Stutter or stall under hard acceleration?
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This is a discussion on Stutter or stall under hard acceleration? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Edit: Problem Solved. But Read on if you want. As of yesterday, when I try to accelerate hard, the engine ...

  1. #1
    Registered User AgentH's Avatar
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    Stutter or stall under hard acceleration?

    Edit: Problem Solved. But Read on if you want.

    As of yesterday, when I try to accelerate hard, the engine stutters, or if really pushed, will stall. This problem normally occurs at 5k rpm but will occur sooner if I push it harder. And it only happens under load. When it does happen, it feels like I hit a wall (is that fuel cut?). I have no CEL and out of precaution, i checked to see if there were any codes w/my Cobb AP and no codes were found.

    Common sense says that it is either a Fuel problem or an Air problem, but I could be wrong.

    I have a Cobb AP and a K&N drop in filter. I changed my fuel filter at 45k and my spark plugs between 45 and 50k to copper NGK BK6RE and paid very careful attention to their gap. I am at 57k now.

    I took the Cobb AP off (flashed back to stock) to see if the problem was still occuring. The problem persisted, but not to as great of an extent. So I put the AP back on knowing that it is not the reason.

    The problem occured with about 1/10 full tank of gas. I then filled it and the problem persisted. ... Looking at my gas reciept from the 1st, it says 2.57/gal... was premium that cheap in NJ? NJ pumps your gas for you for those that don't know. I payed 2.74/gal, so I know i got premium this time around...

    Could my fuel pump have gone? Could my ignition coils have gone bad already? Is my MAF dirty (would that cause a CEL to light?)?

    Any suggestions are greatly appreciated.
    Last edited by AgentH; 10-02-2006 at 02:26 PM.
    2nd WRX...
    More than meets the eye.

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  3. #2
    Registered User AgentH's Avatar
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    Any suggestions will be really appreciated!!!

    I think I'm ultimately going to have to take it to a dealer though....

    What I am going to do though prior to that is the "Grounding Mod" (seems like BS, but I'll give it a try), clean the MAF with MAF cleaner (I really doubt a dirty MAF could make that much of a difference), and check the spark plugs (even though I did them less than 10k ago.

    It runs fine as long as I keep it below 60% strain. So who knows if any of that will do anything.

    Does anyone know how to check the ignition coils?

    Something of note is the noise that it makes when it's straining to accelerate. It makes a noise that sounds like it's comming from the right hand side of the engine as I'm driving. The noise isn't a scapping noise, is faint, and of a frequency slightly higher than the groan of the motor but a lower frequency than that of the turbo. That concerns me as I feel like it could be something mechanical dying. Could it be the turbo? Any way of checking it?

    Thanks again!
    2nd WRX...
    More than meets the eye.

  4. #3
    Registered User dcpatters's Avatar
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    This is going to be difficult to isolate. Out of interest, have you measured or confirmed boost while at WOT? Possibly overboosting and hitting the fuel cutoff? I know it's a long shot but something to cross of the list.

    How about the spark plug gap? You mentioned you paid close attention to this.

    Problems with a dirty MAF sensor or bad fuel (octane) would show up in drivability; idling, throttle response, and hesitation.

    If it feels like you hit a brick wall during hard acceleration, it almost sounds like fuel starvation.
    2008 Evo X GSR. Custom tuned, Works panel filter, Intercooler pipe upgrade, TBE.

  5. #4
    Registered User AgentH's Avatar
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    Since my last post, I have not done any of the things I said I was going to do. I did put $40 worth of premium from 2 different sources into my car however. My car pulls hard now and feels like it's "back to normal". However, I do not know for sure. I have not gone WOT today, but have gone close, and there was no stuttering or hessitation.

    I put $20 worth of gas yesterday morning.
    On my way home, above 4500 rpm, there was hesitation and boost peaked at .05 MPa (7.25 psi). A few random times my car stalled out. And a few times i would be barely moving with low RPM, would go to accelerate in 1st, and nothing would happen. The boost gauge would move but RPM's would sink way low. I would let go, wait a split second, and accelerate again, and everything would be back to normal. I thought things were getting worse.

    Last night, put $20 worth in.
    My drive to work made me thing that everything was back to normal. No hessitation or stuttering, and at about 90% thotle, boost peaks at .05 MPa (7.25 psi) which tells me that the problem is still there.

    I sort of think that I might have filled up with bad gas and it screwed all of the set points up with the ecu... possibly. ...My car seemed to have worked fine until about 1/8th tank. But it seems to have gotten slightly better.

    I'm pretty sure I have a turbo problem. Something is preventing it from boosting above .05 MPa. A leak, a broken solenoid.. ect...? Time for me to figure out how the turbo Really works.

    Does anyone have some informative diagrams that I can check out?

    Things I want to do yet: Clean MAF, replace fuel filter, and check for faulty grounds.
    2nd WRX...
    More than meets the eye.

  6. #5
    Admiral Ackbar the 1st mycologist's Avatar
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    This thread has a diagram, but it is probably too basic for your needs

    downpipe/exhaust question

    Good luck, I'm not going to be able to help here.

  7. #6
    Registered User dcpatters's Avatar
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    Is the car flashed to stock? Have you reset the ECU?

    There is a thread, I think by Damien02WRX?!? I thought he had a problem with the brass pill missing from the vacuum line. If this is missing, the ECU cannot effectively regulate boost. Search around for this thread.

    Cheers!
    2008 Evo X GSR. Custom tuned, Works panel filter, Intercooler pipe upgrade, TBE.

  8. #7
    Registered User AgentH's Avatar
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    Problem still exists.

    While rolling, if I floor it, I get fuel cut at 6k and a considerable amount of stuttering before I even get there. Max boost is still .05 MPa.

    This thread has a diagram, but it is probably too basic for your needs

    downpipe/exhaust question

    Good luck, I'm not going to be able to help here.
    Thanks, but yea, I need something more technical than that one.

    Is the car flashed to stock? Have you reset the ECU?

    There is a thread, I think by Damien02WRX?!? I thought he had a problem with the brass pill missing from the vacuum line. If this is missing, the ECU cannot effectively regulate boost. Search around for this thread.

    Cheers!
    Found a post here: Finally I got full Boost
    which lead me to here (restrictor pill post): Restrictor Pill

    I went out to my car an hour ago. Although I couldn't pull the tube off that has that restrictor pill in it, I felt it inside the flexable tube and know it's there. Plus, why would my car work fine, and then all of a sudden, have errors? Regardless, the pill is there. So is that 1/8" restrictor hose.

    I cleaned my MAF yesterday. Yes, it was all gunked up, but not beyond belief. Went for a spin afterwards and no difference.

    I also reset the ECU. I lost the link, but basically, I unplugged the negative termial on the battery, turned my lights on and pushed the brake pedal a few times to make sure there was no stored energy in the electrical system, let it sit there for 45 min, and then started it up. No change.

    I still want to check my spark plugs and replace the fuel filter (you never know, it could be gunked up from bad fuel and not allow WOT opperation).

    Does anyone know what waste gate flutter is? How to identify it?

    Does anyone know if there are any components on the turbo that fail frequenly? IE, the waste gate, wategate actuator, that solenoid under the plastic quarter turn cover, the turbo it's self (w/60k on it), or anything else I'm forgetting?

    I'm over at Nasioc right now going through "hesitation" threads.
    2nd WRX...
    More than meets the eye.

  9. #8
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    Red face

    the only thing i can think of is vaccume leak, just go crazy, take off the hoses, go to advanced auto or something and replace all the lines around the throttle body and the turbo, this should be an informitive task and not the difficult.

  10. #9
    Registered User speeddr2000's Avatar
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    sounds like ur map in unplugged it happened to me it just came undone . check it out hope it helps

  11. #10
    Registered User sti>evo's Avatar
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    I'm pretty sure it's your fuel pump. I actually think you have 2. One in the tank and one outside the tank. When you first get in your car listen VERY hard and only turn the key to the ON position. You should hear a quiet, high pitch noise. That is your fuel pump engaging. If you don't hear that, it's most likely your fuel pump( one of 2) If you DO hear that sound, it could still be your fuel pump. SO..............have your fuel pump checked out.
    "You were flyin back there when I passed you!"


    NEW ENGLANDF4

  12. #11
    Registered User AgentH's Avatar
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    Update:
    I took my intercooler off last night.

    I noticed a lot of gunk that looks like it either came from outside (through the radiator it's self) or was blown out of the side of one of the y tubes. Does anyone know if this is normal:


    So i took the y hose off and cleaned it. It was really tight so I don't think that it was the problem. I notice there's a lot of oil in there. Is that normal? not like, you turn it over and it drips, but a lot.

    I tested my boost control solenoid. I took a 12V supply and connected it to the leads on the solenoid pins. I then undid the one hose connecting the BCS to the turbo inlet hose (the one connecting the input of the turbo to the snorkle of the intake, and blew on it while switching the solenoid on and off w/the 12V supply. As far as I can tell, it was in working order. It either let air pass or it didnt. learned that the waste gate actuator opens at 7psi. Since i only hit max 7psi, one might think my boost control solenoid is broken. But, as far as I know, it's working. .......

    I then took the airbox out and made sure there weren't any squirrls living in there. There weren't. and I removed a spark plug and it looks good:

    Then i put it back and struggled like hell to put the top back over the filter and box. That, is a royal PITA!!!

    This morning, I didn't know what else to do so I took the heat shield off the turbo. And this morning, i wanted to make sure the waste gate was working and the waste gate actuator too. So I undid the c clip and opened it up. Seemed smooth enough for being covered in rust. The waste gate actuator on the otherhand was not smooth. It felt very rough when I would apply enough pressure to pull the arm outwards. I cleaned the rust off the arm w/a brillow pad and shot some WD-40 into the Waste gate solenoid where the arm moves in and out. It still isn't that smooth. But it's a little smoother. I acutally got this idea from someone at Nasioc: http://forums.nasioc.com/forums/show...1088973&page=2 (I'm K.Linchpin in case anyone cares to know). The guy at the subaru dealer said that in all of his time working there, he's never had a car come in w/a bad turbo. So I opted not to drop the down pipe and check the turbo out for any problems.

    after 7 hrs or so of snooping around and tearing it apart, I decided to put everything back together.

    Fired it up and it started right up. Turned it off and changed the Fuel Filter. This is where my greatest concern is. Here is a look at the fuel that was in the fuel filter:




    That was what came out by blowing on the in side of the fuel filter. Out came that cruddy looking gasoline. It's very rusty looking and the particles are not settling to any great account.

    After replacing the fuel filter, i took it for a spin. Still get fuel cut when hard accelerate in 2nd. Fuel cut before i could get more than 0.05 MPa boost. 1st and 2nd feel kinda weak. In 3rd or 4th, I hit 0.07 MPa (10.2 psi) of boost! which i haven't hit in a long time. Maybe if my fuel didn't look like poo, my car would run good. hmmmm...... Any suggestions?

    I'm pretty sure it's your fuel pump. I actually think you have 2. One in the tank and one outside the tank. When you first get in your car listen VERY hard and only turn the key to the ON position. You should hear a quiet, high pitch noise. That is your fuel pump engaging. If you don't hear that, it's most likely your fuel pump( one of 2) If you DO hear that sound, it could still be your fuel pump. SO..............have your fuel pump checked out.
    I hear the high pitch noise every time, so it would have to be the other pump. I saw a tutorial on replacing your fuel pump. People normally replace the one in the gas tank, right? That means, pulling the cushions outta the back seat and finding that little trap door? I have a pressure gauge for measuring fuel pressure and vaccuum. any idea what the pressure should be?

    sounds like ur map in unplugged it happened to me it just came undone . check it out hope it helps
    do you know if one of these is the map?

    They're both plugged in, although I didn't really check.

    As far as vaccuum leaks go... the look tight. the ones with clamps are tight. But some are burried in there. So I don't know.

    Thanks for reading that novel! Any suggestions are really appreciated! Thanks for everyone's input so far!
    2nd WRX...
    More than meets the eye.

  13. #12
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    Sup Dude,
    Sucks you’re still having issues with this fuel cut. I think after looking at the fuel filter fuel you got some bad gas and your fuel pump assembly could be all fowled up. There is an in tank fuel filter that is attached to the fuel pump. Something that you might want to look into. JSC has a walbro pump and installation kit for $100 bucks. So maybe it might be something to think about. Ohh have you looked at your injectors. Make sure there clean. Could be a junked up injector not flowing correctly and through some kind of weird resistance back the ecu. There are tons of places that can flow test injectors or you could get some STi Pinks. Just some thoughts. Well good luck and I will keep my eye out for any more threads on this.
    Peace

  14. #13
    Registered User AgentH's Avatar
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    The grime in the gas seems to have settled quite a bit. It took a good 12 hours though, so no doubt that crud is going straight into my engine. And that can't be good.

    Sup Dude,
    Sucks you’re still having issues with this fuel cut. I think after looking at the fuel filter fuel you got some bad gas and your fuel pump assembly could be all fowled up. There is an in tank fuel filter that is attached to the fuel pump. Something that you might want to look into. JSC has a walbro pump and installation kit for $100 bucks. So maybe it might be something to think about. Ohh have you looked at your injectors. Make sure there clean. Could be a junked up injector not flowing correctly and through some kind of weird resistance back the ecu. There are tons of places that can flow test injectors or you could get some STi Pinks. Just some thoughts. Well good luck and I will keep my eye out for any more threads on this.
    Peace
    STI>EVO said there's another fuel pump? I don't know which one could have gone bad. I saw a tutorial on replacing the fuel pump (the one that is in the tank it's self). It might be worth a shot. The Subaru tech also said he's never seen a subaru come back with a fuel pump that has gone bad, so I'm skeptical.

    As far as cleaning the injectors. I know people replace theirs all the time, but those things are burried in the engine. I wouldn't doubt it if I had to take the manifold off. And that would really suck. But considering that gunk is going through the injectors, i wouldn't doubt that they are at least somewhat clogged up. Thanks for your input.

    Any more suggestions??? Thanks again!
    2nd WRX...
    More than meets the eye.

  15. #14
    Registered User dcpatters's Avatar
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    I think a good place to start is to drain the fuel tank. Perhaps have the fuel system treated by the dealer as well. Judging by the sample of fuel you have there, this is a good place to start.

    Is the car hesitating in the mid-range and top-end? Perhaps you are not putting enough load on the engine to generate full boost?!
    2008 Evo X GSR. Custom tuned, Works panel filter, Intercooler pipe upgrade, TBE.

  16. #15
    Registered User AgentH's Avatar
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    I will push it hard on my way home and get back to you. I'm fearful of the fuel cut. I don't like the harsh bucking feeling that I get when that happens. So I tend to ease it up to high RPM in 1st and 2nd. Prior to doing all that I stated above, I could be driving it on the verge of fuel cut (floored) and would not boost above .05 MPa. I haven't driven it enough, since putting it back together, to tell you how bad it is now.

    I will look into having the fuel system treated by a dealer. ... time to ask around for a dealer that does a good job service wise...

    ... No offense to any of you who might work as a techs at a subaru dealer (I'm sure you know a helluva lot more than me), but after all the issues that friends of mine have had with service people at dealerships, I am going to be VERY cautious.

    Thanks for you suggestion!
    2nd WRX...
    More than meets the eye.

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