# Cylinder #2 Misfire & Knock Sensor



## dorough (Nov 26, 2010)

Hi all,
I'm visiting my elderly mother who drives a 1995 Nissan Maxima. She said the CEL is on and it's been running very rough and gas mileage is down to about 12mpg. She has been putting 87 octane gas in it for years. 

I pulled the codes this morning and got P0302 (cylinder #2 misfire) and P0325 (knock sensor). I drove it and it's definitely running rough, but a 'steady' rough - like a cylinder is indeed consistently misfiring. It's not sporadic. At highway speed it does seem to smooth out just a bit, but not a lot.

At first I considered just replacing the knock sensor. But I'm not sure if the knock sensor is being tripped by another problem or if it's the problem itself. After feeling the 'steady' misfire, I'm curious if the problem might be a bad ignition coil on cylinder #2.

Any ideas here? Thanks in advance.


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## jdg (Aug 27, 2009)

Check the plug, check the coil, check the wires, check the injector.
If nothing shows up, swap the plug/coil/wires/injectors to another cylinder and see if the problem comes up in another cylinder.


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## dorough (Nov 26, 2010)

jdgrotte said:


> Check the plug, check the coil, check the wires, check the injector.


Considering that the plugs were just replaced and that there are no wires - there's a coil for each plug - would you suspect that the problem is in the #2 coil rather than in the knock sensor?


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## jdg (Aug 27, 2009)

No wires - DOH! - I knew that...
Actually, I'd suspect the injector itself. Plugged injector = lean mix for that cylinder. Lean mix's ping easier and so on.
But the coil is a lot easier to swap around...and I'd swap plugs around too. Never know when one might have cracked porcelain, arcing to a ground, and not know it (sometimes ya just can't see that sort of thing).


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## dorough (Nov 26, 2010)

Suspect the injector moreso than the coil?


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## jdg (Aug 27, 2009)

Total toss-up between the two, and might not even be the problem. But again, I think the coil is easier of the two to start with.


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## dorough (Nov 26, 2010)

Well, I lost the coin toss! Spent $80 on a new coil & that didn't solve the problem. Still getting a cylinder #2 misfire code. So now I guess about all that's left is the fuel injector, right? I suppose I should look at replacing that - after I let a tank or two of high octane gas & the fuel injector cleaner run their course to see if by chance that makes any difference (but I suspect they won't). The only culprits left are the injector and the ignition control module, right?


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## jdg (Aug 27, 2009)

That sucks...but again, total toss up.
Problem with running fuel injector cleaner is that it's not injector specific and it'll get diluted out, but couldn't hurt. I'd say swap the injectors around, maybe look at the tips while they're out...
Module? Couldn't tell you. I would think the ECU could detect a bad module triggering output, but I'm not sure on that one at all. So, I'm left with the fuel injector itself.
Have you done a compression check at all? Just to rule out something bad like a burnt valve or something?


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