*Another* 2000 Audi a4 B5 1.9 tdi pd limp mode

[Disco_jo]

Hi guys,

I have been lurking on these forums for a few years now (yes time flys) trying to solve my problem on my Audi. It will randomly jump into limp mode, at different RPM's , etc. The only thing that is more or less the same every time is that is mostly happens when the weather is pretty hot. The code is p1556.

So far I have :

-New turbo
-New EGR valve
-All new hoses between actuator, n75, airbox, etc
-Run tests with VCDS on N75, working great.

I have a couple logs that might be able to help you guys, Thank you all in advance

[Disco_jo]

Malone Tuning Log Viewer (https://log.malonetuning.com/chart/259814#H8KLCAAAwr4YXQIDTcKMw4EOw4IgEETDv8KFw7PCkhQ 1w7oxwoTDgyobwrpJwoVmw5nCmsOqw5cLNDEeZ8Omw43Ds8OeP MOKw7PDjsKZbMKSwrLCrcOVw4AUwqDCl0sRw75QwotgEmUSVDL Dh8KSXyRqwrXDmMOdw6LDjsO9cXxmwo5kIypWw5Jew55AZcKjw r5gwozDtsO9woPCjXDCmnXDiBrDuTfDuAnDjsOgw6AEV3DDjWj DnGBww5NSw5fChcKHw5NdQsO4AsK1CiDDrsK0AAAA)

Malone Tuning Log Viewer (https://log.malonetuning.com/chart/259813#H8KLCAArwr4YXQIDTcKMw4EOw4IgEETDv8KFw7PCkhQ 1w7oxwoTDgyobwrpJwoVmw5nCmsOqw5cLNDEeZ8Omw43Ds8OeP MOKw7PDjsKZbMKSwrLCrcOVw4AUwqDCl0sRw75QwotgEmUSVDL Dh8KSXyRqwrXDmMOdw6LDjsO9cXxmwo5kIypWw5Jew55AZcKjw r5gwozDtsO9woPCjXDCmnXDiBrDuTfDuAnDjsOgw6AEV3DDjWj DnGBww5NSw5fChcKHw5NdQsO4AsK1CiDDrsK0AAAA)


These might be clearer ;)

[Crasher]

17964 (P1556) - Charge Pressure Control: Negative Deviation
This is usually an air leak in the vacuum system. Apply suction to the 3mm vac hose off of the servo to vacuum pump pump, you should not be able to draw any air.

https://i222.photobucket.com/albums/dd20/Crasher1964/Vacpipewitharrow.jpg (http://s222.photobucket.com/user/Crasher1964/media/Vacpipewitharrow.jpg.html)

[Disco_jo]

Hi buddy, thank you for the reply, I will check that out, I have renewed all of the hoses, but can't remember seeing that one back there

[Disco_jo]

https://cdn.discordapp.com/attachments/431505531631304705/595699440912695318/IMG_20190702_213339.jpg I don't seem to have that vacuum line, and I have a rubber gromet in the firewall where in your picture there is a hose

[Crasher]

That thick plastic pipe is the second vacuum feed from the vacuum pump and at some point (usually very close to the pump) must have a one way check valve which has the small vacuum take off moulded in.

[Disco_jo]

https://media.discordapp.net/attachments/431505531631304705/595704024809078814/IMG_20190702_215349.jpg?width=901&height=676 This is a bigger picture to make sure im not missleading in any way,

https://media.discordapp.net/attachments/431505531631304705/595704103787692033/IMG_20190702_215257.jpg?width=901&height=676 Would it be this one? The is the only one I can see that seems to be like in your picture? I pulled the bigger hose and was holding vaccum, I pulled the 3mm one off and applied suction but it isnt holding it.

https://media.discordapp.net/attachments/431505531631304705/595704059793637428/IMG_20190702_215314.jpg?width=901&height=676 This is where the 3mm goes to and where I can hear air when applying suction.

Thank you again for taking the time to help me

[Disco_jo]

https://forums.audipassion.com/applications/core/interface/imageproxy/imageproxy.php?img=http://nsm08.casimages.com/img/2015/04/27//15042710150818969813210391.jpg&key=d4e8639b4f2d76becb1c066ba70f47d626795a43d24771 202a57fe0fb0021ddb

So if I have got it right, I shouldn't be able to draw air / suction at the blue arrow on the one way valve?

[Crasher]

From the 3mm vacuum hose that connects to the servo feed pipe, you must not be able to draw any air, you should pull a holding vacuum after a few pumps of a Mityvac type hand pump.

[Disco_jo]

I don't know if you can click the links for the pictures to see if i am in the right place? Can't upload the photos as they are too large... Hopefully we can get this sorted ;)

[Crasher]

Private Message me your REG number and tomorrow I will look up the vacuum source point.

[Crasher]

It is an AJM engine and left hand drive which are slightly different to the right hand drive AVF in the picture disconnect the vacuum hose 9 where it goes to servo vacuum feed pipe check valve pushed into the plenum chamber wall rubber bung and apply the vacuum there

This is the EGR vacuum system



To vent port on charge pressure control solenoid valve -N75
Mechanical EGR valve
Vacuum hose from EGR valve -N18 to mechanical EGR valve
To charge pressure control solenoid valve -N75
Vacuum hose to vent connection on air cleaner housing
EGR valve -N18. Fitting location: on rear of air pipe
Vacuum hose to fuel cooling circuit cut-off valve
Cut-off valve for fuel cooling circuit
Vacuum hose from tandem pump
Vacuum hose from tandem pump



https://live.staticflickr.com/65535/48188913347_595a32cb79_o.jpg (https://flic.kr/p/2gqhM4z)

This is the turbo vacuum system

1) Non-return valve, Installation position (light/dark side): As shown in diagram
2) Intake manifold change-over valve -N239
3) To EGR valve -N18
4) Vent line into air cleaner housing, to EGR valve -N18
5) Intake manifold change-over vacuum unit
6) Vacuum unit for charge pressure control. Cannot be replaced separately
7) Turbocharger
8) Vacuum reservoir
9) Charge pressure control solenoid valve -N75 at front right in engine compartment



https://live.staticflickr.com/65535/48189060542_d837d58637_o.jpg (https://flic.kr/p/2gqiwPq)

[Disco_jo]

Wow ! Thank you so much for this. Hope this helps others too.

I pulled the 3mm off number "9" in first photo and can easily draw air in. The air is entering through the Cut-off valve for fuel cooling circuit, number "8" on first photo. Does that mean he has gone belly up?

[Crasher]

Remove the hose, plug it and see what you get then. the valve is 4A0 819 809 and £63 here but normally all the bits attached fall to pieces so the full assembly 8D0 203 514 A at £116 makes more sense. When that valve fails it can cause cold weather running problems. A few aftermarket companies list the basic version from about £10 up
https://cdn1.pelicanparts.com/catalog/images/Connect-Images/4A0819809-M53.jpg

[Disco_jo]

If I plug the 3mm hose that goes to the cooling system cut off valve, the whole system holds vacuum. Looking at the cut off valve it seems that it should let air in? Or should the system hold vacuum WITH the cut off valve? If needed I will order the whole assembly


If I may add, I have never had a problem with my car heating, or in cold weather. Its has always started first time even after sitting a couple weeks in the cold


Could I drive the car with the cut off valve plugged to stop it going into limp while waiting for parts? Or would that be a bad idea?

[Crasher]

The valve should hold vacuum, the exhaust for the system is the vent line into the air cleaner. The valves job is to regulate the coolant flow of the fuel cooler, a very important function on a PD as the returned fuel is so hot it can damage the fuel tank and lift pump so if it fails, it defaults to open and maximum cooling. Later PD’s used a radiator under the right front floor. Yes you can plug the vacuum pipe to test it, it will be just as it was except not leaking.

[Disco_jo]

You are a life saver, I can't thank you enough for your time and help. I will proceed to ordering the parts and will update when replaced.

I thought that I knew what all of the vacuum lines did, didn't have a clue about that one, thank you for explaining its function to me

[Disco_jo]

Had to come by to thank you again for your time helping me with my audi, been driving the car today and feels like a 130hp, no limp mode in sight ! I have had this issue for a couple years now and can't believe that in a couple days you pointed me in the right direction. Just waiting on the parts now. If ever you come to Brittany in France be sure to send me a PM I will have a bottle of wine or 2 for you.

[Disco_jo]

Hi guys,

Back for the conclusion, recieved my parts on tuesday, fitted them strait away. Really easy fix, I am still stunned at how many parts I have changed, and how much time I have spent on the car for it to turn out to be such an easy fix.

Anyways, the car is driving perfectly now, really fast, no limp mode, no choking at red lights or stops, no black smoke.

I could never thank you enough Crasher for your help.

Kind regards, Jo

[Crasher]

My pleasure :D