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2000 forester auto
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Discussion Starter · #21 ·
Yeah for some reason or another I can't find any vacuum leaks anywhere. I have replaced just about everything except buying a brand new motor out of the crate. Replaced parts are timing belt and pulleys, water pump, pcv valve, plugs and wires, a fuel injector for cylinder 4 that is misfiring, new MAP sensor and MAF, I tried a new coil pack to no avail. I tried swapping wires and it still shows cylinder 4. New head gaskets as well so those are fine, does have great compression. The car did sit for about 6 months from previous owner so I don't know the history on the fuel or pump but it does start and revs up fine, and on start up it idles smooth until the computer kicks down the fuel/air ratio due to warning up. I'm at a complete loss because the only code I get is the PO304 and nothing else
I'm just wondering if it's an internal ECU problem that might not be sending the signal to fire cylinder 4! I really have no clue as to where to go other than have the local dealership basically charge me to undo everything that's been done and if that's the case you guys can keep your eyes open because it might become a part out🤷‍♂️
Well after doing one last thing I'm coming to the conclusion that I might have a burnt exhaust valve. Next question is can i remove just the drivers side head with the engine in the car? I'd rather not remove it completely
 

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Lets take a step back and think about, how does the ECU detect a misfire? There is no mis-fire sensor in the cylinder right. The answer is the ECU detects a misfire from the coil pack. When the magnetic field in the coil collapses and sends the energy to the spark plug there is a small amount of energy feed back. If the coil, wire, and plug are working right the energy feedback will be in a measurable value. If one or more is degraded then the feedback value will be different.

Keeping in mind a mis-fire could be caused by the incorrect A/F ratio.

In the non-turbo engines in that generation the coil pack sends spark to both plugs on one side 1-3 and 2-4 at the same time. The firing order is simply the cylinder that is on the compression stroke (turbo does not since each cylinder has its own coil). When you are firing cylinder 1 on the compression stroke, cylinder 3 is on the is on the exhaust stroke, firing the spark plug on the exhaust stroke makes no difference.

With all that being said you have one of 2 problems.

1. You have a bad coil pack. try swapping the wires on one side. If you are not comfortable with that you could try swapping a known good pack. You say your problem is on cylinder 4 then swap the wires for 2 and 4 on the drivers side. Coil could have been damaged when the intake was off the car. That coil pack is not cheap to buy new so you could get a used one at a decent cost from a u-pull it junk yard like LKQ. They will let you return it if you say it was not working right.

2. The other is cylinder 4 has low compression caused by gasket or valves. Since you said the last maintenance was the head gasket there is a chance the gasket is not sealing causing a leak, There could be any number of reasons like, surface preparation, reused head bolts that were already stretched, torque procedure, If this engine is the DOHC you had to remove the cam shafts and lifters, the lifters have shims in them. Hopefully you got them all into the right positions they came out of because each shim is a different thickness. If the shims are off you would have noisy valve train so use a mechanics stethoscope to listen for excessive noise. For a SOHC you do not have to take out the cams and the valves are adjustable so you can check those clearance's and adjust as needed.

Before you start tearing into the engine a compression check would be recommended. Not a easy thing to do on these engines but would recommend over pulling the heads again.
 

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2000 forester auto
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Discussion Starter · #23 ·
Lets take a step back and think about, how does the ECU detect a misfire? There is no mis-fire sensor in the cylinder right. The answer is the ECU detects a misfire from the coil pack. When the magnetic field in the coil collapses and sends the energy to the spark plug there is a small amount of energy feed back. If the coil, wire, and plug are working right the energy feedback will be in a measurable value. If one or more is degraded then the feedback value will be different.

Keeping in mind a mis-fire could be caused by the incorrect A/F ratio.

In the non-turbo engines in that generation the coil pack sends spark to both plugs on one side 1-3 and 2-4 at the same time. The firing order is simply the cylinder that is on the compression stroke (turbo does not since each cylinder has its own coil). When you are firing cylinder 1 on the compression stroke, cylinder 3 is on the is on the exhaust stroke, firing the spark plug on the exhaust stroke makes no difference.

With all that being said you have one of 2 problems.

1. You have a bad coil pack. try swapping the wires on one side. If you are not comfortable with that you could try swapping a known good pack. You say your problem is on cylinder 4 then swap the wires for 2 and 4 on the drivers side. Coil could have been damaged when the intake was off the car. That coil pack is not cheap to buy new so you could get a used one at a decent cost from a u-pull it junk yard like LKQ. They will let you return it if you say it was not working right.

2. The other is cylinder 4 has low compression caused by gasket or valves. Since you said the last maintenance was the head gasket there is a chance the gasket is not sealing causing a leak, There could be any number of reasons like, surface preparation, reused head bolts that were already stretched, torque procedure, If this engine is the DOHC you had to remove the cam shafts and lifters, the lifters have shims in them. Hopefully you got them all into the right positions they came out of because each shim is a different thickness. If the shims are off you would have noisy valve train so use a mechanics stethoscope to listen for excessive noise. For a SOHC you do not have to take out the cams and the valves are adjustable so you can check those clearance's and adjust as needed.

Before you start tearing into the engine a compression check would be recommended. Not a easy thing to do on these engines but would recommend over pulling the heads again.
Thanks for the info, after doing some more research I am pretty confident that it has a burnt valve. I will be looking further into it this weekend
 

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2000 forester auto
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Discussion Starter · #24 ·
Lets take a step back and think about, how does the ECU detect a misfire? There is no mis-fire sensor in the cylinder right. The answer is the ECU detects a misfire from the coil pack. When the magnetic field in the coil collapses and sends the energy to the spark plug there is a small amount of energy feed back. If the coil, wire, and plug are working right the energy feedback will be in a measurable value. If one or more is degraded then the feedback value will be different.

Keeping in mind a mis-fire could be caused by the incorrect A/F ratio.

In the non-turbo engines in that generation the coil pack sends spark to both plugs on one side 1-3 and 2-4 at the same time. The firing order is simply the cylinder that is on the compression stroke (turbo does not since each cylinder has its own coil). When you are firing cylinder 1 on the compression stroke, cylinder 3 is on the is on the exhaust stroke, firing the spark plug on the exhaust stroke makes no difference.

With all that being said you have one of 2 problems.

1. You have a bad coil pack. try swapping the wires on one side. If you are not comfortable with that you could try swapping a known good pack. You say your problem is on cylinder 4 then swap the wires for 2 and 4 on the drivers side. Coil could have been damaged when the intake was off the car. That coil pack is not cheap to buy new so you could get a used one at a decent cost from a u-pull it junk yard like LKQ. They will let you return it if you say it was not working right.

2. The other is cylinder 4 has low compression caused by gasket or valves. Since you said the last maintenance was the head gasket there is a chance the gasket is not sealing causing a leak, There could be any number of reasons like, surface preparation, reused head bolts that were already stretched, torque procedure, If this engine is the DOHC you had to remove the cam shafts and lifters, the lifters have shims in them. Hopefully you got them all into the right positions they came out of because each shim is a different thickness. If the shims are off you would have noisy valve train so use a mechanics stethoscope to listen for excessive noise. For a SOHC you do not have to take out the cams and the valves are adjustable so you can check those clearance's and adjust as needed.

Before you start tearing into the engine a compression check would be recommended. Not a easy thing to do on these engines but would recommend over pulling the heads again.
Yes I pretty much did everything you listed, I put in a brand new coil pack which did increase the speed it started up but it did not take away the misfire. I also swapped wires from working cylinders to this is one to no avail. So the only two options left are either a burnt valve or piston rings. If it was anything else I would think I'd have a check engine light for cam/crank sensor or EGR or anything else I can think of that's ECU controlled.
 

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I had this problem recently after a belt replacement and head gasket job; the car ran great for about 100 miles and started missing a long way from home. It turned out the injector wire wasn't pushed on all the way, but other clues also led me to buy a new Subaru dealer coil pack which I have in the car ready to rock. My mechanic friend says there have been endless problems with aftermarket coils.so just pony up for the real thing.
 

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Discussion Starter · #26 ·
I had this problem recently after a belt replacement and head gasket job; the car ran great for about 100 miles and started missing a long way from home. It turned out the injector wire wasn't pushed on all the way, but other clues also led me to buy a new Subaru dealer coil pack which I have in the car ready to rock. My mechanic friend says there have been endless problems with aftermarket coils.so just pony up for the real thing.
Yeah, I'm going to look into it after work today and see what's going on. I'm hoping it's not a valve issue but I can't see anything else other than rings. The car runs great if you hold the idle up but as soon as it runs after start up about 10-15 seconds it starts to idle rough and it gets worse the hotter it gets
 

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1998 Forester L, 2003 Forester X, 2008 Forester Premium (x2)
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If you can, lower the front exhaust (6 nuts) from the heads and hanger bolt further back, and look into the exhaust ports. I have seen a few that the exhaust valve guides back out of the head, and eventually keep the valve from closing all the way. Seems to be a common problem since the machine shop said they see this regularly. Not very time consuming to look, and #4 seems to be the most common. Come to think of it, there may be a service bulletin on that problem for a range of years.
Also, verify cam timing.
And if you are still driving it be aware, the valve guide(s) can back out until the valve won't close and the piston will snap the head off. that can happen pretty quickly considering how many times a mile that valve is cycling. Drive at your own risk.
 

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Discussion Starter · #28 ·
@halfmillionmile Thanks for the info, yes car is currently not being driven, I took the head off the other day and the valves looked good but I had new exhaust valves ordered so I put them in. One other note is the intake gasket for cylinder 4 was wet around it so its possible it wasn't tight enough and had just enough of a vacuum leak to cause this whole problem. I'll update if and when I can hopefully get this running smooth
 

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Discussion Starter · #29 ·
UPDATE!!!!!
Everything is perfect now. Ended up being a very slightly bent intake valve. Re-did more than I should've but in the end its solved and I'm happy. Thank you to everyone for their insight. 👍👍👍
 
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