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Old 12-30-2008, 09:54 PM   #1
weston666
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Default Engine Misfiring and backfiring when i push the gas pedal more than half way

2003 Subaru baja 100k miles on it.
The car will run perfect under hard acceleration untill I drive it for about 5 minutes, then when i give it more than Half throttle it will start to stutter, backfire and miss on Cylinder 3, I have tested the spark plug wires, looked at the spark plugs, installed new fuel filter, and put in a new throttle body with the 3 sensors, As to no avail. I was also thinking maybe it has a bad fuel injector, but that wouldnt explain why it runs perfect when its cold. Has anyone had these same problems? thanks.
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Old 12-30-2008, 11:15 PM   #2
weston666
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anyone? I also replaced the coil.
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Old 12-30-2008, 11:34 PM   #3
Uncle Scotty
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so...it is fine until the car warms up???

coolant temp sensor may be bad
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Old 12-31-2008, 01:00 AM   #4
weston666
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i think its something more than just that....im thinking a bad fuel injector?>
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Old 12-31-2008, 01:07 AM   #5
Uncle Scotty
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.....

Last edited by Uncle Scotty; 12-31-2008 at 01:27 AM.
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Old 12-31-2008, 01:10 PM   #6
rick-l
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Are there any other codes besides misfire cyl. #3?

This should be low on your list of possible causes but I had an old Audi that kind of acted like this when the timing belt was off by 3 teeth. It did not run perfect until warm however.
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Old 12-31-2008, 02:33 PM   #7
yarrgh
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explain to me how a fuel injector will affect how the engine runs when cold, but not when hot.
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Old 01-01-2009, 09:44 PM   #8
DutchSub99
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I would also relate it to the fuel injector...
If let's say the injector for cylinder 3 is not functioning properly and provides a lean fuel mixture you could get detonation in cylinder 3 when the engine is starting to warm up.

I would seriously take it easy to save the engine in any case now!
Better not to run it at all!!

You can have your injector cleaned by a specialist. (ultrasonic cleansing)
It may be worth to do that before you buy a new one, but first make sure the injector is the actual problem.

Other possibilities:
Blocked fuel line
Petrol pump
etc.

Good luck with it anyway!

Patrick.

ps. Why accelerate hard when the engine is cold?

Last edited by DutchSub99; 01-01-2009 at 09:53 PM.
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Old 01-03-2009, 10:44 PM   #9
joey00
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Ok, lets start from scratch here.

- You've verified the misfire on cylinder 3 through a MIL and/or misfire counter
- usually before replacing anything, you can claim a faulty part by on a cylinder by switching. If you know cylinder 1,2,4 are working good
- start by switch spark plugs, with say..cylinder 1, does the misfire occur on cylinder 1 now? if so replace spark plug and set proper gap.
- use the same method with your coil and fuel injector, does the problem move cylinders?
- fuel filter and throttle probably not the issue, something like that would effect all cylinders

- this is the most cost effective way to diagnose misfire problems
- once you have the simple things covered you can move up
- check valve lash, insufficient lash? once engine is warm valve not seating?
- possible burnt valve, check engine vacuum at idle, leak down test etc
- start simple move on. that's all you can do.
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