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1999 Subaru Forester Question: P0301 misfire

 

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DMBs, 2.5L 4 Cylinder, Champlin, MN, January 03, 2011, 22:26
 Rookie

Code P0301. Checked timing and noticed erratic flashing when clamped to #1 cylinder. Could not see marking on camshaft so could not determine reading. Clamped to #3 cylinder and steady flashing. Measured primary and 2ndary coils-ok. Replaced coil anyway. Same erractic flashing as before. Champion plugs have no oil deposits at .040 - clean tan/brown color. Cleared code and swapped both #1 plug and wire with #3 - code returned next day driving to work (approx 15 miles). Inspected KS and found crack. Replaced and cleared code. Next day to work I got P0301 again. Cleaned throttle body and checked 4-pin TPS pins 1&2 with Fluke 87 VOM. Read 2K-Ohms at closed throttle. Slowly opened throttle and does not go to infinite (open) till roughly 1/2 throttle (erratic resistance variance to that point). Checked resistance on pins 3&4 while opening/closing throttle. Resistance slightly erratic with brief measurements of full short. Suspect TPS but not geting TPS fault code and it's a $250 part replacement. Haven't yet measure voltage levels on TPS. Took vacuum measurement at manifold port (where hose goes in just after the filter). Read about 7inHg (seems Low) but needle did not fluctuate. Note - I have an old vacuum gauge. All vacuum hoses appear fine and connected. PCV valve clicks when I put my finger on it. This car does not have an EGR. I have not measured fuel pressure, but #1 and #3 fuel injectors have identical ohms. I have a basic OBDII tool but am getting the the Equus 3160 delivered on the 5th.

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  • Answer #1

    patrick mannion from Greg Solow's Engine Room, January 03, 2011, 23:01
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     Master

    You have done good work. First adjust the valves, they are screw adjust traditional valves, then change injector from number 1 to another cylinder see if problem moves cylinder. My brother's Subaru had a mis fire I was chasing when it was new dealer couldn't find it it was a bad harness.
    Adjust valves and swap injector to another cylinder. Things I have found to fix several Subaru misfires.
    let me know what you find
    patrickmannion1@netzero.com

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    Visitor, January 03, 2011, 23:21

    Wow! That was a fast response...thank you Patrick. I had thought about swapping the injectors as you suggested, but I kept thinking back to the erratic flashing of the timing light when clamped to #1 wire . I get roughly 10-15 steady flashes then a sudden hic-up. This pattern seams to repeat again and again. Unless mistaken, my understanding is that the ECM tells the coil and injector when to fire based on input data from other sensors... they're essentialy reactive devices. How can an injector send a misfire code, and why would the plug condition look identicle to its neighboring #3 plug?

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    DMBs, January 03, 2011, 23:48
     Rookie

    There's one other thing I noticed but forgot to mention. When at stop sign the idle is rough and the check engine light wil flash. Once I get going again the light goes solid and car runs smoothly. Don't know if that is significant but am thinking the misfire is taking place when idling and not when driving down the road.

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