Buddy has a 2004 G35, picked up at about 135k; ran fairly good.
Replaced plugs, oil, filter, intake filter (Injen replaced with K&N pod), coil packs (one misfiring, replaced all 6).
Now at 137k, runs much stronger minus a small idle issue.

Now we're experiencing at certain times, the car will sit at an idle just fine, but sometimes at stoplights, the car will begin sputtering, the battery will dip down to ~11v, and will die.

Currently, we can make the car NOT die, but giving it some throttle, keeping it at ~1-1.5k RPM, and the car won't sputter to death anymore.

We had an exhaust leak, fixed that; no active CEL code.

Brought it into a local shop, they quoted:
1. Upstream O2 Sensor
2. "Bank 2/Passenger" Knock Sensor
3. Valve Cover Gasket.

Obviously the valve cover gasket is common; but that's a lot of money we're not quite ready to sink in yet.

We looked to see how difficult the knock sensor was, and decided to have the shop go ahead and do the knock sensor, and we would tackle the O2 sensor ourselves (going to replace both upstream/downstream for good measure).

O'Reilly's was thinking a vacuum leak- we ran Seafoam through the engine, but didn't get a big cloud at all, we are assuming due to the massive exhaust leak. However, we did notice some come from the passenger rear of the engine, and not sure if it's a vacuum leak or part of the exhaust leak.

Any thoughts?
Techs said the engine appears to rev fine, looks to be healthy; I requested a compression test for good measure.

 

Are you throwing any codes? I wouldn't just go throwing parts at it. I'd look around for vacuum leaks first. You can make a DIY smoke machine or blow some cigarette smoke or cigar smoke in the intake area to check for leaks.

I tracked down a vacuum leak using a vacuum gauge hooked to the small port on the plenum. It would bounce around like clockwork. So, I then started isolating the hoses and narrowed it down to the brake booster vacuum lines. Ended up being a large o-ring between the firewall and booster was causing all my problems, I built a DIY smoke machine and saw the smoke coming out of the firewall, I fixed it with duct tape until I could track down the 15 dollar o-ring.

Upstream O2 sensors are PITA to swap out and the rears are pretty easy. I attempted O2 upstream, downstream swap, and even spent 300 bucks for a new MAF sensor.

Try unplugging and/or cleaning the MAF that can also cause issues, but it will not put out any error codes if it's just giving wrong values. You'll get a code if it's unplugged, but the engine will run in a default mode and if your issue goes away try getting a used one first.

I just swapped out my valve cover gasket and it wasn't too bad, but the driver side was a real PITA. I had to do the same job on my RAV I am giving my brother. Except this time I bought this permatex form a seal stuff. I wish I had it when I did the G it makes the job a lot of easier of keeping the gasket in place, so you can set it on the valve cover without it moving around.

 

We didn't have any active codes throwing making the CEL turn on, but the shop said they pulled active codes; then again we are using a cheapie wireless OBD-2 hooked up to DashCmd on an iPhone; so not quite the full diagnostic as we could be using.

What was the difficulty doing the upstream O2?
We are deciding whether we want to attempt it or not.

 

Mostly space limitations, but if you aren't throwing codes I wouldn't replace them. I ended up buying a whole O2 sensor kit from Harbor Freight to get the sensor off. I then returned it when I was done, since I didn't have a need for it. The other O2 adapters I tried couldn't fit it where I need it to.

Can you measure short term fuel trim with DashCmd? If you can monitor that information it should give you a good idea how your O2 sensors are working and/or if you have any leaks. Both banks should be about +- 10% in range of each other. For example when I had a vacuum leak both banks were running lean at +125 or+25%. If it's running rich then it should be -75 to 0. If you unplug the MAF I think it drops to -25 to run in an open loop mode, but it stays constant. If you have a vacuum leak it will jump around. Now, after everything fixed it's usually about 105-109 for both banks, they are also usually within +-10 of each other.

I'd also just have you charging system checked to rule out intermittent alternator/battery issues. I have a small plugin charging check from Harbor Freight. You plug it in, turn the car on, and LEDs light up showing if the voltage is green, yellow, or red.

Valve cover gasket you can do yourself for about 30 bucks.

 

Got it, we'll go ahead and order the O2 sensors anyways just to have them on hand in case they fail, anyways.

I believe we were going to pick up the O2 kit from O'Reilly's/AutoZone as they rent them out for 48hrs for free.

DashCmd does do Fuel Trim & O2 Sensors, as well as AFR and a few other neat gizmos that mean nothing to me

What you just said will be very helpful when we get the car back.

We plan on taking the car straight to AutoZone and borrowing their rental "Advanced OBD-II Scanner" to check for cleared codes, etc.

We'll probably run the car for a bit to see if the shop's knock sensor diagnosis (which actually turned into a knock sensor harness suspect) fixed anything, and then to "re-learn" any of the other odds and ends.

He has a Duralast AutoZone battery which has been replaced once or twice; we think the parasitic draw from the Bose amp is draining the battery, just wrecking it; but we haven't really had that issue since.

AutoZone/O'Reilly's has since checked the starter, alternator and battery and all checked out okay.
My big concern is, is why is the battery meter (Innove 3721) clearly dips down to 11V before dying; that part is suspect as if it were JUST the engine dying, wouldn't the battery be able to keep the ~12V charge for at least a few moments?

Mind boggling, really.

 

I would definitely monitor your fuel trim levels, since that can you tell if you're getting extra air into the system, which would explain an idle dying problem.

But, the battery voltage you mentioned dropping down did puzzle me as well. The car should be able to run for a few minutes off just the battery. Is the battery fine after the car dies though?

 

Any time in particular to monitor the fuel trims?
More so in idle than when on the throttle?

Correct, battery dips to sub-11V, then dies (if no throttle is applied).
Once dead, wait about 5 seconds, restarts just fine. (Most of the time. sometimes, it needs to stay off for a few minutes before being able to start back up).

I thought about a bad ground/connection; but wouldn't that be more of a concern...consistently and at random times versus ONLY at idle?

 

I'm surprised no one's mentioned this yet but it sure sounds like a camshaft sensor issue. y car finally succumbed to this common issue this week. Hard start, sputtering, sluggish acceleration etc. They are notorious for gong bad and not throwing a code or any other visual proof there's an issue. My VDC, Brake, and Slip lights all came on along with the SES light so I knew what was up. Sure enough P0340 Bank one Cam sensor. If you end up going this route make sure you buy OEM sensors as our cars don'l play nice a lot of times with aftermarket sensors. And buy it from Nissan, not Infiniti, and you'll save about 20% for the exact same part.

 

when i picked up my 03 G coupe with 113k, I did all the sensors and new plugs, gaskets ..etc.. Had an intermittent stalling issue at stops. turned out it was the fuel injectors seeping and wetting out the cylinders. this doesn't throw a code, and the extra fuel can melt catalytic convertors quickly. worth a check if you are still having problems. I picked up a set of used injectors and sent them to a rebuilder I have used on several of my cars. no downtime and ran like new after I installed them.

 

The shops have mentioned Nissan's being famous for having poor camshaft sensor issues; however they mentioned it's typically stalling/sputters out at ANY time; and not JUST during idle. Additionally, that throttle wouldn't help at all.

Is this not true?
Otherwise, it seems the opposite of a camshaft sensor.
I've never done those sensors, so I wouldn't know.

After the spark plugs, I thought it might've been the fuel injectors, but we're not sure.
Is there any way we can test those besides pulling them out and testing?

 

There is a noid light or another tester like this you could probably use: https://www.amazon.com/Waekon-76462-...XV23JC8H6TED36

 

Hmmm you might have a point. Mine just started Thursday and so far it only happens on idle. However I don't daily the G any more so I haven't driven it much since the issue popped up. I'm pricing the sensor today at our local Nissan dealership, Amazon has authentic OEM's for $74 shipped for the Bank 1 sensor.

 

You want to monitor the fuel trims at idle, since if you rev the engine the extra will kinda be negated. You can check fuel injectors with a noid light or something like this: There is a noid light or another tester like this you could probably use: https://www.amazon.com/Waekon-76462-...XV23JC8H6TED36

Are they doing in-depth tests on your alternator though? Maybe it's not putting out enough of a charge when the car is idling? That could also explain why you have to rev the engine, since it puts out more power when the engine spins faster.

 

lol at the stealerships:

Nissan-$143
Infiniti $170

Same fvcking part...............

 

Infiniti dealership quoted a $1,400 repair for the knock sensor & harness.

We dropped off the harness on Saturday, and plan on picking it up Monday and asking them what they ended up doing with it!

I was also thinking alternator, however O'Reilly and Autozone both sat there with the machines hooked up for a solid minute or so, and stated it was fine- didn't know there were more intensive tests we can run on it.