P0302/P0304 Misfire Codes

[Mikevan10]

1997 Legacy 2.2 Manual Trans California Car Non-Turbo

 

I am very sorry to be back with more OBDII woes. The CEL/MIL had been off for over a week (after finally solving the EVAP sys. P0446 problem). During that week the car was driven about 10 miles daily, mostly around town. Then, my wife took it on a 200 mile round trip last night. The MIL came on after she had driven like 8 miles. She had stopped for gas and then, I believe while waiting at a light, the MIL came on. She proceeded with her trip and, of course, the MIL sayed on.

 

I scanned the codes this morning. Here are the results:

 

Two DTCs: P0302 (cyl 2 misfire) and P0304 (cyl 4 misfire)

 

Freeze data: P0302

713 rpm

Calc load=3.1%

MAP=8.3" Hg

Coolant=201 deg F

LT FTRM1=0%

ST FTRM1=0%

Veh speed=0 mph

Fuel Sys=closed

 

 

Plugs were replace (NGKs) in April this year

Wires are 2 years old (OEM)

Coil is 2 years old

 

Besides replacing plugs and wires, are there any suggestions?

 

Does anyone know if the MIL comes on immediately upon the first time OBDII thinks it senses a misfire or does it have to think it detects it more than once or over some period of time or miles?

 

Very frustrated with this Subaru (actually with the OBDII system). I am driving around with an expired inspection sticker and I wonder if I'll ever resolve it. I could not get the car inspected immediately after I got the P0446 problem solved, which extinguished the MIL, because, of course, OBDII was not "ready"!

 

Thanks again,

Mike V

[ferret]

Mike, few things...

 

MIL is set IMMEDIATELY if Misfire is continuous. MIL will also flash to let you know this.

 

OR MIL is set after 2 driving cycles of non-continuous same cylinder misfire.

 

Does the car idle rough? It can be spark but you already changes the plug, wires and coil. Also cyl 1 & 2 share the same coil as do 3 & 4 in the coil pack, so right now I wouldn't suspect the coil pack.

 

Cyl 2 & 4 share the same fuel rail and it's common for these to exhibit misfires just after a fuel filter was replaced. We clear the code and that time usually doesn't return. Maybe dirty, leaky injectors?

 

Cyl 2 & 4 share the same +12v power lead on that side of the motor. The ECM/ECU once again 'grounds' the other side of the injector to make it fire, so there are separate leads to the ECM/ECU for each injector.

 

Could be a loose timing belt, not getting the proper signal from the cam sensor to fire the injector, or an intermittent cam sensor or fuel injector. You can swap them to the other side and see if the DTC changes.

 

That's just a start.....know it's frustrating, but a misfire means the Crank sensor didn't see a pulse XXms after the cyl received spark, so it can be mixture, spark, timing, valves, almost anything that prevents a cylinder from firing......Good Hunting.....

[Mikevan10]

That's what I was afraid of. It could be almost ANYTHING!

 

And, to answer your question, the idle is not dead smooth.

 

This is supposed to be my wife's Mom car. Not an expensive hobby.

 

Mike

[nipper]

Check the connectors to the coils. When you replaced the coil, where did the replacement come from?

Could it be the ignitor that is at issue? The 2-4 are two differnt coils, so i would look to see whats common to them.. Also is there any liquid inside the spark plugs holes that may be dreating a path (longshot really longshot).

After that i wouldnt know where else to look at except at the wiring harness and connections. You go from the ECU to the ignitor to the coils.

 

nipper

[Mikevan10]

The coil pack was installed by the dealer (don't get me started).

 

I already cheched the connectors at both ends of all spark plug wires. Nice and shiny and seem to snap in nicely.

 

Is there a good way to test injector function, including leak tightness?

 

By the way, I cleared the codes yesterday morning and then went on a 200+ mile trip. The CEL did not come on. When I got home, I interrogated OBDII with the scanner: No DTCs (of course) and only one non-ready item (catalyst mon is incomplete). So I believe at this minute it should legally pass PA emmissions inspection. So I will try to get it inspected ASAP although I expect that the light will come on before I can get the deed done...

 

Mike V

[Mikevan10]

I just got my emmsions inspection sticker!!!

 

Now I am good to go for another year regardless of what the MIL/CEL/OBDII does. Perhaps I will cut the wires to the darn light or put a piece of tape over front of it! Just kidding. I know there's lots of folks around here who actually think OBDII is a good thing and they we should obey it.

 

I expect that the light will come back on soon and that I will have a misfire code or two. I have good intentions to try to find the root cause but I do not intend to shotgun expensive parts into this thing. Other than a less than perfect idles it runs fine and fuel economy is good like it has always been.

 

Thanks to everyone who helped me get through this crisis either with their thoughtful suggestions or even just their empathy. There are some very knowledgeable folks here. But I just can't help being critical: This resource would be alot better if everyone would follow through and post the final resolutions to their problems.

 

Thnaks again.

 

Mike V.

[BigMattyD]

OBD II is great as long as everything is working when you need the car inspected...

 

Actually, having a somewhat universal system for all types of automobiles is a good thing, and the fact that you can use aftermarket readers to monitor/diagnose is excellent. Being able to read sensor outputs is also cool.

 

But having to have it working at the time of inspection can be a hassle, as you found out.

 

Matt

 

P.S. I also think people should update with solutions to their problems, and it seems that a lot of people already do..

[cookie]

Many things can cause misfires, but carbon build up is a cheap one to check. You can use Seafoam or just trickle water in like we used to in the old days.

Then there is always sprinkling water over the plugwires at night to look for sparks.

[OB99W]

Many things can cause misfires, but carbon build up is a cheap one to check. You can use Seafoam or just trickle water in like we used to in the old days.[...]

Cookie, you're revealing your (approximate) age, and since I know what you're referring to, I suppose mine is now showing as well . "Steam cleaning" was a bit easier when just removing the air cleaner exposed a nice vertical carb throat (okay, you may have had to open the choke). I've never tried it on a more modern car, but maybe a spray bottle able to put out a large enough volume of water might work. Besides regulating the amount you use, it helps if you develop the knack of modulating the throttle at the same time. At least water doesn't tend to smoke up the whole neighborhood like the chemical cleaners usually do.

[OB99W]

Mike, congratulations on passing inspection.

 

I have mixed feelings about OBD-II. We need a way to determine what the engine management systems are doing, but the DTCs can certainly be misleading at times, and manufacturers' data seems to have more than a reasonable number of errors.

 

If we're taliking about using OBD-II controlling a MIL/CEL (and whether your state will let you drive the car based on that), I have stronger feelings. I'm sure there are people on the forum who'll disagree, but in my opinion a car that pollutes (significantly) more than necessary isn't something to ignore. I realize that some have made this into a political issue, but our health and that of everything on the planet is directly or indirectly related to things like auto emissions, and that shouldn't be a political football.

 

Thanks for your feedback to the forum. I agree that it would be very useful if more participants got back with info on the outcome. If we got things right, it's nice to get a pat on the back, besides the obvious value of confirming an approach to anyone doing a future search. If we were mistaken or missed something, it certainly helps to know that as well.

[unibrook]

Hi Mike Van,

 

Yes, please do post what the cure/problem was for your codes. I am having the same problem on my 2001 Forester with 83k on it. thanks.

[unibrook]

My fix turned out to be the front 02 sensor. Here is my review from a diff thread: I have a 2001 Forester L with 85k miles on it. I have been chasing an intermittent hesitation under load problem for the past year. Only occurred when engine was warm. The front 02 sensor had been replaced once at 40k miles. I suspected it again this time, but since the only codes thrown had been cyl's 2&4 misfire ( p0302 & p0304) I assumed it must be ignition related. So I replaced plugs and wires 8 months ago...no effect. Did the dollar bill test over exhaust pipe, it was fine. Misted the coil, no sparks. I mentally sort of ruled out the fuel filter since it only happened when the engine was warm. Finally, a week ago while cruising on hwy at 65 mph, I felt the hesitation again (I wasn't even accelerating this time) and a new code was thrown....p0172. AutoZone read it for me, I described the symptoms to the guy and asked if he thought it might be the front 02 sensor. He said, "absolutely." So I decided to replace it next. Cost me $100.75 incl tax for the oem part# 22791aa00a from Cityside Subaru. I asked the Parts guy there if his experience was that this model engine needed a new front 02 sensor every 40k miles. He said, "no, these sensors are good for 100k miles." Well, bullsnot on that. I replaced the new front 02 sensor in 1 hour reaching from the top over the passenger side of the engine using an adjustable wrench. Be sure to use the thread lube so you can get it out easily next time.....after another 40k miles. I took out the air channel assembly first for better access. That seems to be the fix. No further hesitation since. Car runs like new.