View Full Version : Boost Problem.... No idea.

09-19-2018, 04:41 PM
Hey guys,
Believe this is my first post, been a member for a while and have gotten a lot of help from you guys over the years. I have a boost problem that I have no idea how to fix or what is causing it.

I have a 2001 A4 AWM with a stage 1 APR tune (got the apr package with the bigger hoses, R1 DV, and exhaust (cat back)), running 2.0 Coils, and a k04. Chip was tuned for k04, and been having no issues with it. Recently the gasket between my cat and my exhaust disintegrated, and my car was throwing the dreaded cat code. I decided since I would be taking the cat off to change that gasket may as well upgrade to a high flow cat, and installed the 034 HFC. Ran fine for about 20 miles then all of a sudden acted like it blew off a hose from the turbo (went from around 18 lbs of boost to 0). Found no hoses off, ended up pulling the hose from the n75 to the wastegate and car ran with boost and no issues (did not push over 15lbs with hose disconnected). Bought new n75 and installed, drove car with only 5-6 lbs of boost. Tested old and new n75 connecting 12 V to them and could hear the n75 click over and open up, also blew through it and had no issues. Disconnected the wastegate from the new n75 and car ran fine again. Tested for boost leaks and found none, checked DV and wastegate/wastegate actuator with no problems found.

Removed front o2 sensor and stuck bore scope into the cat looking at the wastegate. Pumped 5lbs of pressure using bicycle pump to the wastegate actuator and the actuator opened the wastegate, let off pressure and wastegate closed. Wastegate appeared to open and close fine through bore scope without any problems. Can hear turbo spooling up, not blowing smoke, just only getting around 5-6 lbs of boost as if in limp mode. Hooked up VAGCOM to it, and getting the

"17963 - Charge Pressure: Maximum Limit Exceeded P1555 - 35-10 - - - Intermittent"

Any ideas?

09-20-2018, 06:08 PM
If you clear that code, the boost doesn't come back?

It sounds like your wastegate and actuator are ok. This is true because removing the pressure line gives you good boost, and connecting the pressure line gives you spring pressure.

I think your problem would have to be:
A - Software
B - Wiring to the N75
C - The output circuit of the ECU that drives the N75

Here are some things I would do:
- Output Test Mode on the N75. See if the ECU can make the N75 click.
- Log the N75 Duty Cycle with VCDS. To get full boost on a chip tune you will usually see something like 75% duty cycle.
- If that max limit code keeps setting (even though the boost is way low) - then I'd find out why. Could be a faulty MAP (boost) sensor.

09-20-2018, 10:15 PM
- Software wise, I tried switching programs figuring somehow it switched to valet mode or stock, no difference in 91, 93 or stock programs.
- Wiring to the n75 seems like it is good, if I disconnect the power to the n75 I get a code for it.

- Will try the N75 duty cycle with VCDS and will try to see about testing the MAP. Thanks...

09-21-2018, 12:03 AM
It sounds like an overboost situation to me and going in to limp mode. You say you have APR software for a KO4 but they donít make one for a B5. My guess is with the better flow with the HFC, it is too much boost and the car throws the code you are getting and puts it into limp mode.

Since you donít have a custom tune for you equipment, Iíve read you can install a manual boost controller in parallel to the n75 to controller these spikes. Do you have a boost gage? What is it spiking too? It really sounds like you need to upgrade your programming to a custom tune like Motoza. Many of us have and you would be getting the max out of your setup. I suggest selling your ECU with your APR software to help pay for the custom tune. Been exactly where you are, sold my ECU for $350 and got Motoza. Havenít looked back.


10-03-2018, 12:13 PM
Sorry, been busy at work. Wiped the codes with Vagcom, did output test for my n75 and could hear it clicking over. Swapped out another n75 with a spare my buddy had. Replaced map and maf sensors, and swapped my apr r1 dv for a forge 008. Nothing has changed, still getting around 5-6 lbs of boost, overboost code has not come back but I doubt it would since I cant make more than 6 lbs. Also swapped from 93 octane tune to stock and 91 octane just to see if that made a difference and it did not.