Got cylinder #2 and #4 misfire after a head job. Swapped coil pack, wires, and Subaru timing belt is dead on. Think it's time to swap the head but is there anything else I should check and what exactly is happening to cause this?

 

I've seen folks mention O2 sensor and fuel?

 

Car was severely overheated and I replaced the short block.

 

The heads were resurfaced a bit under spec's by the machine shop - I'm guessing that caused it?

Edited April 26, 201114 yr by grossgary

GG-

 

When you say misfire- is it just throwing codes or actually running poorly as well? Have you done a compression test?

 

How about injectors? Haven't seen a lot of problems in my limited experience, but if the car was sitting awaiting repairs for a long time & the gas went off- or crud got into the lines while it was disassembled.

 

Just a few thoughts.

 

Nathan

You might also want to double check valve clearances- did the machine shop set them?

 

One other thing occurred to me- if the heads were milled too much, the valve timing may be fractionally off (less distance between crank sprocket and cam sprockets.) Might be enough to confuse the ECM seeing too much timing spread between the crank and cam sensor pulses. If this is the case, you might be to fix the issue with adjustable cam sprockets if anyone makes 'em for Subies.

Edited April 22, 201114 yr by hankosolder2
more info.

Did you do a compression check yet?

yes - it's throwing codes and running poorly. like it's got hopped up cams...lumpy, rumbles a little, car shakes, poor power...but it does run and drive around. stalls when decelerating quickly.

 

it did take a couple of months to get around to repairing it. i have no idea how to test the injectors but it would be nice to verify that before yanking heads again.

 

what would/could i look for?

Compression and/or leak down test.

 

You can pull injector plugs to see if it makes a difference. Otherwise I think they need to be out to check spray pattern. If you can smell fuel in the cylinders they are at least spraying fuel, how much is another story.

 

I wanna say there was a thread here some time ago where the poster had several valve guides fall out and lodge the valves open. Maybe a side effect of overheating?

can anyone tell which head this picture is of in my other thread:

http://www.ultimatesubaru.org/forum/showthread.php?t=121793&highlight=thousandth

 

is that the passengers or drivers side head?

 

i don't believe i have the pictures any more, just those little dinky cropped ones and i can't tell which side that appears to be?

Have done a visual check for spark? I've seen an ignitor die in this very way - only half the coil pack will fire.

 

Done a compression check? If you have fuel and spark.... either the valve timing is off or there's not enough compression.....

 

GD

Update: both cylinders misfiring on drivers side. Car runs and drives okay with lack of power - 75% maybe and stalls when decelerating from a high RPM.

 

Spark: good (visual test and swapped coil and wires, no change)

Compression: perfect 175+

Valves adjusted and cam sprockets on the correct sides. Timing belt perfect, no movement when running (tensioner good), verified Subaru part number.

 

Strong fuel smell when spark is disconnected (and i have terrible sense of smell)

Runs noticeably worse when the cylinder misfire spark plugs are disconnected, so those cylinders are doing something.

 

Question:

 

*Can fueling issues cause cylinder misfires - i guess i need to test fuel somehow?

 

If it has good compression, timing, and spark what would cause cylinder misfires?

 

I don't want to replace the head only to find out it was something else.

Edited April 25, 201114 yr by grossgary

Compression sounds good. Did you check the cam alignment at TDC as well as with the marks? Put a straight edge across the center of the cam and line it up with the timing mark. It should be pretty much straight up and down, the drivers cam should be turned just slightly clockwise ( less than ~2° ) if anything.

Compression sounds good. Did you check the cam alignment at TDC as well as with the marks?

i don't know what you mean.

 

i lined up the marks you'd line up to install a new timing belt, the three dashes on the crank and cam sprockets. i lined those up and they're dead on.

Question:

 

*Can fueling issues cause cylinder misfires - i guess i need to test fuel somehow?

 

 

Of course... too rich or too lean can cause missing. I don't remember how the injectors are shaped (symmetrical?) but you could possibly swap injectors from cylinders that are missing to the OK cylinders and see if the miss follows the injectors or stays in the same place.

 

Nathan

Seems like I should verify fuel then. Since the other side is fine then that should rule out the supply side all the way up to the motor.

 

So - what possible fuel issues are there:

Injectors.

Fuel pressure regulator? Is there one per side or one for the entire engine?

Anything else fuel related?

One thing I would check that you have not mentioned is the pigtails wires to the injectors, All you need is a set of noid lights that cost very little at parts store.

 

I had a cylinder 3 misfire that ended up being the E.C.U.

Edited April 26, 201114 yr by tcspeer

i don't know what you mean.

 

i lined up the marks you'd line up to install a new timing belt, the three dashes on the crank and cam sprockets. i lined those up and they're dead on.

 

Set the crank at TDC and make sure the arrows on both cam sprockets are pointing straight up. It's pretty easy to tell if the cam is off time when set at TDC, because all three arrows should be straight up and down. Don't pay attention to the notches in the cover.

Set the crank at TDC and make sure the arrows on both cam sprockets are pointing straight up. It's pretty easy to tell if the cam is off time when set at TDC, because all three arrows should be straight up and down. Don't pay attention to the notches in the cover.

timing is dead on. i've done a zillion subaru belts and checked multiple times on this one.

 

new plugs didn't fix it. and all injectors sound identical.

 

must be the head - but i can't think of what is happening. excellent compression, spark, injectors are clicking and fuel smell.

What you checked and ANY engine would fire unless off time and even then be more a clue. Something the ECU sees tells it not to allow the intensity of spark required directly after it may start. Code check time. I wonder is some relay which powers the starter falls off to a bad contact and defeats ignition.

Swapping the intake manifold fixed it. How bizarre, I had no faith that would work.

 

I guess the fuel supply was hosed to that side? Injectors, regulator....?

 

No idea. Totally pumped it fixed it though.

Good thing you got the whole engine!!

Good thing you got the whole engine!!

yep, thanks dave for the engine, appreciate the help and am excited to be done with this joker.