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Discussion Starter #1
I have a great car. 2005 Nissan Sentra Spec-V 2.5.
I love it. It has 114K miles and never had any trouble with it. Plugs are iridium and were added at about 30K. The crankshaft position sensor was changed out as it failed like is common at 80K. Other than that its never had a starting or running issue. I had the dealer service it for air bag inflator recall and ECU reprogramming. After that I had a few random misfires at higher revs. Then randomly it would start running rough and misfiring. It will usually start that way. I will shut it down, wait a bit and then it will start and run fine. Sometimes it will take 10 times of restarting before the problem will go away. I took it to the dealer who couldn't find anything wrong with the engine. About two weeks after taking it to the dealer it started running rough again occasionally. Also sometimes it will take 3-5 seconds to start. From reading the forums here I got a few ideas:

1. Head gasket in cylinder is leaking coolant into the cylinder which causes it run rough for a while.
2. Ignition coils need to be replaced.
3. A sensor such as the knock sensor is sending bad data.

Any ways I can determine if any of these are happening?

I appreciate your help.

Thanks,
Joshua
 

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Sup Mod keeping the peace
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First thing to do is perform an ECU code readout with a portable scan tool to see if there are any fault codes set. If you're seeing a mis-fire code being set, it should tell you which cylinder. Once you find the bad cylinder, you can run a compression check to see if there's a blown head gasket. That can be followed up with a leak-down test on that cylinder which can show up as producing air bubbles in the coolant. If the ignition coil is causing a mis-fire in that cylinder, swap the coil with one in another cylinder; sure to clear the fault code between swaps.

It's also possible that a fuel injector(s) is dirty causing a random mis-fire. Run some good injection cleaner through the system.
 

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Discussion Starter #3
Thanks for responding!! I appreciate the help. I forgot to say that there are no codes. I've checked and the dealer checked.
A code would definitely help in the debugging process.
As for fuel, I always run 93 and run Shell V-Power which I thought would keep injectors clean. Should I run a system cleaner on top of good fuel?
I'm beginning to wonder if I get inconsistent pressure from the fuel pump. Before this started happening the dealer also did a recall remediation by inspecting the fuel tank which I believe required taking out the fuel pump. Perhaps in that process something was damaged. Is there a way to test the fuel pressure? My idea is that when it runs rough, leave the engine in the on position for 20-30 seconds and give the fuel pump some additional time to pressurize the system. If I could get a consistent problem and solution that might narrow down the problem.

Thanks,
Joshua
 

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I noticed you have 84k miles on your irridium plugs. I am sure the dealer pulled them and checked but maybe you have gone past the point they should be replaced again. NGK suggests they have a max life of 60,000 to 80,000 miles on unmodified engine and a real life expectation of 40K to 50K before performance might suffer. Might be worth checking out. Good luck with it.
 

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Sup Mod keeping the peace
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Thanks for responding!! I appreciate the help. I forgot to say that there are no codes. I've checked and the dealer checked.
A code would definitely help in the debugging process.
As for fuel, I always run 93 and run Shell V-Power which I thought would keep injectors clean. Should I run a system cleaner on top of good fuel?
I'm beginning to wonder if I get inconsistent pressure from the fuel pump. Before this started happening the dealer also did a recall remediation by inspecting the fuel tank which I believe required taking out the fuel pump. Perhaps in that process something was damaged. Is there a way to test the fuel pressure? My idea is that when it runs rough, leave the engine in the on position for 20-30 seconds and give the fuel pump some additional time to pressurize the system.

Thanks,
Joshua
According to the FSM, your engine being a QR25DE takes a double-platinum tipped NGK PLFR5A-11 spark plug which has a replacement interval of 105,000 MI. Using the wrong heat range plug or another aftermarket brand could cause starting/drivability problems.

To test the fuel pressure, you would tee-in a fuel pressure gauge between the fuel tube and the fuel line; there's a quick-connector that needs to be separated and a special adapter installed for the tee connection. The fuel pressure spec is: 51 psi.
 

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Joshua, you need to speak to your dealers service manager. This is going to sound a little weird, but ask to find out if this is the same issue that some of the newer 2.5 Manual transmission cars have regarding the engine flywheel. Ask him to check with Nissan Techline. Good luck and happy holidays.
 

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checking the head gasket is easy if you have a coolant pressure tester. Take the plugs out and pressurize the cooling system overnight. In the AM have someone crank her over and look to see if water or vapor comes out of the plug holes.

On a side note, are you running the correct weight oil in the motor? There are issues popping up where too thick of an oil will not allow the lifters to bleed off fast enough and hold the valves open for just a little bit when starting cold.
 

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This isn't conclusive, but start your car up and put your hand by the exhaust pipe. If your hand starts to get wet pretty quick or there is a lot of vapor, there is a good chance it is a had issues due to water escaping from the water jackets in the motor into the cylinder or straight into the exhaust valves causing the extra moisture in the exhaust. Once again, not conclusive, but if you don't have many specialty tools, this is a fairly reliable method.

Sent from my K01A using Tapatalk
 

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I have a great car. 2005 Nissan Sentra Spec-V 2.5.
I love it. It has 114K miles and never had any trouble with it. Plugs are iridium and were added at about 30K. The crankshaft position sensor was changed out as it failed like is common at 80K. Other than that its never had a starting or running issue. I had the dealer service it for air bag inflator recall and ECU reprogramming. After that I had a few random misfires at higher revs. Then randomly it would start running rough and misfiring. It will usually start that way. I will shut it down, wait a bit and then it will start and run fine. Sometimes it will take 10 times of restarting before the problem will go away. I took it to the dealer who couldn't find anything wrong with the engine. About two weeks after taking it to the dealer it started running rough again occasionally. Also sometimes it will take 3-5 seconds to start. From reading the forums here I got a few ideas:

1. Head gasket in cylinder is leaking coolant into the cylinder which causes it run rough for a while.
2. Ignition coils need to be replaced.
3. A sensor such as the knock sensor is sending bad data.

Any ways I can determine if any of these are happening?

I appreciate your help.

Thanks,
Joshua
These QR25 engines have a known problem of head gasket leaking. I heard that Nissan came out with a new multilayered head gasket for this.
 
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