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05 Redline CTS-V
8,439 Posts
Discussion Starter #1
An ex of mine recently aquired a 99 2.5 RS impreza and recently it has started throwing codes a lot

P0300 random misfire is the main culprit but sometimes it shows up as P0301 P0302 P0303 or P0304 which are dedicated cylinder 1, 2, 3 or 4 misfires respectively.

now... here's what is done to the engine

Full catback exhaust with tubular headers and a CAI

shes currently using a DTEC tuning kit ...i don't know anyting about this but its basically a cheap ass import version of something like FAST, tune on the fly. that type of BS. Its an NA engine so i know its not anything boost related.

Here's what shes done so far, cleared codes to see what comes back as the active code. Its 7 times out of 10 the P0300 random misfire.

I had her replace the plugs, wires, coil, engine ground (just taking a crapshoot after replacing the whole ignition system, yeah yeah spark needs ground). Shes checked for leaks in the headgasket and hasnt seen anything external. I'm nearly 100% sure she doesnt have a coolant leak to cylinder because there is no white smoke, which to me indicates burning coolant. Supposedly the timing is checked and the tuning unit has been disconnected so shes on a stock timing/spark table again.

Any other ideas what this might be? Again its a basically stock with intake and headerback exhaust EJ25 flat 4 boxer engine.
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