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Thread: Boost Cut issue

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    Boost Cut issue

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    So i am having a boost cut issue randomly. Sometimes it will hold boost and sometimes it will cut and go into limp mode and only build 5 psi. I am thinking it might be the N75 valve. I have checked the lines that go to the wastage from the n75 and all is good they hold pressure and crack correctly. I see the other line goes into the crankcase breather spider tube and the other i believe is reference air either vacuum or boost depending on boost level. i think if i can confirm if that is ok I believe i have a n75 issue. Can you tap that line and run a boost gauge off of it and make sure that it is at the same boost as the intake manifold? Or do you guys think i should just replace the N75?

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    Veteran Member Three Rings Corradovolksb's Avatar
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    Do you have any faults in the ecu? What tune are you running? Have you check for boost leaks?


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    Quote Originally Posted by Corradovolksb View Post
    Do you have any faults in the ecu? What tune are you running? Have you check for boost leaks?


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    i am running a NefMoto tune. I have no boost leaks. I fixed them when i bought the car. I'll scan it tomorrow. but its random when it does it it just cuts and goes into limp mode.

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    Veteran Member Three Rings Corradovolksb's Avatar
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    Ok. If the egts are not coded out then that could be your issue if the egts are failing


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    Quote Originally Posted by Corradovolksb View Post
    Ok. If the egts are not coded out then that could be your issue if the egts are failing


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    EGT's have brand new board in them. I don't think i have faults for them. I don't have any Cat's either.

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    i have a p1555 in ecm. i checked my EGT temp sensor and i am reading 350C i believe that is fine.

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    Established Member Two Rings unmarkedA4's Avatar
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    You figure this issue out?


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    Quote Originally Posted by unmarkedA4 View Post
    You figure this issue out?


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    No i haven't. I don't know why its cutting boost. Everything is ok. the only thing is that the n75 is getting lazy and slow.

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    So i found a good deal on a N75 valve new. I ordered that. I think if i get it before this weekend I will do it this weekend. So i am going to try one and see what happens.

    i did a lot of searching with this issue. I really couldn't find much related to me. There was some that was close and a N75 did and did not fix it. I found most people had other issues along with the P1555. I only have this fault code. What doesn't get me is its fine sometimes and not the other. I have checked lots of things and come up empty. So i will try the n75 and see what happens. I am also replacing the fuel pressure regulator. I installed a inline pressure gauge and found that the rail pressure doesn't hold. Im my general experience that it should drop quick. Can someone correct me.

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    Boost Cut issue

    Quote Originally Posted by chaos2984 View Post
    So i found a good deal on a N75 valve new. I ordered that. I think if i get it before this weekend I will do it this weekend. So i am going to try one and see what happens.

    i did a lot of searching with this issue. I really couldn't find much related to me. There was some that was close and a N75 did and did not fix it. I found most people had other issues along with the P1555. I only have this fault code. What doesn't get me is its fine sometimes and not the other. I have checked lots of things and come up empty. So i will try the n75 and see what happens. I am also replacing the fuel pressure regulator. I installed a inline pressure gauge and found that the rail pressure doesn't hold. Im my general experience that it should drop quick. Can someone correct me.
    Doesn't hold? It shouldn't drop it should hold. During load it should raise. WOT fuel pressure will be high and fluctuate up and down, but much much more than 51/58 psi


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    so lotsa good thoughts in this thread

    Did you pressure test your wastegate lines? If you're getting an upper boost limit deviation, I would start there. The code explains limp/cut, and may partially explain a pressure reduction as it cuts. Edit, oh i see you tested them, yeah n75, wastegate actuator, or wastegate itself. Unless you changed the tune or something and it's requesting too much.

    Are you running a stock fuel pump? There are checkvalves that are sometimes omitted in the aftermarket. also the pump may be limiting if it's over the hill and trying to keep up with megaboost.
    Last edited by james 408; 01-18-2018 at 01:26 AM.

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    Quote Originally Posted by james 408 View Post
    so lotsa good thoughts in this thread

    Did you pressure test your wastegate lines? If you're getting an upper boost limit deviation, I would start there. The code explains limp/cut, and may partially explain a pressure reduction as it cuts. Edit, oh i see you tested them, yeah n75, wastegate actuator, or wastegate itself. Unless you changed the tune or something and it's requesting too much.

    Are you running a stock fuel pump? There are checkvalves that are sometimes omitted in the aftermarket. also the pump may be limiting if it's over the hill and trying to keep up with megaboost.
    Edit on the fuel pressure. I will run it shut the car off and it bleeds down to 0 after about 5sec. I run about 47psi at idle.

    I don't think its running out of fuel, I would think it would be more of a constant thing if it was fuel. I am replacing the FPR as well with a new stock on and see what happens. Found a new bosch one for cheap.

    I'm running a Nef Moto tune. Ive tested the waste gates and they are moving correctly. And they hold pressure and the crack at roughly the right pressure. They are probably only 10-15K old. They were almost new when i bought the car. I would say it doesn't have an actual waste gate issue since it had that when i bought the car. I didn't know it under stock boost. Once i got tuned it wouldn't make boost and i found all the boost leaks and other issues and fixed those. Finally found that the Drives waste gate linkage was loose and wasn't closing the waste gate itself. So i had to retighten the nut. That was a challenge i had to use 2 people to get that done. But i guess thats what you kinda get from non factory Ko3's. I don't know what they are but i know they are not factory.

    I will report once i get those parts on.

    I am thinking about running the EGT deletes. Has anyone used these that just plug into the connector and they work fine?

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    Veteran Member Three Rings Corradovolksb's Avatar
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    You should just code out the egts instead of installing the deletes.


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    Quote Originally Posted by Corradovolksb View Post
    You should just code out the egts instead of installing the deletes.


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    Whats the difference if the deletes give a normal standard reading. As long as there is no logic in looking for change it shouldn't set a fault code.

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    Veteran Member Three Rings Corradovolksb's Avatar
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    Quote Originally Posted by chaos2984 View Post
    Whats the difference if the deletes give a normal standard reading. As long as there is no logic in looking for change it shouldn't set a fault code.

    Yes your right. The deletes make the readings constant.


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    Quote Originally Posted by Corradovolksb View Post
    Yes your right. The deletes make the readings constant.


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    So my N75 should be here on the 24th. Also do you know the logic with the EGT's. Is it just to protect the Cat's from melting or does it make fine adjustments depending on what temp it reads. Do you know what the temp threshold is before it makes a major change to protect things?

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    Veteran Member Four Rings vavJETTAw36's Avatar
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    Boost Cut issue

    Quote Originally Posted by chaos2984 View Post
    So my N75 should be here on the 24th. Also do you know the logic with the EGT's. Is it just to protect the Cat's from melting or does it make fine adjustments depending on what temp it reads. Do you know what the temp threshold is before it makes a major change to protect things?
    EGTs are to protect engine. Hot temps will trigger the ecu to dump fuel to cool cylinders down. Temp threshold is 980C. You Think of it as a safety net if a primary 02 was faulty.

    Edit: ideally you should be seeing 945C constantly.


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    Quote Originally Posted by vavJETTAw36 View Post
    EGTs are to protect engine. Hot temps will trigger the ecu to dump fuel to cool cylinders down. Temp threshold is 980C. You Think of it as a safety net if a primary 02 was faulty.

    Edit: ideally you should be seeing 945C constantly.


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    Yea thats what i think i was at was 945c.

    Also replaced my fuel pressure regulator and found that i was loosing 2-3psi of idle pressure and it was causing a leak down when you turn the key off.
    But still cuts boost.

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    Veteran Member Three Rings Corradovolksb's Avatar
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    Quote Originally Posted by chaos2984 View Post
    So my N75 should be here on the 24th. Also do you know the logic with the EGT's. Is it just to protect the Cat's from melting or does it make fine adjustments depending on what temp it reads. Do you know what the temp threshold is before it makes a major change to protect things?
    Like vavJETTAw36 said the EGT sensors are only used when exhaust temps get above 980c as a safety net to keep your exhaust temps from going higher than that. With stock cats the exhaust temps can get that high but with downpipes installed with high flow cats or no cats the exhaust temp will only reach that temp during a very long pull. If your tune is set up to not run egt sensors then it wonít matter since the afr will be a lot richer than stock was keeping your egts in a safe zone.


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    Quote Originally Posted by Corradovolksb View Post
    Like vavJETTAw36 said the EGT sensors are only used when exhaust temps get above 980c as a safety net to keep your exhaust temps from going higher than that. With stock cats the exhaust temps can get that high but with downpipes installed with high flow cats or no cats the exhaust temp will only reach that temp during a very long pull. If your tune is set up to not run egt sensors then it wonít matter since the afr will be a lot richer than stock was keeping your egts in a safe zone.


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    Gotcha, Yea i have full exhaust and no Cat's So i don't think its an issue but i will log to make sure. I did put new boards in them and the codes for them went away.

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    Veteran Member Three Rings Corradovolksb's Avatar
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    Quote Originally Posted by chaos2984 View Post
    Gotcha, Yea i have full exhaust and no Cat's So i don't think its an issue but i will log to make sure. I did put new boards in them and the codes for them went away.
    Ok thatís good. Logging it should pinpoint your issue. Are you logging with me7logger?


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    Quote Originally Posted by Corradovolksb View Post
    Ok thatís good. Logging it should pinpoint your issue. Are you logging with me7logger?


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    what is that. I have vag com

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    Veteran Member Three Rings Corradovolksb's Avatar
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    Quote Originally Posted by chaos2984 View Post
    what is that. I have vag com
    Vagcom works on but you can only log 9 variables at a time. Me7logger is a logging app that allows for over 100 variables to be logged at once. You can check it out here. http://nefariousmotorsports.com/foru...7.0title,.html



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    Quote Originally Posted by Corradovolksb View Post
    Vagcom works on but you can only log 9 variables at a time. Me7logger is a logging app that allows for over 100 variables to be logged at once. You can check it out here. http://nefariousmotorsports.com/foru...7.0title,.html



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    Thanks man.

    So i just for shi** i checked my plugs and changed from unknown stock style coils to factory coils. And i also checked my plugs. All the plugs looked great and clean just a little black around the metal right where the electrode ground attaches. I also checked my gap and it was a little all over the place. So i set them all to .28 there were like .28- .32 changes a little bit.

    But here is what i am noticing more in 2nd gear its fine but 3rd is where it cuts most of the time. in the lower gears that is. It will cut higher up as well.

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    Veteran Member Three Rings Corradovolksb's Avatar
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    Ok thatís good you checked your plugs. .028 might be a little high for stock coils but if itís not misfiring under boost then your good. When you say it cuts are you talking about your boost dropping off and coming back in or are you saying cuts like your loosing power under boost and your exhaust not changes and pops?


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    Quote Originally Posted by Corradovolksb View Post
    Ok thatís good you checked your plugs. .028 might be a little high for stock coils but if itís not misfiring under boost then your good. When you say it cuts are you talking about your boost dropping off and coming back in or are you saying cuts like your loosing power under boost and your exhaust not changes and pops?


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    I get a stray misfire here or there but nothing to crazy. But it will spool to hit the "spike" then it cuts and goes into limp mode. It will stay in limp mode and only hit 5psi and i guess when it thinks its safe to try it will try to go back to normal.

    Also i look at that page where is the d/l for the logger. The only thing i didn't like about that form is its not like here is the d/l link you have to hunt for it. Can you link me the d/l for the logger

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    Veteran Member Three Rings Corradovolksb's Avatar
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    Ok sorry yah your for sure going into soft limp. Try logging mvb 115 and see if your actual meets or exceeds requested. You need to be a member in order to see the download links. Let me know if you donít want to make an account and Iíll try and set you up with it.


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    Quote Originally Posted by Corradovolksb View Post
    Ok sorry yah your for sure going into soft limp. Try logging mvb 115 and see if your actual meets or exceeds requested. You need to be a member in order to see the download links. Let me know if you donít want to make an account and Iíll try and set you up with it.


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    Ok that makes sense then. I will set up an account. Yea So what should I look for as what is considered to much boost? like how much over commanded is not acceptable.

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