Help! Code P0301 Cylinder 1 Misfire 2000 QX4

[FixMySUV]

Hello,
Had a valve cover gasket leak which I got fixed, but upon getting my car back the service engine light came on with codes P0301 for Cylinder 1 misfire and P0325 for the knock sensor.

I changed all the spark plugs, even though they were relatively new and cleared the codes. P0325 didn't come back, but P0301 immediately did with the service light on. And engine runs like crap.

The spark plug wires are relatively new as well. Any ideas what could be causing this? The mechanic had mentioned one of the 02 sensors was covered in oil during the valve cover gasket leak, so maybe it's an 02 sensor? Since the gasket was leaking, which 02 sensor would be covered in oil, the upstream right passenger side or upstream left driver side? I'm assuming the downstream one's wouldn't give this code.

Any help is appreciated!

Thank you

[04pathse]

Cylinder 1 coil pack might be bad, try swapping with the coil pack from a different cylinder and see if the code follows the cylinder to confirm it is a bad coil pack.

[FixMySUV]

Cylinder 1 coil pack might be bad, try swapping with the coil pack from a different cylinder and see if the code follows the cylinder to confirm it is a bad coil pack.

I don't think the 2000 model year QX4 with the 3.3 engine uses coil packs. Does it?

[MisterH]

Cylinder 1 coil pack might be bad, try swapping with the coil pack from a different cylinder and see if the code follows the cylinder to confirm it is a bad coil pack.

I don't think the 2000 model year QX4 with the 3.3 engine uses coil packs. Does it?

Coil packs started with the 2001 3.5 engine. Yours has an HEI distributor. I'd isolate the cylinder 1 misfire by first ensuring that there isn't a break or faulty connection in the cylinder 1 plug wire. given that the wires aren't new and someone just removed all those to get to the valve covers it's a possible cause. If that's not an issue then check to make sure you don't have a faulty injector. The simplest test is to remove the spark plug wire from the #1 spark plug while the engine is running. (do this with a pair of insulated spark glug wire pliers) If the running condition does not worsen or idle drop noticeably then you probably have a bad #1 injector. You have an OBD II code scanner?

[FixMySUV]

I don't think the 2000 model year QX4 with the 3.3 engine uses coil packs. Does it?

Coil packs started with the 2001 3.5 engine. Yours has an HEI distributor. I'd isolate the cylinder 1 misfire by first ensuring that there isn't a break or faulty connection in the cylinder 1 plug wire. given that the wires aren't new and someone just removed all those to get to the valve covers it's a possible cause. If that's not an issue then check to make sure you don't have a faulty injector. The simplest test is to remove the spark plug wire from the #1 spark plug while the engine is running. (do this with a pair of insulated spark glug wire pliers) If the running condition does not worsen or idle drop noticeably then you probably have a bad #1 injector. You have an OBD II code scanner?

Thank you for the info. So I replaced the distributor this morning...and it appears that wasn't the problem either. I had replaced the spark plugs, so those are new also and that didn't fix the issue either. And the wires are relatively new NGK, so pretty certain it's not the wires either.

I don't have insulated spark plug pliers, I'm guessing there is an electrocution risk if I just remove the wire off spark plug 1 completely?

Could any of the O2 sensors be causing this issue? The mechanic had mentioned the 02 sensor was covered in oil from the valve cover gasket leak, and that he cleaned off the sensor. I'm thinking that same sensor is causing all this. But I'm not sure which sensor would have the oil on it, the front upstream left or right, or maybe one of the downstream? What are your thoughts on which one would be covered in oil during a valve cover gasket leak?

Thank you!

[MisterH]

If one of your O2 sensors was failing you would get the error codes associated with it. Second, downstream O2 sensor failure won't affect running condition; only upstream (pre catalyst).
I'm curious as to why you would drop in a new distributor to cure a cylinder 1 misfire. That's not an inexpensive part. A pair of plug wire pliers is $10. Do you have a code scanner?

[QCtech]

You said that you think is not the cable because they are new, but you did not mention at any moment if you changed that #1 spark cable with another. It would be as easy as swapping the cable with any other cylinder. You can even take the spark plug out, connect to the cable and leave the spark plug outside, near a bolt on the engine, and then turn on the engine for a few seconds, and you will see the spark plug discharging if it is working. You can measure the internal resistant of the O2 sensor with the information in the manual and know if it is ok or not, but most probably the O2 sensor have nothing to do with a single cylinder problem. If the cable is not the problem, check your cylinder compression.

[FixMySUV]

You said that you think is not the cable because they are new, but you did not mention at any moment if you changed that #1 spark cable with another. It would be as easy as swapping the cable with any other cylinder. You can even take the spark plug out, connect to the cable and leave the spark plug outside, near a bolt on the engine, and then turn on the engine for a few seconds, and you will see the spark plug discharging if it is working. You can measure the internal resistant of the O2 sensor with the information in the manual and know if it is ok or not, but most probably the O2 sensor have nothing to do with a single cylinder problem. If the cable is not the problem, check your cylinder compression.

If one of your O2 sensors was failing you would get the error codes associated with it. Second, downstream O2 sensor failure won't affect running condition; only upstream (pre catalyst).
I'm curious as to why you would drop in a new distributor to cure a cylinder 1 misfire. That's not an inexpensive part. A pair of plug wire pliers is $10. Do you have a code scanner?

I am using the Torque app as the OBDII scanner, so yes I have one but not sure how good you'd consider this app. Put on a new distributor because I falsely assumed that may be the issue.

Took out wire 1 and with a spark plug in it, tested the spark as suggested above and it was nice and strong. Tested with wire 3 and similar spark, confirming wire 1 is fine.

I'm starting to think it may be the injector. I was going to switch #1 injector with #3, but I can't get the injecter screws unscrewed, the engine is in the way and the screws are angled towards the top of the engine. How is someone supposed to unscrew the fuel injectors when a screw driver just bumps into the top of the engine?

Appreciate everyone's help with this.

[MisterH]

Torque is fine as your scan software. All the 3rd party basic OBD2 readers will do an adequate job for most situations. The only thing better is Nissan Consult application running on a Windows laptop. In any case, you will have to remove the intake to remove any injectors. It's a pain, but the only way to do it.

Another way to help verify what's happening in cylinder #1 is to test the resistance on all injectors at the plug in connector and see if the resistance at #1 is wildly different than the others. This of course is only for spotting an injector failure- not clogging. The only other next step I could recommend would be to have a fuel injector cleaning service done by a professional mechanic. Essentially they slowly feed a special cleaner into your fuel system to try to remove any clogs. That usually runs about $150 but of course there's no guarantee it will cure your problem. To go the real low-risk route just try running some high quality fuel cleaner into your gas tank and hope that cures it over time.

[QCtech]

Before you remove any injector, there is a simple test that you can do. You have covered most of what the manual says. Also, are you using the manual? Sorry but I have to ask. In page EC 548 the troubleshooting for the injectors tell you how to check if the injector is getting the correct voltage.Since you said that you fixed a valve cover gasket leak, what I can think is that however removed the valve cover could have damaged one of the cables of the injector harnmess or even pinched it when the valve cover was installed back. In page EC 552 it tells you to measure the voltage from terminal 2 to ground, with the ignition switch in on and you should have battery voltage.If you dont know how to use the multimeter, set it to Vdc(votage dc) in a range that covers 12 volts, and then put the red probe to the # 2 pin and the black probe to a ground in the engine or to the engine block. If you dont have battery voltage you have to go and check your harness and follow it to see if there is a crack, cut or pinch. It also tells you to use one stetoscope tool(cheap at any autozone, etc) and check if the injector is making a clicking sound in idle with the engine running. These 2 tests will tell you if it is your injector or your harness without taking anything else off. I would incline myself to think that your harness is shorting somewhere or that they damage it during the previous work. Keep us posted what you finally find.

[fueler]

A bad O2 sensor shouldn't even cause a misfire to begin with, but if it was bad enough, it would cause issues across all cylinders - not just one. A bad MAF sensor or rotor position sensor are way more likely to cause a misfire, but it would be a random misfire... so skip the sensors.

QCtech is on the right path... i'd start with the spark plug & wire, and then fuel injector.... the problem has to be local for sure

[FixMySUV]

Problem fixed!

I got a stethoscope to listen to the fuel injectors, and sure enough injector 1 wasn't making the same tick tick tick tick sound as the others. I was now certain it's the injector, but was dreading having to take apart the intake manifold.

So I decided to get a bottle of Techron Concentrate Plus, thinking hey it's worth a shot before I take everything apart. Poured in the 20oz bottle of Techron, started up the car, and went for a drive. Within minutes, yes minutes, the car stopped shaking and idling like crazy. I couldn't believe it. Cleared the codes, went for a nice long drive, and the light didn't come back on and no codes thrown. After I got back from the drive, listened to injector 1 with the stethoscope again, and it was making the tick tick tick tick sound like the others, indicating it's working!

I can't believe it, but a bottle of Techron Concentrate Plus, solved my issue. Must have been a clogged injector! For now things are running fine, if the problem returns at least I'll know it's the injector. Until then, I'm a believer in Techron!