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Jay, Certified Infiniti Technician
Category: Infiniti
Satisfied Customers: 20258
Experience:  20+years, Nissan and Infiniti experience and currently now working for a Infiniti Dealer
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Intermittent p0300. My question is regarding the upstream O2

Customer Question

Intermittent p0300. My question is regarding the upstream O2 voltages. At idle bank 2 holding steady around 0.6 and bank 1 around 0.3, is this normal on a G?
Submitted: 1 year ago.
Category: Infiniti
Expert:  Jay replied 1 year ago.

Hello my name is ***** ***** thank you for your question

Does it feel like the car is running ruff? When you have misfire issues 02 sensor readings are affected by it so you may not be able to use their readings.

Expert:  Jay replied 1 year ago.

What brand spark plugs do you have in your engine?

Customer: replied 1 year ago.
The drive feels normal. I can't confirm the brand, were recently replaced, parts from Bennett auto or Autozone. I've done a bunch so far and could give you some brief history if you like?
Expert:  Jay replied 1 year ago.

Well these engines are very sensitive to the brand spark plugs. If any other brand spark plug was used other than NGK you can get misfire codes. Especially if the are Bosch

Expert:  Jay replied 1 year ago.

Go ahead and give me history and see if you can find out the brand spark plugs installed

Customer: replied 1 year ago.
Sounds good I'll confirm the brand before moving forward. A brief history in the meantime:•After purchasing the car 2yrs ago the p0300 displayed a few days later.
•Current Mileage about 115,000.
•Replaced spark plugs, cleaned throttle body, added fuel injector cleaner to fuel tank, inspected the MAF, ok.
•Found oil in several spark plug tubes
•Replaced all 6 spark plug tube seals,valve cover gaskets, and lower plenum gasket.
•Upgraded to a plenum spacer, k&n air filter, and straight intake pipe (I know I was being 18 again).
•About 6mo later, car died. DTC showed crank sensor error, replaced and tested ok but intermittent p0300 still continues.
•10,000 miles later, problem persists.
•Purchased Centech obd2 scanner.
•Rechecked spark plug tubes, no oil.
•Idle with A/C off around 650
•Sounds like an exhaust leak, ignored for now.Thanks so far Jay, I'll get back to you about those plugs today or tomorrow.-Joe
Expert:  Jay replied 1 year ago.

Well Joe, Here is somethings I will say about your history.

First I am going to speak to you what jumped out at me the most. The cold air intake with K&N air filter. When you have this setup along with a plenum spacer, you need to install bigger injectors. Everything you did as far as the Mods go will make this car run more and more lean. When the car runs lean it can damage the catt converters. K&N Air filters along with cold air intakes cause a air vortex into the intake. Where normally this would be how you want air to enter the engine. How ever, the MAF sensor design is for the factory intake so it is looking for air to hit it straight on because it is recessed into the plastic housing. So if air is coming on it sideways cause of the K&N filter and cold air intake, it is not going to meter air properly. Any time you have a imbalanced of air and fuel you can get misfire issues as well. You can also get it if you use Regular Fuel right now. During the winter months, all fuel manufactures add Ethanol to the fuel. Which acts like Oxygen in the fuel. Which can make a car run lean. So now mix Regular fuel with a K&N air filter with cold air intake and a plenum spacer. This car is for sure running lean!!

So where to begin. First!! Spark Plugs! They are the most common. Make sure you have NGK Platinum Plugs. Second!! Try to use Premium Fuel this time of year. They don't treat premium cause of the high octane level. If you still have the factory Air intake you want to install that until you are ready to install bigger injectors and see a tuner to balance out the fuel and air trim for you.

As far as the exhaust leak goes, it's most likely at the flange at the rear of the car.

Do you have any more questions on this?

Customer: replied 1 year ago.
Hmm makes perfect sense. However, the intermittent p0300 was occurring for about a year before I laid a finger on the car. Everything was stock and garaged kept. I live in FL so winters are mild and always use premium fuel. I've learned to live with this p0300 because it doesn't seem to affect performance much.Assuming we put the vehicle back to stock and I was still getting intermittent p0300 with NGk plugs could you provide a troubleshooting path I could take? I thought I verified the injectors by ohming them out but should I monitor fuel pressure (sounds like a pain to do)? And monitor intake vacuum?I thought working off O2 readings might of been a good start but since you said that's probably not a good idea with misfires I'm at s loss.Thanks Jay
Expert:  Jay replied 1 year ago.

If everything is back to stock. I would be looking at the Catt Converters to see if they are restricting.

Expert:  Jay replied 1 year ago.

Fuel pressure I would be checking as well.

Expert:  Jay replied 1 year ago.

Monitoring the air and fuel trim and then using 02 sensor readings also can help isolate the issue as well

Customer: replied 1 year ago.
Thanks Jay, just 1 last question regarding the o2 readings and if I'm seeing is normal. B1S1 avg 0.3 and B2S1 avg 0.6 is this normal? I would expect to see a rapid change between about 0.1 and 0.9 but I don't see that. Both o2 sensors respond in that range about 0.1 and 1.2 during accel and decel but not idle.Thanks,
Expert:  Jay replied 1 year ago.

The only time I have seen front 02 sensors flat line is if a after market MAF sensor is installed.

Front 02 sensors normally switch rich to lean. But if it has A/F sensors it doesn't switch.

Customer: replied 1 year ago.
Thanks again Jay for the tips! Ill keep at it.
Expert:  Jay replied 1 year ago.

You got it!