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2006 Nissan Altima V6 Random Misfire and High Fuel Trim - Big headache! Will buy beer! :)

Ok - I recently got the random misfire and have basically tried everything and no luck! I also have high Fuel trim in only Bank 1 but no code for it is coming up.

Current issue:
Random Misfire P300
High Short Term Fuel Trim on Bank 1 (+25%) when idling (Bank 2 looks fine)
High Long Term Fuel Trim on Bank 1 (+10%) when idling (Bank 2 looks fine)

Rough Idle

What I’ve done:
Checked compression - All 6 cylinders report around 180psi
Replaced all 6 spark plugs
Replaced all 6 coils
Replaced all 6 fuel injectors
Replaced Fuel Filter Module
Replaced Upstream Bank 1 O2 Sensor.
Replaced intake manifold gasket
Visually inspected for vacuum leak.

What else can I do? This has been a headache for almost 6 months now and finally gave up. Any help or guidance would be much appreciated. Will even send money for beer :slight_smile: if it points me to solution.

Thank you!!!

Lazy O2 sensor.


Sorry - I forgot to mention I replaced that as well. lol

Please clarify: Is the short term fuel trim on bank 1 negative 25%, or positive 25%? What’s the long term fuel trims when idling the warm engine?

@George_San_Jose1 Bank 1 is +25%. Long term is 10%.

+10% fuel trim means the computer finds it has to inject 10% more fuel to meet the demands of the O2 sensor than it thinks it would have to based on the other a/f sensors (maf, ect, tps, etc.) You’ve pretty much already replaced the most likely parts suspects. hmmmm … The best clue in your favor is the +10% long term fuel trim on bank 1, with no fuel trim problem on bank 2. My guess is you’ve got unmetered air leaking (mostly) into bank 1 somewhere, and that is confusing the computer’s calculation for how much fuel to inject.

Here’s where I’d be looking first

  • exhaust system leaks affecting bank 1.
  • fuel injector o-ring seals
  • pcv valve
  • egr valve

Common sense says to check the entire vacuum system function for leaks, including checking the vacuum controlled devices, especially the brake booster. Easily done w/ a hand-held vacuum pump. Spraying starter fluid here and there with the engine idling might provide a clue, if the engine rpm speeds up when spraying in one particular spot. Blocking off entire vacuum lines which aren’t needed when idling (such as the brake booster) and noting the change to the fuel trim might provide a clue. PCV valves do fail on occasion, create difficult to diagnose vacuum leaks, and are inexpensive, I’d just replace that part. Replacing the EGR valve is probably a pretty big job, but you should follow the shop manual instructions on how to test it installed on the engine. On my Corolla to test the EGR I hook up my hand held vacuum pump to the EGR and verify applying vacuum. stalls the engine. Beyond all that, studying the engine configuration and identifying what’s different between bank 2 and bank 1 might be helpful. Hope that helps. Remember you always have the option of taking it to a shop with a Nissan scan tool, with their expertise and diagnostic tools they will likely figure it out eventually. My guess is you’ve got an exhaust or EGR leak. Best of luck.

Thanks @George_San_Jose1. Today I went under the car again and inspected the catalytic converter. I did notice there was one bolt missing thats attached to exhaust manifold. I tried spraying soapy water and a bubble very slowly started to form where the missing bolt is located. Do you think this would cause this dramatic of a change in reading? I’m in process regardless trying to find a replacement bolt in the meantime.

Personally, I’d be looking more closely at the +25% stft

It’s quite substantial

That’s a definite possibility.

eliminate all known intake and exhaust leaks first

Do NOT reset the fuel trims

After the repair, drive the vehicle for awhile and let the fuel trims stabilize on their own

Then report back to us, please

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I’ll add something, in regards to intake and exhaust leaks

Assuming you don’t have an evap/smoke machine . . . few diyers do . . . there is another way to help find those leaks

At idle and with the scanner hooked up, spray carb cleaner at suspected areas, such as intake gaskets. If you see the fuel trims change dramatically, you need to dig deeper

I actually have a smoke machine. I’m just unsure how to best utilize it to find any issues.

Disconnect the air intake at the filter

Now find a way to hook up the smoke machine to pump smoke into the air intake, towards the egine . . . there should be a large cone-shaped adapter that came with your smoke machine

Start dumping in smoke. your smoke machine probably has a knob to modulate the amount of smoke you’re dumping in. The mid-position should do just fine

If the intake gaskets are flat, your exhaust manifold gaskets are leaking, etc., you’ll see smoke soon enough

it should go without saying you’ll be doing this with the ignition off . . .

ok so I smoked it out. There was smoke leaking right before the throttle body where it meets the rubber hose - so I tightened it but still leaking a little there. And very little from the oil cap. Nothing else that I could see.

what bank is the oil filler cap on . . . ?!

what about exhaust leaks . . . ?!

any exhaust leaks on bank 1 ahead of the upstream oxygen sensor . . . ?!

another idea to entertain

I assume this is VQ35 engine, is it not?

if yes, it must be the twin brother of VQ40 I worked on in my Pathfinder

it has a birth defect around the mid-2000s where the secondary chains would eat through the plastic tensioners and camshafts would start banging around, which can lead to random misfires I bet

the tell-tell sign of the problem is the infamous “VQ engine timing chain whine”, you can search for the samples on youtube

@thegreendrag0n Yes I have a VQ35DE and this is DEFINITELY happening in my engine. Thanks for bringing this to my attention. The only thing that I’m confused about is why the +25% fuel trim ratio? Can this be caused by this as well?

I’m not a professional mechanic to make this call, but I would suggest that if you indeed have a problem with secondary timing chains to take care about them ASAP

in my case, one chain was flapping so badly that the imprints of the “back stroke” were visible on the secondary camshaft and per Nissan’s mechanic assessment, whine in my case was not yet very pronounsed, they suggested I can drive it for few more months

if you decide addressing the issue, the work to replace chains is not that bad, but do not trust the Nissan shop manual that you must remove both front and back side of the timing cover, it suffices removing only the front side to make everything work

also, while there, it makes sense to adjust valve lash and to replace valve seals and water pump

after doing all of this, my engine burns virtually no oil with 4-5K miles oil change interval and valve ticking disappeared

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