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Discussion Starter #1
Prior to and after replacing (shop) installed
spark plugs @62K miles, we have a CEL light.

The results show misfires on numbers 1-3-4-6.

However, the car idles and runs great
along with no emissions issues.

Freeway gas mileage is about 24 mpg.

Any thoughts?

Best of Holiday to all,

And,

Semper fi

Gerry
 

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I would think you are getting near misfires on 2 and 5 also.

how old are the o2 sensors.? and what are they. a old / dirty front one can make for minor misfires. and other codes before making a code of its own.

if you need to buy one: Denso is a good brand, cheap and known to work in subarus like OEM, and maybe the OEM maker.

(Bosch etc. just don't perform right).





for future discussion here is a diagram.


 

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Discussion Starter #3
We are the original owners and, I
think the sensors are original.

Here is what I found for Denso.

Not sure about the "Upstream-Downstream" definitions.

Also, during our most recent smog test,
the car showed exemplary values.


Gerry
 

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On the Super Mod Squad
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We are the original owners and, I
think the sensors are original.


Here is what I found for Denso.

Not sure about the "Upstream-Downstream" definitions.

Also, during our most recent smog test,
the car showed exemplary values.


Gerry
upstream = before cats.

downstream = after cats.

if you find out you need to buy, try rockauto or amazon. (getting the stock # from rockauto).

local chains seem to like to overcharge for simple things like o2 sensors and spark plugs.
 

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Discussion Starter #5
O2 Sensors.

Hello eagleeye,

I'm not clear on the location/replacement procedure for
these sensors.

I'll try to pick up a manual soon.

The dealerships are the only qualified wrenches in our area
which means BIG BUCKS$$$$$$$.

Other shops are just guessing..........

Thanks again for your positive comments.

Best,


Gerry
 

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Hello eagleeye,

I'm not clear on the location/replacement procedure for
these sensors.

I'll try to pick up a manual soon.

The dealerships are the only qualified wrenches in our area
which means BIG BUCKS$$$$$$$.

Other shops are just guessing..........

Thanks again for your positive comments.

Best,


Gerry
there is no paper manual with H6 engines in it. (Haynes / chilton Never gave a crap )

try here:
https://sl-i.net/FORUM/showthread.php?18087-Subaru-Factory-Service-Manuals-(FSM)-Every-Model-USDM-EU


download to a flash drive scan with antivirus software, ...and print off what you need as you need it and put it in a folder / binder.



_________

when you get down and look at the exhaust manifolds you will see the o2 sensors in them. (upsteam)


rear downstream ones are further down past the cats.

the parts below in the diagram with the wires on them are the o2 sensors
(a pair of front upstream ones in each exhaust manifold before the cats 22691,..

.and one rear downstream one after the last central cat there 22690,...

24039 = the wire harness extension for that rear downstream one.

(this particular image is a JDM one I think, USDM should be the same).

 
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Judging from the avatar you have a Gen 2 (2001-2004 USDM) LLBean. If you could post your city/area you're in, someone on here can direct you to a trustworthy shop you may have not considered before.

Something that comes to mind is the type of spark plug you used when changed at 62k and what is the mileage you are at now? If you used copper plugs, they wear out faster than platinum or iridium plugs. They also don't fire as well. Battery condition is also something that could be checked. How old is it? How many amps are being supplied? The amp measurement needs to be done with an amp meter, not voltage. A battery can show a 12V output and lack in amperes. Loose ground cables and strapping is also something to check when getting up in miles. Corrosion is a huge deterrent to electron flow which is necessary for electrical parts on the car to operate properly. Once electrical flow is verified as good, then you will be able to look at other areas to determine the fault.
 

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alternatively as you got a like all cylinders misfiring:

could be something electrical like a loose / corroded wire ground.
 

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Discussion Starter #9
Plugs.

Judging from the avatar you have a Gen 2 (2001-2004 USDM) LLBean. If you could post your city/area you're in, someone on here can direct you to a trustworthy shop you may have not considered before.

Something that comes to mind is the type of spark plug you used when changed at 62k and what is the mileage you are at now? If you used copper plugs, they wear out faster than platinum or iridium plugs. They also don't fire as well. Battery condition is also something that could be checked. How old is it? How many amps are being supplied? The amp measurement needs to be done with an amp meter, not voltage. A battery can show a 12V output and lack in amperes. Loose ground cables and strapping is also something to check when getting up in miles. Corrosion is a huge deterrent to electron flow which is necessary for electrical parts on the car to operate properly. Once electrical flow is verified as good, then you will be able to look at other areas to determine the fault.
The plugs are NGK 6458 LSR Platinum.


Mileage is ~67K.


The battery is new, and, checks out under load test.


Cables are clean.


We live in Manhattan Beach CA.


Best,


Gerry
 

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Such as a battery ground cable?


Gerry
There are ground straps in several places on the vehicle. The main ground cable from the battery goes to the engine and to the body. Then you have one each side from the body rail to the valve covers. A series from the harness to the top of the intake on the passenger side underneath the engine cover, at the same place the fastener that holds the cover down is located. Then there's the one from the transmission to the firewall. They all play a part in electrical flow.
 

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Discussion Starter #12
There are ground straps in several places on the vehicle. The main ground cable from the battery goes to the engine and to the body. Then you have one each side from the body rail to the valve covers. A series from the harness to the top of the intake on the passenger side underneath the engine cover, at the same place the fastener that holds the cover down is located. Then there's the one from the transmission to the firewall. They all play a part in electrical flow.
The grounds appear to be clean and secure.


Also, on a 150 mile freeway trip at about 65-75 mph,
we recorded a very accurate 24.85 mpg with the CEL light on.


Maybe It's shop diagnosis time?


Gerry
 

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That or do it yourself data logging and upload the data here. Rom Raider, a Vag-Com cable and a laptop or notebook. A shop would be faster, but you said its running good, so its your call.

4 out of 6 cylinders misfiring and that kind of gas mileage :confused: But then again, fuel delivery. It could be running lean due to lack of fuel creating a misfire. Or the knock sensor is screwed and its really not misfiring the ECM just thinks it is. Is the codes coming back quickly or varying in time frames?
 

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Discussion Starter #14
Mis-fires.

That or do it yourself data logging and upload the data here. Rom Raider, a Vag-Com cable and a laptop or notebook. A shop would be faster, but you said its running good, so its your call.

4 out of 6 cylinders misfiring and that kind of gas mileage :confused: But then again, fuel delivery. It could be running lean due to lack of fuel creating a misfire. Or the knock sensor is screwed and its really not misfiring the ECM just thinks it is. Is the codes coming back quickly or varying in time frames?
The most recent test (yesterday) indicates that all of the cylinders are mis-firing.


The code came back within 200 miles after the last code clear.


We cleared it again yesterday so let's wait and see.


Although we did (very easily) pass smog,
any thoughts about defective O2 sensor(s)?


Clogged fuel filter?


Gerry
 

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clogged fuel filter could be an issue for delivery
easy to change
I would want to see data, but if you have not replaced the fuel filter in the last 20k miles, its due and if its clogged or restricted, it could well be the issue.
I doubt both AF sensors would fail simultaneously.
While you "wait", look into Rom Raider. Free and easy. The cable is available as low as about $8.00 as of this morning.

Does your county/state do tailpipe or OBD port test?
 

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Discussion Starter #16
clogged fuel filter could be an issue for delivery
easy to change
I would want to see data, but if you have not replaced the fuel filter in the last 20k miles, its due and if its clogged or restricted, it could well be the issue.
I doubt both AF sensors would fail simultaneously.
While you "wait", look into Rom Raider. Free and easy. The cable is available as low as about $8.00 as of this morning.

Does your county/state do tailpipe or OBD port test?
If you are referring to the connector near the driver's kick panel,
I had this done prior to my most recent post.


All it showed was a miss-fire on all cylinders.


The state does perform the tail pipe test.


We passed the state smog test with flying colors
during the mis-fires.


Gerry
 

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The state does perform the tail pipe test.


We passed the state smog test with flying colors
during the mis-fires.
That is weird. You're in Cali?

The only way I can think that the car will run with misfires and blow low hydrocarbons and NOx is if it is running lean. Lack of fueling to the cylinder. But, its not running rough, is it? Its getting good mileage.

KNOCK SENSORS :1pat:

The knock sensors on the car pick up vibration/noise from the engine which the ECM translates as a misfire or detonation depending on the noise level. The knock sensor is a microphone made of a series of plates that when vibrated changes the resistance on the 5V signal from the ECM. Different levels of vibration, different feedback. There are 2 on the engine, on top of the block under each side of the intake manifold. They are in a tight spot to get to without removing the intake, but it can be done. Each has a single plug, and held down with a 12mm hex head bolt. If the sensors are corroded, they will vibrate as with a detonation or vibration caused by misfires. Could be cracked, rusted, whatever. Its just a stack of plates and if loose, they move too easily, sending incorrect information.

I've been thinking about your gas mileage, too. My VDC got me 29 mpg before the supercharger installation. Yours should be no different unless you are up and down a lot of hills/mountain roads. In which case 24 is good. If the knock sensors are the problem, new ones will possibly allow for better fuel economy because the ECM will not be fluctuating the fuel and timing to correct for a miss that isn't there.

Knock sensors: https://www.carid.com/standard/inte...FEbKs82uBWeKAXpP5WXDmnFviVdbtXZxoCxAkQAvD_BwE

The knock sensors are circled red in the photo. This is an H6 out of a car with the intake removed.
 

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Discussion Starter #18
Cel

That is weird. You're in Cali?

The only way I can think that the car will run with misfires and blow low hydrocarbons and NOx is if it is running lean. Lack of fueling to the cylinder. But, its not running rough, is it? Its getting good mileage.


The car, ever since new, has always maintained a freeway gas mileage of 24-26mpg.

Also, it idles/runs/accelerates like new.


Were it not for the CEL issue, I would not be concerned.

KNOCK SENSORS :1pat:

The knock sensors on the car pick up vibration/noise from the engine which the ECM translates as a misfire or detonation depending on the noise level. The knock sensor is a microphone made of a series of plates that when vibrated changes the resistance on the 5V signal from the ECM. Different levels of vibration, different feedback. There are 2 on the engine, on top of the block under each side of the intake manifold. They are in a tight spot to get to without removing the intake, but it can be done. Each has a single plug, and held down with a 12mm hex head bolt. If the sensors are corroded, they will vibrate as with a detonation or vibration caused by misfires. Could be cracked, rusted, whatever. Its just a stack of plates and if loose, they move too easily, sending incorrect information.

I've been thinking about your gas mileage, too. My VDC got me 29 mpg before the supercharger installation. Yours should be no different unless you are up and down a lot of hills/mountain roads. In which case 24 is good. If the knock sensors are the problem, new ones will possibly allow for better fuel economy because the ECM will not be fluctuating the fuel and timing to correct for a miss that isn't there.

Knock sensors: https://www.carid.com/standard/inte...FEbKs82uBWeKAXpP5WXDmnFviVdbtXZxoCxAkQAvD_BwE

The knock sensors are circled red in the photo. This is an H6 out of a car with the intake removed.
Perhaps, I should just take the car into a shop for an extended diagnostic.


Unfortunately besides the dealer, we do not have a Subaru trained shop
in the area.


Any shop will tell us that they are qualified, but after a brief conversation,
I can tell they are just guessing........


Just did a 185 mile freeway trip at a consistent non-stop 65-75 mph,
and recorded 28.33 mpg with no CEL light.


I'll just leave things alone for now.


Thanks to all who responded to this concern.


Best,


Gerry
 

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Discussion Starter #19
Fuel filter.

clogged fuel filter could be an issue for delivery
easy to change
I would want to see data, but if you have not replaced the fuel filter in the last 20k miles, its due and if its clogged or restricted, it could well be the issue.
I doubt both AF sensors would fail simultaneously.
While you "wait", look into Rom Raider. Free and easy. The cable is available as low as about $8.00 as of this morning.

Does your county/state do tailpipe or OBD port test?

Not sure if L.A. county does the OBD test.

Changed out the fuel filter today with no CEL indication.


Let's wait and see.


Gerry
 

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Discussion Starter #20
OBD Code P0483.

Took the car in for a thorough OBD code test with the CEL light on again.

https://www.obd-codes.com/p0483
^^^^^
The tech came up with the P0483 error code which appears to be a cooling issue.

However, the temp gauge never exceeds the 9 o'clock position
and, both the A/C and cooling fans activate.

As previously stated on the thread, the car runs great,
and, would it not be for this CEL issue, we would have
no concerns @ 28mpg freeway.


Best,


Gerry
 
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