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Misfire/Backfire on acceleration and LTFT at negative 30


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22 replies to this topic

#1 dballs

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Posted 19 June 2013 - 08:38 AM

I am trying to diagnose a misfire/bogging/backfire problem with my 03 Legacy GT 2.5 with 125,000 miles. It runs better when cold but not perfect but when it gets warmed up the condition gets real bad. It has trouble climbing hills and accelerating, it backfires, pops, shakes and runs horrible. 

 

Plugs are only 10,000 miles old and were gapped to spec, wires look to be in good condition, fuel filter is 3000 miles old. valves were adjusted 10,000 miles ago along with new head gaskets, timing belt and all that good stuff.  If I run 93 octane the condition gets better but is not gone completely. My scan tool shows the following on a long drive:

 

SHRTFT1=0.8

LONGFT1=0.0

 

SHRTFT3= (-28.1)

LONGFT3= (-28.1)

 

Front oxygen sensor is reading 2-5 volts, fluctuating but averaging about 4v

 

Had a flashing check engine light once, shut car off and restarted and it never came back. Showed misfire on cyl3. After that No codes ever returned. If i feather the throttle VERY lightly it will drive ok but anymore than 5-10% it runs bad. I tried unplugging the front o2 sensor and running it and it had no change. There is no exhaust leaks, no vacuum leaks. Stumped and do not want to start throwing unnecessary parts at it unless I run out of options. 

 

According to what I have read, it is running rich or the computer thinks it is and it could be, coil pack, front o2 sensor, stuck open injector, bad wires, bad fuel pressure regulator. The fact that it runs a little better cold makes me think o2 sensor or coil.  Any thoughts???



#2 ivans imports

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Posted 19 June 2013 - 10:33 AM

Probly no going to like thiss was the height of exhaust valve guide checked when head were done ? have had many lately that have droped valve guides on exhaust thiss will hold valves open or make them stick you could remove exhaust header and look up the ports and see if guides are were they should be about 1/8 inch below head casting any more and problem. Also what were valves addjusted to ? posibly to tight 0.25 mm ex 0.20 mm in and must be done exactly in the right order by the subaru clock on ps cam pully



#3 dballs

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Posted 19 June 2013 - 10:47 AM

Probly no going to like thiss was the height of exhaust valve guide checked when head were done ? have had many lately that have droped valve guides on exhaust thiss will hold valves open or make them stick you could remove exhaust header and look up the ports and see if guides are were they should be about 1/8 inch below head casting any more and problem. Also what were valves addjusted to ? posibly to tight 0.25 mm ex 0.20 mm in and must be done exactly in the right order by the subaru clock on ps cam pully


The valves were adjusted exactly to spec in order
. Ran fine since job until recently. I'll pull the header and look at the guides but I don't know if they were inspected. Had a Subaru shop do the job. The for the info

#4 dballs

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Posted 19 June 2013 - 10:54 AM

Now that you mention it, it got a lot worse after I changed the oil last. Had semi synthetic in and went with conventional.

My last Subaru had a similar problem. Would run like
DeaTh unless I ran full synthetic... It had sticking valves too. I'll also change back to full syn oil and see what happens

#5 ivans imports

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Posted 19 June 2013 - 10:55 AM

Very few people understand the valve addjustment procedure and is easy to mess up on but if was running ok then mabee not. Plug wires wrong plugs tracked wires or cam timing or feul pump low output. Any oil in the plugwire holes ? and also check main engine harness is pluged in tightly and all the way and grounds on ps top of intake are tight



#6 dballs

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Posted 19 June 2013 - 11:21 AM

Plug oil seals were replaced with head gasket. I will check the fuel pressure. I will check wiring harness and grounds and probably replace wires for the heck of it. Thx for the info. Will report back

Very few people understand the valve addjustment procedure and is easy to mess up on but if was running ok then mabee not. Plug wires wrong plugs tracked wires or cam timing or feul pump low output. Any oil in the plugwire holes ? and also check main engine harness is pluged in tightly and all the way and grounds on ps top of intake are tight



#7 Gloyale

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Posted 19 June 2013 - 11:47 AM

Oxy sensor reading 2-5 volts? Sounds like Its got a short from the heating cicuit to the signal circuit.

Good readings should fluctuate from around .05 to .80 volts.

#8 dballs

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Posted 19 June 2013 - 01:47 PM

i thought that seemed high but didn't want to blow $150 on an o2 sensor without knowing for sure



#9 nickb21

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Posted 19 June 2013 - 02:14 PM

Are these the original wires at 125k? I would replace those first before anything else. Even if they look okay, they could still be arcing. (Sometimes you can test this by spraying/misting the wires with water while running).



#10 Fairtax4me

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Posted 19 June 2013 - 07:59 PM

Check timing belt alignment.
Check all vacuum hoses for proper fitment, might spray some cleaner or WD-40 around the intake gaskets to make sure they are not leaking.

O2 voltages that high usually means the sensor is a A/F sensor which runs on 3.3v reference. Sitting around 4V means the sensor is reporting a very lean mixture. Should be right at 3.3v and fairly steady.
Possible the sensor is bad but check other things before dropping big $$$ on a new sensor.

#11 dballs

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Posted 20 June 2013 - 07:17 AM

Nick B- I am definitely going to change the wires, they look like aftermarket with mismatched cylinder numbers on them.

 

Fairtax- I will check the vacuum and intake this weekend. I will take a look at the timing belt alignment but im certain its good especially after what I found last night. I believe I have a Ho2s, thats what it says on the hood emissions sticker and it is a 4 wire unit.

 

I dont have time to change the oil to synthetic until at least the weekend so I decided to throw one of those bottles of "oil treatment" that are the consistancy of honey in. I figured for $2.50 why not try, I also filled up with 93 instead of 87 and After about 20 mins of drive time the problem was 90% gone. Accelerates very strong with a slight hesitation in the midrange. I pulled a local hill at 80+ no problem, before I would be lucky to make it past 45 up the same hill. 

 

Fuel trim reading about negative 25 now.  New question: On my scan tool, for the oxygen sensor, should I be looking at the reading from the Oxygen Sensor bank 1 (Reading 2-5v) or the "equivelance ratio (lambda)" Which is reading 0.8 - 1.0

 

Thx for all the help and replies


Edited by dballs, 20 June 2013 - 07:20 AM.


#12 ivans imports

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Posted 20 June 2013 - 09:04 AM

Did you take a peek up her ports ?



#13 dballs

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Posted 20 June 2013 - 10:31 AM

Not yet, wont be able to until sometime this weekend, working double shifts. I think you are on the right track about the valves sticking though, good call.



#14 dballs

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Posted 27 June 2013 - 09:49 PM

Things looked good in the ports. Put a set of OEM wires on and set the plug gap and it runs perfect now. Fuel trim still around negative 30 but it seems to run great. Checked the compression while i was there and 3 were at 205 and one was at 210. Thx for the help

#15 ivans imports

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Posted 28 June 2013 - 09:33 AM

sweet



#16 Cougar

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Posted 28 June 2013 - 10:24 AM

Have you tried swapping the injector out for cylinder 3? I would suspect that injector is leaking since the fuel trim number is so high in the minus direction.



#17 dballs

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Posted 28 June 2013 - 10:46 AM

I'll have to try changing the injectors out. The timing advance shows 40° on the scan tool which seems abnormal but I'm not sure what a normal reading is.

#18 Cougar

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Posted 28 June 2013 - 09:23 PM

If you are talking about the timing for the injectors I would guess that to be ok. I assume the trouble is only with #3 cylinder and a bad injector would  be my top suspect for this kind of problem.



#19 Fairtax4me

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Posted 28 June 2013 - 10:46 PM

I'll have to try changing the injectors out. The timing advance shows 40° on the scan tool which seems abnormal but I'm not sure what a normal reading is.


Ignition timing advance can be as high as 44° or slightly higher depending on several conditions.

#20 unibrook

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Posted 03 July 2013 - 06:02 AM

Change your front 02 sensor.

The fact that the symptom only occurs when warm.......points directly to this.


Edited by unibrook, 03 July 2013 - 06:03 AM.


#21 ivans imports

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Posted 03 July 2013 - 09:50 AM

I think #3 has a problem on all subaru engines seems to be the hole that gives me the most trubble i think it runs leaner than the rest



#22 bluedotsnow

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Posted 04 July 2013 - 04:29 PM

just thought I'd chime in doesn't sound like this but I was talking with my roomie and he said that on a manual trans if you move the car while in gear engine off you change its timing. these cars are tempermental when it comes to timing half a tooth off will run like crap.is it possible you parked it on a hill in gear then released the ebrake and let the car roll? engine off of course  



#23 Kcohol

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Posted 04 July 2013 - 05:55 PM

Hey guys im new to this but im gonna let u know what i just went through.

Ive been following this for a while till i got my car fixed 96 subaru 2.2l legacy.

Driving to work on the freeway 65mph it started bogging down lost speed backfire all that fun stuff.Checked the codes and it was a miss fire #2 cyl.

Took it to a mechanic he told me,Bad valve seat,Clogged cats (both),And had a oil leak from the front main seal.

So i dident have all the money to get all that fixed so i told him to fix the oil leak(new timing belt)and new front seal.

Got a phone call the next day a miracle happend My car was a tooth out of time and the front main seal was put in backwards.

Sorry for the spelling but i hope this helps!!!!






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