Good morning all!

 

I need some help confirming an issue we are having with our 1999 Forester, 2.5 automatic, 128,000 miles.

 

We had the head gaskets done 2 weeks ago and everything turned out fine. Yesterday, however, the check engine light began flashing then went to steady-on. I pulled the codes and one was P1325 and the other was P0304. The P0304 showed up just prior to us doing the head gaskets, too. With the gasket job, we did complete timing belt kit (the one highly recommended Gates kit from Amazon), new gaskets all around.

 

Research last night shows the P1325 indicates a faulty knock sensor, which can possibly cause a misfire, rough idle and poor fuel mileage. The car idles horrible at idle, but smooths out at cruising speed. The fuel mileage seems bad, as well.

 

Any thoughts? Thanks in advance.

Knock sensors do cause all sorts of issues but not typically at idle.

 

How old are the spark plugs and wires? These are the usual cause for misfires.

Plugs and wires were done roughly a month ago. NGK plugs, Standard Motor Products wires. I've heard Subaru's are picky about the wires, but these were listed as high quality

I've always had good luck with Standard wires on other cars, but the Subarus are especially picky.

 

Make sure the wires are clicked on properly. Try swapping the number 4 wire with number one and see if the misfire moves with it.

 

If the plugs were changed before the head gaskets were done they could be fouled. I would pull the plug on cylinder 4 and check it for buildup.

Plugs were done after the gaskets, wires before. A coworker has a 2000 Legacy GT and he offered to let me swap parts out to try and diagnose. I tried his wires and coil pack; no change in the idle on my Forester. One new thing, however, is the CEL only flashes now intermittently and hasn't stayed on steadily. The idle is still rough, but once the RPMs are over ~1000, the engine seems to smooth out. Merging onto a highway this evening on my way home from work, I had to get on the gas, and it got up and went strongly. Another new thing I noticed this morning when I initially started driving the car, there was some blue colored smoke from the exhaust. Is that unburnt fuel?

The blue smoke was probably just oil that got its way into the cylinders or exhaust manifold when the heads were pulled. I did the head gaskets on an 04 outback earlier in the week and it did the same.

A flashing CEL indicates a condition which has the potential to damage the catalytic converters by flooding them with raw fuel. Usually this is due to a steady misfire.

 

Low RPM stumbles and shaky idle, smooths out at higher RPM, probably a burned exhaust valve.

Time for a compression or leakdown test.

Edited August 8, 201411 yr by Fairtax4me

Was a valve adjustment done when the head gaskets were replaced? If the valves are too tight, they hang open just a bit and can cause a misfire and roughness at idle. I recently diagnosed the same vehicle with a cylinder misfire and found all the valves on one side to be too tight. Adjusted them and the misfire and rough idle went away.

So I have multiple issues going on then, correct? Is there an easy way to test for a burnt valve without taking the engine apart again?

I'm not sure about the valve adjustment. A friend of the family who is very good with Subaru's engines did the work for us. He said he sent the heads out to be surfaced and cleaned up. I can confirm with him this weekend exactly what was done.

IIRC those heads also have issues with the valve guides dropping and holding the valves open.

 

Yes, likely two separate issues.

More than likely the knock sensor code is just because the sensor is bad (very common).

 

The possible valve issue will need more looking into before pulling the head again.

the 99 forester ej25 is a sohc and the valves are pretty easy to adjust.

unlike the eh25dohc engine.

 

this is not a conclusive test,

but if you hold a dollar bill over the exhaust while the engine is running,

and it ''sucks back in'' as opposed to always being push away,

it could indicate a burnt or open exhaust valve.

 

but if the heads were sent out,

the valves should have been checked.

did this issue start as soon as the engine was back together?

or did it develop later?

It developed later. About a week after we got the car back it started idling rough. You can hear the exhaust at the back of the car doing that put put put put put put sound.

I tried the dollar bill trick today and it does not get sucked back in at all - it's always being pushed away from the tailpipe. Odd thing, however, is the engine has smoothed out, still a slight shake to it, but nothing like before. It did throw a code for the same P0304, misfire on cylinder 4. It's driving better for her, but I'm still pulling my hair out over this intermittent idle issue. I'm about to go get a set of Subaru plug wires and try them. The plugs were new a month ago and appear fine. Any other thoughts?

nvrmd

Edited August 12, 201411 yr by 1 Lucky Texan