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MAF reading / measurements. Nissan Altima 2000

506 Views 10 Replies 4 Participants Last post by  VStar650CL
For testing the MAF (mass airflow sensor), the manual gives specs given in the pic (see attachment).
I done voltage test at first and all look fine (numbers are within given ranges).
To double check, I also used the scan tool via the "Torque" soft.
It gives MAF reading in the units "g/s".
However, the Nissan's manual has numbers in "g m/s". What this extra 'm' means and stand for?
How to convert this reading in order to compare?


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As nouns the difference between gram and gms
is that gram is a unit of mass equal to one-thousandth of a kilogram. Symbol: g while gms is plural of lang=en; grams.
Thanks for prompt replay.
. So, you would say that, "g/s" reading is same as "g.m/sec" ?
Let me note that there is dot (".") between "g" and "m" . I thought that dot stood for multiplication.
g/s should be gram per second. Thus, I am still confused ..what is "g.m/sec" ?
Thanks .
For me this measurement is important to decide if MAF sensor is bad or not.
I am getting P0171 code, which, besides other reasons, can be due to the bad MAF sensor.
By voltmeter measurement, I am getting:
1.3 V at idling; and 2 V at 2500 RPM.
These are within allowed ranges.
However, scanning tool shows:
2.3 g/s at idling; and 9.1 g/s at 2500 RPM.
Both these are out of the ranges (are low).
So, I do not know replace the sensor or not. Since it is not a cheap part,
I'd like to be sure..
Any other ideas, how to pin point and resolve these two "controversial measurements"?
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Yes, short term trim is about 25% at idle, and goes down to 0--5 % for 2000--2500 RPM.
Should I look for leak at intake or at exhaust?
Intake leak gives non-accountable air in the system.
At the same time, I guess exhaust leak before cat converter, would affect O2 reading..
It's an intake leak, exhaust can cause codes but not a P0171. Check for cracks in your intake boot, leaky gaskets at the Throttle Body/MAF, and the intake manifold gaskets particularly around the #4 runner. Those are all common issues on KA24's, but it's an old engine, a lot of your rubber stuff could potentially be dried out and cracked. Spray around the all the induction parts south of the MAF and all the vacuum hoses with something combustible like Gumout or Brakleen. Listen for idle surges, the combustibles will get sucked into any vacuum leak and temporarily richen the mixture, causing the RPM's to rise.
So far, I was unable to find any leak (used whole can of carb cleaner, to spray at different spots).
Can open stuck PCV valve be the culprit?
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