GRRR Limp Mode at it again

[rovert6]

It all started when I installed a new 3" test pipe from 034. It fit great, and sounded great. I had a boost gauge installed before the test pipe, and before the TP install, I was maxing out at 7 psi. After the install, I was getting much better boost with spikes to 15 and dropping immediately to 11-12. All was great, and was enjoying the newfound power.

I went for a spirited drive the next day, and I went WOT down a stretch of road, and it kicked into the dreaded limp mode. I maxed out 3-4 psi and it would slowly go to 0 when trying to accelerate. I heard because I'm running a catless pipe, it would get to rich from the missing cat, and it would be a good idea to throw on a spacer to fix the check engine light. I did, and the car ran great

for a while. I've been able to prevent limp mode by not going WOT, and only going 3/4, and it seems to collect full boost at 11-12 no problem. But, if I slam the gas, and go for a bit, it cuts the power, and I hit limp. It stays that way for and indeterminate time, and sometimes it would come back when I'd least expect it.

tl;dr Car goes into limp mode after install of TP. No solutions. Need help

[rovert6]

bump. I'm still in limp mode. Need some help

[old guy]

What level of tuning do you have? Stock? Stage 1?

Adding a test pipe will increase flow but it shouldn't really increase your boost level unless the cat was partially clogged.

Stock tune typically peaks at 10→11 psi and tapers to around 7 psi.

A stage 1 tune (depending upon tuner) will typically peak around 16→18 psi and taper to around 15 psi.

If you are running a stock tune but hitting 15 psi that is probably enough to put you in an overboost condition and thus the limp mode. Do you have the ability to log requested versus actual boost? That would tell you for sure.

If not, another thing you can check for is that one of the boost signal hoses connecting the N75 to the wastegate is leaking. Maybe it got disturbed during the test pipe installation. If one of the hoses is leaking it will dump some of the boost pressure that should be going to the wastegate for boost control and thus the overboost condition. That's where I would start looking first.

[rovert6]

What level of tuning do you have? Stock? Stage 1?

Adding a test pipe will increase flow but it shouldn't really increase your boost level unless the cat was partially clogged.

Stock tune typically peaks at 10→11 psi and tapers to around 7 psi.

A stage 1 tune (depending upon tuner) will typically peak around 16→18 psi and taper to around 15 psi.

If you are running a stock tune but hitting 15 psi that is probably enough to put you in an overboost condition and thus the limp mode. Do you have the ability to log requested versus actual boost? That would tell you for sure.

If not, another thing you can check for is that one of the boost signal hoses connecting the N75 to the wastegate is leaking. Maybe it got disturbed during the test pipe installation. If one of the hoses is leaking it will dump some of the boost pressure that should be going to the wastegate for boost control and thus the overboost condition. That's where I would start looking first.

I have a feeling it has something to do with my n75. I don't have a tune on it. It's completely stock atm. I don't have an ability to log unfortunately, don't have vagcom. When it hits 15 psi, it immediately drops to 10. That's the wastegate opening up to protect from overboost. I didn't remove anything on the front of the TIP that would offset the N75 in any way. Could a faulty one be the reason why I never saw enough boost without the TP?

[old guy]

Certainly a possibility. If it was sticking a little and didn't open to dump enough boost back into the TIP you would have an underboost condition. Now you are experiencing the opposite effect which is more likely a leaking boost signal line either from the turbo high pressure port to the N75 or from the N75 to the wastegate. You can remove the N75 and try cleaning it with some contact cleaner, brakleen or such to see if it frees it up.

[rovert6]

Update: Just replaced the n75 with a brand new one. as I was taking it out, I saw on the turbo cold side hose, it was torn on the bottom. So, I got a new hose and put the new n75 valve in and put it together. I unplugged the battery for over 2 hours to reset the ECU, and to no avail, I'm still in a sort of limp mode. I max out at only 5 psi now. No matter what I do, it won't go passed that amount. Any ideas?? Everything is hooked up right, and I double checked it after work when I got home.

[rovert6]

Bump any suggestions?? Could a faulty O2 sensor give me issues? I have no check engine light, but when I checked for codes before, it showed the O2 sensor faulty.

[old guy]

It sounds like one of two things. Either your new N75 isn't opening properly (stuck? Defective? No signal from the ECU?) or your DV isn't getting a boost signal from the intake manifold to help keep it closed.

[rovert6]

It sounds like one of two things. Either your new N75 isn't opening properly (stuck? Defective? No signal from the ECU?) or your DV isn't getting a boost signal from the intake manifold to help keep it closed.

I'm assuming it's the new n75 that's faulty/defective. when swapping the new one in, I noticed a large hole on the boost line from the turbo to the n75. I'm thinking this caused my overboost issue. When I fixed that hole, and put the new valve on, it only ran 5psi. I swapped the old one back in after cleaning out the lines with carb cleaner, and now I'm gaining boost again. Thing is, it's only boosting to 7-9. Sometimes 10. I thought the AWM heads did 10-12? Could the valve still be faulty?

Edit: I'm going to Black Forest tomorrow and try and swap out the valve with a different one to test if it's actually defective and if I'll get the 10-12 it should be. If not, then staying with the original because of the no overboost now. lol Also going to swing by Apex Tuning to have them log some data for me to see requested vs actual boost to see what's going on.

[rovert6]

hate to double post, but I got back from Apex Tuning, and they said the ECU is requesting 8psi and actual is 8. So, something is definitely off with the software. Don't know how that can happen. They found a small leak at the PCV line under the intake with a smoke test. Could there be any other reason why the requested is so low? Any way it could be a small/large boost leak? Any help is appreciated

[shoemaker617]

While your in there you should pull the grommet back on the harness goin to the n75 to make sure the wires are intact. Should also pressure test the mechanical wastgate while your in there

Sent from my SAMSUNG-SM-G900AZ using Tapatalk

[rovert6]

While your in there you should pull the grommet back on the harness goin to the n75 to make sure the wires are intact. Should also pressure test the mechanical wastgate while your in there

Sent from my SAMSUNG-SM-G900AZ using Tapatalk

I've been thinking about doing the boost leak test. Does a normal boost leak test check the mechanics of the wastegate? Or is there another way to do what you're saying?

[diagnosticator]

Update: Just replaced the n75 with a brand new one. as I was taking it out, I saw on the turbo cold side hose, it was torn on the bottom. So, I got a new hose and put the new n75 valve in and put it together. I unplugged the battery for over 2 hours to reset the ECU, and to no avail, I'm still in a sort of limp mode. I max out at only 5 psi now. No matter what I do, it won't go passed that amount. Any ideas?? Everything is hooked up right, and I double checked it after work when I got home.

Are you sure the N75 is installed correctly? Explain how you know this is true if you believe it is.

[rovert6]

Are you sure the N75 is installed correctly? Explain how you know this is true if you believe it is.

I installed exactly as I took it out. I also posted a response saying that the old one being put back in was working. The new one must have been faulty. I returned the new n75 and I'm using the original as of now. The new question is why is the ECU only requesting 8? I thought the stock boost was 10-12?

I'm assuming it's the new n75 that's faulty/defective. when swapping the new one in, I noticed a large hole on the boost line from the turbo to the n75. I'm thinking this caused my overboost issue. When I fixed that hole, and put the new valve on, it only ran 5psi. I swapped the old one back in after cleaning out the lines with carb cleaner, and now I'm gaining boost again. Thing is, it's only boosting to 7-9. Sometimes 10. I thought the AWM heads did 10-12? Could the valve still be faulty?

[old guy]

I've been thinking about doing the boost leak test. Does a normal boost leak test check the mechanics of the wastegate? Or is there another way to do what you're saying?

You can test the waste gate by using an air nozzle to apply pressure to the waste gate. Disconnect the hose that runs from the N75 to the waste gate and apply 10→15 psi to the hose. There should be no air leakage anywhere. I doubt that this is your problem because a leaking waste gate diaphragm will typically give you an overboost condition.

Next check the waste gate opening pressure. This requires a bit of contortion. Having an assistant really helps. Slowly increase the pressure to the waste gate. Reach up underneath the turbo to where you can at least get a finger on the waste gate actuator rod. The rod should not start to move until the line pressure is around 5→6 psi. If it moves sooner you have a weak waste gate return spring internal to the diaphragm.

Here's a good visual.

[rovert6]

You can test the waste gate by using an air nozzle to apply pressure to the waste gate. Disconnect the hose that runs from the N75 to the waste gate and apply 10→15 psi to the hose. There should be no air leakage anywhere. I doubt that this is your problem because a leaking waste gate diaphragm will typically give you an overboost condition.

Next check the waste gate opening pressure. This requires a bit of contortion. Having an assistant really helps. Slowly increase the pressure to the waste gate. Reach up underneath the turbo to where you can at least get a finger on the waste gate actuator rod. The rod should not start to move until the line pressure is around 5→6 psi. If it moves sooner you have a weak waste gate return spring internal to the diaphragm.

Here's a good visual.

Always quick with perfect explanations. I appreciate it. If my wastegate actuator was weak, wouldn't it open at the standard 5 or even less? As I'm getting 8-9 now.

[old guy]

Not necessarily. It has to do with the N75 duty cycle along with the waste gate spring pressure. Even with a 3 or 4 pound waste gate spring you could probably hit well over 10 psi of boost. If you disconnect the N75 line altogether the only pressure on the waste gate would be the exhaust pressure trying to force it open.

Exhaust pressure and boost pressure are obviously two very different things. The N75 works in conjunction with the spring pressure to force the waste gate open when the ECM says "enough already!" If the spring is a few pounds week it may open the waste gate a few pounds sooner.

I don't think that is your problem if the ECM is only calling for 8 psi and your actual is 8 psi it sounds like the waste gate and N75 are performing as expected by the ECM.

[old guy]

Let's go back to your original post. Before you installed the test pipe you were boosting around 7 psi. Shortly after installing the TP you were boosting up to 15 psi but going into limp mode.

You determined that you had a hole in the N75 boost signal hose, thus the overboost condition. You fixed the hose and now are back to where you started, around 7 to 8 psi of boost.

With a stock tune having a 3" TP and an AWM head isn't necessarily going to give you any more boost. Neither of those components are going to make much of a difference with the overall flow through the engine while on a stock tune. They will help as you start to make additional changes to enhance the performance (injectors, tuning, turbo upgrades, etc).

It's your level of tune that will determine your level of boost up to the point of needing additional hardware. That's where the TP and AWM can start to come in to play. But for now you are only going to get what the ECM is asking for and if it's 8 psi then so be it.

Something else to consider is the ambient air temperature. As the air gets colder it gets denser. Consequently you will see a bit less on the boost gauge for the same amount of performance. With my GIAC 1+ (big injector) file I would typically see a boost pressure differential of 2→3 psi between the middle of the summer to the middle of the winter.