[Demon Dave]

I have a 2001 outback (4cyl 2.5)........its never been good on gas approx 380km on 46litres,but recently its started to intermittently lose power when cruising (speed is irrelevant but mainly between 50-100kph).

Initially the loss of power was accompanied by the engine warning light and occassionaly a sudden splutter/shudder. It went into the garage and had its knock sensor replaced but still didnt run perfectly.

After about 5 weeks the engine light reappered together with a slight 'miss and power reduction'. Back to the garage and another knock sensor but still an issue - the garage is now suspecting the 'link' between the knock sensor and ECU/management system!

The loss of power is slight and short lived and the light is also intermittent!

Any ideas please - I have looked at similar threads, but most seem to loose all power, not just dip!

Would appreciate any assistance please chaps!

 

[DavidPeab]

Stupid question time: Have you done the plugs and wires? I had a similar situation with a P0302 engine code signifying a misfire in the second cylinder. Have you read the CEL code? I started by replacing the plugs and wires and problem solved. It may also be your coil.

Mine occurred when giving it a little more gas to get up even the slightest hill and got much worse when trying to merge into fast traffic.

 

[1 Lucky Texan]

I assume the code retrieved is for the knock sensor? If possible, tell us the actual DTC (Pxxx) number.

Perhaps the shop is improperly aligning/torquing the sensor?

 

[cardoc]

Mileage on the car?

The code is the place to start. Always when the light comes on, even if it flashes and goes out, the codes are in memory along with freeze frame information. Ask the garage that has the car to tell you what codes they retrieved and, if any, the freeze frame info.

Various things can cause it, but suspect fuel filter, ignition coil, plugs, wires or fault with a knock sensor signal to the computer last. It may, big may, cause timing retard that would limit HP/KwH but is rare.

 

[subiesailor]

Never had a coil failure with the subarus but it sounds exactly like what our VW did many times seems that VW buys junk yard coils - cleans them up and re sells them LOL

Only thing I have read about a few times now with the older high mileage subarus is the igniter either ground wire having a short or some other issue with the igniter that kicks the coils into action.

But the symptom sounds text book coil failure. At high speeds power loss and engine light is not as obvious as with low speeds and being short a full cylinder due to a coil not firing off.

 

[Demon Dave]

.....Outback intermittently losing power

:17:Thansk guys - will see what info I can get from the garage regarding coding.

Full service given prior to initial problem occurring.

Car has don 92000k's

 

[cardoc]

:17:Thansk guys - will see what info I can get from the garage regarding coding.

Full service given prior to initial problem occurring.

Car has don 92000k's

That is still low for the age and being a Subaru.

What kind of full service? Got a list?

 

[DavidPeab]

When I do a full service to mine I replace plugs, wires if they don't meter well, air filter, fuel filter, oil and filter.

But, the CEL - DTC P... codes are what you really need now to help diagnose the problem. A lot of parts stores like Pep Boys, Advanced Auto Parts, or Autozone will read the OBD II codes for free or a nominal fee.

 

[subiesailor]

Ngk plugs only! High quality wires only or your just creating more issues. Subaru engins are very picky about plugs and wires

 

[Demon Dave]

Ok all ............we now have codes p1307 and P1309........and the problem persists .......All above possibilities exhausted!???????

 

[1 Lucky Texan]

for some reason, the ECU thinks the AVCS control valves are drawing too much current. Perhaps there is an oil pressure problem or a wire harness has been chafed/chewed-thru by rodents, and is shorted out. Or some connectors were jammed together and pins are bent.......?

the above should probably be investigated.

I would have the codes cleared and see how quickly they return - but if the AVCS is not working, that will diminish power.



there's an explanation of the system here;http://forums.nasioc.com/forums/showthread.php?t=134854

 

[Novablue]

Ok all ............we now have codes p1307 and P1309........and the problem persists .......All above possibilities exhausted!???????

Could be electrical or a bad sensor. As 1 Lucky Texan said first thing to do is check the wires. During that check I'd also check the sensors listed in his post he nicely linked for you. This is definitely a non-standard issue that will require more advanced diagnostics.

 

[1 Lucky Texan]

are you sure about the codes? did you see them or could someone be confused telling you what they are?

I thought AVCS was in newer cars than yours. what year car again?

 

[lockmedic]

for some reason, the ECU thinks the AVCS control valves are drawing too much current. Perhaps there is an oil pressure problem or a wire harness has been chafed/chewed-thru by rodents, and is shorted out. Or some connectors were jammed together and pins are bent.......?

the above should probably be investigated.

I would have the codes cleared and see how quickly they return - but if the AVCS is not working, that will diminish power.



there's an explanation of the system here;A technical primer on Subaru AVCS Engines. - NASIOC

Unless it's different from USDM, 2001 EJ25-powered Outbacks do not have AVCS. That didn't start until 2005 or so.

 

[Novablue]

Unless it's different from USDM, 2001 EJ25-powered Outbacks do not have AVCS. That didn't start until 2005 or so.

Curiouser, and curiouser...

 

[Demon Dave]

Still ongoing!!

No progress - now suspect Oxy sensor (up stream) - another mechanic suspects MAF meter - who to go with??

 

[1 Lucky Texan]

do we know precisely what codes have been set?

MAF is pricey - unless they can test it to confirm it's bad, go with the O2 sensor first. (actually, it, too, can be scoped - hope BOTH these mechanics aren't just throwing parts at the car, you could do that yourself!)

 

[Demon Dave]

No other codes yet other than those the above and original knock sensor code P3028 but appeared ok (2.4v) at this stage code went away. Tried second hand comp but no change. Funnily enough the MAFM is half the price of the O2 sensor! the MAF is reading 1.35v (recommended 0.8-1.2)......so what to swap?

 

[1 Lucky Texan]

No other codes yet other than those the above and original knock sensor code P3028 but appeared ok (2.4v) at this stage code went away. Tried second hand comp but no change. Funnily enough the MAFM is half the price of the O2 sensor! the MAF is reading 1.35v (recommended 0.8-1.2)......so what to swap?

oh, maybe I'm confused - I thought they were over a coupla hundred bucks.

anyway - if all other avenues have been ruled out (vacuum leaks, corroded grounds, alternator/battery problems) , seems like changing it is a good idea.

 

[Demon Dave]

Both options now done and whilst I dont get the shudder i still get an engine light when i throttle off from about 2000rpm. the revs drop and then bounce back up 300-500, before dropping again. You can feel the car retard/hesitate (simialr to when Air Con engages) .........and light appears............$1300 spent and no major gain!!:17: no codes tho'?