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Discussion Starter · #1 ·
Ok so I have a 04 wrx sedan. Rebuild ej205. Bpt 16g. Catless exhaust. DW 650cc. Walbro 255. Cobb sf intake. Inlet tube aftermarket. Protuned.

Ok so the problem is the tach jumps from 4k to 5.5k back fires and runs like poop. No CELS though. Changed plugs and added some ground from the ecu ground (local tuner and subaru speed shop told me too). They also said to do coils too. I haven't tried that yet.

The weird thing was I did grounds and plugs tonight. It ran good for about 2hrs and it then started to do it again. I have no clue on what's going on. I'm getting a tactrix cable and a laptop so I can datalog and send to my tuner.

I was hoping someone on here had some answers or had this problem before.

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Back fire or after fire? If it's after fire I'm guessing that's from it missing at the higher rpm and expelling fuel into the exhaust.

What conditions cause it to run up to 4k+? While driving or at idle? If it's at idle you may have a lean issue or even a stuck throttle.

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Discussion Starter · #3 ·
Back fire or after fire? If it's after fire I'm guessing that's from it missing at the higher rpm and expelling fuel into the exhaust.

What conditions cause it to run up to 4k+? While driving or at idle? If it's at idle you may have a lean issue or even a stuck throttle.

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After fire and driving. It runs great from idle to 4k then does it. Even in neutral or in gear

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Check the coils for sure, because the after fire is fuel entering the exhaust. As for the surging, it could also be related to a bad coil, or coils.

However I'm no pro, that is just where I would start. I've chased a misfire now for months and haven't solved it.

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Discussion Starter · #5 ·
Check the coils for sure, because the after fire is fuel entering the exhaust. As for the surging, it could also be related to a bad coil, or coils.

However I'm no pro, that is just where I would start. I've chased a misfire now for months and haven't solved it.

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Okay I was going to check coils next and crank position sensor. But it's not throwing a CEL though

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My misfire didn't throw a code until yesterday when I was messing around trying to figure out something. So my trust of that light is zero.

If you can identify what cylinder you think the problem is you can try swapping that coil to another cylinder. I'm assuming the car is tuned for the equipment on it?

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Have to complete two "consecutive" drive cycles (any combo of the three below) to get the light.
Drive cycles A: Drive for 20 minutes or more at a constant speed of 80 km/h (50 MPH) or more.
Drive cycle B: 1) Drive at 10 km/h (6 MPH) or more. 2) Stop the vehicle and idle for ten minutes.
Drive cycle C: (A) Shift the select lever to “P” range or the shift lever to the neutral position, and let the engine idle for 10 seconds or more. (B) Accelerate to 97 km/h (60 MPH) or more within 20 seconds. (C) Drive for 20 seconds or more at 97 km/h (60 MPH) or more. (D) Decelerate with fully closed throttle to 64 km/h (40 MPH) or less. (E) Drive for 20 seconds or more at 64 km/h (40 MPH) or less. (F) Accelerate to 97 km/h (60 MPH) or more within 10 seconds. (G) Stop vehicle with the throttle fully closed.
 

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You could have an ECU problem it isn't common but isn't unheard of. You could also have a com problem between the laptop and the obd2 adapter

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