2001 Infiniti I30 - O2 Sensors Flatlining

Specific repair issues for Nissan + Infiniti vehicles
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protraxrptr17
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2001 Infiniti I30 - O2 Sensors Flatlining

Post by protraxrptr17 »

The customer complaint is the car stumbles and stalls when cold. Of course it runs perfect here. No codes. The only thing I see as a problem is all four oxygen sensors flatline lean at idle. Rev the engine a little and it goes back to crossing like its supposed to. I thought for sure it was a vacuum leak, but I smoked it and got nothing. What am I missing here? Can the heaters be bad on the sensors? All four of the sensors follow each other almost exactly when graphed. If one was way out by itself I would suspect sensors but....
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Re: 2001 Infiniti I30 oxygen sensors flatlining

Post by ricmorin »

What are your fuel trims? Sounds like a bad MAF to me.
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Re: 2001 Infiniti I30 oxygen sensors flatlining

Post by Tim Martin »

Well I am not all that experienced with the Infiniti vehicles but in looking at a wiring diagram for that particular car there is 2 Oxygen Sensors and 2 Catylist Monitors often called Oxygen Sensors as well. They all 4 have one thing in common and that is a power supply from Fuse #8 (15A) for the heaters in these sensors. I have never seen any vehicle where all 4 or even in a 2 or 3 Sensor system followed even close to the same pattern on a scan tool or lab scope. It would be my hunch that that common factor could be a clue to what the problem is. I have seen erratic power supply to Ford heated O2 Sensors give grief that can be hidden behind driveability symptoms. Can't be sure that is what you got here but it's just my thought.

Is idle speed too low for whatever reason?
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by steven kiser »

i'm with ric on the maf......
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by Tim Martin »

steven kiser wrote:i'm with ric on the maf......
Does a faulty maf affect the performance of post converter sensors? Those sensors usually monitor emissions out of the converter. Or am I wrong? Its looking like I gots me a few things to learn yet.
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by ricmorin »

It doesn't directly, but a MAF that is reading incorrectly will be in conflict with the sensors. The PCM will only give the engine so much fuel for a given airflow. I'm willing to bet there will be lean codes as well or at least LTFT at max. This is very common on that vintage of Infinity. There may be an updated MAF and I recall some PCM reprogramming as well. May or may not be a TSB on this particlular year.

Fuel trim diagnosis is critical here to differentiate between vacuum leak and bad sensor. Trims lean at idle only indicate leaks, whereas lean across the throttle range will indicate a sensor malfunction. Not set in stone, mind you, but a good rule of thumb.
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by Tim Martin »

Very interesting. I will be doing some testing here in my shop with regards to this.
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by steven kiser »

i've found that a bad maf will cause flat line readings, stumble, poor performance, etc, without throwing a code. i know it's taboo but when i have a vehicle, especially an older ford come in for any poor performance issues with no codes i replace the maf. some manufacturers claim a cleaning will resolve this issue but many times i've tried and more than enough have returned for replacement.
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by protraxrptr17 »

I dont recall the trim numbers, but they didn't really cause me much alarm, but I couldn't get the problem to happen while I was watching. The owner won't let me keep the car long enough to do a real good diagnosis. She only lets me have it while she's at work. I think yall are right on the MAF. I'm going to get the car back on monday and check it some more.
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by steven kiser »

good luck.
never argue with a fool, they'll drag you down to their level and beat you with experience
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by crmeyers »

The most problematic components on these vehicles are MAF's, coolant temp sensors, IAC's, and bad grounds. Nissans (Infinitis) are FUN!
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by steven kiser »

there's nothing like a ground bolt corroding internally. i remember my first like it as yesterday. after hours of banging my head i found the threads corroded. the ground bolt went through an intake. i loosened and looked and it was clean so off i went. well the gasket between the intake and block kept the intake from grounding. it was designed to be grounded through the bolt. all the bolts were corroded at the threads and the manifold along with everything else tied to it had lost ground. one of those "never assume" lessons.
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Re: 2001 Infiniti I30 - O2 Sensors Flatlining

Post by protraxrptr17 »

Well, I think the customer took it to somebody else. I had my secretary/wife call her to see if I could get it back to do some more checking and she said that it wasnt acting up any more (strange, because she called me every day for about two weeks when I didn't have time to look at it). She's one of those that asks everybody she knows about the problem and reports back to me what they said was probably wrong, and expects me to be thankful. :roll: Lost my diagnostic time, but probably better off.
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