More positive deviation

[Speed4Avant]

So my car is stage 3 f21 550cc 044 pump ect. Yesterday it started running like shit, idling erratically and sitting super lean. So anyways I boost leak tested and couldn't find any leaks on the larger pipes (or anywhere). I changed my oil today and then while the engine was running I cleared my codes which included some misfires and the positive deviation. After clearing the codes idle returned to normal and AFRs were back in the normal range for idle. I took the car out for a drive and the car was normal when not in boost but once I hit boost it would only go up to 4psi and misfire. Got home and read the codes and it's good old positive deviation. My question is what is the best way to find out what is causing the positive deviation? I'm thinking there could be some issues with the waste gate lines but I'm not sure how to test. Let me know if anyone has any suggestions for troubleshooting this issue? Car was fine a few days ago and can't find leaks in the usual spots (tbb, intercooler hoses, any of the main pipes).

[vavJETTAw36]

Leak in your WG lines would give you bunch of boost before you'd go into limp. I'm betting a decent boost leak in your charge pipes.

Is pressure leak test the whole system. If you still want to test your WG line, put a mity vac on it that can pressurize the lines (positive pressure) or use an air compressor set low.


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[vavJETTAw36]

Somehow quoted my own post. Disregard this.

[Speed4Avant]

Leak in your WG lines would give you bunch of boost before you'd go into limp. I'm betting a decent boost leak in your charge pipes.

Is pressure leak test the whole system. If you still want to test your WG line, put a mity vac on it that can pressurize the lines (positive pressure) or use an air compressor set low.


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I tested (@24psi) and sprayed soapy water at every pipe around top and front of the engine. Would have to be something that doesn't show up when pressure testing through the intake. The leak was acting like when I've had leaks on my intercooler piping but there's literally no air coming off tbb, bipipes, intercoolers, and around n75 area. I'm stumped and feel like I should be pressure testing through another area or it is a sensor problem. Another key thing is I haven't had full boost for at least 6 months: been hitting 21 psi when I should be around 24.

[vavJETTAw36]

Hmmm. You should log the car and compare actual boost to requested boost.


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[Speed4Avant]

Hmmm. You should log the car and compare actual boost to requested boost.


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can do that tomorrow. before I cleared out the codes and changed my oil today: (two days ago) I was hitting 20 psi and then got sent into limp mode at 9psi after doing a few pulls and the deviation/misfire codes started coming up. Then idle was really shitty and was going up and down, car was also running really lean. Then cleared the codes with engine running and at idle and while driving with no boost was somewhat normal. now its really weird how it's only hitting 4psi and misfiring at anything past 0 psi.

[james 408]

what are your codes? Doesn't really sound like boost or wastegate line to me. Vacuum leak would be more likely, or something else entirely like a bad maf

[Speed4Avant]

what are your codes? Doesn't really sound like boost or wastegate line to me. Vacuum leak would be more likely, or something else entirely like a bad maf

codes are positive deviation, also misfire on 2 and 3. I do have extra used sensors including map, maf, and n75 so can do some troubleshooting. If it's a leak it's not one of the usual spots and I can't find it with my pressure tester hooked up to the intake.

[jimmer009]

I would look at the map sensor. Mine is bad and I'm changing it this weekend. But it causes misfires and sporadic limp mode. It won't always throw code either. I'm going on my 3rd one. High boost really shortens the life span of them

[Perth_RS4]

is it possible that you have a failed diverter valve?

[vavJETTAw36]

is it possible that you have a failed diverter valve?

Failed DV? How would that cause a bad idle? A possibility under boost yes but if it's causing a bad idle too, no. The DVs are open during manifold vacuum.


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[Speed4Avant]

swapped the map sensor, idle is slightly better especially when warmed up. Still can't boost past 1-2psi and it feels like a heavy misfire. Also I noticed the car feels really rough when I let off the throttle. I cleared codes and it's still coming up as charge pressure control positive deviation (no misfire codes or anything else). I'm stumped: can try swapping dvs as I have a few sets but I am running 710n.

[Speed4Avant]

Swapped maf and dvs with an extra set I had, no difference. Haven't messed with changing the n75 but I'm thinking it has to be a leak at the back of the engine maybe to the wastegate lines. Never encountered a leak like this where I can't get any boost and it is rough when letting off throttle.

[christianb5s4]

I know you said you checked it already, but I would re-examine the usual places (turbo/intercooler hoses, TBB, turbo inlets, etc). Double and triple check those in every way.

Next, I would look at pressure testing the wastegate lines. You can take the lines off the N75 and blow smoke into them (use cigar, vape, whatever), looking down the lines with a flashlight and see if smoke comes out (indicating a leak). This is an incredibly helpful technique to quickly diagnose without using a mighty vac.

[Speed4Avant]

I know you said you checked it already, but I would re-examine the usual places (turbo/intercooler hoses, TBB, turbo inlets, etc). Double and triple check those in every way.

Next, I would look at pressure testing the wastegate lines. You can take the lines off the N75 and blow smoke into them (use cigar, vape, whatever), looking down the lines with a flashlight and see if smoke comes out (indicating a leak). This is an incredibly helpful technique to quickly diagnose without using a mighty vac.

I did multiple pressure tests with the car in the air but not too much hassle to do another. I've never tested off the n75 lines before but that is the plan tonight. Thanks for the help!

[Corradovolksb]

If you are 100% sure you don't have any leaks on the pressure side than there is a really good chance the one ore both of your turbos failed and they are not allowing boost to be built. Usually when this happens the car runs ok and boost is not built so I'm still thinking you have a large leak on the pressure side I just wanted to throw the bad turbo idea out there.

[Speed4Avant]

If you are 100% sure you don't have any leaks on the pressure side than there is a really good chance the one ore both of your turbos failed and they are not allowing boost to be built. Usually when this happens the car runs ok and boost is not built so I'm still thinking you have a large leak on the pressure side I just wanted to throw the bad turbo idea out there.

I hooked up my air compressor to the passenger side of the t below the n75 valve. Wastegate isn't moving with 10-15 psi running through the line, bad news? Also it isn't like when I blew a ko3, the 1-3 psi I'm getting of boost comes with stumbling/misfire (although no misfire codes come up).

[slowSfaux]

Blown turbo would still theoretically idle fine. How are your inlets connected to the turbos? Again I know you pressure tested already, but your symptoms point to a sizeable boost/vacuum leak.

[Speed4Avant]

Blown turbo would still theoretically idle fine. How are your inlets connected to the turbos? Again I know you pressure tested already, but your symptoms point to a sizeable boost/vacuum leak.

I have frankenlets, and have tested with the car up in the air (though I'm gonna test again tomorrow). I've never had a boost leak where it will only boost to 1-2psi and stumble super hard without throwing any codes besides positive deviation. Also it's weird how rough the car is when I let off from partial throttle. That's why I'm pretty confused. In the past even when I've had intercooler hoses slip off it runs smoother than this, would still build boost and I could hear whooshing.

[Zba]

Not related to your positive deviation but what condition are your EGTs in? If I remember correctly you've had positive deviation codes forever so I'm thinking the two are unrelated. Does the positive deviation set every time?

[Corradovolksb]

How does it run with your Maf unplugged? If it runs fine with it unplugged than you prob have a large boost leak.

[Speed4Avant]

Not related to your positive deviation but what condition are your EGTs in? If I remember correctly you've had positive deviation codes forever so I'm thinking the two are unrelated. Does the positive deviation set every time?

EGTs are coded out along with rear o2s (EGTs are bad). Haven't had a deviation code since I had a boost leak months ago. Positive deviation just showed up with these problems this week, at this point I think I have a leak somewhere in the vacuum tubing behind the motor or something is seriously wrong.

Another thing is I'm testing the waste-gates as suggested in this guide http://allroadfaq.com/downloads/tech...re_testing.pdf by blowing air from my compressor through each hose on the connection to the plastic t. On the passenger side I don't see the wastegate moving, how noticeable should the movement be?

edit: also if any of this is helpful in diagnosing: last 3 months I have had issues with the car getting too hot at idle, dying while driving at 80 mph, and then not starting till the car cooled down (I thought it was the CPS but didn't end up replacing because I solved my overheating issue and the car hasn't died recently). Also replaced coolant temp sensor. 1.5 months ago I replaced an o2 sensor. Also in the last month I developed a power steering leak and the pump died (replaced with rebuilt pump), then the starter died (replaced with a used starter), then the battery died. Now the last week I had limp mode every so often and now I can't even hit 1-2 pounds of boost and had that bad idle (weird the idle today was somewhat back to normal).

[Zba]

Have you checked all of the one way check valves?

[Speed4Avant]

Have you checked all of the one way check valves?

the four way check valve on the drivers side of the engine is good. but is there a way to check the rest of the check valves without removing every single one of them?

[zillarob]

You have anybody handy that is good at sucking and blowing?

Pull off one of the black hoses that runs from the fuel rail down to the inlets. (this is the one you will be working with)
Plug or pinch off the other.
n80 should be closed with key off.

If your blower can blow through it, the top center is bad.
If your sucker can suck through it, the one by inj 1 is bad.
Assuming the n80 is closed (and good), and the other evap hose to the inlet is plugged or crimped off, you should not be able to blow or suck air through.
If you can get a golf ball through there, I got $20 in my pocket

[christianb5s4]

To follow on from what Rob said, the N249 lines and solenoid are another potential vacuum leak culprit if you've crossed everything else off. If that solenoid or any of the lines have a leak, that would make for a difficult to find vacuum leak.

[vavJETTAw36]

I hooked up my air compressor to the passenger side of the t below the n75 valve. Wastegate isn't moving with 10-15 psi running through the line, bad news? Also it isn't like when I blew a ko3, the 1-3 psi I'm getting of boost comes with stumbling/misfire (although no misfire codes come up).

Not moving? Maybe they are actually not returning to closed? Is the wastegate arm (for lack of better terms) vertical or slightly at angle? If vertical, wastegate is stuck open. Doesn't explain idle issue though.


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[Speed4Avant]

You have anybody handy that is good at sucking and blowing?

Pull off one of the black hoses that runs from the fuel rail down to the inlets. (this is the one you will be working with)
Plug or pinch off the other.
n80 should be closed with key off.

If your blower can blow through it, the top center is bad.
If your sucker can suck through it, the one by inj 1 is bad.
Assuming the n80 is closed (and good), and the other evap hose to the inlet is plugged or crimped off, you should not be able to blow or suck air through.
If you can get a golf ball through there, I got $20 in my pocket

To follow on from what Rob said, the N249 lines and solenoid are another potential vacuum leak culprit if you've crossed everything else off. If that solenoid or any of the lines have a leak, that would make for a difficult to find vacuum leak.

Thanks for all the great suggestions, I'm waiting on some replacement crimp clamps to come tomorrow so I can continue testing the vacuum lines and will update this thread later this weekend with what I find out. Trying to avoid going to a shop as I'm working a shitty job right now and haven't gotten hired yet for what my degree is in.

Not moving? Maybe they are actually not returning to closed? Is the wastegate arm (for lack of better terms) vertical or slightly at angle? If vertical, wastegate is stuck open. Doesn't explain idle issue though.

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I might just be looking at it wrong from the top. The wastegate arm is definitely slightly angled, going to try and see if it looks different from down below.

[christianb5s4]

Don't use the crimp clamps, these are far superior than those single use clamps. They are called mini screw style clamps, ECS has em or you can get a set at Autozone/O'Rielly's.

https://www.ecstuning.com/ES2940/

[Speed4Avant]

You have anybody handy that is good at sucking and blowing?

Pull off one of the black hoses that runs from the fuel rail down to the inlets. (this is the one you will be working with)
Plug or pinch off the other.
n80 should be closed with key off.

If your blower can blow through it, the top center is bad.
If your sucker can suck through it, the one by inj 1 is bad.
Assuming the n80 is closed (and good), and the other evap hose to the inlet is plugged or crimped off, you should not be able to blow or suck air through.
If you can get a golf ball through there, I got $20 in my pocket

To follow on from what Rob said, the N249 lines and solenoid are another potential vacuum leak culprit if you've crossed everything else off. If that solenoid or any of the lines have a leak, that would make for a difficult to find vacuum leak.

check valves are fine after doing some blowing and sucking. On to the next vacuum line section

edit: my other question- idle is a lot better with the maf sensor unplugged although it runs richer. Idle with maf plugged in is sitting at 17+ afr while idle with maf unplugged is around 14. Is it safe to drive with the maf unplugged to see if the misfires under boost come back? I'm thinking the connector is busted, the two used mafs I have are bad, or there's the phantom boost leak I can't find. Or it could be a combination of things.

[Corradovolksb]

You can drive it with the Maf unplugged just keep an eye on your AFR under boost and make sure it doesn't go Leaner than 12.9 if your Maf connector or wiring at the connector is bad that will cause crazy readings. You could have 2 bad mafs in a row but it would be pretty rare. The fact that you can't build boost is still bugging me and a bad Maf shouldn't cause you to not build boost.

[Speed4Avant]

now we have some new codes. Unplugged the maf and when I was revving it a bit in my garage I got a b1s1 o2 sensor code along with a few misfires. I cleared the codes and took the car for a drive. No more stuttering under boost but it is still only hitting 3psi and is lean under boost (~14 afr). When I got home I scanned codes again and I got the maf code and now instead of positive deviation I got a negative deviation code. O2 code and misfires did not come back....

[erykv1]

You can drive it with the Maf unplugged just keep an eye on your AFR under boost and make sure it doesn't go Leaner than 12.9 if your Maf connector or wiring at the connector is bad that will cause crazy readings. You could have 2 bad mafs in a row but it would be pretty rare. The fact that you can't build boost is still bugging me and a bad Maf shouldn't cause you to not build boost.

what do you mean leaner than 12.9? proper AFR mixture should be around 14.7ish no?

also, OP, have you checked your wastegate cracking pressures?

[Speed4Avant]

I think he meant leaner than 12.9 under boost. I'm going to pop off the n75 again tomorrow and jack up my car to try and see if I can see the wastegates move when running air through the t. I tried to test it a few days ago and could not see the passenger side wastegate move at all when looking at it from the top. I've never tested wastegates before so I'm not 100% it wasn't moving, I assume will be easier to tell from underneath.

edit: going to check the wastegates tomorrow but saying fuck it and going to take it to the shop this week, don't really know enough to keep dealing with this (will update this thread with findings, hopefully I missed something stupid).

[Corradovolksb]

what do you mean leaner than 12.9? proper AFR mixture should be around 14.7ish no?

also, OP, have you checked your wastegate cracking pressures?

I was referring to AFR under boost. AFR at idle and cruise should be as close to 14.7 as possible but under boost you want AFR to be close be between 11.8 and 12.5 depending on what set up and fuel you are running.


That fact that your still not building boost is pointing to a bad turbo or a large boost leak. The shop should be able to tell if a turbo is seized or you have a stuck open WG.

[Speed4Avant]

My hose clamp on the throttle body boot was bad and leaking at the bottom (probably cause of my boost issues for months), glad it was something simple. will need to do a better job boost leak testing in the future.

[Corradovolksb]

Awesome you found it man. The throttle body boot is one of the most hated things about our cars.

[Speed4Avant]

Awesome you found it man. The throttle body boot is one of the most hated things about our cars.

welp, boost is back where it should be but even after having the shop fix/pressure test my car yesterday negative deviation is back along with o2 sensor code and limp mode. It seems to trigger limp mode when I'm doing a third gear acceleration from low rpm. doesn't trigger when I do a pull from higher rpms

[Corradovolksb]

What tune are you running. It's possible that the requested load is set too high at low rpms and your turbos can't spool fast enough to meet requested causing the deviation. What is the o2 fault that is stored? That could also cause limp mode.

[Speed4Avant]

What tune are you running. It's possible that the requested load is set too high at low rpms and your turbos can't spool fast enough to meet requested causing the deviation. What is the o2 fault that is stored? That could also cause limp mode.

solo motorsports tune, I'll probably just send him logs again its been a while since I got a revision. Its my passenger side b1s1 o2 forgot which code (has been coming on/off for a few weeks at least, weird because I replaced that side a few months back. I might just bite the bullet and replace the pair of o2 sensors.