Mis fire all cylinders. Only when it wants too. All major ignition components replaced

Tiny
Z3504SPD
  • MEMBER
  • 1999 SUBARU LEGACY
  • 150,000 MILES
Ok.I really need a good tech here. Car runs fine for random amounts of time. Could be an hour. Could be for a week. Car will start to hichup and mis fire codes for all cylinders.P301 p302 p303 p304.(Driving with snap on scan tool hooked up. Not a random misfire. Have to pump gas like a mad man just to keep it from stalling. Mis firing the whole time. Turn ignition off and let set for 10-15 min. It will run fine again. Like a new one. For another randome amount of time.
I have replaced plugs, wires, ignition coil, ignitor, fuel pump, fuel filter, mass air flow sensor and idle air control valve.(Had code for iacv. That problem is fixed)
I have ran all tests available to me through the snap on scanner. Short fuel trim and long fuel trim are good. All the sensor test (map, mass, tps, coolent temp, ect) are all with in standards. Engine compression is good. This car runs like a new one untill it decides not too. You can NOT keep this car running when it is acting up to use scan tool. It just can not be done. Please help.I have gone as far as I can!
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Sunday, September 11th, 2011 AT 5:04 PM

7 Replies

Tiny
DANAUTHIER
  • EXPERT
You did not specify if your vehicle has a 2.2l or 2.5l engine. One problems that can affect both engines & produce your symtoms is a cracked/damages air intake box. There is a TSB from Subaru on this (# 11-59-00) Check the air intake box for leaks & send me any more infor that you can.
Thank you for your question, I hope this helps. Thank you also for your donation, it helps keep this site up for everyone. Let me know what you find.
Dan
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Sunday, September 11th, 2011 AT 6:53 PM
Tiny
Z3504SPD
  • MEMBER
I did leave that out. How dare me. Its a 2.5. This does not have an air box at all. It has an after market cold air pipe with air filter and and elbo running into the throttle body. Mass air sensor is located at air filter.I bought the car this way and has been my daily driver for almost a year without any issues.I have checked for vacume leaks 2 ways. First by soaking all vacume related areas (hoses, gaskets etc) with brake kleen. Then by removing air filter and closind off intake with my hand. Engine dies instantly. Last time I drove this car for 1 week everyday.80 miles a day. Stop and go traffic and highway and had no issues. Then next day. Made it 6 miles from home and felt it start. It starts off as a small hichup between shifting gears. Then progreses to start off from a dead stop. Then the more you drive it just starts getting worse and worse to the point that you are more concintrated on just keepeing it running. Pumping the gas without hitting WOT seams to keep it runing but u cant drive it. Then if you pull over and cut off ignition. Wait 15 min. And start it back up. It might run flawlessly for a week. Or an hour. It hickupped on and off sor severel miles today b$ the engine light kicked. Giving me miss fires an all 4
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Sunday, September 11th, 2011 AT 7:14 PM
Tiny
KHLOW2008
  • EXPERT
You have covered almost aspect of the mechanical and system components and there don't seem to be anything wrong with them and I would suggest checking the electrical side.

Seems like something electrical is loosing continuity/contact maybe due to heating up and it could be a poor connection somewhere or a failing relay.

Have the fuel pump and main relay.
Check the ECM grounding circuit.
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Sunday, September 11th, 2011 AT 11:17 PM
Tiny
Z3504SPD
  • MEMBER
Ok. Grounds have all been checked and cleaned. Fuel pressure test was good according to alldata specs.A little low on the regulator test but still ok. Today I hooked a timing light up to each plug wire and could watch it mis fire through the light.1 and 3 were worse than 2 and 4. Especially at idle. When reved up it seemed to clear up. Its like the signal to or from the ignitor is being interrupted. Or maybe its recieving it that way?. Crank sensor or cam sensor maybe? Im tapped
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Wednesday, September 14th, 2011 AT 2:41 AM
Tiny
KHLOW2008
  • EXPERT
Have you checked the valve clearances?
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Wednesday, September 14th, 2011 AT 3:02 PM
Tiny
Z3504SPD
  • MEMBER
Ok so. Just for future referance. It was the purge control valve that was causing all the problem. It was stuck in the closed position. Replaced the valve. Runs fine
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Wednesday, November 9th, 2011 AT 12:26 AM
Tiny
KHLOW2008
  • EXPERT
Thanks for the input, it sure would be helpful for others.

Have a nice day.
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Wednesday, November 9th, 2011 AT 12:11 PM

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