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Forums > > 05 Sentra Misfire on Startup- Code P0300
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Old 11-29-2009, 09:08 AM
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Default 05 Sentra Misfire on Startup- Code P0300

My 2005 nissan sentra with a 1.8L engine has been having a misfire problem on startup for about 6 months now (I was going to let it go and hope it went away). The car starts fine (on the first try) but misfires for 3-5 seconds on startup almost every start. After the initial 3-5 seconds the misfire goes away and the car runs fine. The check engine light came on and I read the codes with a scan tool. The code came back P0300 - random misfire.

I changed all the spark plugs about 3 weeks ago. No change in the startup condition, but now the car misfired really badly on the highway. Got back and had two codes, P0300 and P0302. Swapped #2 and #4 plugs, cleared the codes, test drove, now P0300 and P0304. figured bad spark plug. Replaced the plugs again. Car now ran fine on highway, but still misfire on startup and P0300 code.

When i changed the plugs, the #2 cylinder spark plug was very hard to get out, and looked much worse than the other cylinders. See the attached pic. Mind you, these plugs have about 1k miles on them. I tested the compression on the engine- #1-158, #2-145, #3-165, #4-165. Nissan spec says 168 min, 190 standard, so they were all low. I might try retesting the compression, but im pretty sure i did it right (I screwed the tester as tight as i could get it into the spark plug hole).

The coolant level in the car has also been low- ive had to top it off about once a month or so. Do you think its a head gasket? Would buying a cooling system pressure tester and seeing if the cooling system holds pressure tell me anything additional?

I shined a flashlight down into the cylinders when i had the spark plugs out to test the compression- the #2 cylinder piston top was much shinier than the others.

Sorry for the long post, thanks for any help!
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Last edited by tman17m; 11-29-2009 at 09:52 AM.
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Old 11-29-2009, 12:05 PM
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Swapped #2 and #4 plugs, cleared the codes, test drove, now P0300 and P0304
Do you think it is possible that you may accidentally swap the coil as well? The problem sounds like a bad ignition coil and Nissan has had many ignition coils issues.
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Old 11-29-2009, 12:46 PM
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after i had the P0302, i first tried swapping the #2 and #3 coils. cleared the codes and went for a test drive. car still misfired, read the code and it stayed at P0302. At this point i swapped the #2 and #4 spark plugs, cleared the codes and went for a drive. code moved to P0304. thats how i determined it was a spark plug

i left this part out (about swapping coils) because it didnt help me diagnose the P0300 code. presently, i am only getting the P0300 code which doesnt help me since i cant pinpoint a specific cylinder. i could do an ignition coil test per the service manual, but i havent done that yet.

edit: I could be wrong, but wouldnt a faulty ignition coil make the engine miss all the time? I didnt do the ignition coil test because after the initial startup and misfire, the car runs fine, so i ruled out the ignition coils.

Last edited by tman17m; 11-29-2009 at 12:50 PM.
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code, misfire, p0300, sentra, startup

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