I have a 96 Max with over 285k miles. I have never really had many
issues with it beyond the usual maintenance and wear and tear.
However, for the last 3 years, almost all of my emission sensors have
been replaced. I thought I was through with all that for another 200k
when my "Check Engine" light just recently came back on. It was 0503,
the RH Heated O2 Sensor.

I purchased the normally $80 part online for about $50. It was an SNG
sensor. I replaced it, reset the computer and drove. I also replaced
my fuel filter and added a short-ram intake kit all on the same day.
Almost a week later, the light came back on. It was the same code. I
cleared it, and it came back on the within miles.

I have reset it a few times. Since all of this, my car has been
getting less MPG, from about 27MPG to 18. Moreover, it has now
started to hesitate when I am accelerating from a stop or from less
than 20mph. It is almost acting as if it is not getting gas or
something.

It drives fine on at highway speeds. It accelerates a little faster
to 60, 70, 80 and so on. In addition, I have been able to drive at
80, 90 and even 100 without the car going over 3,000RPM. I attribute
that to the air filter mod, but I could be wrong.

Therefore, Nissan community, what do you think the problem is? Is my
new O2 sensor bad? If I had bought it locally, would you have
suggested I returned it already? On the other hand, is it the mod or
something else?

* I will let you all know that I am no expert but I have done most of
the work on my car (CV axle replacement, radiator and such), so I am
no slouch. However, I am lost on what I should do next.

On Mar 6, 9:02 pm, "Charlie 3" <Just... (AT) gmail (DOT) com> wrote:
Have you changed the coolant temp sensor? When that sensor goes bad
you never see a code. The car's milegae gets worse and power gets a
bit weaker. Before you replace the O2, I would try that.

Also, once changed, the ECU needs 2 or 3 tankfuls to relearn its feul
curve according to the readings that its now getting from the replaced
temp sensor.

CD

Not true, if the ECM detects a problem with the coolant temp sensor it will
flag a code

On Mar 7, 5:55 pm, "NissTech" <Haywood_Jablo... (AT) msn (DOT) com> wrote:
I should clarify then, and say that when the coolant temp sensor
starts to fail, but not quite, the ECM will not pull a code. Symtpoms
of a dying temp sensor are the bad gas mileage, some loss of power,
and the car never quite getting to operating tempurature.

The O2 sensor is that way as well. I've replaced dying ones that never
pulled a code and the car just came back to life with the new one.

CD

SO put the stock airbox back on. You should only create ONE problem at a
time! (-:

-SP

Charlie 3 wrote:

You're saying that the air filter mod changed the RPM to MPH ratio?
It wouldn't.

"Charlie 3" <JustCS3 (AT) gmail (DOT) com> wrote