Misfire or CVT failure imminent?

[Ilya]

It's there still a chance it'll get better? Or is the current state best I can hope for for the next few years (hopefully)?

Drove to church and it drives seemingly okay but definitely misses when at lights, etc.

Should I change the plug one more time in like a week incase some of the sealer got to it?

Drive to church, almost 20 miles.

[VStar650CL]

It wouldn't hurt to change the plug. Give the sealer some time to work, each time you shut the car down it will try to clot any remaining opening. If it doesn't improve then maybe it's not a head gasket. I don't recall, did you ever try a new injector on #2?

[Ilya]

It wouldn't hurt to change the plug. Give the sealer some time to work, each time you shut the car down it will try to clot any remaining opening. If it doesn't improve then maybe it's not a head gasket. I don't recall, did you ever try a new injector on #2?

Understood. Never did a treatment like this before so not sure of when to expect results hah.

I didn't change the injector as it's a bit more involved (and now I can't get the engine cover off although I haven't tried to pry it yet).

[Ilya]

Mid-week update after driving 5-6 times for 20+ minutes each time.

Car still misfires every few seconds while idling, but don't seem to feel it while driving however it may be slight. CEL has lit up with P0302 two times now.

I bought a new spark plug but haven't installed it yet...nor have I drained the coolant to put in the Zerex I bought (will do that on Saturday).

[Ilya]

I'm in a pickle and incredibly disappointed/frustrated. Don't know what's going on or what next step to take. Went from a mostly drivable car to a driveway queen in a matter of hours.

Today I got to draining the coolant and refilling it properly with the 50/50 Zerex Asian I've had. I also wanted to replace the spark plug with a new one just in case the sealer did do something ever so slightly to the barely old one. Lastly, I wanted to sort the engine cover and bolt because it's just in the way and would prevent me from doing future maintenance like PCV, etc.

Coolant and spark plug went fine, just as always. The engine cover gave me a bit of an issue and the bolt is still in the dowel or whatever but the cover is off.

This is where things go off the rails.

Took the car for a drive and it drove worse than it EVER has with this P0302 issue. Got it back in the garage and took off the engine cover (now only held on by 3 bolts). Evidently, in the process of removing the engine cover, I must have somehow used the VAIS solenoid right next to it (passenger side above the fuel rail) as a fulcrum and broke one of the vacuum line connectors. Had to go buy a $130 sensor from Autozone.

Got home, installed the new solenoid and the issue is still just as bad. No difference. Then I realized I flipped the vacuum lines...but same deal.

I've gone back to older spark plugs, my old coil pack, reseated the injector plug for cylinder 2 (when unplugging the idle gets worse suggesting the injector is at least operational), cleaned/inspected the MAF and air intake system. AI is CONVINCED that I broke the manifold seal OR cracked it somewhere when I tried to get the bolt out and caused an air leak. I don't know if the amount of leverage I was putting on it could do that considering its bolted to the motor with like 6-7 bolts. I'm a decent sized guy but I ain't no hulk.

Do I just fall on my sword and take it to a shop to do a smoke test or vacuum test or something? I know this is going to cost me hundreds at this point. But I'm so tired of dealing with this issue. Probably should have taken it in a long time ago but no, I need do DIY like some sort of idiot...only to make things somehow worse.

The other weird thing is that the other 'good' engine cover bolt hole is hissing/causing STFT1 to be high if there isn't a bolt in it or finger on it - is that normal? Or is this also a byproduct of my man hands and I broke something?

Here is the AI summary of today's mess of a day:

Persistent P0302 & +25% STFT2 Post-Service - Diagnostic Data Included

Vehicle: 2016 Infiniti QX60 (148k miles)
Primary Symptoms:

• Hard Cylinder 2 Misfire (counts climbing rapidly, ~1,000+ per session).
• Bank 2 Short Term Fuel Trim (STFT2) pegged at +25.00%.
• Bank 1 (Rear) STFT is stable at ~0% after clearing self-learn.
• Rough, surging idle (800–850 RPM).
• Misfire is present at idle; unplugging Cylinder 2 injector causes a noticeable idle drop, confirming the cylinder is partially contributing.

Recent Work Performed:

• Drained/refilled coolant with Zerex Asian 50/50.
• Replaced VIAS Control Solenoid (original snapped during engine cover removal).
• Spark Plug replacement on Cylinder 2.
• Recent "BlueDevil" coolant stop-leak treatment (context for potential fouling).
• Note: Engine cover removal was "aggressive" due to a spinning brass insert.

Diagnostic Steps Taken & Results:

• Ignition: Swapped Coil #2 with Coil #4; misfire remained on Cylinder 2. Swapped new plug back to old plug; no change. Well is dry and clean.
• Fuel: Verified Cylinder 2 injector is pulsing (audible click). Unplugging/reseating injector connector (confirmed "click") did not resolve the +25% trim.
• Vacuum/Air:
  - Checked VIAS solenoid routing and pinched hoses; no change in trims.
  - Pinched EVAP purge line; no change.
  - Checked intake snorkel/MAF seating; cleaned MAF.
  - Performed brake cleaner "spray test" around plenum and Cylinder 2 intake runner; no surge detected.
  - Confirmed one intake manifold dowel/bolt hole was "hissing"; sealing it with a bolt improved trim slightly, but Bank 2 remains pegged at +25%.
• Software: Successfully completed Idle Air Volume Learning via CVTz50, but idle remains high due to fuel trim compensation.
• O2 Data: Bank 2 Sensor 1 (Wideband) shows erratic AFR swings from 12:1 to 26:1, frequently sticking Lean (High Voltage/Lambda), triggering the +25% dump.

The Conflict:
Despite ruling out a dead coil and verifying injector pulse, the ECU sees a massive Lean condition on Bank 2. Unplugging the MAF causes both banks to jump to +25%, but after clearing, the fault remains localized to Bank 2.

Request for Insight:
Is it possible that the "aggressive" prying on the front engine cover bolt caused a localized internal plenum crack or a lower intake gasket breach at the #2 runner that isn't reacting to external spray tests? Also, could "BlueDevil" residue in the combustion chamber be poisoning the B2S1 O2 sensor to report a false lean?

Any advice on the next "precision" step would be appreciated.

[VStar650CL]

Those bolt holes shouldn't be hissing. Nothing on the plenum should be. The VIAS solenoid only changes state above idle, so that can only cause problems at idle or above idle but not both. I'd stick some sort of temporary plugs into your hissing holes and see if the engine steadies out. You can confirm leaks by spraying something combustible like Brakleen or Gumout on the suspect area, if there's a leak the stuff will get sucked in and momentarily rich the mixture, causing the idle to surge.

[Ilya]

I did spray brakleen all over the place at the behest of AI. No changes to idle or STFT. Do I need a new intake manifold or at minimum a new gasket?

[VStar650CL]

Well, there pretty much has to be a leak with b2 STFT running at +25%. Might be underneath where you can't get enough spray on it to make the engine react. If you can do smoke then a smoke test would show it up. The lower manifolds on VQ's are metal, so that pretty much limits it to a cracked plenum or a bum gasket. If you didn't have the plenum off then the latter is unlikely, so I'd say you probably cracked it.

[Ilya]

Since I'll have to remove the plenum to replace it, will obviously do the gasket - how much more work is it to do the fuel injector at that point?

Upper Intake Plenum: 14010-JA10D
Plenum Gasket: 14032-JA10A
Throttle Body Gasket: 16175-JA10A
Fuel Injector: 16600-JA10A

Are these the right parts?

[VStar650CL]

It's fairly easy once the plenum is off. There are 4 screws holding the rail down (two each side) and then you wiggle the whole rail loose with the injectors. The FSM will tell you to relieve the fuel pressure first, but safety glasses and a shop rag over the coupler are all you really need. You're going to have a gasoline mess anyway once you part the rail from the injectors. You do need a set of quick-coupler sleeve tools if you don't already have them. Douse the electrical connectors with WD40 before you remove them, and a small channelok is handy to relieve the connector latches (the pawls can be very stubborn in old age). Make sure you lube all the o-rings before reassembling, vaseline is best. I usually smear a bit inside the bores as well. Just don't get carried away, a thin film is all you should need.

[Ilya]

I'm trying to source the plenum used on eBay (found a used one from a 2018 Murano with 97,xxx miles from the looks of it), but everything else new without having to wait for Amayama (OEM) from Dubai or Japan. Any thoughts on these injectors? Should I do just #2 or #4 and #6 while I'm in there?

[VStar650CL]

The Murano plenum should do fine, it's the same part from '15~'24 and also fits '07~'18 Altima 3.5 and '13~'17 Pathy. At 125K you're getting to the kind of mileage where they sometimes start to fail, so if it was my ride I'd do them all. However, my experience with injectors is that even the China-cheapest brand new ones are less likely to give you grief than any brand of reman. With reman injectors I always give the same advice, get at least one or two extra and don't be disappointed if you have to redo it.

[Ilya]

Hmm okay. I will likely go local then through Advance/CarQuest incase there are warranty issues so I don't have to deal with shipping, etc.

[Ilya]

I ordered three (3) CarQuest reman. injectors from Advance Auto - trying to decide if I'll replace just #2 or all front three. Or if I should get 3 more and just replace all six. Hoping to get everything in time to do this on Saturday - otherwise I'll take everything apart on Saturday and prep it for when the stuff arrives.

I run fuel injector cleaner (Seafoam, Chevron, BG) every 10kmi or so - is that just snake oil? Or is 150kmi realistically the most one can expect these days from an injector? Worried the others will follow suit shortly. The dilemma I have is I don't plan to keep the car past 200kmi so likely another 2-3 years...I don't want to drop a ton of money on OEM injectors, etc. but I also don't want to do this job 2-3 times lol.

[VStar650CL]

No, Seafoam and BG are great, but varnish isn't the only thing that goes wrong with injectors. They're basically tiny solenoids, and moving parts of any kind can fail mechanically, not just electrically.

[Ilya]

Two steps forward, one step back.

New to me intake plenum arrived 2 days early. Required a ton of cleaning but anyway.

While taking the old plenum of out the car, I removed 3 of the 4 Throttle Body bolts and the 4th stripped. CRAP. I gave the old plenum to my neighbor who works in a shop; hope it doesn't cost me more than $20-30 bucks to do so. I ordered a lower mileage used one from eBay just in case that one gets damaged or can't be removed from the old plenum so may have to wait till Wednesday or Thursday to replace. However, I left some hoses and such on the old plenum and don't want to bother the neighbor so I wasn't able to install and prep the new plenum for the new throttle body...ugh.

I did install the new remanufactured injector in #2. I decided that, other than the throttle body, it wasn't all that much work so I'll return the other two I bought.

Interestingly, I had zero fuel pressure and removed the fuel rail with minor fuel leaks. It did sit for a few hours before I got to that point, so maybe that's why?

To do list:

- Install gaskets on new plenum
- Get new throttle body
- Install it onto new plenum
- Reinstall everything
- Pray it all works

The new plenum came with a bunch of VIAS solenoids, etc. so I stripped it and will try to sell those spare parts and vacuum line things on eBay to recoup some cost.

If it doesn't work or still has a cylinder 2 issue...then either the head gasket is truly done for...or I'm a terrible mechanic and didn't do something right...right?

[VStar650CL]

Two steps forward, one step back.

New to me intake plenum arrived 2 days early. Required a ton of cleaning but anyway.

While taking the old plenum of out the car, I removed 3 of the 4 Throttle Body bolts and the 4th stripped. CRAP. I gave the old plenum to my neighbor who works in a shop; hope it doesn't cost me more than $20-30 bucks to do so. I ordered a lower mileage used one from eBay just in case that one gets damaged or can't be removed from the old plenum so may have to wait till Wednesday or Thursday to replace. However, I left some hoses and such on the old plenum and don't want to bother the neighbor so I wasn't able to install and prep the new plenum for the new throttle body...ugh.

Amazing. If you didn't have bad luck with this thing, you wouldn't have any.

Interestingly, I had zero fuel pressure and removed the fuel rail with minor fuel leaks. It did sit for a few hours before I got to that point, so maybe that's why?

Yes. The drainback valve won't keep a lot of pressure in the system, it mainly makes sure that what's in the rail is liquid and air can't creep in. If you put a pressure gauge on it, most Nissan drainbacks will fall to below 30 psi within a few minutes and then very slowly drop to near-zero from there.

If it doesn't work or still has a cylinder 2 issue...then either the head gasket is truly done for...or I'm a terrible mechanic and didn't do something right...right?

Considering that it's a single-cylinder issue, I'd say the former is more likely than the latter. Your luck as a technician, as noted earlier, is a different matter.

[Ilya]

lol...yeah it's been brutal. I'm seemingly more handy/DIY'y than the average joe but also have a TON of stories about jobs that should take 2hrs taking 20hrs lol (Suzuki SX4 Alternator comes to mind).

[Ilya]

How is this freakin possible!? Got everything I need to put the car back together and I put the new plenum in...but the drive side stud is too short? Looks like it was broken off at the top? I unscrewed it just fine, no struggle on that nut. How did I manage to break this!!?!?!?!?

What the heck do I do now!? There is no way this will seal correctly as is, right? I just want to light this car on fire at this point. I'm assuming I need to tow the car to a shop to get a new stud put in? Does this require a significant tear down or part replacement?

EDIT: There isn't really enough thread on the remaining stud to try to do the two-nut method of removing it. I got two nuts on, but the top one was just barely on and going counter clockwise on the bottom one just removes the top one. Gonna try vice grips...

I guess there is a kit I can buy at the parts store that has such a stud? This endeavor has been insane.

Passenger side stud:



Driver side stud:

[VStar650CL]

Dunno how you did that, but the studs are readily available from both Nissan and Infiniti. P/n 08246-63810.

[Ilya]

Dunno how you did that, but the studs are readily available from both Nissan and Infiniti. P/n 08246-63810.

I'm absolutely shocked at what I am accomplishing on this vehicle. I need to walk around with a warning sign that reads: will break anything.

I need to get a new vehicle ASAP that only requires tires, brakes, filters and oil. That I can manage without breaking anything.

[Ilya]

I got the stud out and it's missing about 3/4" of it's total size give or take compared to the other one (the threaded top part seems to be 1" and I only have 1/4").

I did order another one from Nissan which will be here tomorrow, but my wife just notified me she has an urgent appointment tomorrow and doesn't want to drive my M56x (she's scared of the beast ) so I want to try and find a stud locally. Google seems to suggest it is M6 x 1.0 and approximately 55-60mm long (I'll measure that part although I don't think it matters if it's slightly too long on top part). Might just get a long bolt, not necessarily a stud.

[VStar650CL]

M6 x 1.0 sounds right, but use the thread gauge at Lowe's or Home Depot if you don't own a set. The stud doesn't have a lot of torque or tension on it, so you could even use regular threaded rod from the hardware section. Just cut it to length and double-nut the top to spin it in.

[Ilya]

M6 x 1.0 sounds right, but use the thread gauge at Lowe's or Home Depot if you don't own a set. The stud doesn't have a lot of torque or tension on it, so you could even use regular threaded rod from the hardware section. Just cut it to length and double-nut the top to spin it in.

Yeah, it's M6X1.0 but I decided to wait till tomorrow to get the real thing. I bought some but I'm afraid they aren't the right class of bolt to withstand the heat cycles, etc. and could lead to issues later. Wife will just have to be light on the throttle tomorrow lol.

[Ilya]

I'm once again at a loss.

I got the new intake manifold stud, installed it, put everything back together and...somehow I have 4 10mm short bolts left over. I've checked and re-checked everything and re-watched the videos I followed to remove stuff. I don't know what I'm missing but AI thinks it's some brackets for wiring, etc. The four fuel rail bolts are bigger and installed. The plenum bolts are all there. The 5 bolts holding the vacuum lines and VIAS solenoids are all installed. There is one bolt on the back of the plenum for a harness thing that I know I installed as well. There are no other bolts I'm aware of that were removed to get to anything.

However, it gets worse if you can believe it.

I'm still waiting for my throttle body bolt to come (on friday) so for now I have it installed with three OEM bolts and one hardware bolt.

I went to start the car and it's clattering badly somewhere at the top (in intake plenum?). AI thinks it's the throttle body plate spazzing out due to signal issues.

On the first run I got codes:

- P0123 - Throttle/Pedal Position Sensor/Switch A Circuit High
- P0300 - Random/Multiple Cylinder Misfire Detected
- P0302 - Our old friend

With pending codes:

P0113 - Intake Air Temperature Circuit High Input
P0223 - Throttle/Pedal Position Sensor/Switch B Circuit High
P2101 - Throttle Actuator Control Motor Circuit Range/Performance

With historic code:

P0102 - Mass or Volume Air Flow Circuit Low Input

I reseated the TB and MAF harnesses, reset the codes, and now I have:

P0300 (Pending)
P0102 (Historic)
P0302 (Historic)
P2101 (Historic)

I idled a little longer and the sound did briefly go away or weaken for a second or two, but came back.

Did I get a bad plenum even worse than my factory one? Did the shop who removed the bolt for me somehow damage my throttle body? Is my unoriginal 4th TB bolt from the hardware store letting in air or something?

I have another throttle body that I ordered that I can install (when I thought I wasn't going to be able to get the bolt out). I guess my next move is to swap the TB.

Video of the sound:

https://streamable.com/vro9he

[Ilya]

It does actually sound like this, no?

https://www.youtube.com/watch?v=MM_QpWHZJgs

[VStar650CL]

It does actually sound like this, no?

https://www.youtube.com/watch?v=MM_QpWHZJgs

It sort of does, but I've never heard of a Nissan having an oscillating butterfly problem like those GM's. Yours is more regular, something spinning that's hitting something else. Like a collapsed lifter, except you didn't go near those. Have you put a steth on it to see where it's loudest?

[VStar650CL]

Uh-oh, wait a sec. You have a missing piece of stud. Did you ever find that?

[Ilya]

Uh-oh, wait a sec. You have a missing piece of stud. Did you ever find that?

You're right, I didn't. But I imagine that broke when I removed the nut so would have fallen away before I removed the plenum no? I didn't hear any sounds of anything falling inside the ports and a stud would have made a metallic noise.

This sounds like something fell into the holes?

[Ilya]

Changing the throttle body didn't make a difference and with a slight tap of throttle the noise got louder.