smoke trailing behind and whizzing sound while revving. At first I thought overload from something on the serpentine belt, whizzing from belt slipping - but she runs normal in idle. The serpentine belt tensioner bounced a bit much but not today. I changed my timing belt about 2,000 mi ago and thought maybe the injection pump was out of alignment or a clogged fuel line. I did notice bubbles in the fuel supply line. Or worse a loose bolt I didn't torque enough or ...:confused:

All that didn't make any sense with normal run in idle.
Had my wife rev the engine today w/o load and also dragging locked back wheels over gravel: Couldn't reproduce whizzing. The hick-up in revving however is consistent between 2,500 and 3000 rpm. I can push past that hiccup in idle, but not under any load. Had the timing belt cover off and all looks good.

So I found your thread "How to troubleshoot low power on the A3/A4 engine" , had no MIL Codes other than my usual spark plugs. So I did the Step 3 tests with these results:

3b: Vag Com gives normal airflow rate of 270 mg/stroke on idle, with active EGR solenoid cycle of around 60 after revving and 84 pegged while revving.

3c: vacuum present at EGR diaphragm line.

3d:W/o EGR control hose and a accelerator blip i did get a different measured intake air, but MORE!: 730mg/stroke instead of the suggested 480+/-20.

3e: I left the vacuum line off and drove out of the driveway and even up the hill, with a lot of smoke trailing behind, mind you. Definitely more consistent power, but nowhere near normal power. No shuddering and bucking, but I think some whizzing.

3g: Air filter was relatively clean.

3h: There was about 1/4" of build-up on the EGR plunger.

So I'm getting ready to clean the intake. Except I'm not sure that'll do it b/c aI had more air that I should have had - not less.

Any insights are much appreciated.
 

VANCE HARRELL

Member
Joined
Nov 2, 2007
Location
WILSON N.C.
TDI
PASSAT
i have a1996 passat tdi installed 205nozzles last year, slight shudder problem. connected vag-com to adjust fuel quantity and the stored value displayed was 126 instead of the 32768 that i thought was the stock setting.is it the ecu or did i go to the wrong page? any help would be much appreciated.
thanks, vance (dieselsniffer)
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
VANCE HARRELL said:
i have a1996 passat tdi installed 205nozzles last year, slight shudder problem. connected vag-com to adjust fuel quantity and the stored value displayed was 126 instead of the 32768 that i thought was the stock setting.is it the ecu or did i go to the wrong page? any help would be much appreciated.
thanks, vance (dieselsniffer)
Did you try to change it?
 

vwxyzero

Veteran Member
Joined
Jul 12, 2004
Location
Los Angeles, CA
TDI
'96 Passat Sedan, '96 TDI Passat Wagon, & Jetta Sedan, '83 Turbodiesel (IDI)
Vance H this thread is titled "How to troubleshoot low power on an A3/B4 engine". it's ment more for reading then asking.

Since you're new here; sometimes it's better to start a new thread (after searching) specific to your problem... that way it gets more attention ;)
Personally I can't help you on this one except to reiterate what was just said: Did you try and change it?
 

VANCE HARRELL

Member
Joined
Nov 2, 2007
Location
WILSON N.C.
TDI
PASSAT
Sorry Guys I Am A Newbie. To Answer Your Question, I Did Ghange The Setting From 126 To 120 And It Seemed To Help. I Had No Info With Just Three Numbers In The Stored Value. Is This The Correct Setting For A 1996 Tdi?
 

riofrio

Veteran Member
Joined
Apr 14, 2006
Location
New Haven, CT
TDI
96 Passat, 2002 Jetta Wagon
Quick question: why/how would a partially clogged intake prevent full boost pressure from developing? If the MAF sensor sees less flow than normal, wouldn't the ECU have more of a reason to increase boost pressure??? (This question obviously assumes that it does not go into limp mode).
 

TonyJetta

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Joined
Sep 15, 2005
Location
Tucson, Az
TDI
'15 Jetta TDI SE / '06 Jetta TDI DSG Pkg0 / '96 Passat TDI
Pressure does not always equal flow. So, more pressure through a choked system would not give the same mass of air into the system.

Tony
 

riofrio

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Apr 14, 2006
Location
New Haven, CT
TDI
96 Passat, 2002 Jetta Wagon
TonyJetta said:
Pressure does not always equal flow. So, more pressure through a choked system would not give the same mass of air into the system.

Tony
Sure, I understand this; but the MAF readings are taken into account by the ECU among other things (i.e., boost pressure feedback), for the N75 duty cycle setpoint, right?
My question is, in the context of step 2h of the original post, how can a clogged intake be a possible cause for the turbo not developing pressure? What electronic signals result from a clogged intake that will prevent from the N75 from closing the wastegate?
 

50harleyrider

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Jun 16, 2007
Location
charleston,wv
TDI
2005 B5.5 TDI/geared BSM, BV43A turbo,stage 2 TDTUNING. 2005 5sp manual passat tdi stage 2 tdtuning,BSM delete. 2015 Passat TDI 6sp manual.
b4 loss of power

I've tried all the tests in this post and no luck. Can one of our veterans please check out my post on my problem in this forum and help?
 
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