question about maf sensors

Z_ealot

ok, so going over the FSM I was curious about the section concerning MAF voltage readings. from what it looks like the FSM specifies that MAF voltage readings should be at 2.4V at 4,000RPM, is this right? or is it saying the voltage reading should be between 1.7V and 2.4V? anybody with knowledge on this would be helpful if anyone knows. Thanks in advance!

Z_ealot

Anybody?

SouthArk370Z

Post FSM page number so people don't have to search for what you are looking at.

__________________
Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

Z_ealot

EC-175 under "without consult-III"

SouthArk370Z

Voltage should be 0.7-1.2 at idle, rising to about 2.4 at 4000 RPM.

__________________
Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

Z_ealot

Well guess that solves it then....my maf sensors are officially on their way out....backprobed the sensors and both of them dont even make it over 1.9V at 4,000 rpm. Idle and 2,500 rpm readings are fine, but 4,000 rpm they faceplant....guess it's time for new maf sensors lol

SouthArk370Z

If both MAFs are reading low by the same amount, I would suspect a source voltage problem (eg, wiring) or a meter that is not up to snuff (eg, low impedance).

__________________
Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

Z_ealot

Tested both connectors, getting a steady 12 volt power supply and steady 5 volt reference voltage and good continuity for ground on both connectors

phunk

What are you trying to diagnose? What running symptoms are you having?

__________________

Z_ealot

Hesitation on snap acceleration and engine stumbling at idle...went and redid the testing....bank 1 (passenger side maf) reads 1.90V at 4,000RPM....bank 2 (driver side maf) reads 1.95V at 4,000RPM. Bank 1 maf at idle reads 0.70V and bank 2 maf reads 0.94V at idle

phunk

Mass Airflow Sensors increase voltage with airflow, not with RPM. Your MAF sensors sound typical to me. Just give it more throttle if you want to see more MAF voltage. 370zs often dont idle perfectly flat smooth, most cars dont. If you feel yours is outside average, post a video for us to see. The closed loop feedback will compensate for minor discrepancies in airflow readings. Ive never heard of a VQ MAF sensor going bad, so 2 at the same time in the same car would be quite the coincidence. Check your short and long term fuel trims for confirmation that your airflow readings are close enough.

__________________

Z_ealot

I understand what you're saying, but I'm just following the testing procedure by the book which is why I'm quoting the RPM's as the FSM specifies that the voltage of the mafs is supposed to be at 2.4V @ 4,000RPM, as for fuel trims that has been the other part of the equation as to why I'm testing them as my long term fuel trims have been consistently running at -10% for both banks and while short term fuel trims are ok at first staying within about 5% positive or negative, eventually after running the car for a bit they always end up closer to 20% in the positive and sometimes above that.

SouthArk370Z

Yes, but air flow varies in a predictable way with RPM. All stock 370Z engines should have very close to the same flow at any specified RPM and load conditions.

__________________
Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

phunk

So which load condition are you confident that the FSM intends you to find 2.4V?

__________________

phunk

Since the voltage does not specify engine load, the test is essentially erroneous. It also does not say 2.4V its says APPROX 2.4*. Thats a pretty vague range especially since technicians will decide on their own how to drive the car at 4000rpm. What the * leads to is a comment that says to look for a linear increase in voltage as you increase engine speed.

__________________