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Discussion Starter · #1 ·
I can't seem to find the cause! 05 frontier 4.0
Was running mint until last sunday...came out of walmart and when I cranked it up I could tell one cylinder wasn't happy. Drove it slowly home.
P0301 code...I figured it was a bad coil...replaced it that night. Truck drove fine monday...a few short trips around town.
This morning I drove it 8 minutes to a job, and when I was done (45 minutes later) and started the truck, the misfire was back. Same codes.
So this time I replaced the spark plug as well. And since pulling the coil without pulling the intake plenum is a real PITA, I pulled the plenum (not really that bad) and
replaced its gaskets as well.
I drove 25 minutes to Lowes, and when I came out and started it up...the misfire was back! 7-8 minutes down the road, it went away.
I tried swapping 2 ignition coils (hoping the new one was bad) and the misfire was still on cylinder 1.
I tried swapping 2 fuel injectors...the misfire stayed on cylinder 1.
The misfire seems to be happening more often now as well...just took the truck 4 minutes down the road and the misfire popped up.
With it misfiring, I put a vacuum gauge on the port on the front of the plenum...the needle stayed steady.

I'm at a loss what to check next. Unless I am wrong about which cylinder is #1 (front left, closest to the throttle body) I have no idea what could cause it...why it initially was only showing up when the motor was warm and had sat for a short time or why it can go away on it's own while driving.
 

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When you change the coil do you get a new boot and connection to the plug? Can the connector have a crack in it and the coil is grounding out. Sort of like a bad spark plug wire from way back?

Clint
 

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I'm at a loss what to check next. Unless I am wrong about which cylinder is #1 (front left...)
I believe that you ARE wrong. #1 is front right, and left and right are looking forward from rear of truck, so passenger side (USA) is right.


 
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Discussion Starter · #4 ·
When you change the coil do you get a new boot and connection to the plug? Can the connector have a crack in it and the coil is grounding out. Sort of like a bad spark plug wire from way back?

Clint
yes, replaced boot as well.
 

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Discussion Starter · #5 ·
I believe that you ARE wrong. #1 is front right, and left and right are looking forward from rear of truck, so passenger side (USA) is right.


I was speaking as if you are looking at the engine from the front of the truck, those are the same pictures I was working from...front right from the pics, front left if you are looking at the motor from in front of the truck.
 

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Discussion Starter · #6 · (Edited)
I should also add that bank 1 has a higher long term fuel trim than bank 2...I think bank 2 was around 3.4 and bank one was above 8 or 9. Can't remember specifics, getting tired!

I also tried to do an intake leak test...it read about 20 and was stable. I also tried spraying the intake plenum with WD40 to see if it would affect RPMs. Nothing.

So, so far, I've checked spark, fuel and for vacuum leaks as best I know how and can't find anything that makes any difference.
 

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Discussion Starter · #8 ·
side question...when you pull an injector out of a fuel rail on the VQ40...how much fuel should come out?
I kind of expected a big spray of fuel when I swapped 2 injectors, but each only dribbled out a little fuel when I pulled them from the rail.
 

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Does B1 LTFT go back toward zero at higher load (throttle)? If so, check exhaust for leaks on both flanges of B1 primary cat.
 

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What can cause a misfire? No fuel, no spark, no compression, wrong A/F ratio, something in the cylinder. You have done a lot of leg work with no results. If there is an exhaust leak, why not #3, and #5? The fact that the misfire only happens when the engine is warm means the defect occurs in closed loop operation. Fuel trim is a global parameter based off the upstream O2 sensor. This is an area to explore.
 

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Discussion Starter · #11 ·
this morning, the misfire was present on startup...so either the original problem has gotten worse, or was never related to the engine being warm.
I can feel the misfire change in severity but it doesn't seem to be going away now.
 

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Discussion Starter · #12 ·
Does B1 LTFT go back toward zero at higher load (throttle)? If so, check exhaust for leaks on both flanges of B1 primary cat.
I can't say I've looked, but I'm pretty sure I would notice an exhaust leak. Yesturday my neighbor was over and couldn't even notice the mis at idle, but I could hear it clearly. The truck has been running well since Feb, I would have noticed any change in exhaust note.
 

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compression test

verify spark

long term trim makes it sound like no fuel to the bad hole, are you getting the command for the injector to fire at the injector?

just to verify if you unplug the injector and run the engine any change in the misfire? try a different injector any change then?
 

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Discussion Starter · #14 ·
compression test

verify spark

long term trim makes it sound like no fuel to the bad hole, are you getting the command for the injector to fire at the injector?

just to verify if you unplug the injector and run the engine any change in the misfire? try a different injector any change then?
compression on cylinder is about 145psi

spark plug does look like it hasn't seen much fuel

I made 5 short trips today, and it was misfiring during all of them.

I checked to see that both the ignition coil and injector are receiving 12 volts...which they are.

I don't know how to test and see if they are receiving a fire signal...especially for the injector since it is pretty much covered by the intake plenum...like you can see it, but good luck getting your hand or any tools to it with the intake on.
 

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compression on cylinder is about 145psi

spark plug does look like it hasn't seen much fuel

I made 5 short trips today, and it was misfiring during all of them.

I checked to see that both the ignition coil and injector are receiving 12 volts...which they are.

I don't know how to test and see if they are receiving a fire signal...especially for the injector since it is pretty much covered by the intake plenum...like you can see it, but good luck getting your hand or any tools to it with the intake on.
145 seems a little low...anybody have a spec? and did you try one of the good holes to see if 145 seems reasonable?

there are ways to do an injector test but that will require spending some cash for a competent technician

 

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Discussion Starter · #16 ·
145 seems a little low...anybody have a spec? and did you try one of the good holes to see if 145 seems reasonable?

there are ways to do an injector test but that will require spending some cash for a competent technician

might be a little low, but this was also done with the engine cold. I'd assume that with the engine warm, it would be closer to spec. 185 is spec according to a google search, but with 190k miles and being cold, 145 seemed fine to me. But, I'm not really a mechanic so 🤷‍♂️

I back probed the fuel injector, it is getting 12v and a pulse signal from the computer.

I just got done putting new plugs (connectors) on cylinder 1's ignition coil and fuel injector. The misfire was worse today, and last night I plugged and unplugged both several times, and there was some visible damage to the ignition coil's plug...so I was hoping a bad connector connection was to blame. Sadly, the misfire remains.

I'm pretty much at the point where an experienced tech is going to have to sort this out. I have $, but right now any decent shop is booked out a week or more.
 

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might be a little low, but this was also done with the engine cold. I'd assume that with the engine warm, it would be closer to spec. 185 is spec according to a google search, but with 190k miles and being cold, 145 seemed fine to me. But, I'm not really a mechanic so 🤷‍♂️

I back probed the fuel injector, it is getting 12v and a pulse signal from the computer.

I just got done putting new plugs (connectors) on cylinder 1's ignition coil and fuel injector. The misfire was worse today, and last night I plugged and unplugged both several times, and there was some visible damage to the ignition coil's plug...so I was hoping a bad connector connection was to blame. Sadly, the misfire remains.

I'm pretty much at the point where an experienced tech is going to have to sort this out. I have $, but right now any decent shop is booked out a week or more.
did you watch the vid he discussed briefly at home injector testing with a fuel pressure gauge an an injector pulsing tool
like these

 

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Discussion Starter · #18 ·
did you watch the vid he discussed briefly at home injector testing with a fuel pressure gauge an an injector pulsing tool
like these

I did a test to show that the injector is getting signal from the computer...but I have also swapped injectors on that bank...so if cylinder 1's injector was bad, the problem would have moved to cylinder 3.

I though about manually testing the injectors...supply 12v and then use a ground to trigger them with the system primed, but since swapping cylinder 1 and 3's injectors last night didn't move the misfire, I didn't see much reason to do so.

I might have time tomorrow to compare cylinder 1's compression to cylinder 3's to see if it is off by a lot. I really didn't want the issue to be internal, but so far as I can tell...it has spark and should be getting fuel.
 

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How did you perform the compression test on #1? Did you take the plenum off again?
 

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Discussion Starter · #20 ·
How did you perform the compression test on #1? Did you take the plenum off again?
yes, I had the plenum off...at this point I've had the plenum off 5 times...now I can pull it in 5 minutes. It's the kind of skill you really don't want to have to gain, lol. I did a compression test this morning on cylinder #4 and got 155. I think I'm going to have to have a mechanic dive into it...nothing I know how to do has shown any reason for it not to be running. Maybe 145psi is just low enough? Could be a valve sticking, crack in the head or headgasket (though it would have to be tiny, she isn't blowing any smoke)
 
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