Most likely a misfire, no cel though

[Cscribble]

I've got a 2002 WRX with the 2.0l and I've got a misfire but no CEL. I've had this same thing happen before but it's been a few years, last time I got it to throw a CEL by getting pissed off and hammering down while going up a hill in second gear. I thought about doing the same thing on the same hill again but while that may be a quick way to figure it out it's probably not the most mechanically sympathetic way lol


So far I've changed the spark plugs and cleaned the MAF and it didn't change anything. I didn't see anything noteworthy when I pulled the plugs but I marked which cylinder I pulled them from in case I needed to go back and look again. I found that if I ease into higher revs it doesn't misfire but if I accelerate quickly it stutters every time.



I already did a bit of digging about this and it was suggested to use the cylinder roughness monitor on the accessport but I went through the list and didn't see that as an option on it and that was the only real idea I found when looking through the old posts.

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[Cscribble]

Like usual I forgot to explicitly state the question.... What methods can I use to figure out which cylinder is causing the misfire?

As I said in the first post, I do have an accessport but it doesn't have the cylinder roughness monitors... or at least I didn't see them.

[Charlie-III]

I would contact COBB with your year/model car and AP SN and ask about the roughness monitor (after rereading it's manual).

Does ambient temp make a difference?
Does ECT make a difference?
Does it do it at a certain time after getting gas?

[Cscribble]

Originally Posted by Charlie-III

I would contact COBB with your year/model car and AP SN and ask about the roughness monitor (after rereading it's manual).

Does ambient temp make a difference?
Does ECT make a difference?
Does it do it at a certain time after getting gas?

I just figure the roughness monitor wasn't an option due to the car being an 02 as opposed to being an 05+. There is some options with the accessport that aren't available to things from before 04 like Flat Foot Shifting and
aunch control or 2-step.... I dont have it as an option so I forget which it is lol


Ambient temp? I don't think so, its a persistant misfire and the weathers been up and down in temps since it started.


I hadn't monitored the ECT's with the AP but the gauge stays the same so I'd say it's a safe bet it doesn't make a difference.



As far as I can remember it's on the same tank of gas since it started the misfire. I hadn't driven it much lately because it snowed but I was wondering if it was just bad gas. It's at a little under a half a tank now and I've been trying to get it as low as possible before I put more in just to rule that out and maybe putting some Techron fuel treatment in before I refill the tank.


I ended up hammering down on it going up that same hill in second but still no check engine light. Surprisingly I don't recall a misfire at all going up there, I may have just gotten used to easing into it lol

[Charlie-III]

Thanks for update, keep us posted.

May be just poor gas. Do you remember if you last got gas somewhere else?

[Cscribble]

I always go to the same place in town to get gas, there's only two gas stations that have 92 octane and one of them is too far in the wrong direction.



I am starting to wonder about ambient temps though lol unfortunately the Forester has the outside temp guage but I haven't swapped the newer cluster into the WRX yet so I don't know exactly what the temp is as I'm driving it around.

[Elbert Bass]

double post

[Elbert Bass]

Originally Posted by Cscribble

I always go to the same place in town to get gas, there's only two gas stations that have 92 octane and one of them is too far in the wrong direction.



I am starting to wonder about ambient temps though lol unfortunately the Forester has the outside temp guage but I haven't swapped the newer cluster into the WRX yet so I don't know exactly what the temp is as I'm driving it around.

When refering to "ambient" air temperature for the ECM the reference is the Intake Air Temp sensor value - not the sensor in front of the radiator for the dash display.
And yes, until it actually becomes enough of an issue to trip a misfire event a roughness monitor or multi-channel oscilloscope would be your only options. With the scope you can compare primary coil and also injector patterns which may indicate the fault.

[bo2o]

You should inspect the injectors while also searching for a vacuum leak because the fuel quality might also need inspection. The fuel might be bad too. The temperature at the intake pose unexpected complications to various components.

[Charlie-III]

Originally Posted by Elbert Bass

When refering to "ambient" air temperature for the ECM the reference is the Intake Air Temp sensor value - not the sensor in front of the radiator for the dash display.

When I say ambient, I mean the outside air temp. When I have people check temp sensors with a scanner that also does realtime data, I have them check ECT, IAT against ambient. If outside, what is the temp, if in a closed garage, what is its temp. After sitting a few hours (I prefer overnight, check first thing in morning before starting car) all 3 temps should read within a degree or 2.

ECT=Engine coolant temp.
IAT=Intake air temp