subaru 2.5 ej25 engine.misfiring at idle only.
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Do you have access to your fuel trim numbers? Giving us an idea of what the ST and LT numbers are doing at idle and 2500 rpms would provide us with some very relevant information. Very well could be a vacuum leak of some sort...though I've also seen a blown head gasket leaking coolant internally cause idle misfires, particularly on first start when the engine is cold.
Thanks!
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- Andy.MacFadyen
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" We're trying to plug a hole in the universe, what are you doing ?. "
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Also, does that fuel correction number do when you raise the rpms to 2500-3000? Does it stay really negative or does it get closer to zero?
Checking the fuel pressure regulator on these engines is really easy. it sits on the fuel rail below the air intake duct and has a vacuum line attached to it. Unplugging that vacuum line when the engine is running and looking for fuel spitting out will tell you if the diaphragm in the regulator is ruptured. A quick, easy to perform test.
Rob
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- ScannerDanner
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agree with Andy, your symptoms describe a mechanical problem to the letterAndy.MacFadyen wrote: Thinking old school, have you done a compression test? A leaking exhaust valve will smooth out at higher RPM.
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A relative compression test would give you great direction, before pulling the plugs and doing compression testing. Even if you don't have a scope, you can disable fuel and just listen to the engine cranking.
The Jeep 4.0L timing problems video has a perfect example of this. Listen to the engine around 7:42.
If you hear something like that during cranking, then I'd say you can move directly to compression and leak down testing.
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Still very happy you came up with a fix, sir. What led you to checking the EGR valve?
In retrospect, the fuel trims being way negative could have steered us towards a stuck open EGR, oh well. Why the PCM didn't pick up on that would probably depend on how it monitors the EGR position, and what the code set criteria is. If this uses a potentiometer in the EGR valve, then it may only code when the position exceeds a certain point. Knowing what a known good closed position value is might be useful for the future.
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