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Code P0303 - #3 cyl misfire


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23 replies to this topic

#1 alia176

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Posted 04 November 2003 - 12:28 PM

Howdy folks,

I've been round and round on this fault code. Quick referesher - engine runs fine and usually this problem surfaces during hwy driving. While cruising along, the engine simply quites, throws the code. Or sometime, all of this is preceeded with engine shuddering then dying. My wife's nerves are shot due to the last time when her car slowed considerably and almost got run over by a 18 wheeler. As you know, their air horns can hit the nerves when they're directly behind you! :madder:

Anyway, I replaced the knock sensor and the ECU plus the usual maint items: plugs, wires, etc. After the ECU was replaced, the problem was gone for a few months. The ECU was used but known good from a Subi tech. If this is indicative of a valve dropping or such, I'll gladly fix it. But I hate to tear into it w/o substantial proof.

I can use some quick help on this one since my wife drives for her work carting kids around. She has lost total confidence in her baby. What's worse, she now has my SVX :cornfuzz:

Thanks a bunch.
'95 Legacy wagon
130k miles
no other issues!

#2 color-blind

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Posted 04 November 2003 - 04:00 PM

Is this vehicle a 2.2 or a 2.5 engine?

Does the vehicle actually stall out?

If the vehicles actually stalls/dies is it up a steep hill?

Are there other codes besides cylinder #3 misfire?

#3 alia176

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Posted 04 November 2003 - 04:06 PM

Aw crap, I wish I knew the engine size. I want to lean toward 2.2 but don't know for sure. Single overhead cams, if that helps!

The vehicle does indeed stall out. Can't tell you about hills since there aren't any around here! :-\

As far as other codes, if memory serves, there was a code that said something like "catalyst below threshold" or something similar. This occurred many months ago, on the old ecu.

Perhaps O2 sensors? I don't see the correlation though!

Thanks for your reply.

:headbang:

#4 color-blind

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Posted 04 November 2003 - 04:16 PM

Ok, sounds like you have two problems.

First remove the exhaust y-pipe. Inspect the guides on #3 cylinder. If they have dropped down you will need to replace the cylinder heads.

For the stalling I would suspect a failing air mass meter. Yet you need to go after the mis-fire codes first. Just to make sure the mis-fire is not causing other problems.

#5 1 Lucky Texan

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Posted 04 November 2003 - 06:57 PM

possibly a heat sensitive coil/igniter?
just a guess

#6 color-blind

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Posted 04 November 2003 - 07:01 PM

Originally posted by 1 Lucky Texan
possibly a heat sensitive coil/igniter?
just a guess



If they coil is failing there will usually be a mis-fire on more than one cylinder. For example there will be a misfire code for cylinder #1 and #2 since they are tied together. Other times you may get misfire codes for all 4 cylinders that too is usually coil failure.

#7 gbhrps

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Posted 04 November 2003 - 08:06 PM

My 97 OBW developed an inconsistent miss that the codes said was a misfire in cylinder #3. Plugs, wires and everything else checked out perfectly. Technician couldn't find the problem. Another Sub technician said try the ignition coil. Tested fine, but when it was replaced with a new one, the misfire problem disappeared for good.

#8 1 Lucky Texan

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Posted 05 November 2003 - 12:13 AM

maybe swap the coils around and see if the failure follows it to a new cylinder?

#9 alia176

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Posted 05 November 2003 - 09:02 AM

Originally posted by 1 Lucky Texan
maybe swap the coils around and see if the failure follows it to a new cylinder?



If this was the case, wouldn't the sister cylinder (#2) misfire as well? I'll try it just for ****s and giggles.

I'll drop the exhaust pipe and take a looksie. If the guide did indeed fall down, I wonder if machining out the hole then using a larger OD guide with the same ID would work? Just thinking out loud. Hate to plunk down for a new head at 130k miles. Unless these are dime a dozen!

Thanks.

Ali

#10 meep

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Posted 05 November 2003 - 10:07 PM

I've had a T-belt with 40,000miles stretch to the point of throwing a misfire code.

Does the stalling always happen at speed?

Not sure if the 2 are related, frankly. I'm wondering when the fuel filter was last replaced, and if the fuel delivery is involved.

Wouln't MAF failure throw a MAF code, and then enter "limp" mode, running very poorly but still running?

Auto or manual trans?

VWs experienced this with the relays that power the FIs. Almost need a few small lamps on the dash-- one from fuel pump, one from injector power--- to indicate if power loss is playing a part.

Mike

#11 frag

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Posted 05 November 2003 - 10:28 PM

Meep,
you idea is to my liking. How would you wire those lights? Would it be best to use leds or normal 12 lamps?
Would be a nice thing to know rapidly when things stop working what is involved.
I have a system (part of my home made anti theft system) that allows me to know immediately if voltage is going to the starer solenoid if the starter suddently refuse to turn over. I will immediateley know if it's the starter's relay or the starer's solenoid. But it's not a lamp nor a lead, just a contact to which i put a test light from inside the car.

#12 alia176

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Posted 06 November 2003 - 05:45 PM

Some answers for you:
T belt and fuel filter are brand new.

The stalling does take place at hwy speeds as far as I know.

I do like Meep's idea of LEDs for dx reasons. Should be easy to make up a bread board from Radio Shack and a few LEDs. They make 12 vdc LEDs. I'd need to make up a FIFO (first in first out) latching circuit to know which one shut down first. Since it's my wife's car, she can call me and tell me which one shut down first before resetting the ckt for the next time. Theoretically, all the wires are coming into the ECU, under the passenger carpet. So, just some vampire taps into the appropriate wires should be a snap.

It seems to me that I've heard the "valve guide dropping" theory somewhere else too and that's what I'm leaning towards right now. Should that be the case, I suspect there isn't a whole lotta room to remove the heads with the engine in situ, right?

#13 meep

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Posted 06 November 2003 - 06:08 PM

no need to buy the fancy 12V LEDs with internal resistors. Buy the normal ones and add a 1kohm resister inline. If you're loading up for a project, buy from digikey.com and save some $$.

Remember KITT? How 'bout a nice and pretty dash-mount, or better yet, overhead... :-)

Not sure the latch circuit is needed, but it's a good idea.

Mike

#14 frag

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Posted 06 November 2003 - 07:43 PM

I really need to be taught the basics here guys. If you wire in a led to know if voltage is present in a particular wire, what do you do: splice one lead in the wire and the other to ground ? That simple?

#15 99obw

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Posted 06 November 2003 - 09:25 PM

Originally posted by alia176
After the ECU was replaced, the problem was gone for a few months. The ECU was used but known good from a Subi tech.


That makes me think to a certain extent it may be related to the ECU. Perhaps a bad connector or ground. Maybe something external is damaging the ECU over time. Just WAGs.

I like the sounds of the homebrewed monitoring system. Your FIFO idea sounds cool too. I would be interested in hearing your thoughts. Maybe a synchronous FIFO with the write always enabled and a relatively slow clock to sample the signals. Maybe you could run the signals into the clocks of some D latches, then or the outputs together to control the enables. It's tough to reliably connect fast logic chips to noisy car signals though. Some hardware or software debouncing may make the results more trustworthy. It would be cool to use a microcontroller if your into that.

#16 alia176

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Posted 06 November 2003 - 11:19 PM

Yeah, let me just get my microcontoller and the assembler out of the closet and I'll get right on it :banana: I just gotta decide if I want a Motorola or an Intel microcontroller! Like I can actually remember how to program all that stuff from way back when!

But the ECU theory does make sense. Maybe I'm frying something and it just took a while to occur on this go around. I'll check for obvious signs.

Thanks for the inputs guys.

Ali













:headbang: :headbang:

#17 alia176

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Posted 06 November 2003 - 11:26 PM

Yeah, let me just get my microcontoller and the assembler out of the closet and I'll get right on it :banana: I just gotta decide if I want a Motorola or an Intel microcontroller! Like I can actually remember how to program all that stuff from way back when!

But the ECU theory does make sense. Maybe I'm frying something and it just took a while to occur on this go around. I'll check for obvious signs.

Thanks for the inputs guys.

Ali













:headbang: :headbang:

#18 99obw

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Posted 07 November 2003 - 05:24 AM

I am just wrapping up a relatively huge 8051 assembly language project at work. We are traditionally a motorola house though.

For home projects I prefer the PIC. They have a part called a 18F452 that kicks some serious butt!!!

www.microchip.com

#19 DAB

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Posted 15 June 2006 - 08:42 AM

I had a similar problem in my 94 Legacy...usually when there was some kind of load on the car, like accelleration, or high outside temp with air on. I learned to live with it until I was listening to car talk and reading a manual, and had done things like change plugs and wires. I changed the Coil pack...4 screws and ten dollars about a year ago and have had no problems since. I don't understand a lot of the issues discussed by the moer experienced, but I did try to sort this out, and even the dealer seemed stumped, so maybe this is why they sold the coil pack to me at wholesale. No problems since..though I have heard of other Legacy and Outback owners with the same problem...I even called the national Subaru center to see if there had been a recall since I knew several folks with the problem. We have this one fixed, and are driving a '05 for long trips.Maybe this will help...codes were of no help, even though the dealer extracted them at least three times at no cost.DAB
I've been round and round on this fault code. Quick referesher - engine runs fine and usually this problem surfaces during hwy driving. While cruising along, the engine simply quites, throws the code. Or sometime, all of this is preceeded with engine shuddering then dying. My wife's nerves are shot due to the last time when her car slowed considerably and almost got run over by a 18 wheeler. As you know, their air horns can hit the nerves when they're directly behind you! :madder:

Anyway, I replaced the knock sensor and the ECU plus the usual maint items: plugs, wires, etc. After the ECU was replaced, the problem was gone for a few months. The ECU was used but known good from a Subi tech. If this is indicative of a valve dropping or such, I'll gladly fix it. But I hate to tear into it w/o substantial proof.

I can use some quick help on this one since my wife drives for her work carting kids around. She has lost total confidence in her baby. What's worse, she now has my SVX :cornfuzz:

Thanks a bunch.
'95 Legacy wagon
130k miles
no other issues![/quote]

#20 Lawsonmh15

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Posted 16 June 2006 - 03:49 PM

Howdy folks,

I've been round and round on this fault code. Quick referesher - engine runs fine and usually this problem surfaces during hwy driving. While cruising along, the engine simply quites, throws the code. Or sometime, all of this is preceeded with engine shuddering then dying. My wife's nerves are shot due to the last time when her car slowed considerably and almost got run over by a 18 wheeler. As you know, their air horns can hit the nerves when they're directly behind you! :madder:

Anyway, I replaced the knock sensor and the ECU plus the usual maint items: plugs, wires, etc. After the ECU was replaced, the problem was gone for a few months. The ECU was used but known good from a Subi tech. If this is indicative of a valve dropping or such, I'll gladly fix it. But I hate to tear into it w/o substantial proof.

I can use some quick help on this one since my wife drives for her work carting kids around. She has lost total confidence in her baby. What's worse, she now has my SVX :cornfuzz:

Thanks a bunch.
'95 Legacy wagon
130k miles
no other issues!


What plugs? If other than NGK or Denso (i.e. Bosch) replace and your issue will disappear.

#21 nipper

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Posted 16 June 2006 - 05:52 PM

For some reason missfire #3 cylinder seems to be the death wale of an ignition coil on subarus. I suspect the actual prblem is #4 side of the coil, and the #3 side is getting the higher voltage at the wrong time

Just an idea, but i would try a coil

nipper

#22 1 Lucky Texan

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Posted 16 June 2006 - 11:30 PM

whoa - a zombie thread.




;^)



Carl

#23 Lawsonmh15

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Posted 17 June 2006 - 11:34 AM

For some reason missfire #3 cylinder seems to be the death wale of an ignition coil on subarus. I suspect the actual prblem is #4 side of the coil, and the #3 side is getting the higher voltage at the wrong time

Just an idea, but i would try a coil

nipper


Yeah. The more I think about it, it seems as though you get both 301/303 302/304 if it's the Bosch issue. Do what Nipper says, I believe he has got the better idea.:)

#24 unibrook

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Posted 04 June 2007 - 09:09 AM

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.




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