Infamous misfire issue, with increasing rattle/ knock noise.

Hey everyone! Im new to the forum, and just bought an '07 LGT Limited 5MT back in September of 2014. It has a stock intake with a K&N panel filter, and a catback magnaflow exhaust system on a stock tune. It has 135k and about 2k ago I started having misfire issues. Sorry for the long winded post, but I want to make sure I give you the info you need to properly assess my situation.

 

So far I have replaced intake O-rings, and plugs and have been using lucas injector cleaner religiously in mobil 93 octane gas bought from one of two stations. There doesn't seem to be any correlation to type of gas so far as I can tell. Have full service history and the car has been running full synthetic most of its life and has been well cared for.

 

The intake O-rings addressed an extremely rough cold idle that has not come back, but the car still throws a CEL and codes for misfires in all 4 cylinders. The most recent codes were P0304, P0301,P0302,P0303, and P0304 (again) in that order. Turbo shaft was recently checked by a dealer and they said it was in great shape. The car has moments of greatness and runs like a champ at idle and boost, but randomly goes back to nearly dying at idle and stuttering during acceleration.

 

I have not seen any other codes since I have had the car, so I am hoping that it is just a bad IC, or Injector in cylinder 4 (where the misfires originated), that has thrown off the VVT just enough to cause misfires in all four cylinders when I reset the ECU after I changed the plugs. Does this sound feasible?

 

The other thing that is more concerning to me is that there has been a rattle/knocking noise that has been increasing in volume over time. The noise seems to be rhythmic, comes and goes as it pleases, and the weirdest part is that I can only hear the noise in the cabin. I cannot locate it in the engine bay. Could this noise be attributed to misfires? or should I be woried about OCV's and banjo bolts?

 

Please help a Subie newbie out! Thanks for reading!

when was the timing belt changed? those tensioners have a tendency to leak and they will make a knocking type of noise as evidenced here.

 

Supposedly it was changed at 105k along with the water pump, and all belts. I have a receipt for the work, but unfortunately I have no way to verify that the work was done on MY car. The info on the receipt is from the previous owner's old 98 LGT. Would I be able to tell if the parts were actually changed just by visual inspection?

 

All of the other receipts are accurate, and he was completely honest about all of the other flaws in the car, so I have no other reason to suspect I got duped by this guy.

 

Would I be able to hear the knock from the timing belt from inside the car though? I just took her out for a ride to buy some washer fluid and noticed that the noise does not start until after it runs for a minute or so, and seems to dissipate at higher rpm (over 2 grand), and come back when I let off the throttle.

not sure if it would make any difference, but was the fuel filter ever replaced?

It doesn't appear so, and I had that thought too. From what I have read from other contributors here, you don't replace just the fuel filter on these. The fuel filter is a part of the pump assembly, and you are supposed to replace the entire thing ($250).

 

I could be wrong though, does anyone know if that is the case?

Supposedly it was changed at 105k along with the water pump, and all belts. I have a receipt for the work, but unfortunately I have no way to verify that the work was done on MY car. The info on the receipt is from the previous owner's old 98 LGT. Would I be able to tell if the parts were actually changed just by visual inspection?

 

All of the other receipts are accurate, and he was completely honest about all of the other flaws in the car, so I have no other reason to suspect I got duped by this guy.

 

Would I be able to hear the knock from the timing belt from inside the car though? I just took her out for a ride to buy some washer fluid and noticed that the noise does not start until after it runs for a minute or so, and seems to dissipate at higher rpm (over 2 grand), and come back when I let off the throttle.

 

the Subaru dealer/ shop may or may not change the tensioner during the T-belt service, if they do it adds about $180 to the cost. My local dealer did mine with t-belt and it was close to $700. It is easy to check and replace though

Ok, thanks for the tip! I will have the tensioner checked next week.

 

With regard to the misfire issue, I cleaned my MAF today and filled up with Sunoco 93 octane and lucas injector cleaner. Even without an ECU reset the engine seems to be idling a lot smoother, and the rattle/knock noise is not as apparent. I will try an ECU reset tonight/ tomorrow morning and post again about my status.

 

If I had a bad IC on cylinder 4 and I let it go for too long, would the issue propagate to other cylinders? Hopefully I haven't been doing any major damage to my engine by running several tanks of gas through on a bad coil...

the filter is about $80. its replaceable without buying a pump housing.

Update;

The mysterious knocking noise has gotten much louder, and prompted me to take it in to Motive Auto Works in Woburn, MA (and park it!). Alberto has been great so far helping me narrow down the possible problem(s), but I'm still racking my brain to figure out what the heck is going on.

 

Alberto over at MAW completed a compression and leak down test for me with the following results;

 

Cyl1- 142 psi- 0% loss

Cyl2- 130 psi- Less than 5% loss

Cyl3- 142 psi- Less than 5% loss

Cyl4- 121 psi- Less than 5% loss

 

Just as a recap, I have a stock tune with a K&N box filter and Magnaflow exhaust.

 

Given that the stock tune on these cars is awful and tends to burn up valves, does it make sense that the poor compression in cylinder 4 could be due to burnt valves?

 

Burnt cylinder 4 valves could explain my mystery noise as well, so I am sort of leaning that way, but I wanted to run that by those of you who are most familiar with this motor. I am hoping that I can address my issues now before they propagate and lead to a rebuild... Thanks for reading!

#ynansb

I'm not sold on Lucas injector cleaner. Ever consider Techron? Auto Zone and Advance are always running 2 for 1 deals on the 20 oz size.

Not that a cleaner would solve a misfire issue.

Berryman Chemtool B12.

My turbo started to knock in a very similar manner. It would knock softly at low rpm after the engine was warm, but the sound dissappeared after 2000-2500 rpm. If its gotten louder you should be able to narrow down where its coming from.

 

Burned valves shouldn't cause the noise. At least my valves didn't make any noise when they burned up. The cylinder with failed valves was only holding about 60 psi.

 

Try the "stethoscope" method and dig around the engine bay to locate that knock.

 

Burned valves shouldn't cause the noise. At least my valves didn't make any noise when they burned up. The cylinder with failed valves was only holding about 60 psi.

 

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60 compression or 60 on the leakdown test?

I had a feeling it was the turbo. It's nice to get confirmation from someone else though. The car is at the shop, and I will not be driving it until its fixed. My mechanic is taking an oil sample to send to blackstone labs to determine the severity of this issue. I am hoping that I caught it early enough that I didn't ruin the entire motor, but I guess only time will tell...

60 compression or 60 on the leakdown test?

 

Compression... but when I say burned valve in my case it was split across the face and you could see right through it. Also the circumference of the face was reduced considerably as well. I replaced the turbo (along with a few other things) and the knock went away. Then during tuning a misfire appeared. So I still had the valve issue after the knock was rectified.

 

If the knock goes up and down with the rpm but doesn't stay exactly step for step then it could be turbo. Engine internals knocking should coincide with rpm almost exactly where the pressure driven turbo takes longer to respond. It's still spinning so you could be alright. Best of luck, and don't forget to remove those banjo filters if they already haven't.