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This is a discussion on Need help diagnosing hesitation problem within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I have a USDM 02 WRX pretty much stock except a COBB ram air intake that is hesitating and throwing ...

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    Need help diagnosing hesitation problem

    I have a USDM 02 WRX pretty much stock except a COBB ram air intake that is hesitating and throwing a misfire code every few weeks. I've had the car since 4/2001 and never had any problems with the thing until a few months ago when my check engine light came on. I bought a tactrix cable and downloaded ECUExplorer, code it's throwing is misfire on cylinder 2. Cleared the code and reset my flash and immediately noticed that my car was hesitating during acceleration now. Throws same code after a few days, clear code and reset flash, and repeat. I've changed out my plugs (which were NGK Iridiums with maybe 30K miles) to Denso Iridiums, no change. Changed my fuel filter, no change. I've run Redline fuel injector cleaner several times now and it SEEMS to have gotten better, but that may just be subconscious hope. What's weird is that the hesitation only occurs around 4000 RPM's and in 1st gear is hardly noticeable, and gets more noticeable until when in 4th gear the car does not want to accelerate past 4000 RPM's.

    Forgot, I did replace the intercooler air intake gaskets with new ones since a few years ago I replaced my starter and didn't replace those gaskets or use a torque wrench at that time. Also, when replacing my starter and re-installing the BOV, I over torqued one of the bolts and it completely tore out the threads so that the BOV could be a little loose. But if this were the problem, why would it start causing problems now. I put teflon tape around the bolt and was able to get some descent torque on the bolt. I also replaced BOV gasket as well.

    Sorry for the long post. Any suggestions?

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    Registered User teflon_jones's Avatar
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    1. Get rid of the BOV
    2. Clean your MAF sensor
    2. Switch the coil packs on cylinders 2/4 and see if the code changes to cylinder 4.
    Scott
    Past Subies - '11 STI Limited stage 1+ and '04 STi stage 2+
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    Quote Originally Posted by teflon_jones View Post
    1. Get rid of the BOV
    2. Clean your MAF sensor
    2. Switch the coil packs on cylinders 2/4 and see if the code changes to cylinder 4.
    Thanks for the tips, but how/why would I get rid of the BOV? That would leave a gaping hole in my intercooler. I'm talking about the stock BOV, not an aftermarket noise maker.

    I planned on cleaning the MAF sensor, just haven't had time to. I did log some runs though and it appears to be getting proper readings (from what I can tell). I did notice some serious knock correction at on one run though.

    I planned on trying the coil pack swap also if absoultely possible. I hate messing with the coil packs. I'll probably just measure the impedance to see if there is any difference first. Hopefully I can get some time on friday to try this and cleaning the MAF sensor.

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    Registered User teflon_jones's Avatar
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    Quote Originally Posted by youngblood View Post
    Thanks for the tips, but how/why would I get rid of the BOV? That would leave a gaping hole in my intercooler. I'm talking about the stock BOV, not an aftermarket noise maker.
    That's a BPV, not a BOV.

    Based on the behavior and CEL code, the coil packs and MAF would be where I would start. I meant to put one more thing and forgot, which is to make sure all of your hoses are tight.
    Scott
    Past Subies - '11 STI Limited stage 1+ and '04 STi stage 2+
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    Quote Originally Posted by Timdog1650 View Post
    Click the link in my sig about hesitation.
    Yeah, I've read that post and searched through the NASIOC forums quite a bit. Working on those steps as I get the time.

    Quote Originally Posted by teflon_jones View Post
    That's a BPV, not a BOV.

    Based on the behavior and CEL code, the coil packs and MAF would be where I would start. I meant to put one more thing and forgot, which is to make sure all of your hoses are tight.
    You're correct, sorry for the confusion. I always call it a BOV and confuse the hell out of my friends. The hoses are tight, and I have even replaced all the gaskets on my intercooler (air intake ducts and BPV ) but like I said the BPV is not exactly torqued down to spec on one bolt due to lack of threads. I'm definitely looking at that as the potential problem, but I'm a little suspect since it's been that way for several years with no problem.

    The thing I'm most curious about is why this hesitation is only a problem around 4000 RPM's. What's so special about 4000 RPM's? In the NA region, the car runs fine, and in the upper RPM's (say >4600) the car runs great.

    One more potential cause, bad gas with 10% ethanol. I've read some threads where people have questioned the effects of running 10% ethanol gas and noone seems to think this should cause a problem. But I had been running Exxon 93 Oct gas almost the cars entire life until about a year ago when I moved and have been running Texaco 93 Oct with 10% ethanol almost exclusively. That's why I've been running that Redline fuel injector cleaner like a mad man the past month. It feels like it has made an improvement, but maybe I'm just crazy.

    Thanks for the advice so far, keep it coming!

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    Registered User teflon_jones's Avatar
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    Quote Originally Posted by youngblood View Post
    Yeah, I've read that post and searched through the NASIOC forums quite a bit. Working on those steps as I get the time.
    I missed a couple of things, the biggest being the spark plug gap. Did you gap your plugs?

    Quote Originally Posted by youngblood View Post
    the BPV is not exactly torqued down to spec on one bolt due to lack of threads. I'm definitely looking at that as the potential problem, but I'm a little suspect since it's been that way for several years with no problem.
    I doubt that's the problem too.

    Quote Originally Posted by youngblood View Post
    The thing I'm most curious about is why this hesitation is only a problem around 4000 RPM's. What's so special about 4000 RPM's? In the NA region, the car runs fine, and in the upper RPM's (say >4600) the car runs great.
    That's where your car really starts to pull in air, make boost, and generate a lot of power. So that's where a lot of problems start to show up.

    Quote Originally Posted by youngblood View Post
    One more potential cause, bad gas with 10% ethanol. I've read some threads where people have questioned the effects of running 10% ethanol gas and noone seems to think this should cause a problem.
    Anybody that thinks 10% ethanol causes issues is an idiot. That's all they sell in a lot of states, including both states where my STi has spent all 50k miles of its life.
    Scott
    Past Subies - '11 STI Limited stage 1+ and '04 STi stage 2+
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    Moderator Donkey's Avatar
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    Try getting the injectors professionly cleaned.Dirty/clogged injectors can also cause missfires.The way to check is just like the coil packs.Switch the #2 and #4 injectors and see if the missfire code changes.Like suggested clean the MAF first before anything else as it is the easiest.
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    Quote Originally Posted by Donkey View Post
    Try getting the injectors professionly cleaned.Dirty/clogged injectors can also cause missfires.The way to check is just like the coil packs.Switch the #2 and #4 injectors and see if the missfire code changes.Like suggested clean the MAF first before anything else as it is the easiest.
    I hadn't cleaned the MAF because when I log the MAF it appears to be reading temp and air flow fine, but I went ahead and cleaned it this weekend. No change in performance. I still haven't switched the coil packs because I can't remember if it was the #2 or #3 cylinder and it hasn't thrown the code in a few weeks. Once it does, I'll switch the coil packs. BTW, I can't remeber the cylinder numbering isn't it

    back of car
    3 4
    1 2
    front of car

    Quote Originally Posted by teflon_jones View Post
    I missed a couple of things, the biggest being the spark plug gap. Did you gap your plugs?
    Actually, I'm running NGK Iridiums and I checked the gap of each one before installing and was reading about .031 so I didn't change them. I later realized the factory gap is .032. But the problem was there before I changed the plugs. Iwas running Denso Iridiums with a gap of about .029 that only had about 30-40K miles on them.

    Quote Originally Posted by teflon_jones View Post
    That's where your car really starts to pull in air, make boost, and generate a lot of power. So that's where a lot of problems start to show up.
    True enough, but no different than say 3500 RPM's or 4500 RPM's. That's what's puzzling me.

    Quote Originally Posted by teflon_jones View Post
    Anybody that thinks 10% ethanol causes issues is an idiot. That's all they sell in a lot of states, including both states where my STi has spent all 50k miles of its life.
    I didn't say myself or anyone said it causes any issues, just said some people question the effects of running it. Big difference. I wouldn't consider myslef an idiot by any means. A little harsh. I would say it's wise to question and study any changes made in maintenance when a problem arises. Just because you have 50K miles on your car running 10% ethanol doesn't mean it wouldn't cause a problem in someone elses car. That's really not that large of a sample and not a full life cycle. It's just another factor to consider.

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    Registered User teflon_jones's Avatar
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    Quote Originally Posted by youngblood View Post
    I didn't say myself or anyone said it causes any issues, just said some people question the effects of running it. Big difference. I wouldn't consider myslef an idiot by any means. A little harsh. I would say it's wise to question and study any changes made in maintenance when a problem arises. Just because you have 50K miles on your car running 10% ethanol doesn't mean it wouldn't cause a problem in someone elses car. That's really not that large of a sample and not a full life cycle. It's just another factor to consider.
    I wasn't calling you an idiot. I just said anybody that thinks it causes problems is an idiot.

    Yes, I only have one car with 50k miles on it, but my sample size is the tens of millions of cars that run 10% ethanol in many states across this country every single day. Nobody has problems in cars due to 10% ethanol. That's like saying if you use windshield washer fluid with more than 10% water your windshield washers aren't going to work.
    Scott
    Past Subies - '11 STI Limited stage 1+ and '04 STi stage 2+
    '13 Wrangler Rubicon - custom front bumper w/12k lb winch & off-road lights, skid plates, diff guards, etc.
    '04 Porsche 911 Turbo GT2 clone 600 HP/TQ
    '77 F-150 heavily modded for off-roading

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    Registered User Dropzero's Avatar
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    I had similar issues with my 02. I had the bolt stripped on the BOV (yes i mean BOV) and it misfired all 4 cylinders troughout the rpm range. I doubt its that but it is a cheep fix that you might consider doing to prevent anything from messing up in the future. What I DID see, is after the BOV issue the car misfired on all 4 from time to time. It would hesitate around 4k as well. what fixed it was a new O2 sensor. Or they call it a fuel/air sensor i believe on the wrx. I say get that checked out.
    Hey buddy its a subbie... good luck

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    Registered User Dropzero's Avatar
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    Oh and one more thing. It may have just been my WRX, but the vacuume hose to the BPV has two parts. My connector was leaking and that threw the code as well as hesitation when the boost kicked in.
    Hey buddy its a subbie... good luck

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    OK, so two new developments today in my quest to solve my hesitation and misfire problem.

    First, I posted earlier that I hadn't gotten the chance to switch my coils because I hadn't gotten a CEL in a while. I had previously observed that each time my CEL came on it was on Thursday morning at almost the exact same point in my drive to work (about two minutes after starting the car). I was suspecting that this was because each time my CEL came on, I would wait until the weekend (which is when I fill up my tank) and clear my code. 4 days later when my CEL would come on, my tank was about 3/8 full. To see if this was really an issue, I had purposely been filling my tank every two days keeping it pretty much full all the time and haven't had CEL in 240 miles. This morning when I started my car and began my trip to work, I was staring at my instrument panel fully expecting the CEL to light up (I had finally let my tank get to about 3/8 full), lo and behold it did. Maybe coincidence, but seems pretty consistent to me.

    Second, I just checked the codes (and cleared them), this time it was mis on cyl 2 and AND 4. So, I think that probably rules any kind of plug, valve, or coil problem. Wouldn't that be true?

    So my suspicion now is kinda far fetched but seems plausible, a faulty fuel pump or pressure regulator or something of that nature. Maybe some sort of soot in the tank that gets sucked up into the pump once the fuel is low enough? Any thoughts?

    Of course, the hesitation does not change with how much gas is in the tank, so maybe I'm completely off now that I think about it. The car has had the hesitation problem starting with or right around the first CEL but never seems to improve.

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    Registered User Timdog1650's Avatar
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    Quote Originally Posted by youngblood View Post
    First, I posted earlier that I hadn't gotten the chance to switch my coils because I hadn't gotten a CEL in a while.
    Not that a failing/failed fuel pump has never caused anyone a problem before, but I wouldn't pass go nor would I collect $200 before I checked the coilpacks and/or the sparkplugs and their gap. 99% of misfires on an otherwise mostly stock car (stage 2 and below) are from either bad coils or improperly gapped plugs.

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