Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting]

[Tdipower86]

thanks flee

 

[Madmax78]

Just wanted to write Canadian Grizzly (if he’s still around) and thank him for posting his piece on diagnosing limp mode problems (trouble shooting) with the 1.9l ALH engine. I recently installed a new turbo and his step by step analysis of the vacuum system saved the day - specifically his reference to the N75 solenoid having « unregulated » vacuum - meaning straight from the brake booster line. On close inspection (tracing out his diagram of the system he posted) - I noticed the T connectors to the N75 and N18 were crossed! Problem solved. Runs like a top now. Many, many thanks.

 

[Jenhockey]

Where can one find vacuum line to replace the lines in my car? It seems simple enough to do myself, hopefully fix my stupid limp mode problem, and also doesn't seem like it would take too long. I just don't know where to find the vacuum line, what it's called, size, etc. Any help?

The main vacuum lines are just regular 5mm (inside) tubing. You can find them almost anywhere I got mine from lordco

 

[lauski_don]

Hi everyone, just want to know do cracked/leaking egr pipes cause noise when shifting (owl noise) and limp mode?
Thanks

 

[Jr mason]

Should not cause limp mode.

I'd take a hard look at all the turbo, intercooler, associated piping and connection clamps.

Do you have a way to monitor boost?

 

[TornadoRed]

Hi everyone, just want to know do cracked/leaking egr pipes cause noise when shifting (owl noise) and limp mode?

First off, some TDIs make that sound and some don't. And most people seem to like that sound and wonder how to replicate it in a TDI that doesn't make it. It really has nothing to do with limp mode.

Secondly, many things can cause limp mode, but typically either the turbo actuator is sticky or there are one or more leaks in the vacuum hoses. Remember, limp mode is generated by the engine computer to protect the turbo.

 

[lauski_don]

Should not cause limp mode.

I'd take a hard look at all the turbo, intercooler, associated piping and connection clamps.

Do you have a way to monitor boost?

Thank you for reply. My mechanic tested the boost, and he says it's fine. I also have elm327, if that can help.

I started driving a lot in city, and sometimes when I speed up to 2.3k rpm, I got limp mode. But I just shut on and off and it went fine.
But it started to get more frequent. So I went to my mechanic. He replaced the pipe and said it's fine.
After a few days I needed to drive ~100km and started gassing it, then it happened again and my ic hoose popped of at 120kmh, which is below car battery. I managed to get it back and drove back, barely!
Went to mechanic again, and he just put screw right through that pipe and said that turbo is a bit dirty but boosts well and it shouldn't pop off hosses. Then I tested it with driving for 30mins with 3-5k rpm (when it heated up of course). And no hosses popped off but I still have that noise when I let off gas pedal, like a whoosh, and still get limp mode when trying to go over 100km/h. I can make that sound constantly without changing gears, just it's more louder when I change gears.
I went to second car mechanic and I noticed when he was in neutral revving engine from egr cooler side there was a blunt of smoke when he hits 3-4k rpm.
Really don't know what to do now? Change car mechanic or try to wiggle it on my own?
My theory is that some of the piping is cracked or leaking under pressure and causing that sound (and smoke), but I'm not sure.
And I'm sick of changing mechanics.

 

[lauski_don]

First off, some TDIs make that sound and some don't. And most people seem to like that sound and wonder how to replicate it in a TDI that doesn't make it. It really has nothing to do with limp mode.

Secondly, many things can cause limp mode, but typically either the turbo actuator is sticky or there are one or more leaks in the vacuum hoses. Remember, limp mode is generated by the engine computer to protect the turbo.

@TornadoRed
Thank you for reply. Do you think is that noise dangerous in any way? Can I drive without thinking about it?
I have tested the turbo actuator before I went to my car mechanic. Also I changed my tandem pump recently.
Vacuum hose from solenoid box to turbo actuator is changed also. And my mechanic says that turbo is dirty but it give good boost (and he said it gives maybe a bit more boost than it should).

 

[TornadoRed]

@TornadoRed
Thank you for reply. Do you think is that noise dangerous in any way? Can I drive without thinking about it?
I have tested the turbo actuator before I went to my car mechanic. Also I changed my tandem pump recently.
Vacuum hose from solenoid box to turbo actuator is changed also. And my mechanic says that turbo is dirty but it give good boost (and he said it gives maybe a bit more boost than it should).

I just remembered the name of the sound you described; it's called a "choo." It's more common with the VE engines, but if you have a tandem pump then you must have a PD engine. I've not owned one of those and don't know enough to make any other suggestions.

 

[lauski_don]

@TornadoRed Thank you for reply.
Does anyone else have it's 2 cents on this problem?