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Discussion Starter · #1 · (Edited)
Hi All im new on here but had a 07 altima 2.5s for about 3 years

i recently had a #1 cylinder misfire problem

(post issue ) i replaced all coil packs , all plugs ,
coil harness plugs on 1&2 cyl, , but still had the issue. (yes i swaped the plugs and packs no change .
so i figured i would replace fuel injectors as i thought air and spark was not the problem. as well as valve cover and gasket w/ pcv valve (had a history of leaking into plug holes )

now i have only missfire on cyl # 2 and it now occasionally goes to a multiple misfire. then back to just cylinder #2 (with or without a engine light )

no coolant issues , good compression , no white smoke.
(and i have a additional 5 wire ground attached )

any ideas im a bit low on options ?

thanks
 

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The first thing to check (because it's easy) is your engine grounds. Because the packs use N-channel FET transistors to drive the coil primaries, they're very sensitive to poor grounding. Use voltage drop to check it, put your meter on the lowest scale so you can read millivolts and measure between the block and the negative battery post with the engine idling. Anything 50mV (0.05V) or higher is a problem. You can back-probe the ground pins on the coil connectors with a safety pin to do the same check for individual coils. If your grounds are good, my prime suspect would be the crank sensor (CKP). Nissan ECM's can easily detect flatlined crank and cam sensors, but aren't very good at detecting weak sensors which are misbehaving but not dead. Since the ECM derives its spark timing directly from the CKP, that would be my next guess.
 

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Discussion Starter · #3 · (Edited)
so I check things they appear to be OK. Turns out I accidentally swapped two of the wires on my harness pigtail when I replace the plug it’s running better now, but oddly it’s now going back to a cylinder one misfire but the problem with number two cylinder is not the same as number one cylinder, all of the coil harness wires are correct

now I see a new code P0507 idle speed control system. and a P0301 cyl 1 missfire
 

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Discussion Starter · #4 ·
so I have a slight update on my problem. I still have the number one cylinder misfire, but I noticed that I don't really have much of a reaction when I unplug the number 1 injector power in fact, it seems to almost run better. Information online tends to say that I have a missfire and injector. But I have replaced all 4 injectors. And I had that issue with the old injectors as well so I'm thinking it's the harness. What you guys think?
 

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Check pin-fit on the connector and make sure both pins are seated and not pushed out. If you put a test light across the injector connector, you should get no light with key-on-engine-off, then a blinky light when cranking. If so, either the new injector is bad or the problem is something else. If you get a light all the time, then either the wire between the injector and ECM has a ground short or the injector driver inside the ECM is melted short. If you get no light but one of the terminals has power, then either the wire to the ECM is open or the driver in the ECM is blown open.
 
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