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2007 2.5i 5MT
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90 Posts
Discussion Starter · #1 ·
Hey guys,

since I had the heads machined, I've had some obnoxious ... let's call it noise since I'm not positive ... when the engine is hot (like, has idled or city driven for a bit, not just full running temperature) and under load. I thought it was the heat shields until I finally removed them... then I used premium (93) fuel for a couple tanks and it almost completely went away.

My cylinders are, in order: 210psi, 193psi, 206psi, and 197psi. Is this on its own enough to warrant higher octane fuel? Or do I need to look into a potential problem with the knock sensor or something?
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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16,223 Posts
The knock sensor does not cause knock or noise. That would be the pinging (detonation)

If higher octane fuel solved the problem, it may be a few things. If the heads were machined, the engine was out. If there is an intake leak or an exhaust leak somewhere, even very minor...the air-Fuel mix could be off.

The motor can ping (knock) from either too lean or too rich a mixture.

Get a hold of some type of logging software. RomRaider is a good standby. But you need a EDIT: WINDOWS laptop and it also needs a vag com cable. You need to be able to look at manifold pressure, AFRs, knock and knock correction, timing....

Then you may get some direction as to the issue.
 

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OBW H6 VDC, Tribeca, XT6
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12,385 Posts
Looks like one side is different than another? Might just be testing variance - intake/throttle no opened or as flow favorable?

Is it like a light rattling in a tin can sound?

Maybe try different gas stations?
Gas treatment - MMO, Seafoam?
Check timing marks?
 

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Premium Member
(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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18,333 Posts
knock sensors are cheap/easy to try - if it's bad and the ECU is pulling timing, I think pinging is possible.

might not hurt to confirm cam timing too.
 

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On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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2010 2.5 CVT Limited
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1,808 Posts
Do you know how much was machined off the cylinder heads?

It is possible the compression ratio has increased enough that higher octane is needed. This is an old hot rodder's trick to increase C.R. without replacing pistons. But it usually requires a rather significant milling of the cyl head. Normally, resurfacing the cyl heads to get good planairty should only be a few thousandths. If a cyl head is so warped it needs much more, the other surfaces are at risk of not aligning with manifolds, brackets, etc.

Your cylinder pressures are strong, but it is a complicated relationship to C.R. so it is unknown if the milling has caused a C.R. increase.
The suggestion to try the knock sensor is a good first step.
 

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2007 2.5i 5MT
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90 Posts
Discussion Starter · #7 ·
Forgot to mention, things I've already replaced that are possibly related:

- PCV valve (11 months, 23k miles ago)
- A/F sensor (2 months, 4k miles ago)
- O2 sensor (2 months, 4k miles ago)

I was getting P0420s and the latter two fixed that... was hoping it would fix this along with it but no cigar.

knock sensors are cheap/easy to try
I've had really bad experiences with el cheapo aftermarket parts, and it looks like the OEM part is about $120... Any suggestion for an aftermarket one? or are you calling $120 cheap? :p 22060AA111 right?

Looks like one side is different than another? Might just be testing variance - intake/throttle no opened or as flow favorable?
Hmm, I'm reasonably certain the difference was front/rear, which he said was typical; perhaps the cylinder numbers were copied down incorrectly on the service writeup. I don't know what the parameters were but it was at the dealer so I trust it was done to spec.

Is it like a light rattling in a tin can sound?

Maybe try different gas stations?
Gas treatment - MMO, Seafoam?
Check timing marks?
Yes it is a tin can rattling sound, sometimes it gets louder, gives one slightly larger bang, then is quiet for a bit.

I have tried different gas stations (that are supplied by different companies - I typically go to Costco, who use the same as Speedway does IIRC).

I used Royal Purple cleaner and I did get slightly better gas mileage, or it's my imagination, but it didn't touch this issue.

Timing marks - as in, physically inspect the belt to make sure everything is lined up?

Get a hold of some type of logging software. RomRaider is a good standby. But you need a EDIT: WINDOWS laptop and it also needs a vag com cable. You need to be able to look at manifold pressure, AFRs, knock and knock correction, timing....
I've got Torque via OBD and I will see what I can get out of it - romraider isn't compatible with my ECU last time I checked. Currently I'm knee deep in some electrical gremlin investigation, but I will get back to this soon hopefully.

Do you know how much was machined off the cylinder heads?
I do not have a number from the machine shop, but the car shop measured .102mm of warpage, so somewhere in the ballpark of slightly more than that. I can call and ask, but this was a year ago, and I doubt the number was actually written down and saved anywhere.
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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I think an intake or exhaust leak is possible. Between the MAF and the throttle body. Or a vacuum line. Possible exhaust leak close to an AFR (O2)
 

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. . . .romraider isn't compatible with my ECU last time I checked. . . . .
How did you determine it's not compatible?

Romraider's Logger function (but not the Editor) will probably work with most every 3rd gen Outback.

When I first started with Romraider Logger, after loading it, linking to the downloaded Logger and ECU definition files, and connecting to the OBD data port with the Vag-Com cable, it displayed pretty well all the parameters listed in the 2007 FSM for the ECM (and TCM (in my case).

And, if the specific ECU in your car has been "defined", then there will be a number of additional "extended parameters" and functions (e.g. Learned Values Table).
 

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Premium Member
(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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many folks have reported good luck with the $15 ebay knock sensors so, maybe you just had bad luck, over-torqued the new ones or ; based on what I have read, there is a boss/lump on some engine castings that is reported to break the connection if the cable isn't 'dressed' away from the sensor in the stock direction.
 

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2003 OBW 2.5L 4EAT
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860 Posts
The Airtex/Wells knock sensor from Rockauto.com is an OEM Subaru Japanese Niles part. I try to go with genuine or reboxed genuine for electrical parts at least.
 

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2007 2.5i 5MT
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90 Posts
Discussion Starter · #12 ·
How did you determine it's not compatible?

Romraider's Logger function (but not the Editor) will probably work with most every 3rd gen Outback.
Well the MT version of the 07 isn't in the compatible list. But I remembered that I also still don't have a laptop.... so yeah.


Possible exhaust leak close to an AFR (O2)
How might I go about finding this? My car does burn a bit of oil, so an exhaust leak shows up with a sooty black streak. But I did have the exhaust manifold off recently (it's got no heat shields, so it's easy to see), and there are no sooty marks indicative of a leak. The only one I know of is at the Y after the resonator - but nothing after the cat would have any bearing on anything except noise right?

The Airtex/Wells knock sensor from Rockauto.com is an OEM Subaru Japanese Niles part. I try to go with genuine or reboxed genuine for electrical parts at least
Hmm, do I need black connector or brown connector? I suppose I will have to go find out. Why is the latter $23 more?

maybe you just had bad luck, over-torqued the new ones or ; based on what I have read, there is a boss/lump on some engine castings that is reported to break the connection if the cable isn't 'dressed' away from the sensor in the stock direction.
The knock sensor is OEM (or at least predates my owning the car), and AFAIK has never been removed.
 

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On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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Well the MT version of the 07 isn't in the compatible list. But I remembered that I also still don't have a laptop.... so yeah.




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that list is full of crap. whatever group is in-charge of it does not have access to all the cars it works on,..or update it properly.

...you plug the car in and it works. the end. (maybe have to try 3 x. with a $10 cord though....but so is life on the cheap, without a $170 tactrix like the tuners need).

lots of people including @plain OM himself has a car just like yours.... people with earlier and later H4 N/A cars use it too....so.
 

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Well the MT version of the 07 isn't in the compatible list. But I remembered that I also still don't have a laptop.... so yeah.
Some ideas . . .

In regard to a Romraider "compatability list", when I first started with the Romraider Logger, I couldn't find my 2007 2.5i 4AT; nevertheless, as I noted in post #9 above, the Logger worked.

As I understand it, the Logger uses file lists of "definitions" that include both the standard Subaru SSM parameters (the ones that the dealer's Subaru Select Monitor III will display and are listed in the FSM), and "enhanced parameters" which are data series that are available only if the specific ECU in the car has itself been "defined". Consequently, even if a particular car/ECU isn't listed, the Logger can still provide almost all, if not all, the standard data series. In addition, as I subsequently found out, the logger definition file for a "similar" car might help complete the list of available standard parameters -- in my case the file for a 2006 2.5 MT/AT worked.

When checking on the Romraider site for compatability, and for specific ECU definitions, the Romraider forums are best searched also using the ECU ID number. This avoids the possibility of not finding the car because the descriptive keywords being used are slightly different from what someone used when listing the car. The ECUID might be indicated by Torque (not sure), but if not, then when the Logger is set up and running, it will be shown at the bottom of the screen.

Equipment-wise, if the intent is to keep the car for a while, and given the functionality of Romraider's Logger, one option might be to find a used laptop. Many are being sent off to "recycle" depots because the CPU and/or memory is insufficient for today's program needs, including the more recent versions of Windows. As long as it still works on battery power (for data observation/recording while driving), an earlier version would probably still be sufficient for Romraider. (For some time I used the Logger on a basic "netbook" running Win 7. Inexpensive then, and probably give-away now.) And, if it doesn't have a useable battery, it perhaps could still be used with its power adapter and a 12VDC-to-120VAC inverter.
 

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Discussion Starter · #15 ·
Here's a log of every sensor I have access to that has anything to do with fuel, air, or exhaust. Hopefully it's enough to tell somebody something, or else i'll have to look into getting a laptop and cable.

City driving, engine at temperature, no knock, then I parked at the store for a bit, left it running (omitted most of these lines because there's a 1MB attachment limit), came out, and drove it home with knock. Happens while accelerating only.
 

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. . . City driving, engine at temperature, no knock, then I parked at the store for a bit, left it running (omitted most of these lines because there's a 1MB attachment limit), came out, and drove it home with knock. Happens while accelerating only.
The absence of knock in the first part of the trip and then it appearing later reminded me of your problem in http://www.subaruoutback.org/forums/80-electrical-electronics/420930-intermittent-high-voltages.html where the unstable system voltage seems to also suddenly appear.

Any sign, or recollection, of the knock and unstable voltage coinciding?
 

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Discussion Starter · #17 ·

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Discussion Starter · #18 ·
So the knock sensor tests out good - 4.75V from the confuser, and 2.45V solid with the sensor plugged in.

I've got a vag-com cable on its way to me so I shall get more numbers soon.

In the meantime, while I was testing the knock sensor, I found that I need a new drive shaft :( I don't have an axle puller so that might not be something I do myself. Looks like the advance auto near me has one to borrow, so maybe. But I also see lots of advice saying all aftermarket shafts are junk and that an oem shaft should be rebooted.
 

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Discussion Starter · #19 ·
I am up and running with RomRaider. Woo.

First things first: ECU ID is 4B12188007

Aaand here's my first romraider log: https://drive.google.com/open?id=0B_ReOljJ96U_NEprQzBQSllGUnc

Warm start, aggressive driving, no noticeable knock. I'm running 93 at the moment because I just hate the noise so much, and it's not hot out, so that's not a surprise. I will fill up with 87 the next time and get more logs with knock this weekend when I put another 500 miles on it.
 

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I am up and running with RomRaider. Woo.

First things first: ECU ID is 4B12188007.
That ECU ID doesn't appear anywhere in the Romraider site. There is a listing for "2007 USDM Subaru Outback 2.5i MT" which has a slightly (one digit) different ID. I think such differences could reflect Federal vs CA emission specs. Do you know if your 07 is FED or CA spec? In any event, and just to be sure, could you double-check that it's recorded correctly?
 
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