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Discussion Starter · #1 ·
Hello there. I am a new member on these forums and am requesting some assistance if some people would be so kind. I have done some looking on these forums for a few weeks now and I cannot seem find a thread that fits my vehicle's problem. I believe my problem is overboost based on what problems others have had and their vehicle's symptoms. Before we get started I should say I am from Australia, so I am not sure how much my vehicle differs from the members who reside in the States.

A little bit about my car:

My car is a 2005 WRX blob eye with what I believe is a EJ205 engine and is a 5 speed manual. My car has 164000kms on the clock (or 100k miles approx). It is completely stock except a set of rims and a catback exhaust. It was a beautiful example of what a WRX could be which leads me to believe there isn't a trojan performance mod, however could be wrong. I have owned the car for 3 years and done 40000kms in that time. The only problem I have ever had with the car is a slight 'surging/jerking' feeling at 100kph/60mph which turned out to be a faulty spark plug. I changed them all 20000kms ago. I change my oil and oil filter every 5000kms.

My problem lately is that I enter an on-ramp on the highway in 4th at around 4000rpm (approx 100kph/60mph) and my car has a large jerk motion which feels like im about to go through the windscreen. Correct me if I am wrong but I believe it is a fuel cut off to save the turbo/engine? This is not an isolated incident, it occurs under somewhat of a load but not full throttle whether in 3rd/4th or 5th. Has happened about 6 times in a month. I am now driving cautiously as it is quite a violent jerk when it happens and does not feel pleasant. Unfortunately I cannot tell you what boost I am running as I do not have a boost gauge currently installed, although one is ordered. I always warm my car up for a few minutes before I go anywhere, no exceptions. It is also coming into summer and approaching 30 Celsius/86 Fahrenheit ambient temperature. The car does not produce a check engine light at all when this problem occurs.

I have been told around town to check leads, spark plugs and coilpacks. The spark plugs seem good as they haven't long been replaced and the leads all read 0.7 ohms. I am handy with tools being an electrician but I won't pretend I know what I am doing around an engine. I look forward to hearing what you guys reckon should be the next course of action as I have no idea where to begin.
 

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I used to have that problem when I first got mine. It was from a fouled maf and a cheap piece of junk aftermarket intake and filter. Once I swapped out the filter and intake for an aem system and got a new maf sensor, it stopped having that problem. I would try cleaning the maf sensor and see if that helps. Mine was so bad from that oiled pos filter the previous owner had on it, that I just opted for a new one rather than trying to clean it. Lol
 

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Discussion Starter · #4 ·
Been abit busy lately and havent had a chance to look the car in depth. I will check the maf sensor on the weekend and see what I come up with. Reading up on others problems, if the sensor is dirty does it look like it has a residue on it?

Mainframe: the car does not show a check engine light when this occurs
 

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I will check the maf sensor on the weekend and see what I come up with. Reading up on others problems, if the sensor is dirty does it look like it has a residue on it?

Mainframe: the car does not show a check engine light when this occurs

I would just clean the sensor (with aerosol electronics cleaner) regardless of what it looks like. It's not likely that you would be able to see the sensor wire being dirty.




If there is no check engine light, then it's not overboost/fuel cut. I would start checking the most common culprits and work down from there.. start off with a boost leak/vacuum test. Once you've ruled out the possibility of a leak in the intake system, then I would replace the spark plugs with OEM NGK (different plugs can have issues with boost.. namely Champion) iridium plugs. They should come pregapped, but be sure to check the gap on each plug before installing it anyways.

Violent jerking does sound like a spark issue.. so if new plugs doesn't fix it I would look more into the coil packs. Usually a failing coil pack will throw a misfire code for that cylinder, but not always. The old coil packs on my 2002 WRX all showed ~0.7 ohm, and I never had a misfire, but the engine would cut out under boost. Finally I borrowed four different coil packs from a friend, and voila, the problem was solved. Unfortunately coil packs aren't cheap, so I would see if you can borrow some from a friend/shop before going out and buying new ones.
 

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Discussion Starter · #6 ·
I cleaned the maf sensor with an electronics cleaner yesterday. After attempting 6 highway entries I didn't experience the jerk at any gear or any rpm up to 5k. Ill see if it happens again this week. I replaced the spark plugs 12 momths ago with NGK iridium plugs.

Just out of curiosity, if it is a coilpack issue/misfire issue, why is it only occurring at certain rpms and not across the board?
 
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