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P0300 Random Misfire with no luck pinpointing it.

15516 Views 47 Replies 9 Participants Last post by  mpardhal
Hello, first post, great info on here. I have a 2016 Versa Note with a P0300 code and running horrible. I replaced plugs, crank sensor, battery, made sure it had good fuel, replaced the intake gaskets, couldn't find any vacuum leaks, compression is good. What might i be missing? If i understand things correct, if it is a bad coil or fuel injector I should get a specific cylinder misfire and not a random code correct? Could a failing fuel pump be the problem?
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A few more thoughts. If your cat is hogged out, the o2 should be oscillating like you would expect to see a front o2, after it's warmed up.

I don't trust the fuel trims because At idle, your total trim was like 18 (lean), but the a/f says it was 2.18v (rich). I'm not confident that the oud you used to get that info was correct though.

Let's only look at lambda for upstream and o2 for down. Pull a vacuum line and make sure lambda goes above 1.0 and o2 goes down to at least . 200. Then add propane and make sure they both do the opposite. This will tell us that the sensors are reading properly. Watch stft to see if you get correlating changes. Remember that the o2 has to be very hot or this won't work. The a/f heats up within a few seconds. If all of this looks ok then we can trust the sensors and the stft.

It looks like you already know that lean condition at idle that improves with rpms is a vacuum leak, very good. If we can trust the data we just checked, then use your propane or brake cleaner to spray around suspect locations while watching stft or lambda and watch for a rich spike. Graphing is ideal for this if your tool offers it. Not sure if this is how you checked for leaks before, but listening for a change might not work. I'd suspect an intake leak with your cylinder misses, but also pinch of the purge line and brake booster hose and see if you get changes.

If it's not a vacuum leak, you can swap coils, plugs, injectors to see if the problem moves, and while you have plugs out, do a compression test.
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Great ideas. Will work on this weekend and report back.
I'll try to lean it out and watch lambda numbers. If it leans out, I'll drop the exhaust and see if the guy really did gut the cat or just drilled holes in it.

Bank 2 02 doesn't ocillate because I used a spark plug fouler to pull it out of the exhaust stream.

And, it is running rich.

Another thing is the engine falls on its face when shifting and there's a pause to rev it up.feels like a long pause to me.
Everything is pointing to a clogged up exhaust.

Thank you and the forums help. Iam a first time poster and hope it helps someone else.
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A few more thoughts and possibilities, ha, I've wondered for a while if an O2 spacer would impact fuel trims since Nissan does use the rear sensor for some fuel adjustment. If it's being tricked, I'm not sure how it will react. I don't know if pulling it from the exhaust stream has the same affect as good cat o2 storage capacity, if that makes sense? Let me know how it responds to those forced rich and lean tests I mentioned before. If it responds and how quickly it does.

The other thing is that a rich cylinder can impact the compression if that cylinder if the walls gets washed down with fuel. If you end up doing a compression test, you want to hold the throttle open, and make the needle bounce up about 4 times, but the important bounce is the second one. It should be pretty close to the final number. If you have any low cylinders, squirt some oil in the cylinder and try again. It could be low because of wash down. I've seen people replace engine because of this. Heck, I got my current car for a deal because it was thought to have needed an engine because of this.
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The cat is definitely hogged.

Forced lean with brake booster line.lambda went to 1.3 and car stalled immediately. Then, just made a very small leak and was able to watch lambda run 1 to 1.15 without stalling out.Upstream 02 responded correctly and followed lambda.

Ran propane again across engine bay and seen no changes. Opened air filter and flowed propane in there. Both lambda and upstream 02 responded correctly.

Don't have a compression tester and iam sick and tired of removing the entire intake manifold to get to the coil packs and spark plugs.
Looks like there are 2 injectors per cylinder (wtf). That's the only thing I never changed.
Injectors were reading something like 2millisecond at idle. Unfortunately I can't read them independently.

Any other crazy ideas before I take it in for you injectors or sell it?

Thank you and the Nissan versa forum for letting me post and helping me out.
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One more clue. When the car falls on its face when shifting and there's that 1 second pause to rev up from idle,
If I turn the car off and then back on, it runs perfectly fine for 3 to 5 minutes and then goes back to a turd.
Only that there could be a restriction in the exhaust still, after the cat. That's why disconnecting the pipe before the converter is good. It eliminates everything after it too.

I'd move the injectors around and borrow a compression gauge from a parts store for free.
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.
Good advice
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So, the solution was to change de coils using Nissan oem coils?
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