Can't figure where my misfire is coming from!

[nguye569]

I have a 2001 Infiniti Qx4. In the past 2 weeks I have been having rough idle issues when the car starts to warms up. Scanned for codes and got P1320 and P0303. My research on this forum led me to believe that I have ignition coil starting to fail and that the P0303 was pointing to cylinder 3.

Last night I decided to replace ignition coil 3 and spark plug with an NGK, but that doesn't seem to have solved the problem. Now I have codes P1320 and P0300. I only had 1 new coil and no stores around me had them in stock or were open, so I decided to test the new coil in each cylinder except for 1 since it's different and nothing seemed to solve the problem. Now I have a new ignition coil 31 on the way, and hoping that solves the trick. As I went around and tested the coil in each cylinder, i also replaced the the spark plugs.

Is there anything else I can do to figure out where the misfire is coming from? I'm freezing my bum off spending hours in the garage of this cold Minnesota weather.

P.S I also had a camshaft position sensor code pop up and replace that and the MAF for surety as well.

[atraudes]

Well, you did right by replacing the #3 ignition coil. P0303 is indeed a cylinder 3 misfire. P1320 seems to be the cylinder misfire's ugly sister that always tags along. I've seen a number of experiences here and seen it myself that it pretty much always accompanies a bad coil pack and its presence doesn't necessarily indicate anything.

P0300 on the other hand is not the same good news and could be the result of many things. I have a few questions.

1. Now that you've swapped out the bad coil pack, besides the codes it's throwing, are you seeing any problems like stumbling or shaking, or are you just trying to get the codes resolved?
2. If so, how rough is the shaking, do you hear knocking as well, is it consistent or random, and does it go away after letting the car sit for 30 minutes?
3. Have you been clearing the codes after every step? The codes will generally stick around for a while even after the problem is resolved.
4. What brand/model ignition coil did you use?

In case you didn't know and it helps your future ordering, the OEM Hitachi packs can be had from Amazon for $50 a pop, which is half the price of local stores.

[nguye569]

thanks for your response! here are the responses to your questions.

1. My car is still running rough, not anymore than it was previously. I took the car to the grocery store this morning and when i got home, I started noticing a backfire coming from the exhaust that I didn't hear before.
2. The shaking sin't too rough right now, but it's definitely noticeable. Its ligher when the car is idling in Park/Neutral (sometimes not noticeable), and you definitely feel it when the car is put into drive/reverse.
3. Yes I have been clearing the codes.
4. I used the Hitachi one, exactly the one that is for my car bought off of Amazon. Should I just be replacing all the coil packs or is that just another way of throwing money at the problem. I essentially at this point jsut want this car running better and last me the next few months while I shop for a new car, its at 208k miles.

[asnorton44]

Given the prices of coils have gone down so much I would just replace them all and be done with it...I'd also clean the MAF while your at it.

[atraudes]

My guess is the coil packs aren't likely to blame. When I had the coil pack go bad on mine, it was a really violent shaking when it completely gave up the ghost. So bad you didn't want to consider driving it. Up until then, there were occasional large shakes but nothing much in between. That is to say, it either completely worked or completely didn't.

The backfire is disconcerting, though, and gives more credence to an ignition problem. Unless your spark plugs are nearly new, replacing (or at least inspecting) all of the plugs feels prudent. When were they last changed? Are they all NGK PLFR5A-11? People have had problems with other brands and even models.

I'd run through the troubleshooting steps in the FSM for P0300, or at least as many as you can.

[nguye569]

I changed out all the spark plugs last night with NGK's as I was swapping the new coil pack in each of the cylinders to try and see if it ran better in any of the cylinders, and just couldn't do this same test for coil #1 since it's a different shape. I wouldn't expect these new plugs to be the problem, my previously ones were autolites that were probably put in from my cousin when I bought the car off of him.

[Leo1998]

When was the fuel filter last changed? Check for vacuum leaks around intake manifold and check hoses for cracks that could be leaking. Can't believe it even ran with Autolites in it, lol. To me you went from a misfire in cylinder 3 to now a random misfire after installing a new coil pack to that cylinder, which means it's not the coil pack anymore and it's something else. Run some injector cleaner through your next tank of fuel. Idk good luck.

[nguye569]

I'm going to check for vacuum leaks this evening. Based on the FSM, it seems like this error code can also be related to the O2 sensors. Is there an easy test for these? I doubt they have been replaced on this car but also haven't seen a specific code for them pop up.

[rgk]

I was experiencing a random misfire in my old Mazda and ruled out the coil packs after cleaning the springs and checking the resistances. The numbers checked out fine, but after a while I decided to finally replace the coil packs, which solved the problem. I received both specific and random misfire codes at different times. Bad coil packs can do some really funny things.

[Leo1998]

You will get a specific code for the O2 sensors. I believe you can test them at their connectors with an ohm meter. I haven't done it, maybe someone who has will chime in. Did you rule out the fuel filter?

[nguye569]

I have not replaced the fuel filter and will do that today along with checking again for vacuum leaks. I did not do that after doing the spark plugs, so hopefully I will discover that I did not tighten something up as needed.

As for the o2 sensors, I know there is usually a specific code for them, I just thought it was interesting that the FSM has a line that says P0300 could be related to the sensors. I also had spoke to a mechanic friend that suggested looking at the 02 sensors because he has had a few clients that had misfire codes and it was finally fixed with the o2 sensors after checking for vacuum leaks and replacing spark plugs.

[nguye569]

Replaced the fuel filter today and used throttle body cleaner to spray around hoses, especially near the intake and throttle body, to try and detect a vacuum leak. I did not notice and fluctuations in the engine idle. Are there any areas I should concentrate on when spraying or areas that are easily not noticeable that I should spray?

I believe I have already officially rule out the 02 sensors as well. I have torque pro and the readings for the sensors seem to be fluctuation between 0 and a bit between over.5, which seems like it's normal.

Still getting P0300 and there is still a pop/backfire coming from my catalytic converter.

I have an ignition coil pack #1 coming in tomorrow, going to swap that in for safe measure since it's already ordered and try to look for a vacuum leak. Hopefully I can figure out what's going on soon.

[atraudes]

Have you had a check on the fuel pressure yet? I'm curious if the fuel pump is dying or something.