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Discussion Starter · #1 ·
Hi All,
New member here, I have a 2011 qx56 with 143k miles . recently i started noticing rough engine/hickup when the vehicle moves at 1500-2000 rpm . This is always the case when the speed is in around 30-40miles as though its trying to shift to the gear when i try to slowly rev up .. like a misfire at that stage. once the speed is above 40mph its smooth and rpm is also smooth( i did notice the rpm needle move quickly sometimes on 1k-1.4k . there is no rough idle when not in motion or no roughness when its above 45 mph.
After this started happening for a few weeks i got the P0420 .I was suspecting it to be air issue and I removed the MAF and cleaned it and it appear to smooth out a bit and the P0420 went away for couple weeks. i checked with advanced diagnostic tool and there were no codes and it Passed for inspection.
After couple weeks the P0420 is back i am in the same boat as before with above symptoms. I now suspect its due to misfire so i used the adv diagnostic tool to check the cylinder info and i do see 6 out of 8 cylinder show misfire count increase from 2-16 . is this normal ? do i have bad spark plugs? The system doesnt report of any other codes other than P0420.
there is the history on the repair on this at dealership during warranty
2014 : cat on b1 replaced
2015 : cat on b2 replaced
2015: all spark plugs replaced at 99k miles ( factory reccomended to change every 105k miles with iridium SP)
2017: timing chain replaced as part of recall.

I always use premium gas but at diff locations.I have also used the fuel cleaner that goes with the gas few times.
I have not replaced the MAF or spark plugs or coils yet at this time. Can someone guide what i should look at to possibly fix this issue? I do have dusty air filter that i will be changing. Should i replace all the 6 spark plugs that show increased misfires on the diagnostic tool and the MAF sensor or is there any other area i need to look at . Should i be looking at some other values on diagnostic tool to determine the failure of any other parts..

Please advice,

thanks much!
Aj
 

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check your coil packs. it doesn't hurt to remove a spark plug or two to see the tip and if its fouled up, darkened with soot, etc.

i guess you did not buy this new, so how long have you had it?

i see the iming recall was done, but how long ago was it done? its possible the chain may have jumped a tooth causing the misfire.

ive a 2012 qx fully loaded with 81K on the clock and the car runs buttery smooth. its my daily driver. you should not experience any issues you are seeing.
 

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I'll be watching this. I have nothing groundbreaking to add here, but I will say I wouldn't change 6 out of 8 spark plugs. I'd change them all if I was going to change any.

How did it go after changing the air filter? I know it sucks to pay someone but it might be worth it to get a competent diagnosis before implementing the parts changing shotgun method.
 

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Discussion Starter · #4 ·
check your coil packs. it doesn't hurt to remove a spark plug or two to see the tip and if its fouled up, darkened with soot, etc.

i guess you did not buy this new, so how long have you had it?

i see the iming recall was done, but how long ago was it done? its possible the chain may have jumped a tooth causing the misfire.

ive a 2012 qx fully loaded with 81K on the clock and the car runs buttery smooth. its my daily driver. you should not experience any issues you are seeing.

Thanks will check the coils and SP. I have had this for couple years now and added 25k miles on it since i bought in end of 2016. The timing chain recall was done in jan 2017.
 

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A misfire will immediately yield a P0300 and highly doubt the spark plugs or coil packs are the issue. An easy way to rule out the plugs or coil packs is to get the engine running at operating temp/idle. Disconnect each coil pack plug one at a time and listen to how the motor idles. If the idle becomes rough, that plug and coil pack on that cylinder is good. If the idle stays the same without any audible changes, then you'll know which plug or coil pack is causing the problem.

With the history of repairs you've posted, one thing that wasn't mentioned is whether or not the dealer replaced the air/fuel sensors on both Banks (1 & 2).
I don't know the range of your diagnostic tool, but if it can display wave forms of the O2 sensors, you'll be able to figure out if the the converters are failing. If the wave forms on the front O2 sensors are switching from high to low (rich to lean) with their corresponding rear O2 sensors showing an almost linear, straight line, the converter(s) is doing its job. But if the rear O2 sensor(s) show similar wave forms as the sensors up front, the converter(s) are on their way out.

But in your case, with the converters being replaced, you'll want to check the O2 values (mV) and their switching rates. If the switching rate seems slow or it shows spikes and drops on the values for extended amounts of time, the O2 sensor(s) have begun to deteriorate and the likely cause of the P0420.
 
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Discussion Starter · #6 ·
A misfire will immediately yield a P0300 and highly doubt the spark plugs or coil packs are the issue. An easy way to rule out the plugs or coil packs is to get the engine running at operating temp/idle. Disconnect each coil pack plug one at a time and listen to how the motor idles. If the idle becomes rough, that plug and coil pack on that cylinder is good. If the idle stays the same without any audible changes, then you'll know which plug or coil pack is causing the problem.

With the history of repairs you've posted, one thing that wasn't mentioned is whether or not the dealer replaced the air/fuel sensors on both Banks (1 & 2).
I don't know the range of your diagnostic tool, but if it can display wave forms of the O2 sensors, you'll be able to figure out if the the converters are failing. If the wave forms on the front O2 sensors are switching from high to low (rich to lean) with their corresponding rear O2 sensors showing an almost linear, straight line, the converter(s) is doing its job. But if the rear O2 sensor(s) show similar wave forms as the sensors up front, the converter(s) are on their way out.

But in your case, with the converters being replaced, you'll want to check the O2 values (mV) and their switching rates. If the switching rate seems slow or it shows spikes and drops on the values for extended amounts of time, the O2 sensor(s) have begun to deteriorate and the likely cause of the P0420.
Thanks for your reply!.
Yes per the service report i gathered the A/F sensors on both the banks were replaced when Cat's on both banks were replaced. (in 2014 and 2015)
i am using the actron cp9180 tool and i am kind new to these diagnostic. I did check the o2 readings with engine On. here they are (wasnt seeing the fluctuation on the bank2 sensors.
o2s12 v .86
o2s22 v .84
o2s11 v 1.49
o2s21 v 1.48
cat temp11 shows 320
cat temp21 shows 320
Ho2 B1S1 v Max 4.79 , meas:.73 min. 0.17
Ho2 B1S2 v Max 4.71 , meas:.92 min. 0.12
Ho2 B2S1 v Max 4.71 , meas:.70 min. 0.17
Ho2 B2S2 v Max 4.71 , meas:1.06 min. 0.12
not sure if i should have reved it for few mnts to get the cats more hot.

I did replace the dirty air filter with a OEM oil based air filter and the p0420 went away the next day. not sure if the p0420 pops up periodically. I still do however have the hickup symptom when moving from 1k to 1.3k as though the gear is trying to shift or something and then once the rpm is above 2k all is normal. This symptom was there even before the P0420 showed up .. and i was thinking if it was normal behavior for a v8 engine as i reacall someone mentioning that somewhere. i am new to v8 suv's so i am not sure what to expect.
I also changed the MAF sensor, cleaned the intake valve as it was dirty per the dealer report . I did notice slight improvement in smoothness of the movement of the vehicle but the hesitation hasnt gone since last 2 days of the change. Now i am ready to check if the spark plugs are bad. Its about 40k miles since the last time the plugs were replaced.
I just got 8 of the NGK iridium Spark plugs and ready to change it this weekend.

Anything else i can check before i replace SP?
Please advise ..

thanks
 

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Discussion Starter · #7 ·
Guys, Looks like my p0420 has gone away. It hasn't come back after i replaced the air filter and cleaned the throttle body. Both were dirty. Its been almost a week now and no pending or any other codes.

I do however have the other issue with misfire type symptom when on 1k-1.4k RPM although i don't have any engine light on. i did replace 6 out of 8 Sparkpulgs that i could work on but that doesn't seem to help. I do see a bit of better performance after the spark plug change, throttle body cleanup. Here is what i observed - the misfire symptom mostly/only happens when the vehicle is warmed up. I don't experience the slight hesitation when i start first thing in the morning and the gears appear to shift smoothly as RPM increases . The fist few mnts appear to be OK and then as i drive around i notice more of this condition. I also don't see this condition if i were to rev the gas quickly from 1 to 2k rpm after warmed up and it shifts and drives ok without this hesitation.Only when i try to slowly rev up i notice this under that 1 -1.4k rpm range. not sure if this is normal. do i need to relearn the throttle body? - if so i would like to know the procedure for this qx56 2011 model. i tried to follow the other nissan models steps on YT but my CEL never blinks during one of the stages.not sure if i am missing something.

Anything i can check live with the diagnostic while this happens to identify the cause.. please help.. this is driving me nuts..

thanks
 

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You should change all the plugs to rule out the plugs. I understand you have difficulty getting to them but still ...

I have not followed the thread but did you have the recall done?
Have you changed transmission fluid? Transfers case fluid?
Battery replaced? Checked for proper voltage in the charging system?

You may need to re-learn the ECM. It’s the same procedure that you are mentioning. Timing is critical (i do this procedure often and it DOES work, but you have to have the timing down).

The transmission will “rev up” then rev down into gear if you are in a gear and you idle then give it petrol. This is only the torque converter getting into the “locked” phase with the trans, so if you are referring to that, this is normal.
 

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2009 Nissan Armada LE
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Guys, Looks like my p0420 has gone away. It hasn't come back after i replaced the air filter and cleaned the throttle body. Both were dirty. Its been almost a week now and no pending or any other codes.

I do however have the other issue with misfire type symptom when on 1k-1.4k RPM although i don't have any engine light on. i did replace 6 out of 8 Sparkpulgs that i could work on but that doesn't seem to help. I do see a bit of better performance after the spark plug change, throttle body cleanup. Here is what i observed - the misfire symptom mostly/only happens when the vehicle is warmed up. I don't experience the slight hesitation when i start first thing in the morning and the gears appear to shift smoothly as RPM increases . The fist few mnts appear to be OK and then as i drive around i notice more of this condition. I also don't see this condition if i were to rev the gas quickly from 1 to 2k rpm after warmed up and it shifts and drives ok without this hesitation.Only when i try to slowly rev up i notice this under that 1 -1.4k rpm range. not sure if this is normal. do i need to relearn the throttle body? - if so i would like to know the procedure for this qx56 2011 model. i tried to follow the other nissan models steps on YT but my CEL never blinks during one of the stages.not sure if i am missing something.

Anything i can check live with the diagnostic while this happens to identify the cause.. please help.. this is driving me nuts..

thanks
Any Updates? i have the same exact problem
 
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