boost cut issue!
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This is a discussion on boost cut issue! within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; hey guys am new to the forum. i am trying to help my brother out. he has a 96 wrx ...

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    boost cut issue!

    hey guys am new to the forum. i am trying to help my brother out. he has a 96 wrx impreza wagon with an ej20 turbo motor.

    the trouble is when you do a boost pull in like 4th gear the boost climbs to 14psi at about 4000rpm and it feels like you stomp on the brakes for half a second then it picks up again and does it again about 4500 or 5000. i really know nothing about subarus but i am familiar with turbo cars. to me what is happening is boost cut but you all might have a different idea!



    what boost should this car be running?

    I thought to start with the wastegate was stuck but i checked that and it moves fine. so my next thought was the boost control solenoid which we swapped one out from a wrecked car (yeah ok it may not be working either but the best we could for now) and it seems to be still doin the same. just above the boost control solenoid there is a little black box with what looks like a little air filter on it. what is that?

    I am thinking the prob may be a vac leak. can someone point me in the direction of a vac hose diagram so we can do a vac job to see if that fixes it for us.

    Cheers Mark

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    Good news, everyone! xxxxxxxAnub1s's Avatar
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    Sounds more like a fuel problem to me, to be honest.
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    Quote Originally Posted by Anub1s View Post
    Sounds more like a fuel problem to me, to be honest.
    as in a fuel cut or blocked injector or dodgey pump or what sort of fuel prob? thanks

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    Good news, everyone! xxxxxxxAnub1s's Avatar
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    Quote Originally Posted by schwass View Post
    as in a fuel cut or blocked injector or dodgey pump or what sort of fuel prob? thanks
    As in clogged fuel filter, stuck injector, dodgey fuel pump

    Fuel dilivery can be spotty when the fuel pump is beginning to go out.
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    Quote Originally Posted by Anub1s View Post
    As in clogged fuel filter, stuck injector, dodgey fuel pump

    Fuel dilivery can be spotty when the fuel pump is beginning to go out.
    the fuel filter is new, we ran some injector cleaner through to see if that would help but no difference. short of taking the injectors out is there anyway to check if they are stuck? how would you check if the fuel pump is dodgey? would you have to log fuel pressure some how? cheers

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    confused

    Anubis... read this thread. It sounds more like a boost issue.
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    Good news, everyone! xxxxxxxAnub1s's Avatar
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    Quote Originally Posted by Sinister View Post
    confused

    Anubis... read this thread. It sounds more like a boost issue.
    Very well could be, I'm not completely ruling it out by any means.

    I looked up the stock boost pressure for the 96 WRX and it's supposed to be set to 12.7. So if there isn't a tune and it's hitting 14 psi this could very well be your issue.

    If you want to test the fuel pump, there is a way to do it that involves a multimeter and some tracking down of connectors.

    Is the wastegate arm adjustable at all, I'm not sure about the overseas WRX's so, this is going to be a bit of an adventure to diagnose.

    edit: From researching online I'm seeing information stating that the 94-96 WRX ECU is set to cut fuel at 16-16.5 psi. Is that boost guage accurate? If the ECU is seeing 16psi from the MAP sensor, it's going to cut fuel to protect itself.
    Last edited by xxxxxxxAnub1s; 05-27-2010 at 11:11 PM.
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    yes the waste gate arm is adjustable. there is a locknut on the thread where it links to the pivot arm of the waste gate. i guess i should take the arm off and make sure it is opening fully. is there a way to adjust it to make sure its set correct?

    the boost gauge is from the local auto store repco. its brand new so have no reason to think its out. on talking to my brother today he mentioned that it was spiking to 15 or 16 so i think it might be the fuel cut. if the waste gate is working fine can we put in a manual boost controller to bring the boost down? or if its the exhaust and lack of tune thats causing the boost spike will the boost just keep spiking?



    Quote Originally Posted by Anub1s View Post
    Very well could be, I'm not completely ruling it out by any means.

    I looked up the stock boost pressure for the 96 WRX and it's supposed to be set to 12.7. So if there isn't a tune and it's hitting 14 psi this could very well be your issue.

    If you want to test the fuel pump, there is a way to do it that involves a multimeter and some tracking down of connectors.

    Is the wastegate arm adjustable at all, I'm not sure about the overseas WRX's so, this is going to be a bit of an adventure to diagnose.

    edit: From researching online I'm seeing information stating that the 94-96 WRX ECU is set to cut fuel at 16-16.5 psi. Is that boost guage accurate? If the ECU is seeing 16psi from the MAP sensor, it's going to cut fuel to protect itself.

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    Good news, everyone! xxxxxxxAnub1s's Avatar
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    Quote Originally Posted by schwass View Post
    yes the waste gate arm is adjustable. there is a locknut on the thread where it links to the pivot arm of the waste gate. i guess i should take the arm off and make sure it is opening fully. is there a way to adjust it to make sure its set correct?

    the boost gauge is from the local auto store repco. its brand new so have no reason to think its out. on talking to my brother today he mentioned that it was spiking to 15 or 16 so i think it might be the fuel cut. if the waste gate is working fine can we put in a manual boost controller to bring the boost down? or if its the exhaust and lack of tune thats causing the boost spike will the boost just keep spiking?
    Ah, wasn't aware of the exhaust. Due to the nature of certain turbos, a more free flowing downpipe can cause boost creep and increase already present spiking problems, it's odd that it's so severe though. Some amount of tuning can help to alleviate SOME of the creep problems, but if it's spiking, it's another issue altogether. That car needs a tune. I think the wastegate might need to be adjusted though, but to what on that car, I have no idea.

    Stay away from a manual boost controller unless you get the car tuned to use one. With an MBC, the turbo is ALWAYS going to want to be at the boost pressure you set it at, causing problems like partial throttle full boost, and other potential issues. Timing and fuel MUST be adjusted for this, even if it's for stock boost pressures.
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    Quote Originally Posted by Anub1s View Post
    Ah, wasn't aware of the exhaust. Due to the nature of certain turbos, a more free flowing downpipe can cause boost creep and increase already present spiking problems, it's odd that it's so severe though. Some amount of tuning can help to alleviate SOME of the creep problems, but if it's spiking, it's another issue altogether.
    Its not so much creep as it will be spiking and flat out over boosting. By removing the exhaust restriction less wategate duty cycle/exhaust gas is needed to control the target boost setting. I agree,the vehicle needs to be properly tuned.
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    i have the same problem.. my wrx is completely standard though. when this happens i hear air escaping like a blow off valve. ( but mine is standard and recirculates back into the air intake )
    im going to change the fuel pump tomorow, fingers crossed thats the problem
    also my car is fine under light acceleration. but anything more than quarter acceleration it cuts out. seems like a fuel problem to me. ie fuel pressure is not at 39 psi and when accelerating heavy it doesnt have enough fuel pressure to keep it going.

    no cel lights come on.

    Matt

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