P0300 Random Misfire with no luck pinpointing it.

Well long needed update. So about 4 months after the coils, it starts missing again, back to the shop it goes, figured one of the coils went bad again, $2000 dollars later they said the MAF sensor needed replaced and the 4 month old spark plugs. Ran ok for about 2 weeks then started missing again. I heard a funny rattle in the exhaust so I yanked it off. Looks like the misfires took out my cat and shot the particles into the muffler. I was hoping the particles plugged the exhaust a bit to cause the miss so I Hollowed out the cat to test out my theory and put on a new muffler. Still misses. Back to the dealer it goes…. I hate this car…

SlickVersa said:

I am very sorry that your Versa gives you so much trouble, where you spent a lot of time and replaced a bunch of parts. Not to mention a lot of frustration.

Now, looking back, do you think it would be less trouble to bring your car in the first place to the reliable shop, where they do a proper diagnostic before they change parts, and attempt to fix it right the first time? Do you think even with their fees it still would be less expensive than the amount you already spent?

Click to expand...

As it sits right now, definitely not, it seems the reliable shop is throwing much more expensive parts at it with no fix yet. I think I’m $3200 in at the dealer and I’m not any closer to finding the problem.

Sounds like it was just a bad coil. The car doesn't know what kind is on there.

Now cross's your fingers and hope that p0420 doesn't pop up soon from the misfire!

For future readers, these don't have egr valves. The same effect is achieved with variable valve timing.

tutti57 said:

Sounds like it was just a bad coil. The car doesn't know what kind is on there.

Now cross's your fingers and hope that p0420 doesn't pop up soon from the misfire!

For future readers, these don't have egr valves. The same effect is achieved with variable valve timing.

Click to expand...

Actually, I still have not found the problem. So far I have replaced, the cam sensors, crank sensors, coils twice, spark plugs twice, intake gaskets twice, MAF sensor, fuel pump, fuel filter, hollowed out the cat (because it had melted from the misfire), the muffler, and had the fuel system professionally cleaned.

It still misfires. I hate this car....

bswift79 said:

It still misfires. I hate this car....

Click to expand...

This is a little out there, but is there any chance a rodent chewed on any of the wiring and something is shorting out - occasionally. Can you do a visual inspection of your wiring??

The reason I bring this up is... my neighbor had a large truck that was his tow rig for his camper. Mice or rats or some type of rodent made a meal out of some injector wiring, sometimes the wires would short out (going around a turn, hitting a bump, etc.) other times the current flowed, as the wires weren't grounding out.

I found the chewed area doing a quick visual inspection. As a test, I put liquid electrical tape on the exposed wire. Reset the ECM and had him drive it.. no more misfires. So he ordered up a new wiring harness as a permanent fix.

Desert Rodent said:

This is a little out there, but is there any chance a rodent chewed on any of the wiring and something is shorting out - occasionally. Can you do a visual inspection of your wiring??

The reason I bring this up is... my neighbor had a large truck that was his tow rig for his camper. Mice or rats or some type of rodent made a meal out of some injector wiring, sometimes the wires would short out (going around a turn, hitting a bump, etc.) other times the current flowed, as the wires weren't grounding out.

I found the chewed area doing a quick visual inspection. As a test, I put liquid electrical tape on the exposed wire. Reset the ECM and had him drive it.. no more misfires. So he ordered up a new wiring harness as a permanent fix.

Click to expand...

Thats a good thought, I never saw any chewed wires, but that doesnt mean there may be some wires that wore through the insulation. I'll have to chase the wiring harness and see if i find anything.

bswift79 said:

Thats a good thought, I never saw any chewed wires, but that doesnt mean there may be some wires that wore through the insulation. I'll have to chase the wiring harness and see if i find anything.

Click to expand...

I have one other suggestion, but it is not free.
There are companies on ebay and for $100+/- they will test/fix your PCM/ECM and see if there could be anything wrong with the injector driver in the computer.
I've never used any of these companies, but since you have already poured a lot of money into the car, maybe another $100 to rule out the PCM/ECM may be worth the investment.
These companies can also VIN code a used PCM/ECM from a junkyard and you could swap in a different computer and see if the misfire still exists??

There is still quite a bit that can be tested, bit at this point I'd recommend finding a local diagnostic tech to just tell you what it needs.

You really want to ignite everything you e done and follow the data where it leads, but it doesn't sound like you have the equipment to do this accurately, and it takes knowledge/experience to evaluate the data.

There is still injectors and compression that I didn't see mentioned. In theory I believe bad belt tension could cause the computer to think there is a misfire. How did you test for vacuum leaks?

Any new updates on this issue? You have taken care of many of the things that could have caused the issue. Intermittent/ re-occurring problems are some of the hardest to track down.Most people don’t have the skill set to solve just the basic stuff, much less this. You should feel good on the operations that you have performed as they are not for the faint of heart and more than just the work of a parts changer as they indicate a level of diagnostics and skill not found in the average person. The only thing that I could suggest at this point would possibly be either an electrical contract (plug) issue or possibly injector(s) issue. Without some live data it’s really difficult to accurately diagnose.

Live data IS the key to figuring this out. I'd order a cheap Bluetooth OBD2 dongle on Amazon or your favorite shopping site, and get an app to use it on your phone. I prefer incardrpro over others I've used and the whole rig will only set you back like $15. No need for any expensive ones like bluedrive or that despicable Fixd one.

Agreed, live data is the key. Using your stft and ltft data you can probably diagnose most misfire issues. Other data like O2 and MAF data is also helpful. I had a similar issue and replaced the coils and plugs and it went away for about 50 miles, then bam, it came right back. Come to find out that one of the coils failed again. Been driving it around for about three weeks now and no issues! Manufacturing quality is not always what it used to be, regardless of who made the goods. I try to stay away from the dealership as much as possible because they are no better that a lot of the independent garages out there. Although difficult to find a competent shop they are out there.
Even a cheap scan tool that gives live data can be very helpful in diagnosing an issue like this.
I did make sure that I force triggered a “bad MAF sensor code” to clear out my LTFT and it was part of my repair. Of course I reset it and cleared the code to force a re-learn on that parameter.

I have the same or similar issue with my 2018 versa. Started with clogged cats( yes cats). There is an exhaust manifold cat and a cat after that.
Never got a cat code so never knew it was the problem until I couldn't go over 50mph.
Punched out both cats and car ran great for 2 months. Misfire came back and mph went down. Changed upstream 02 and mpg is back except for when the car is under a load or accelerating. Started toying with down stream 02 with fouler's and is getting worse. Going to the store to get new down stream 02 and test with and without fouler.
OBD2 says it's rich which I believe is coming from down stream 02 leaning it out.
Stft is running 0 to -?? . I think the random misfire is a fuel issue. It does not feel like a spark or coil issue. Misfire only occurs (flashing check engine light) at idle and stops flashing when driving.
It would be great to fix this POS because I am getting 35mpg + and 45mpg at 62mph drafting and vehicle.

TimT said:

I have the same or similar issue with my 2018 versa. Started with clogged cats( yes cats). There is an exhaust manifold cat and a cat after that.
Never got a cat code so never knew it was the problem until I couldn't go over 50mph.
Punched out both cats and car ran great for 2 months. Misfire came back and mph went down. Changed upstream 02 and mpg is back except for when the car is under a load or accelerating. Started toying with down stream 02 with fouler's and is getting worse. Going to the store to get new down stream 02 and test with and without fouler.
OBD2 says it's rich which I believe is coming from down stream 02 leaning it out.
Stft is running 0 to -?? . I think the random misfire is a fuel issue. It does not feel like a spark or coil issue. Misfire only occurs (flashing check engine light) at idle and stops flashing when driving.
It would be great to fix this POS because I am getting 35mpg + and 45mpg at 62mph drafting and vehicle.

Click to expand...

What is your LTFT?
If it is normal then I hate to say it but look at your spark plugs.
You can reset the STFT and LTFT by forcing a bad MAF code. Disconnect the MAF plug (carefully) and start the car up and run it for a few seconds. Clear the codes and reconnect the MAF plug and your LTFT should be reset. Not you can get some accurate and current data to work with. That should help with the diagnostics part and hopefully point to the culprit.
Good luck!

Fuel trims are not what you'd expect on nissans. You may not get any changes with them. They use what they call alpha value, but you need a scantool with enhanced data to see this pid, so you can use the rear o2 and the equivalence ratio or lambda pids, which are your a/f sensor. These dont use an O2 sensor in the front.

If this is only occurring during idle, I'd expect a vacuum leak, misreporting MAF, leaking injector, or compression issue. With the car fully warmed up, and misfiring, what is the o2 sensor showing? You can tell if it's a lean misfire (fuel) or spark by watching this.

You can also introduce a small amount of unlit propane into the intake and and see if the condition improves, which would indicate a lean mis.

You can put a vacuum gauge on the engine and see if you have a steady needle with 17-21". If it's bouncing around, you have a mechanical issue, like low compression.

Worked on the car again this am. Stft is +/- 3 and left is 8.5 at idle and 7.5 at 2500rpm.
Replaced coil pack #3 (p0303).

Upstream 02 at 0.7 volts moving up and down and down stream 02 at .2 at idle and .35 at 2500 rpm.

Got some new codes too. Air/fuel balance along with maf low voltage.

Replaced with new maf and still the same faults after replacing and clearing codes.

Not sure I can keep going with the car like this. Don't think iam gonna get it fixed beforing selling it.

Took the car for a spin and rechecked fuel trims and 02 readings.
Idle:
Stft 6/8 ltft 9.38
Upstream 02 at 2.18 and down 02 at .275

2500rpm:
Stft 1.57 ltft 1.57
Upstream 02 at 2.17 and down at .295

I think you're going to chase this in circles. There isn't an upstream O2 sensor, so I think the data is not something to follow. Fuel trims are going to mess you up here too, like I said, they do not respond like other vehicles. Look at the o2 values you posted, the a/f sensor doesn't oscillate like that at all. It stays right around 2.2v instead of moving between . 1 and . 9 like an O2 sensor. This is why we look at lamda or equivalence ratio for upstream and o2 for down.

What exactly are the code numbers you are getting, without the descriptions, since some code readers do not accurately describe the code.

I meant catalytic converter not gutted good.

Disconnect the exhaust and drive it. It'll run better if it's still plugged, or replace the a/f sensor with a gauge. I made one out of a cheap vacuum/low pressure gauge and and I believe old spark plug threads (it's been a long time). It should barely have any pressure in the exhaust, a restriction will have pressure.

I'm having some trouble with the data, not being able to see it on a graph with rpms. The fuel imbalance code is usually injector related in my experience. It means that a cylinder is messing with the mixture, and it can tell by the pulses it's sending to the a/f sensor in the exhaust.

If I'm reading the data right, it appears to be running rich, but it's hard to say. Could be a leaky injector, or exhaust restriction. Anything under 1.0 on lambda is rich, over is lean. The o2 on these doesn't do squat until it's super hot, like been driven. Not sure if it's even possible to get it working at idle. You see about .27v ish on the tool until it starts working.