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Old 02-23-2007, 05:37 PM   #1
dpenn
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Default causes of P0301 misfire cylinder 1

I have a blinking check engine light...i got codes scanned and came up with P0301...i have already tired replacing the plugs and coil pack. when i disconnect the wire running to the coil pack while the engine is running there is no difference...but if i disconnect any other coil pack it seems like the car will stall...I have checked the coil pack and spark plug and are making sparks...the spark plug for cylinder 1 smells strongly of gas...I dont know what else to check...
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Old 02-23-2007, 06:16 PM   #2
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Maybe the ignition wire going to that coil pack is bad. But do yourself a favor and stop swapping parts to troubleshoot and remedy. That can get expensive.

Logic tells me that it would be the next item in line to suspect if you are backtracing the issue from the sparkplug back. Use a multimeter and try checking the contact points at each connector from the coilpack back. If there is no power at the coil, check the other end of the lead for power. If no power there, the keep backtracing until you find power... and that will tell you where the problem lies.

Proper troubleshooting is the difference between a good technician and a poor part swapper.
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Old 02-23-2007, 06:21 PM   #3
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when i connect a spark plug to cylinder 1 it sparks...so it seems the connection and coil pack are good...
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Old 02-23-2007, 06:55 PM   #4
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Do you have spark at all of the plugs? If so, then it might be timing, fuel, or (worse) mechanical like a bent or stuck valve. Try a compression test to make sure everything is sound and if so, I'd take it to get some data logs. The log file will tell you enough about what is going on to find the source.
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Old 02-25-2007, 02:29 AM   #5
dpenn
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so the next step to take would be to get a compression test kit...
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Old 02-25-2007, 01:53 PM   #6
chrisarella
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Why not take it to a shop and get the compression test and the data logs in one place.
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Old 08-23-2007, 10:24 AM   #7
BlackEyeII
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Default There are several threads

You may want to swap injectors in two cylinders there are several threads about injectors causing this.
R.
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Old 08-23-2007, 11:18 AM   #8
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Causes of misfire codes are as follows.
1-bad spark plug, coil, or coil boot (carbon tracking around outside of spark plug, you can see this on the out side of the plug, replace the plug and coil boot if any tacking at all) also check that you have power to the coil, and that the ECU is grounding it.
2-vacuum leak (look for any hoses or possible problems on the intake runner to the cyl. that is misfiring)
3-injector (check that the injector is firing, you can use a stethoscope, if it is not clicking, you will need to check that you have power to the injector and that the ECU is grounding it)
4-compression (perform a compression test on both cyls. on the side that has the misfire, if both are around the same, do a running compression test, remove the check valve from the compression gauge and install it and start the engine, you need to do it on another cyl. to compare readings if low you may have a sticking valve, broken valve spring, or such. I have started doing this test on most misfire problems) we don't even use a vacuum gauge anymore.

5- last is when it starts to get hard, I would recommend taking it to a pro at this point. we start looking at O2 readings, fuel trims and the like. flow testing injectors, and possible head gasket issues. carbon on the intake valves (although we have not seen this to be a issue with subaru)
I am sure I have missed a few things, but this is the way we go about troubleshooting misfires.
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Old 08-24-2007, 10:21 AM   #9
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Default Awesome..

So far I have just taken a look at the plugs. They looked like they are in pretty good shape. No fouling, good beige color on diode, with a dry black soot around the collar. No small metal balls or anything fouled or damaged.

I also swapped plugs from 1 to 3 on that side. The car still misses, I am going to drive it a bit today to see if the CEL indicates cylinder 3 now, if not I will check all the wiring to the injector, and coil-pack.

I did schedule a compression / leakdown test on Wed next week, as well as some diagnostic work on the misfire/coilpack.

Car seems to run strong dispite the miss. It seems to clear up under more loaded conditions.

R.
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Old 08-25-2007, 01:13 PM   #10
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my 2005 sti just started showing misfire on cylinder 1 let me know what you come up with, i will do the same.
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Old 08-25-2007, 08:25 PM   #11
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Quote:
Originally Posted by BlackEyeII View Post
You may want to swap injectors in two cylinders there are several threads about injectors causing this.
R.
try this
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Old 08-28-2007, 01:21 PM   #12
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i just throught a cel, but its not blinking. and i checked the codes and they are P0301, P0303, AND P0300. how hard was it to change the spark plugs???
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Old 08-29-2007, 12:29 AM   #13
BlackEyeII
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Default Easy...

I think it is fairly easy.

Takes me about a half hour taking it slow. No big deal.

R.


Remove airbox, remove wiper tank, battery > pull coil packs two at a time and swap out each set of two plugs.
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Old 09-08-2007, 10:58 AM   #14
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i don't KNOW if this will help anybody but my CEL cyclinder 1 misfire was solved by---fixing the exhaust leak i had between my catless down pipe and my stock exhaust. a piece of the gasket had broke off and there was a small leak that was slowly getting bigger and bigger.
i am stage 2 but as said with stock cat back, and catless invidia DP
when i got working on it, i did not think the exhaust leak would fix it, but may have.
the guy helping me also recommended running dextran 3 transmission fluid through the gas tank;
1 quart in a full tank of gas and then when down to 1/8th of a tank refill to FULL again with premium of course, to dilute and get rid of it. It made it run better, not positive which thing fixed it but i lean towards the exhasut leak---SOOO
you guys with CEL cyclinder 1 misfires might want to sound off on what exhaust's you have???? just a thought
i am NOT recommending the transmission fluid to anybody--just saying what he said and what i did
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Old 09-09-2007, 05:21 AM   #15
xXFiendXx
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Threw the same code in my 02. Took it to suby and it was a faulty o2 sensor. Same symptoms and code!! Hope that helps
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Old 09-13-2007, 01:16 AM   #16
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fixed exhaust leak = no more CEL misfire
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Old 09-13-2007, 02:47 PM   #17
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NGK Coppers gapped to .028 fixed my misfire issues.
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Old 09-14-2007, 10:23 AM   #18
BlackEyeII
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Default hmmm....

I am happy that your exhaust leaks cured your misfires, but I just don't see how something that far down stream can affect 1 cylinder and not them all.

<doubter> Yeah sorry I could see something right at the head, like a manifold leak...

Doesn't matter though good for you.

I am going to start looking at the injectors for mine since they are the component that is "New" to that scene on my subi.

R.

Plug gap may be a factor, but I will go there next since my iridiums look good.
R.
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Old 09-19-2007, 04:03 AM   #19
Crazy650
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did you come up with something on this? i have to do the swap of the coil pack tommorrow on a 04 sti
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Old 09-19-2007, 10:00 PM   #20
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Quote:
Originally Posted by crampfan View Post
Causes of misfire codes are as follows.
1-bad spark plug, coil, or coil boot (carbon tracking around outside of spark plug, you can see this on the out side of the plug, replace the plug and coil boot if any tacking at all) also check that you have power to the coil, and that the ECU is grounding it.
2-vacuum leak (look for any hoses or possible problems on the intake runner to the cyl. that is misfiring)
3-injector (check that the injector is firing, you can use a stethoscope, if it is not clicking, you will need to check that you have power to the injector and that the ECU is grounding it)
4-compression (perform a compression test on both cyls. on the side that has the misfire, if both are around the same, do a running compression test, remove the check valve from the compression gauge and install it and start the engine, you need to do it on another cyl. to compare readings if low you may have a sticking valve, broken valve spring, or such. I have started doing this test on most misfire problems) we don't even use a vacuum gauge anymore.

5- last is when it starts to get hard, I would recommend taking it to a pro at this point. we start looking at O2 readings, fuel trims and the like. flow testing injectors, and possible head gasket issues. carbon on the intake valves (although we have not seen this to be a issue with subaru)
I am sure I have missed a few things, but this is the way we go about troubleshooting misfires.
6- Change out your front (air/fuel) O2 sensor. <---- If you've been running leaded gas, gotten coolant onto the O2 sensor or it's been a while, it's time to replace it. A lot of people overlook the importance of this little culprit.

Goodluck,

Ric-
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Old 09-21-2007, 10:31 PM   #21
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I'm back, the new gasket between the down pipe and the cat back fixed the problem until IT developed a leak and low and behold the CEL misfire on cyinder 1 came back, tightened it till i can get a gasket to replace it. but after i tightened it and reset the code, cel has not gone again.

I agree i really didn't think that was the cause, but it sure looks like it to me, NOW fyi

Last edited by jr4jc; 09-21-2007 at 10:55 PM.
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Old 02-19-2008, 01:06 AM   #22
rafacz2002
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same thing happened here...i replaced coils because i had a misfire in all four cylinders... after that had misfire in first and second cylinder...got new plugs had them replaced and gapped to .028 and it runs fine, no cel or anything..
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Old 02-19-2008, 12:41 PM   #23
sideburns
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I had a cylinder misfire a long while ago (somewhere near 50k). I'm at about 112k now (and getting an oil change today) and I got a CEL over the weekend. It was another cylinder misfire (0304).

Two months ago, I had driven with a bad O2 sensor and then a bad exhaust temp sensor for a week or two (don't remember the CEL #s). Both the O2 sensor and exhaust temp sensor were replaced. Could this misfire be associated with these? Ric just said that the O2 sensor could be involved with the misfire, I'd just like some more info.

My 2002 WRX is completely stock. Let me know if you need more info.

Thanks,
Mike
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Old 02-26-2008, 10:31 AM   #24
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I got the same blinking cel that started last week Thrusday after reversing out of a driveway with a steep incline. After driving around a bit I had the codes pulled and I got P0301 and P0303, cylinder misfire on 1 and 3. After changing spark plugs and gapping them to .30 I got cylinder 3 misfire. Since the coil packs are on the easy side I swapped 1 and 3 and cleared the codes. Drove around and got the blinking light again. Now it's cylinder 1 misfire. From what I've read some people have had these codes from fouled up gas filters, dying fuel pumps and bad O2s. I really haven't read a lot of problems with the coil packs but I've got mine on order from the dealer and I hope it fixes the problem. Good luck to the rest you guys. I also replaced the fuel filter since it probably had over 60000 miles on it. I should post a picture of the plugs for show. It was horrible.

Los
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Old 03-06-2008, 03:45 AM   #25
howboutthemapplz
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bump, i am misfiring in #4. i need to know which cylinder this is, i have read the manual and cannot find out.

anyone else currently having this problem?!? i need some help!

ive switched coils around, changed plugs, fuel pump is working, installed deatsch werk 740cc injectors.
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