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Discussion Starter #1
I originally posted this

http://www.b15u.com/threads/40584-Only-getting-spark-on-cyl-4

But not getting much love, so maybe this is the right spot for the post?

Cliff notes: Head gasket went bad on 03 QR25DE, replaced everything myself using the awesome "how to" posted on these boards(which was extremely helpful) After putting everything back together the car wouldnt start. Traced it down to no spark on cylinders 1-3 with some spark on cylinder 4.

I have now traced it down to cam sensor. Unplug or remove sensor and car starts and runs fine. Plug it back in and car will remain running just fine. Shut car off and try to restart.....nothing. Unplug sensor....car starts just fine. So I bought a new sensor from the zone and replaced my old sensor......no help. Now I am back to wondering what the hell is going on. If its not a bad sensor then what? Checked harness connection and everything looks to be in good shape, no obvious fails. Checked all fuses and everything is in good shape.

Any ideas or help would be most appreciated, Thanks!
 

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I have not yet. If no current when sensor is plugged in, then why would it deliver current when its unplugged? Trying to wrap my head around how the cps even works. Figured it sensed where in the rotation cam was at a given point sending power to coils at appropriate time. But if it runs fine when unplugged then whats the point of the sensor at all? lol this one really has me confused.
 

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Well they read the RPM of the engine and adjusts the timing of the ignition and fuel. Cars will run without them because the ECU has the stock data for ignition. They are mostly involved with variable valve timing.

I'd go back to Autozone and return the sensor and get a Nissan sensor, or try a replacement one. I work at Autozone and I know Nissan's don't like our sensors unless it's OEM. So you have three options, try a new sensor from them, buy a new one from Nissan, or go to a junkyard and find another QR25 engine in a Sentra, or an Altima.
 

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Well maybe the op had theirs fixed once they got oem sensor, you might want to try to test out your coils, see if they give spark, then check the sensors.
 
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