Advice needed - A4 TDI wagon

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Jetta16v
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Advice needed - A4 TDI wagon

Post by Jetta16v »

Hey guys

So, we've been struggling with my wagon. Ray from Solid has been doing everything he can to sort the issues out but we are just not winning.

Issue nr 1

Boosting - The turbo isnt boosting at all. Now we got an error on the N75 so that was replaced. Error came straight back after replacing it. The error says "Short to plus". Now, Ray traced the wire and it looks as tho someone was in there before, and looks like the issue could lie with the ECU

Question - How true can it be that there might be hardware issues on the ECU for the N75 valve?

Issue nr 2

Brakes - Brakes are rock hard as if there is a vacuum leak, but there are none.

The following has been done:
- Replaced the tandem pump - Old one had a broken outlet
- Removed and had the booster tested - Perfectly fine
- Checked the master cylinder - Its also good
- Replaced the ABS pump - Also works well
- Cleaned all the brake lines and bleed nipples as they were gunked up - Still didn't fix the issue
- Bled the brakes normally as well as with VCDS - Still no change
- Checked the slider pins on the callipers and those are also fine

Question - WTF else could it be? We are seriously at a loss as to what else can be wrong or done.


Any assistance or advice will be greatly appreciated as I really need to get the car running.

Cheers
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Re: Advice needed - A4 TDI wagon

Post by aristo92 »

Howsit bud, speak to Adrian from TPH. He knows the tdi's well.

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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

aristo92 wrote: Tue May 04, 2021 4:42 pm Howsit bud, speak to Adrian from TPH. He knows the tdi's well.

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Thanks bud. Will do
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Re: Advice needed - A4 TDI wagon

Post by aristo92 »

Jetta16v wrote:
aristo92 wrote: Tue May 04, 2021 4:42 pm Howsit bud, speak to Adrian from TPH. He knows the tdi's well.

Sent from my SM-N986B using Tapatalk
Thanks bud. Will do
Anytime. You have his details?

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Regards, Armand.

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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

aristo92 wrote: Tue May 04, 2021 4:44 pm
Jetta16v wrote:
aristo92 wrote: Tue May 04, 2021 4:42 pm Howsit bud, speak to Adrian from TPH. He knows the tdi's well.

Sent from my SM-N986B using Tapatalk
Thanks bud. Will do
Anytime. You have his details?

Sent from my SM-N986B using Tapatalk
Yeah I do thanks bud. Known him for years
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Re: Advice needed - A4 TDI wagon

Post by aristo92 »

Jetta16v wrote:
aristo92 wrote: Tue May 04, 2021 4:44 pm
Jetta16v wrote:
aristo92 wrote: Tue May 04, 2021 4:42 pm Howsit bud, speak to Adrian from TPH. He knows the tdi's well.

Sent from my SM-N986B using Tapatalk
Thanks bud. Will do
Anytime. You have his details?

Sent from my SM-N986B using Tapatalk
Yeah I do thanks bud. Known him for years
Haha great stuff, no one better when it comes to diesels.

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Regards, Armand.

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Re: Advice needed - A4 TDI wagon

Post by PapaJo »

As for the boost issue, do you have a boost gauge rigged up to measure and confirm no boost?

Any leaks on secondary pump pipework as this may add to this situation?

Have you tried bypassing the n75 and take input direct from manifold to actuator?

That turbo should have vnt. Check if it is not seized up?
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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

Thanks Jo.

Here are the messages I got from Ray

Secondary pump is tandem pump

I have not tried bypassing the n75.
Turbo spins by hand.
I have a boost gauge I can connect through the obd port will see if it works


N75 is electrical issue
Brakes is possibly vacuum issue. But also doubtfully because tandem pump has vacuum pipe direct to booster


One way valve is good. And tandem pump is providing sufficient vacuum


Test vacuum from tandem pump - check

Test one way valve - check

Test booster for vacuum - check


The reason for thinking the N75 is ECU related:

- I was testing continuity from the n75 plug and tested to the other plugs in the harness. Didn’t get unnecessary continuity ie. from the n75 connector to another sensors connector

- Also tested the fuse holder that’s for the n75 in the ecu tray to positive, no short found

- The 15a fuse had a hair line crack in the plastic but I replaced it and no change
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Re: Advice needed - A4 TDI wagon

Post by PapaJo »

Jetta16v wrote: Wed May 05, 2021 8:51 am Thanks Jo.

Here are the messages I got from Ray

Secondary pump is tandem pump

I have not tried bypassing the n75.
Turbo spins by hand.
I have a boost gauge I can connect through the obd port will see if it works


N75 is electrical issue
Brakes is possibly vacuum issue. But also doubtfully because tandem pump has vacuum pipe direct to booster


One way valve is good. And tandem pump is providing sufficient vacuum


Test vacuum from tandem pump - check

Test one way valve - check

Test booster for vacuum - check


The reason for thinking the N75 is ECU related:

- I was testing continuity from the n75 plug and tested to the other plugs in the harness. Didn’t get unnecessary continuity ie. from the n75 connector to another sensors connector

- Also tested the fuse holder that’s for the n75 in the ecu tray to positive, no short found

- The 15a fuse had a hair line crack in the plastic but I replaced it and no change
Did Ray tried to drive the n75 output via diagnostics to verify signal is coming to n75 plug at n75? Is n75 internal coil resistance within spec? Does n75 seal off when not energized?
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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

Ok we getting somewhere. I took the ECU to get tested and that was 100%. Then we re tested the N75 plug and there is a break somewhere in the wiring, so Ray is busy looking for the break now.

Also looks as tho the rear calipers are binding a little, so thats next on the list to check.
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Re: Advice needed - A4 TDI wagon

Post by VAG Fan »

I think Jo meant that you should check that the VNT mechanism is not seized up. (Not the turbine.) If you disconnect the spring-loaded actuator, the VNT lever should move freely and smoothly from one end to the other. No "crunchiness" or "stickiness" inside. If my turbo is anything to go by, the typical stroke of the lever is perhaps 15 mm.

Ray would probably know this, but I thought I'd add it anyway. A sticky VNT mechanism can lead to chronic overboost (like mine did) or underboost.
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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

VAG Fan wrote: Wed May 05, 2021 3:04 pm I think Jo meant that you should check that the VNT mechanism is not seized up. (Not the turbine.) If you disconnect the spring-loaded actuator, the VNT lever should move freely and smoothly from one end to the other. No "crunchiness" or "stickiness" inside. If my turbo is anything to go by, the typical stroke of the lever is perhaps 15 mm.

Ray would probably know this, but I thought I'd add it anyway. A sticky VNT mechanism can lead to chronic overboost (like mine did) or underboost.
Thanks bud. At the moment there is no boost at all, but like I said, its the "short to plus" error we have been getting. Hes busy checking the wiring now but there is a definite short on the N75 wiring according to the multimeter
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Re: Advice needed - A4 TDI wagon

Post by PapaJo »

Jetta16v wrote: Wed May 05, 2021 3:16 pm
VAG Fan wrote: Wed May 05, 2021 3:04 pm I think Jo meant that you should check that the VNT mechanism is not seized up. (Not the turbine.) If you disconnect the spring-loaded actuator, the VNT lever should move freely and smoothly from one end to the other. No "crunchiness" or "stickiness" inside. If my turbo is anything to go by, the typical stroke of the lever is perhaps 15 mm.

Ray would probably know this, but I thought I'd add it anyway. A sticky VNT mechanism can lead to chronic overboost (like mine did) or underboost.
Thanks bud. At the moment there is no boost at all, but like I said, its the "short to plus" error we have been getting. Hes busy checking the wiring now but there is a definite short on the N75 wiring according to the multimeter
@VAG Fan
that is what I meant.

@Jett16v
The "short to plus" and no continuity or measurement at plug end tells me the positive is somewhere in that loom cut or open insulation and shorted out to ground. Only way to find it is by going through the whole wiring harness. Most common places are where loom make sharp turns and or pass through the firewall, but rather check the whole harness to be sure there is no other hidden gremlins. Might even be bad connection right at the plug where it is connected to the ecu due to some sealing issues on the plug and getting corrosion on pins.
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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

PapaJo wrote: Thu May 06, 2021 1:49 pm
Jetta16v wrote: Wed May 05, 2021 3:16 pm
Thanks bud. At the moment there is no boost at all, but like I said, its the "short to plus" error we have been getting. Hes busy checking the wiring now but there is a definite short on the N75 wiring according to the multimeter
@VAG Fan
that is what I meant.

@Jett16v
The "short to plus" and no continuity or measurement at plug end tells me the positive is somewhere in that loom cut or open insulation and shorted out to ground. Only way to find it is by going through the whole wiring harness. Most common places are where loom make sharp turns and or pass through the firewall, but rather check the whole harness to be sure there is no other hidden gremlins. Might even be bad connection right at the plug where it is connected to the ecu due to some sealing issues on the plug and getting corrosion on pins.
Thanks Jo. At the moment I need the car to run so I think we are just going to run 2 new wires instead of trying to find the breaks in the wires.
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Re: Advice needed - A4 TDI wagon

Post by missioner »

I'm with Jo on the VNT being stuck open.

Common problem on those type of turbo's.

It should move even with the actuator connected.
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Re: Advice needed - A4 TDI wagon

Post by PapaJo »

Any update??
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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

PapaJo wrote: Wed May 12, 2021 6:23 amAny update??
Yip! So ray had to strip the harness down yesterday to find the 1 wire that was causing kak, replaced it and re-joined to the ECU and the plug. After he put everything back together, he scanned with VCDS and the error was gone. Before the error used to come back as soon as you cleared it!

The right rear calliper was also locked up, so got sent in yesterday to get redone and will get it back today. Once its back on and the brakes have been bled, then Ray will take it for a drive! Holding thumbs that everything is now sorted!
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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

missioner wrote: Sat May 08, 2021 12:51 pm I'm with Jo on the VNT being stuck open.

Common problem on those type of turbo's.

It should move even with the actuator connected.
You and Jo were right... :sad:

After checking the VNT yesterday, its stuck. Cant move it at all. So will have to remove the turbo and clean it up when I can. * sigh *
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Re: Advice needed - A4 TDI wagon

Post by PapaJo »

Jetta16v wrote: Fri May 14, 2021 8:30 am
missioner wrote: Sat May 08, 2021 12:51 pm I'm with Jo on the VNT being stuck open.

Common problem on those type of turbo's.

It should move even with the actuator connected.
You and Jo were right... :sad:

After checking the VNT yesterday, its stuck. Cant move it at all. So will have to remove the turbo and clean it up when I can. * sigh *
Another thing of the list now.

Soon list will be complete. Brakes to sort next.
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Re: Advice needed - A4 TDI wagon

Post by Jetta16v »

PapaJo wrote: Fri May 14, 2021 6:05 pm
Jetta16v wrote: Fri May 14, 2021 8:30 am
missioner wrote: Sat May 08, 2021 12:51 pm I'm with Jo on the VNT being stuck open.

Common problem on those type of turbo's.

It should move even with the actuator connected.
You and Jo were right... :sad:

After checking the VNT yesterday, its stuck. Cant move it at all. So will have to remove the turbo and clean it up when I can. * sigh *
Another thing of the list now.

Soon list will be complete. Brakes to sort next.
Thanks again for all the help with info as always! You were a huge help!
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Re: Advice needed - A4 TDI wagon

Post by PapaJo »

Jetta16v wrote: Fri May 14, 2021 6:36 pm
PapaJo wrote: Fri May 14, 2021 6:05 pm
Jetta16v wrote: Fri May 14, 2021 8:30 am
missioner wrote: Sat May 08, 2021 12:51 pm I'm with Jo on the VNT being stuck open.

Common problem on those type of turbo's.

It should move even with the actuator connected.
You and Jo were right... :sad:

After checking the VNT yesterday, its stuck. Cant move it at all. So will have to remove the turbo and clean it up when I can. * sigh *
Another thing of the list now.

Soon list will be complete. Brakes to sort next.
Thanks again for all the help with info as always! You were a huge help!
:thumbup: You're welocme.
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