Identifying a power loss problem TDI 1.9

[DJJoker]

Hi everyone,

I have an 1996 Audi A4 (B5) 1.9TDI @ 164,000 miles and have had a few issues recently with the "limp" mode problem. Within the past few weeks though things have got worse and I now suspect that the issue may be something other than the MAF.

A quick summary of the events recently include noticable power loss going up hills, inability to push much past 70mph (overtaking only of course!!), a change in the sound of the engine, Coolant temp won't go above 80c and then much more concerning is that the car has started to spit out some smoke during hard acceleration.

At first the smoke was black although after putting in an injector treatment I would now say it is more a white smoke. The treatment restored some power but I knew something wasn't right. I got myself a VAG-COM cable and hooked it up to the laptop and discover a few faults including the following:

Address 01: Engine
Controller: 028 906 021 CE
Component: 1.9l R4 EDC 00SG 0803
Coding: 00002
Shop #: WSC 06325
1 Fault Found:
00575 - Intake Manifold Pressure
17-00 - Control Difference

I decided to then log some data during a short run in the car and I notice a few strange trends, including the EGR valve. Please see the graph below.



I am not too sure where to start and would appreciate any advice on how to proceed with identifying the root cause of my problems.

Thanks
DJJoker

[Teflon]

Take a look at this thread. It is for 2.5TDI, but the principles are the same. I don't know if the 96 B5 engine had the variable vane VNT turbo, but if it does, just follow the links in the thread. https://www.vwaudiforum.co.uk/forum/s...ghlight=teflon. There are some links to diagnostic info at TDIclub.com, including a very detailed description of how to interpret the diagnostic graphs you have. Look also at the TDIClub.com turbo101 forum for lots of info - it takes a bit of rooting about to find useful stuff though!

If you are showing an intake manifold pressure fault, there are 1/2 a dozen possible causes but the most likely are either a duff MAP sensor or an overboosting turbo because the vanes are sticking. The MAP sensor is about £60 but before you dive in to replace it I would recommend that you check for free movement of the turbo actuator.

A duff MAF sensor is always the first recommendation when limp mode shows up, but I don't believe it shows the fault codes you have.

[ini]

I would first check/replace all the small braided hoses in the turbo vacuum control system (the small hose from the turbo vnt actuator to the N75 is very common for leaking). Any worn rubber/small leak in this system can cause limp mode.

Your turbo VNT mechanism may be sooted up, or vac capsule leaking.

Your N75 valve may be worn or blocked.

Otherwise your CAT may be partially blocked, or timing off etc.

Your MAP sensor is ECU mounted, and is less prone to wear than later models. Check the small hard tube that runs from the underside of the top boost pipe to the ECU for leaks or oil contamination (it is badly positioned and collects oil).

Or, as stated above the problem could be caused by a failing air mass meter.

[Crasher]

00575 could be a problem with the signal hoses by detached, split, collapsed or wrongly connected or a faulty N75 but usually it is jammed or sticking vanes. Does the power come back each time the ignition is cycled off to on or when you clear the code? Does it do this all the time or just every now and again? Do another run in MB08 but this time only log Display Group 11 Display Field 3. If the figure goes to 2880mBar and sticks there then that probably is the Thrust (MAP/IAT) sensor.

[DJJoker]

Hi guys,

Thanks for the advice

Let me start by saying the problem does cycle with the ignition being turn off and on again but will happen on any run longer than a couple of mins. Clearing the code doesn't seem to have much impact in the period of time before the problem arises again.

In regards to the N75, it seems to be ok (clicking regularly) and all the pipe work connected to it seems in good condition and securely fastened in place. Some of the other hoses and pipes seem a bit worse for wear and one area in particular gives me cause for concern. I will throw up a photo a bit later when it stops raining !!!

Unfortunately I don't know enough about the turbo to confidently examine the VNT mechanism but I will have a friend take a look.

Also I will log some more data as specified by Crasher and will post ASAP.

Regards,
DJJoker

[smokey0123]

Last time i saw that code it was on a AHU engine and was caused by split pipe that goes from the inlet manifold to the map sensor in the ecu. What is your engine code?

[DJJoker]

The engine code is AFN

[Crasher]

An AFN is getting old enough to suffer from split piping so I would thoroughly inspect each and every pipe right from the vacuum pump which generates the vacuum used to control the turbo and the EGR to make sure there are no leaks. A routing diagram of the piping would also be very helpful in case you lose track and to make sure someone else hasn’t connected some incorrectly. If it is suspected of being sticking vanes you have a number of choices, chemically cleaning the turbo’s exhaust hosing with Inotec cleaner, removing/striping and cleaning the turbo or fitting an exchange unit.

[Teflon]

If the problem cycles with engine on/off but also happens on anything but a very short run, my money is on a clogged up VNT in the turbo.

Try this............. start the car from cold and try and cause the problem. Then try it from stinking hot. If you can't make it happen until the engine is warm, but it is immediately there when things are hot, then this is symptomatic of a sticking VNT (the turbo has a lot of slack in it when cold but as it gets hot the expansion takes up all the wiggle room and it jams up on the carbon). It you are very lucky, you can listen to the engine cooling down and hear a "clonk" as the VNT is freed and drops back to the low boost position. If the symptoms are consistent when hot or cold, this maybe points more toward hoses and leaks.

Look at the thread on TDIclub.com, it tells you how to check the mechanism, complete with a handy little video.

[DJJoker]

Ok I finally got out to taking some photos - the car has not be cared for and I haven't even put my head under the car yet !!!

First - a picture of around the Turbo and VNT area. There is quite a build up of crap around the pipe pointed out and looks nasty.



Second is a photo of a small split in the hose connected to the EGR valve - I am not sure if it is just the braiding but this will need replaced for sure as running along the same pipe and I spotted the damage as shown in the third photo.





On the other side of the engine I noticed a bit of (un)handy work by someone that looks out of place. I am not sure what this tubing is for but I am guessing it is most likely electrical cables?? However I am sure it should be protected by something more than a rag, lol.



I hope to get a really good look around the rest of the car during the weekend. In the mean time I will try some of your suggestions guys such as trying to force the problem and I still have to log another run in the car.

Once again thanks for all the help
DJJoker