ive been battling a stumble/misfire when taking off from a stop for the past month or so on my 2001 outback. so far ive changed the spark plugs changed the wires and coil pack and done a compression test witch came out to 175 175 175 and 165  after changing the plugs it did fix it for about 2 days but the issue returned the coil and wires dident do anything for it. compression seems good to me the engine did get all new gaskets bearings and rings 2 years ago. yesterday found a vacuum leak and no change by fixing that. i tried to reset the ecu by unhooking the battery and touching the 2 wires together for 10 seconds that did stop the stumble for about 30 minutes but it came back half way to work. air filter is good exhaust not plugged. what the hell is going on with the car?

Edited May 4, 20223 yr by sirtokesalot

Have you pulled the plugs out to see if any of them are fouled? Leaking injector could foul a plug.... etc. Sounds like a classic misfire to me. 

Diamond coil, NGK plugs and wires? 

GD

19 minutes ago, GeneralDisorder said:

Have you pulled the plugs out to see if any of them are fouled? Leaking injector could foul a plug.... etc. Sounds like a classic misfire to me. 

Diamond coil, NGK plugs and wires? 

GD

it does feel like a misfire. its not throwing any codes at all. the plugs are ngk wires and coil i robbed off my plow car "an 01 legacy sedan" witch was running fine and not misfiring at all.i did the compression check 2 or 4 days after doing the plugs and all the plugs looked same dident seem fouled out. once i get moving the miss stops and it runs smooth its only doing it when taking off from a stop or if i floor it to pass and the rpm is low enough. the miss/stumble also seems kind of random like its not happening every time it fires that cylinder. also while running if i unplug the wires from the coil all cylinders are contributing the idle will dip lower for each cylinder i pull the wire for.

 

Edited May 4, 20223 yr by sirtokesalot

could this be a valve issue or a cam issue? or would that be more consistent

Update it is becoming worst the more I drive it. Still no cel even thogh it will skip and miss from 0 up to 40ish on 4 out of 10 accelerations and the other 6 times would just be a stumble on take off. 

Edited May 4, 20223 yr by sirtokesalot

Could it be bad gas? But if you've been experiencing this 'misfire' 'for the past month or so', I would expect that you've had to refill the gas-tank a few times - if so, 'bad gas' would probably not be relevant.

As of now it's starting to backfire and seems like it's more of an Ignition cut than a misfire I can't see it being bad guess I buy my gas the same station all the time And I fill it up twice a week

Edited May 4, 20223 yr by sirtokesalot

check the vacuum line on the fuel pressure regulator for wetness/fuel.

maybe try a throttle body cleaning? like the SeaFoam with the curved nozzle gadget.

 

check the knock sensor for cracks.

 

can you get live data or freeze-frame data? what are the fuel trims? ignition timing/knock events?

the fuel pressure regulator was my vacuum leak the other day no wetness at that. i dont beleive my scanner is capable of getting the data and fuel trims. heres 2 clips of how it is running starting from a stop and flooring it. dont mind the tape on the left of the dash its hiding the air bag light i was going to fix before this started happening badly.

 

 

Edited May 5, 20223 yr by sirtokesalot

Yeah might want to check fuel pressure. Those cars are known for the metal cap inside the fuel pump assembly blowing off. 

Also may be a partially plugged exhaust. Do you have a gauge you can install into the O2 sensor port before the cat?

Beyond that - don't expect to see misfire codes immediately - these ECU's are pretty dumb and may take a pretty severe misfire and running them for quite a little while before they toss code. 

 

GD

Edited May 5, 20223 yr by GeneralDisorder

1 hour ago, GeneralDisorder said:

Yeah might want to check fuel pressure. Those cars are known for the metal cap inside the fuel pump assembly blowing off. 

Also may be a partially plugged exhaust. Do you have a gauge you can install into the O2 sensor port before the cat?

Beyond that - don't expect to see misfire codes immediately - these ECU's are pretty dumb and may take a pretty severe misfire and running them for quite a little while before they toss code. 

 

GD

i do know of the fuel pump cap issue however i was not aware it could happen and still let the car run. every time ive seen it the car wouldn't run at all.

fuel pressure seems ok to me sit around 30 to 35 idle and comes up when reving the engine to around 40.

 

update i pulled the drivers side valve cover off the side that had one cylinder lower compression than the rest checked valve clearance it was fine not sure what i did exactly but after putting it back together the miss/stumble is gone as of the moment. i dont really believe i fixed it though.

did any ground connections get re-connected with the VC cover r&r ? vacuum lines re-seated?

along with what GD suggests, next time it's misfiring/stumbling at idel, squirt some starting fluid/brake cleaner in the intake. If it smooths-out, maybe that points to a fueling problem?

is system voltage OK at idle?

2 minutes ago, 1 Lucky Texan said:

did any ground connections get re-connected with the VC cover r&r ? vacuum lines re-seated?

along with what GD suggests, next time it's misfiring/stumbling at idel, squirt some starting fluid/brake cleaner in the intake. If it smooths-out, maybe that points to a fueling problem?

is system voltage OK at idle?

i only pulled the stuff connected to the drivers side head. breather tube spark plug wires took the fill neck off removed battery and washer fluid tank. did not have to unhook any grounds or vacuum lines. voltage is good at battery.

Edited May 5, 20223 yr by sirtokesalot

just gonna throw this out there... one of my Legacy's acted similarly & it turned out to be a bad O2 sensor..

it would start and idle fine, but get into the throttle and it would stumble and what seemed to be a misfire... took a long time for it to finally throw a code, tho Was about at my wits end with the damned thing when it finally got around to throwing the code.

9 hours ago, heartless said:

just gonna throw this out there... one of my Legacy's acted similarly & it turned out to be a bad O2 sensor..

it would start and idle fine, but get into the throttle and it would stumble and what seemed to be a misfire... took a long time for it to finally throw a code, tho Was about at my wits end with the damned thing when it finally got around to throwing the code.

so if it starts missing and acting up again would resetting the ecu and unplugging the front o2 sensor be a good test to see if the sensor is an issue? drive it with the o2 unplugged and if the symptom doesn't return with it unplugged then assume the o2 is bad?

I beleve the ECU needa  good O2 sensor Reading for proper opertion.

 

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unplugging it would cause similar symptoms (and throw a code right away) - ecu does need proper o2 readings to make the right fuel/air ratio adjustments.

now, here is the kicker... o2 only comes into play once things are fully warmed up..  cold engine runs on set values until it reaches operating temp, then o2 readings take over to make minute adjustments while driving.

not saying that this is definitely your issue, just something else to think about/consider.

hope you get it figured out soon

2 minutes ago, heartless said:

unplugging it would cause similar symptoms (and throw a code right away) - ecu does need proper o2 readings to make the right fuel/air ratio adjustments.

now, here is the kicker... o2 only comes into play once things are fully warmed up..  cold engine runs on set values until it reaches operating temp, then o2 readings take over to make minute adjustments while driving.

not saying that this is definitely your issue, just something else to think about/consider.

hope you get it figured out soon

ah i had thoght with the o2 unplugged the car would just run at a default value in open loop. ill probly just buy an o2 sensor anyways seeing as its probly original. ive never changed it.

yeah, it would only run that way until it reached operating temp..

 

Don't buy a cheap one or you'll be relacing it again soon.

O.E. or denso

Actually the O2 comes online much sooner than operating temp. The sensor has it's own heating element and will be online and operating within about 2 minutes typically.

GD

Immediately (before 2-3 drive cycles) after a battery disconnect 'reset', the ECU uses the factory base map in firmware to run the car. If the car's symptoms get better after a reset, that may point to a bad signal from a sensor. If it doesn't get better, might something physical like a dropped valve guide or ???

the car made it 1100 miles to and from my mas in vermont over the weekend issue did not return.