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Discussion Starter #1 (Edited)
Hi All,*A little background. Car was diagnosed, cleared, and rediagnosed with P0303 cylinder 3 misfire several times. I swapped out coil pack 1-2 with 3-4. Same problem. Changed spark plugs. Runs beautifully for a couple thousand miles, until...*So a couple days ago I get the same P0303 cylinder 3 misfire.*What could be the cause? Plug wires? Something is causing the plug to foul maybe? Edit: No plug wire for cylinder 3What are the next logical diagnostic steps?*Thanks for your help,*-V
 

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You've changed the plugs. You've swapped coil packs. Next, I would look at the spark plug wires. What kind of plugs did you use? These cars are pretty finicky about anything but the original ND plugs. NGK would work good, also.
 

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Discussion Starter #4
Hmm, I used the stock plugs from the Toyo dealer. I think I'll have to check the coil packs again. I may have gotten them mixed up somehow. If that's not it I don't know what the heck is going on.
 

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Discussion Starter #5
Freeze Frame Data

Fuel Sys 1 CL
Fuel Sys 2 CL
Calc Load(%) 16.0
ECT(°F) 167
STFT B1(%) -2.3
LTFT B1(%) -9.3
STFT B2(%) 0
LTFT B2(%) -10.9
Eng RPM 867
Veh Speed (mph) 0
IAT (°F) 42

Maybe someone who knows a lot more than me can do something w/ this info?

Thx,

-V
 

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Hmm, I used the stock plugs from the Toyo dealer. I think I'll have to check the coil packs again. I may have gotten them mixed up somehow. If that's not it I don't know what the heck is going on.
You can't mix up the coil packs, they're all the same part no. It's bizarre that you changed the plugs and it ran great for a while. Try looking under the hood when it's dark and see if you can spot some arching going on. I would still look into new plug wires.
 

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When you pulled cylinder 3's plug what did it look like? was it fouled more than the other plugs?
 

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Discussion Starter #8
When you pulled cylinder 3's plug what did it look like? was it fouled more than the other plugs?
When I originally pulled the plugs I couldn't see any difference from cylinder to cylinder. I had also checked the coil pack resistence per the service manual and it seemed fine. I changed the plugs because it was the cheapest thing to do and worth a shot. I used the Denso plugs recommended in the service manual. Like I said, after the plug change the car ran great. I also cleaned the throttle body as much as I could. I did a road trip to Denver shortly afterward and got close to 30mpg.

Previously, I had cleaned the MAF, air filter, and run injector cleaner several times without success. Also, I looked for fluid around the plug and saw no evidence.

Plug wires would be cheap but I haven't done that because cylinder 3 sits right under the coil pack and that doesn't make sense to me. I might do it anyway. I think I just need to tear things apart again and look very closely. I hope there's nothing wrong with the igniter module 'cause that thing is like $450 :(.

Any other suggestions out there? Thanks for the help guys,

-V
 

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Pull the plug again, see if it's fouled with oil or anything. Pull the plug take a picture of it and post it up so we can see. You spark plugs are the window to you combustion chamber and your best insight as to what is going on.

BUN
 

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Agreed with above, I have seen a clogged injector cause a misfire that you swear up down left and right is an ignition problem until you see the plug is bright white from running lean and then realize you have a fuel problem! Youve just scratched the surface myfriend. keep digging.
 

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Discussion Starter #11
Thanks guys, I will pull the plug and post a pic here in the next couple days. I've been out for the holidays and had no time!
 

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If it looks clean and no oil or antifreeze is on it then the next step is to check for fuel since we can already rule out ignition. Get a noid light and check to make sure the injector is gettin a signal then swap the injector to see if the misfire now occurs in a different cylinder.

BUN
 

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Discussion Starter #13 (Edited)
Spark plug inspection

Ok guys, thanks for your replys.Here is a look at my plugs.I pulled the 3 and 4 for comparison.


I don't see anything but if you all do let me know.

I've got to put it back together to move the vechicle but I guess the next step is to pull the injector. I haven't done this yet and don't know how but I've got the service manual and the "search function".

Oh yeah, noid light = solinoid light? Sorry not familiar...

-V
Oh, btw I was wrong about the plug wire thing as the coil sits on cylinder 4. Plug wire and coil pack resistances come out in spec.
 

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I had the same problem a while back and I think it might have been bad gas, I ended up rebuilding my injectors and changing my sparks with the denso iridiums and also getting a new MAF sensor. After all that my cylinders still showed a misfire. The cause ended up being my SUN VOLTAGE STABILIZER because it was grounded where the ignition module was. Bad gas could also be it so maybe you might want to drain the tank and fill it with cheveron or something. I did end up using seafoam to clean the injectors and gas tank. Good luck.
 

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Discussion Starter #15
I'm sure I found the problem...

Tonight after I put things together (I swapped 3 and 4 plugs) and ran the vehicle, the problem persisted. However, with the hood open I noticed a ticking noise. Upon further inspection, I noticed a spark. It turns out that the spark from the #3 plug was gapping to the intake manifold. This must mean that the plug wire is bad. I'm gonna replace it and hopefully my problems go away. Thanks again for the help everybody,
-V
 

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I am having the same problem with the po3o3 code. I would step on the gas and the car would just choke and then like someone flipped a switch it took off. so I changed the plugs and noticed cylinder 3 was wet. i then ordered injectors and replaced those today. The car runs good until it see's load. then misfire same 303 code. i then switched the coil packs and drove. same 303 code again. cleared the code and let it run in the garage for 15 min ran great no codes. put it in gear and held the brake no studder spun the tires. not sure what next.

Oh i think #3 is a coil pack and not a wire so you might need a coil pack.
 

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Discussion Starter #17
I replaced my plug wire and everything is great now. #3 plug definitely has a wire. #2, #4, and #6 sit under the packs. Anyway, it was quite obvious once I noticed the spark arcing to the throttle body out of the boot.

So, you've replaced the plugs, coil packs, and injectors. For $16 I'd replace the plug wire. It's called plug wire #1 btw.
 

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+ rep for u...

This should be added to a database if more people are having this issue.


d
 

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i bought new wires and NGK plugs today. I will install those and let you know what happens. Good to hear you solved your problem. Did you actually see it arcing or hear it?
 

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Discussion Starter #20
i bought new wires and NGK plugs today. I will install those and let you know what happens. Good to hear you solved your problem. Did you actually see it arcing or hear it?
I could actually see it (and hear it). It was arcing right where the long bolt connecting the throttle body to manifold gasket is located (bottom one). Good luck...
 
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