Yet another po303, po304 question

[nelstomlinson]

This is in my 2002 Legacy four-banger.  The short of it is that I've changed the plugs (new NKG, gapped at 0.044), new plug wires (NKG again), and swapped in a coil from a car that didn't have this particular error, and still I have a consistent po303 and po304. 

When this started, I had misfires on all four cylinders.  I checked the plugs, and they looked awful, so I put in new plugs.  All was well for a day or so, then the problem came back. 

I swapped in a coil from a 2001 Impreza which was a good runner until its head gasket went.  All was well for a day or so, then the problem came back. 

Then the new wires arrived from Rock Auto, so I put them in.  All was well for a day or so, then the problem came back, but now it's only cylinders three and four that are misfiring.  

I'm starting to think I have some non-ignition problem which might be intermittent.  What should I try next? 

[1 Lucky Texan]

is there oil on the plugs or their boots?

[brus brother]

What Lucky said.. Is the valve cover leaking/spark plug seals hard and leaking? Might be coincidence that 3 and 4 are opposing cylinders.

LINK here and posted by Bagshaster he describes similar opposing cylinder codes (1 and 2) and his turned out to be a bad tensioner!

Edited March 16, 2020 by brus brother

[nelstomlinson]

No, the seals are still pretty good, no oil in the spark plug wells, the plug wires come out clean not oily.  These are new plug wires, only a week or so old.

[brus brother]

properly torqued plugs? without torque wrench tighten until you feel them bottom then 1/4 to 1/2 turn to crush washer.

[montana tom]

Could be dirty  injectors.

[nelstomlinson]

Brus, yes, I turned them in until I got some resistance, then about another 1/2 turn.  Threads must be pretty clean down there, because they went easy until the washer contacted the head.

Montana tom, I'm starting to think that it's fuel not ignition.  On NASIOC I found a little list of causes of misfires that included things like fuel injectors, a bad-ish knock sensor and a dirty MAF.  That last one is easy enough that I'll try it after work.  Is there a way to check fuel injectors without special tools?

 

Edited to add that I have a 2001 Impreza with a blown head gasket that I'm robbing parts from.  It ran pretty well before the head gasket went.  I could rob injectors from it?

Edited March 16, 2020 by nelstomlinson

[1 Lucky Texan]

does it idle rough? if so, try a stream of propane from a handheld torch or some ether-start into the intake. If idle smooths-out, that may point to a fueling issue.

check all grounds.

[montana tom]

They make machines to test injectors.  I've never had access to one.

Here's what I do.  Remove each injector.  Place a foot long rubber tube (fuel line) over the inlet.   Fill tube with liquid , I generally use Kroil but gas works , it just tastes crappy.

This is easier with a helper but I do it alone more often than not.   You will need power and ground wires attached to the battery.  

Apply power and ground to the injector terminals  while blowing pressure into the fuel line.   If your injector is clean you will get a spray of liquid ,if they are shot  liquid will dribble, spit out .  Its very obvious when you find a bad one.    

If you look for used ones. be aware that automatics and standards use different injectors.

[nelstomlinson]

Lucky and Montana, those are both good ideas.  I'm back to work through Thursday, will try to get back onto this project in the evenings.  The spring thaw is starting soon, and we've had to start canning the food that was frozen outside all winter, so as usual, everything is demanding attention at once.  Spring thaw is at least a nice problem to have.

[nelstomlinson]

I ran out of time, took this to a local mechanic.  He found that the heater on the front oxy sensor was defective, and replaced it.  That was definitely a problem, but not the only problem.  The car now starts fine when cold.  Still getting intermittent misfire errors, but since it's running better, I still don't have time to chase them down.

I'll update this once I make some progress.

[1 Lucky Texan]

hmmm, wonder why that didn't throw a code?

 

[Rampage]

On 3/16/2020 at 12:03 AM, nelstomlinson said:

I've changed the plugs (new NKG, gapped at 0.044),

Pull all 4 spark plugs and keep them in order. See if they have a four digit number stamped on the hex. If not then they are FAKE NGK plugs.

Go to Google.com and type in Fake NGK spark plugs.

If they are ok, swap 1 and 3 then 2 and 4. If you still get 3 and 4 misfire check the fuel injectors. The FSM says 5 to 20 Ohms. That seems like a wide range to me, so unplug the connectors and compare all 4. See if 3 and 4 are different than 1 and 2.