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Discussion Starter · #1 ·
hello please help
2008 subaru outback 57,000mi misfire after idle for 20-30 sec at 3k. if i idle at 2800 for ever no codes but over 2800ish every single time throws misfire 3 and 4 . car runs great no issues whats-so-ever besides the constant codes . heard the vvl solenoids to rarely cause this problem
so far . clean oil clean car 1 owner dealer maintained
changed 2coils . one new. one from running good identical car
plugs wires
adjusted valves
valve cover gaskets
changed tensioner and timing belt
changed throttle body
changed cat and o2's upstream and downstream
did compression
leak down
no vac leaks
changed injectors
checked fuel pump
changed ecu's
changed knock sensor

got desperate so took out engine . valves are all good . cylinders as well .no issues anywhere. .so reassembled with new gaskets .

im stumped . if i idle under 2800rpm,... no codes . when i go over 3k then boom misfie 3 and 4 on the dot every time. been researching that the vvl solenoids have caused this in some rare cases. no other codes ever . have driven car 1000miles to see if i can get any new codes and nothing just the 3 and 4 misfire. before i go throwing more money away .. does the vvl system turn on at 3k ish?
 

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if i idle at 2800 for ever no codes but over 2800ish every single time throws misfire 3 and 4 .
Based on tests I did with my 07 (2.5 non-turbo), when the car is stopped and the engine is being revved up (in Neutral or Park), the VVL transitions from low to high, and from high to low, at around 3000 rpm.

if i drive under 2800rpm,... no codes . when i go over 3k then boom misfie 3 and 4 on the dot every time.
Again, based on the tests I did when driving, the transition point is lower and is determined by more than just engine rpm. In normal light throttle driving, it will transition from low to high as engine speed increases past 1600-1800 rpm; however it will switch back to low when the throttle is released (engine rpm still above 1800 rpm) or if the throttle is advanced for very rapid acceleration.

When cruising on the highway with the rpm at around 2600, the VVL is consistently in high mode.

If the VVL system on your 08 is the same, and if the misfires are related to the VVL being in high lift mode, when cruising at above 2000 but below 2800 rpm, we might expect the misfires to appear as well, but that doesn't seem to be the case.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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kinda seems like some live data would be good to see.
 

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Discussion Starter · #4 ·
would it be possible for the vvl solenoid to malfunction without throwing a code for the solenoid?
and its on cyl 3+4 so could one bad vvls casue misfire on both sides?
The vvl is strongly considered here bc of it always throwing the codes when rev is pass 3k at idle .
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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does your cel 'test' before you start the car? maybe the bulb is out?

anyway, you could scan for pending/stored codes.

how did the inside surfaces look when you had the valve covers off? clean or sludgy ?
 

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Discussion Starter · #6 ·
the bulbs are all there . there is no sludge in the motor . the engine looked as clean as the car with 57k inside and out .if idle below 2800k ish mark there is no cels after 3k ish boom misfire 3 and 4 every time, i can set my watch to it :)
there is no electrical work or evidence of tampering .
wonder if one of the solenoids is stuck or not opening when it should or how well it should?
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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1 owner....someone you know?

kinda wonder if it's possible someone tuned the codes out. I have 13 codes tuned out of my WRX for stuck air-cut valves.

I think, if the vvl switches don't report activation to the ECU, you should get a code. Knock sensors and temp sensors might fail without getting a light, but the vvl system, if not 'tampered' with, should have feedback when activated.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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3 and 4 share a coil due to spark waste.... but you say you changed those.
 

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Recently, I've been getting the same 2 codes on my 08 2.5i with 135k mi. Even got a cat code once. Tried cleaning throttle body, replacing the coil pack (because 3 and 4 are common as mentioned), plugs, and front AF sensor. Doing things one at a time to find out the cause. But the missing kept reocccuring at light throttle (might correlate to what you are doing). The next thing I tried was changing the EGR valve as they do carbon up a bit. Even though the plug wires looked good with no signs of any arcing, I changed them at the time as EGR valve. I have not noticed a surge/misfire in several days and no CEL yet. The car feels much better. Wish I would have stuck to doing one thing at a time so I would know for sure what made the difference. I will post back if problem reoccurs but this is the longest I've went wo the code in a month. I believe it was the EGR valve.
 

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would it be possible for the vvl solenoid to malfunction without throwing a code for the solenoid?

There's two separate control and mechanical engagement systems for each bank. The only common aspect is the ECM, which commands the VVL mode and sends control signals to the oil control solenoids ton each bank. There is an oil pressure sensor switch on each bank as well. The switch monitors the oil pressure going to the valve lifter assemblies and signals to the ECM when the pressure is high (for high lift) or low. As was mentioned by 1 Lucky Texan, a discrepancy between the ECM command mode and either pressure switch status can lead to a CEL.

and its on cyl 3+4 so could one bad vvls casue misfire on both sides?
One bad VVL solenoid would not affect both sides. Also, if there is a bad solenoid on one side, it's more likely to affect both cylinders on that same side.


The vvl is strongly considered here bc of it always throwing the codes when rev is pass 3k at idle .
As I noted earlier, the VVL seems to change mode at a far lower rpm when driving the car. Have you had any misfires when, say, driving at 65 mph, when the rpm would be around 2500?

. . . if idle below 2800k ish mark there is no cels after 3k ish boom misfire 3 and 4 every time, i can set my watch to it :)
there is no electrical work or evidence of tampering .
wonder if one of the solenoids is stuck or not opening when it should or how well it should?
This is where live/recorded data might be of help. Romraider, or FreeSSM can access the ECM VVL mode signal, the duty cycle signals to both oil control solenoids, and the status of both oil pressure switches. If the misfires can be repeated "like clockwork", these parameters will verify if the VVL control system is functioning properly at that time.

It should be noted, however, that there's no monitoring of the actual lift of the intake valves. While it's possible that a lift-changer mechanism (there's one for each valve) can fail to function, it's would seem far less likely that two would fail, and consistently in opposite cylinders.
 

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Recently, I've been getting the same 2 codes on my 08 2.5i with 135k mi. Even got a cat code once. Tried cleaning throttle body, replacing the coil pack (because 3 and 4 are common as mentioned), plugs, and front AF sensor. Doing things one at a time to find out the cause. But the missing kept reocccuring at light throttle (might correlate to what you are doing). The next thing I tried was changing the EGR valve as they do carbon up a bit. Even though the plug wires looked good with no signs of any arcing, I changed them at the time as EGR valve. I have not noticed a surge/misfire in several days and no CEL yet. The car feels much better. Wish I would have stuck to doing one thing at a time so I would know for sure what made the difference. I will post back if problem reoccurs but this is the longest I've went wo the code in a month. I believe it was the EGR valve.
That's an interesting result.

I'm not sure about the 2008, but on my 07, the EGR valve seems to be mounted on the #4 intake manifold runner. I've not had it off, but wonder if it actually returns the exhaust gases into that runner, or if there's some form of passage that directs the exhaust so that it is delivered to all four cylinders more-or-less equally. When you had it off, did you notice if it opened right into the #4 runner?
 

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PlainOM, no, the intake port does not lead into the #4 runner. It appears to go up towards the TB where it can mix in for all cylinders. However, the opening is likely nearest cyl 4, would need the manifold off to know for sure. If you look at the back of the runner, you can see what appears to be the passages towards the TB and towards cyl 4 exhaust, a pipe connects the port in runner to the exhust port.

I'd put the old one on to confirm, I do still have it, but one of mounting bolts was warped and damaged the intake threads when I removed it, had to be a defective bolt from the factory. I was able to repair some of the threads but not all. I had to reistall with a 10mm longer bolt and a couple spacer washers to reach the undamaged threads further in. Would rather not take off unless prepared to tap new threads.

This was supposed to be a 15 min job, take valve off, try cleaning, and reinstall. Replaced due to thread problem.

I also have the old wires, suppose I could put 3 and 4 back on as a science project...
 

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Thanks for the reply. I was hoping the EGR feedback was balanced, and it sounds as if it is. Had a closer look at mine and with your description could see the casting going toward the TB. Great.

A few moments of thought and . . .

If the EGR is routed to the TB area for even distribution to the four cylinders, it begs the question as to how/why a faulty valve might have affected just those two rear cylinders. Interesting . . .
 
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