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Old 08-08-2006, 07:12 AM   #1 (permalink)
mcmillon
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Default Cylinder 3 and 4 misfire

I could use some help guys. Just got moved in here in SLC,Utah after dealing with Uhaul and their utter incompetence.
Anyway I'm still getting the cylinder 3 and 4 misfire upon startup(cold start)2000 forester 125k miles.
At this point, I'm thinking I should replace the o2 sensor because the car idles very rough and the smell of raw fuel is killing me.
So far I have the following parts replaced within the last few months with oem parts.
plugs,(ngk copper) wires, fuel filter, air filter, plugs, coil pack
The throttle body and Iac valve is clean.
Basically when I start up the car, it runs very rough, kicks idle up to 2000 rpm then kicks the engine light, then I check the codes with my reader, reset p303 and p304 and the car runs okay when warm. But gas mileage is down to less than 20mpg where it was always over 24mpg.
If anyone has any thoughts, this would be great as I am suppose take the wife and kid to my sister in laws wedding in Colorado and really dont want to hear the wife say," why is the check engine light on again?"
thanks guys
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Old 08-08-2006, 08:51 AM   #2 (permalink)
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replace the knock sensor first, then try the o2
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Old 08-08-2006, 09:31 AM   #3 (permalink)
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Quote:
Originally Posted by Philistine
replace the knock sensor first, then try the o2
Second that. Crank angle sensor might be a good thing to look for as well. It's also fairly cheap (about $25, iirc, whereas the knock is closer to $80)

If memory serves, the ECU is not supposed to check the knock sensor when the engine is cold. not sure if that behavior would be undone if the knock sensor is bad, though.

Also - it's the Front o2 that does air/fuel, and is the one to replace, not the rear. If you have never replaced the front o2, it's worth doing anyways.... safe to assume it should be done every 60-70k. I had used a generic bosch replacement at one point in my SF, in an effort to save a few $. I think the OEM ones are much much better, and most certainly worth the extra $15 it would have cost to buy one.
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Old 08-08-2006, 09:37 AM   #4 (permalink)
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I think I'll check into the o2 sensor since we bought this car used with 107k with limited history. Ill look around my area to see if I can get a good oem replacement.

The car started up today with no codes and ran just like it use to. I may just wait to try and get another set of codes besides the 303 and 304.

thanks for the help, just wanted to check before wasting money on something that wont fix it.
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Old 08-08-2006, 09:54 AM   #5 (permalink)
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Quote:
Originally Posted by mcmillon
I think I'll check into the o2 sensor since we bought this car used with 107k with limited history. Ill look around my area to see if I can get a good oem replacement.

The car started up today with no codes and ran just like it use to. I may just wait to try and get another set of codes besides the 303 and 304.

thanks for the help, just wanted to check before wasting money on something that wont fix it.
With all three of the sensors in question, they need to be really far out of spec before they'll throw a code. When my front o2 was going, i never got the code for a failing sensor, just the misfire codes. Nothing wrong with waiting though, unless you're due for an emmissions inspection soon.
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Old 08-08-2006, 09:56 AM   #6 (permalink)
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I would suggest front A/F sensor (O2) as well, they are very common to fail. It's a recall item, I've seen numerous ones go out on Legacy's, Impreza's and Foresters during those years from 00-01. When they do, I have the customer check first with the dealer to see if it can be replaced under the recall. Otherwise we do it for them and solves a lot of the mysterious problems.
Also consider a valve adjustment and running 89 octane, hopefully the timing belt has been done as well since it was due at 105k. Hope this helps.

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Old 08-08-2006, 11:57 PM   #7 (permalink)
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What about testing the coil pack. It seems odd that O2, knock sensor etc.... if they are going bad only affecting 3 and 4 cylinder. Should they not affect all the cylinders!!!!! Also bad spark plug wires could be a culprit!!!
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Old 08-09-2006, 04:30 AM   #8 (permalink)
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he said he just replaced the coil pack and ignition wires
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Old 08-09-2006, 08:11 PM   #9 (permalink)
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Default problem fixed finally!

Thanks guys for all of your help. I went over to the dealer and bought a new o2 sensor. But the prongs were way too short so not until I had the manifold dropped did I realize this. But they gave me another one and it seems to run much better, idle improved at cold startup and much improved engine flexiablity.

Drove about 50 miles today and no check engine light, guess Ill keep the scanner in the glovebox.
I would highly recommened dropping the y pipe at the manifolds unless you have access to a lift, it made the job much easier and along with the o2 sensor tool that i bought at pep boys for $10, this was a pretty easy r2.


have a nice weekend all,
thanks
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Old 08-10-2006, 11:43 AM   #10 (permalink)
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Default problem continues

OKay guys:
I went to start up the forester this morning after it sat all night and the good old p303 and 304 came back on my scanner. Engine runs really rough for about a minute, check engine light blinks contiual then throws the codes, then the engine runs just fine after that.
T/belt and water pump was changed at 105k miles. I changed the o2 sensor yesterday seemed to help, coil pack was replaced a month ago, plugs a week ago, plug wires are checking good with ohm meter check for resistance(less than a year old.
I am stumped why only 3 and 4 or misfiring when then are on seperate banks.
Why would the knock sensor be a possible cause?
What about the coolant temp sensor? could it be running lean/rich because it cant read the correct coolant temp as cold?
this only happens after the car sits overnight and other than that the car seems to run well, plenty of power(for a n/a) 23mpg city etc.
any other ideas would be great.
thanks
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Old 08-10-2006, 11:57 AM   #11 (permalink)
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I was just thinking about this, a month ago when the car starting having trouble starting from a cold start, I got all four cylinder misfires, so I assumed that it was the coil pack, but even after i changed out the coil pack a few weeks ago, there was one instance where it took me about 5 minutes to get the car started to the point of nearly killing the battery, even though i allowed for time in between attempts to let the starter cool down.
the crankshaft sensor seems like a canidate for replacement now.
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Old 09-05-2006, 09:16 PM   #12 (permalink)
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Default after $350, You would think it would be fixed

Hey Guys:
I had to use another user name my email is messed up, but anyway I took the Forester in last week to the dealer to see if they could better diagnose the problem, they said the one month old coil pack was bad, so they replaced it and I assumed that everything would be fine. But less than a week later, same 3 and 4 misfire.

I gave the tech everything that I have done in the last few months and I even had to replace the weak battery a few days ago.

to recap, about a month ago, I had a 1,2,3,4 misfire. The car would barely run so I replaced the plugs with oem ngks. I checked the coil pack and the secondary resistance was out of range from the goodwrench.com specs. I then replaced the coil pack and the car ran fine for a couple of weeks. Then the 3 and 4 misfire began. I replaced the front o2 sensor as well. The coil pack was replaced again at the dealer last week.

The plug wires are oem from the dealer and are less than a year old and the resistance is within specs. The plugs are fine, the fuel filter was replaced a few months ago. The car had its 105k service before I bought the car where the subaru dealer replaced the tbelt and adjusted the valves.
This car ran fine for about 20k miles before this headache began.


Im taking the car back to the dealer tomorrow so if anyone has any ideas, this would be great. This is the 4th subaru I have owned and I have never had any problems, even with the last one that I gave to my dad after 230k miles. If this problem persists, I guess this car will go in on trade for something that runs. Thanks guys
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Old 09-05-2006, 09:38 PM   #13 (permalink)
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Before anything else is done, I would get a compression test done. If the compression test is a negative, I would look first to the valves for improper seating or clearance. Valve problems can throw misfires. Why replace the 02 sensor when it is not the problem code? I'm guessing valve work is in the order because the smell of raw fuel and misfire. Could be that your engine has too much carbon buildup and cause valves to not seat correctly. A bad oxygen sensor will have a sulfuric or rotten egg smell and throw a different CEL code.
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Old 09-06-2006, 11:02 AM   #14 (permalink)
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I just finished compression test, 155 psi in all 4 cylinders. Unlikely its the valves. The drama continues. Lets see what the dealer says.
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Old 09-06-2006, 12:26 PM   #15 (permalink)
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PM me your email and I'll send diagnostic info your way.
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