vac leak maybe
pressure test the charge system
Ok, so I am overboosting to well over 30 PSI. My 25 PSI boost gauge pegs right out at 30 psi+ and my torque phone app is calculating 34 psi! Ignoring the sketchyness of the phone reading I still have a major issue.
I went thru today and set my wastegate tension to factory specs. When I unplug the N75 I hold exactly 5.0psi spot on.
I have stock n75, and stock diverter valve. I have a Forge TIP, and a catless 3" turbo back and Unitronic stage 2 software.
Why am I over boosting like crazy? I'm making soo much boost it slips the clutch!
What should I be looking for? How can I troubleshoot this issue? This is super dangerous for the motor. I am going to run with the N75 unplugged to keep 5 psi untill i can get this sorted out.
Inspect/Replace vacum hose to wastegate and from charge pipe to N75.
Your problem should be there.
Also, pressure (bike pump is enough) the vacum hose to wastegate, to see if it moves (opens wastegate).
EDit: just read the post correctly, after the reply after mine.
Yes, if it boost that little with N75 unplugged, it could be the software, or the N75 being busted.
Last edited by HidRo; 07-31-2012 at 10:20 AM.
I hold 5 psi like a death grip with the N75 unplugged.
I speculate that my problem can only be one of three things.
1. The N75 is bad and gets stuck closed when it sees any sort of square wave duty cycle at all.
2. My diverter valve has a problem with the vacuum hose, or is stuck closed.
3. My brand new Unitronic stage 2 software sucks.
Believe it or not i searched before posting this tread, and I read your frankenturbo overboost thread completely before posting. However, I do feel like with a properly set wastegate, which i have, a functioning N75 should allow me to regulate 18 psi with no problems.
How about pressure testing the system? A leak in the wastegate actuator signal hose (coming from the N75) would definitely make you overboost. I'm not saying it's not software related but there are mechanical possibilities as well (a leaky hose to the actuator would still allow 5 psi with N75 unplugged).
I do not have any of the tools required to do the pressure test.
I replaced the N75 today and the DV with different used stock parts my friend had lying around. No difference whatsoever, except that I have developed an incredible hatred of the stock hose clamps. Those MFers are impossible to get off.
Thoughts? Help? At this point I have no recourse. I dont even know of any places around me I could bring it to and be like "please make this work"
I am near Albany.
So, I found something!
This hose is ripped UNDER where the little rubber band holds it next to another line. However I am not sure what these lines are for, and if they could be causing my overboosting issue? They are on the divers side of the engine bay, you can see my forge TIP in the background for a spatial reference.
What do these hoses do? Can they be causing my overboosting issue?
If possible I would like to simplify the ridiculous hose setup, and maybe replace them with hoses that are of higher quality.
I am not sure what this hose is or what it does to be honest. It runs into the abyss of hoses and stuff under the manifold.
How does the N249 system work? At this point i am almost positive the DV is not opening at all. Does the DV work on boost pressure or a vacuum signal? How does the N249 system work if you eliminate the valve under the manifold? I have seen in the cleaning up the engine bay thread that some people delete the solenoid completely?
Can a huge PCV leak prevent the DV from opening?
That's definitely the breather hose for the pcv system. That won't cause problems with the dv, it may just act like a small vacuum leak. The N249 allows the computer to control the dv by opening and pulling vacuum on it when the computer tells it to. If you bypass it, you run the dv directly off of manifold pressure, so that the natural vacuum created by the manifold when you let off of the accelerator will open the dv. This will be quicker acting because its not relying on the computer to turn on the valve. Boost keeps the dv closed and vacuum opens the dv.
Perhaps I am confused about this system. I know the N75 controls the waste-gate, which controls the shaft speed of the turbo.
I was under the impression that the DV was regulating the pressure-flow relationship of the compressor wheel to keep the boost pressure equal to the pressure demanded by the software, and read by the MAP sensor. For example I think the Unitronic Stage 2 software is going to request 18 psi from the map sensor. As I see it, when the MAP reaches 18 psi, the N249 will release some vacuum to the DV which will recirculate the excess pressure back to the intake to maintain that 18 psi.
Something about my N249 system is not allowing the DV to open at all. I need to find that issue. Please correct me if any of my assumptions are incorrect.
For example I am not sure if the target for the N75 valve is also MAP sensor based? When I reach 18psi, I would assume i would want to crack the wastegate to keep the shaft speed in the highest efficiency region, but I have no idea how the computer thinks about this and makes decisions. I also dont know how the computer chooses to slow down the shaft speed with the N75, or just bleed off more pressure from the wheel and put it back in the intake.
The map sensor and n75 control boost levels. The n249 and dv evacuate the system of boost pressure when the throttle plate is closed, this is to prevent compressor surge. Basically, if the boost pressure has nowhere to go when the throttle closes, its going to push back the opposite way on the compressor wheel causing compressor surge, which is bad for the turbo.
*Edit: If your dv isn't opening, you'll have bad surging when you let off the throttle. Your overboosting is likely because the n75 isn't working right or there is torn hose between the n75 and wastegate, or because of a software issue.
Here is a good explanation of how the n75 controls boost levels:
There has been several mentions of "software issues" in this thread, which is quite unsettling. I just paid 600 dollars for this ECU flash and it had damn well better be flawless. Are there know software issues with the Unitronic stage2? From what I have read this is THE software to be running on a AWP 1.8t.
I would make sure all hardware is 100% correct before blaming software. Remember that running the higher boost is placing more stress on system components that were designed to run at half of those boost levels. Any hardware that was on the verge of breaking, will break once you get a tune. People always come up here blaming problems on software and it almost always is hardware related.
I'd take this issue up with unitronics support. They are very helpful and will help you figure things out.
However, I'm leaning toward an intermittently bad n75 or perhaps a bad MAP sensor.
The N75 determines its duty cycles based on the specified boost and the feedback from the MAP sensor on what the boost really is.
Do you have vag com?
Also, a log of block 115 in vagcom comparing requested and actual boost would be helpful. I would think that if you are overboosting that much, you would go into limp mode unless the map sensor is bad and not correctly reading pressure.
*Edit: ^^Beat me to it.
Neezy13 I dont know who you are but I like you!
Firstly, I am 99.9% positive there is no issue with the software, and this is why i have not even entertained this as being the cause of my problem. I have never blamed the software for anything except putting a big grin on my face.
I completely agree with all of your conclusions Neezy, but when i get under the hood, and start looking at things, replacing the DV and the N75, nothing fixes the problem which is super frustrating. Aside from my gaping hole in the PCV hose, i cannot SEE anything wrong with the vacuum lines. However as we all know it is not easy to actually see most of the lines in the system, even though i just replaced my TIP with a forge one.
I guess i will once again have to get under the car, and replace all the vacuum lines associated with the stupid N75 valve. FML.
What sizes are the factory vacuum hoses? I will have to stock up on vacuum hose and clamps before I start this project.
Am i better off leaving all the factory things in tact, or should I go and eliminate everything according to this thread: http://forums.vwvortex.com/showthrea...-N249-PCV-EVAP
Most of the vacuum lines are 3 or 5 mm but I think the n75 are 7mm (I could be wrong here). As far as doing the deletes, it probably won't help you with this issue, but it will simplify the jumble of hoses and make it easier to work on the vacuum system in the future because you will know exactly how you routed everything. Also take into consideration emissions regulations in your area. If there is a visual check, you probably won't pass. Also you may need to have some of that stuff deleted in your tune to eliminate cels for missing emissions stuff.
So I fixed that broken hose tonight and as predicted the problem persists.
I tried to log the MAP sensor tonight using a friends Vag-com. I was able to see something called "absolute pressure" i read 980mbar when off, which is to be expected, but the value never reached 1340mbar as i would expect to have seen. The number went up or down a little but never accuratley reflected the values i would expect. I was running with the N75 unplugged and boosting a rock solid 5 psi, or 1300mbar.
Is the "absolute pressure" log I was looking at my map sensor or something else?
Your plan of attack should be to fix all the mechanical issues first:
-pressure test (visual test does not reveal the majority of leaks except for gaping holes)
-make sure that you're getting proper operation from your N75, N249, and map sensor (the fact that you're allowed to boost 30 psi without limp mode suggests n249 malfunction)
When all that is taken care off, you can start looking into software issues. However, if you're not addressing the possible mechanical issues first, you're going to be chasing your tail later.
To be honest i feel like i have only addressed mechanical issues, I have never questioned the software once. I spent every night for the last week in my engine bay which is hot as the sun. I don't have Vag com, a garage or compressor so it is going to be quite an undertaking for me to pressure test the system.
What are your thoughts on the "absolute air pressure" block? Is this the MAP sensor?
What is limp mode triggered by? How is it that I can boost 30+ psi without triggering it. I am not the original owner of the car, perhaps the previous owner did a diode mod or something?
Is the MAP sensor the input to the computer that triggers The 249, N75, and limp mode? Should my absolute pressure block read 1300mbar is I would expect? I unplugged the MAP last night, and the car runs like ASS and an unplugged MAP triggers the N75 to be shut off and I hold the 5 psi wastegate pressure. What are your thoughts on this?
Also my boost is never flat, always hump-shaped. no matter what, if my N75 is plugged in my car is trying for max boost no matter what. Strangely my boost tapers off quickly in second gear, spiking to 25ish and then tapers quickly down to 12ish psi. In third gear or higher, even at the same rpm and vehicle speed it is boost city and im at 30 or more.
You HAVE to test some stuff, if you don't want to just spend money.
So, you don't have a garage, nor a compressor but you do have to get one. Get a friend, get someone, go down to a shop and do it!
Hell, I've even done it once on the gasoline pump! Just have the tire nipple connector on the pressure gadget!
"Absolute air pressure" block that is recorded in VCDS is taking its reading from the "MAP" sensor. Technically, not really a MAP sensor (manifold absolute sensor) because it is located outside of manifold and really is an Absolute Pressure sensor.
Limp mode is triggered by the ECU to prevent a potentially dangerous situation and preserve the motor. Several things, including overboost (preset pressure ceiling exceeded), can cause limp mode. Usually the limp mode is executed through the N249 that simply bypass/bleeds pressure to limit the system at around 5 psi.
To boost 30 psi without triggering limp, a few conditions would have to be met. One could be fooled (clamped pressure sensor aka diode mode) or faulty pressure sensor. Another cause could be a malfunction of the N249 which would make it not capable of properly executing the limp mode.