question about maf sensors
 

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! :)

Anybody?

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

EC-175 under "without consult-III"

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

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

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).

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

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

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

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.

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.

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.

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

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.

Standard safety procedures will mean the car is in P or N, ie, no load.

I havent seen that stated anywhere.

But I think I will step aside and let you spearhead the diagnostics of his MAFs :tiphat:

If the Nissan engineers wanted the engine tested under load, they would have said so. Procedure says to hook the harnesses back up, start the engine, check idle V, rev to 4K, check V - no mention of loading the engine.

Please don't. Everything else in your post made very good sense. Going by the many "odd" problems OP is having with his Z, it looks like he needs all the help he can get.

If it helps any my scantool reads the airflow at idle at 3.5 g/s

Since, as phunk said, it is unlikely that both MAFs went out at the same time, I'm still leaning toward a high resistance somewhere in the wiring common to both MAFs.

You said you had 12 and 5 V at the MAF harness connectors but that was at no (electrical) load. To check for high resistance between source and sensor, you need to check V when the MAF is operating.

But it's possible that they went bad together. With all the other problems you are having, it wouldn't surprise me if they all have a common cause, ie, wreck, water damage, etc. I'd see if I could find someone that would loan me (or sell cheap) a known good, used MAF and see what it reads before buying a set. If the same MAF is used in other, more popular Nissans, it will help your search. CourtesyParts.com has a good parts look up for 370Z - look and see if they have some kind of cross-reference for part numbers.


Edit: Or you could have a problem totally unrelated to the MAFs. Lots of weird things going on with your car. :(

Did exactly that while i was waiting for a response....both connectors show 12V or above while engine is operating and same for the 5V reference wire

Edit: went and double checked since i could not remember exactly....both bank 1 and bank 2 12V wire reads 14.1 volts while engine is running while bank 1 5V reference wire reads 2.54V and bank 2 5V reference reads 1.30V while engine is running and harnesses are connected to mafs

Maybe you do have two bad MAFs.

Have you cleaned the MAFs and changed air filters?

Cleaned the mafs multiple times and air filters are brand new changed out 3 months ago and no leaks or blockages in intake tract or intake manifold

Late and tired so didn't fully read everything but honestly I would never ever ever diag MAF's with a basic DMM. You really need a scope to watch the curve. Even with that it has to be fairly fast for some cars today, my old scope I had I car I absolutely knew it was the maf, I could just tell by the sudden fuel cut and then jump right at 2k rpm it had to have a drop out but my slow scope couldn't see it and now sadly that scope screen is deing so a PICO may be in my future but a DMM for maf, nah.

Keep in mind your scan tool baud rate is not as fast as your PCM inputs just an FYI.

just an update, but I decided to disregard the maf sensors for now and look at the main issue which is the fuel trims indicating a lean condition. decided to start with the simplest thing I could think of which is the vacuum hoses and pcv hoses and valves. brake booster hose and all other hoses connected to the intake manifold or had anything to do with vacuum checked out visually OK so moved on to spraying around each hose to see if that did anything....nothing. lastly decided to pull off the hoses for the pcv valves and guess what I found.....a nice little puddle of oil on the connectors where the pcv hoses meet with the intake manifold. pulled the hose off the pcv valve itself and same thing so popped one of the pcv valves off for testing and here's the video of what I found.....



if I remember right from reading around these valves shouldn't be hissing like that and there should be next to no suction at idle if the valve is operating correctly, can anybody confirm this or am I getting faulty information?

P.S.

when holding the valve in my hand I can feel vibrations coming from it while vacuum is being applied to it.

totally normal.

It sounds like there is a hole in the PCV hose where it meets the intake. This could definitely be why you have been running lean since there is unmetered air entering the engine.

So this information is wrong?

AGCO Automotive Repair Service - Baton Rouge, LA - Detailed Auto Topics - What are the Symptoms of a Bad PCV Valve

Also, the system has thrown a p0171 at me before in case that helps any. I replaced both the throttle body gaskets and the upper intake manifold gasket thinking those might be the culprit and havent had that code come back after that but fuel trims still indicate a lean condition.

Only if it says the video you posted isn't normal!

Shouldnt there be no oil in the pcv hose though if the valve is functioning correctly?

Oil coming through the PCV and into the intake is completely normal. The PCV system does not discriminate oil and vapor from clean air.

What would you suggest is causing the lean condition then? Fyi LTFT is considtently over negative 10% with STFT going up to over 15%

if long term and short term are opposite but the final product is a satisfactory AF, I'd figure perhaps varying blends of ethanol in the fuel just making the fuel trims do their job.

So what about the hesitation and stumbling at idle?

I haven't seen that yet so cannot really comment. Sounds normal in the PCV video though.

Someone is selling a nice pair of catch can's for around 3k on here.

Are they made of gold? lol

Not Sure-It's Top Secret Brand.

Would not be bad to install a pair;as long as they are functional.
over time the sucked oil (blow by from engine) will gum up in the combustion chamber.
unsure your milage on engine or fuel type/quality being used,,,but i've seen lot's more harm than good from the 10% ethanol blended fuel's.
Ethanol fuel (e-85 etc.) work's great when all supporting components are in place for it & the car is tuned for it.....unsure the shelf life or how long you would want it sitting in your tank;as conventional 10% ethanol gas will begin separating as soon as 1 month (+ or - a bit).
I pay more; but continue my ethanol free93 fuel without problems.
The factory fuel system on these car's don't have a return fuel line-as there was one occasion that i had a stumbling under hard load & not accelerating,,,i checked all known connection's from electrical to vacuum & then removed fuel line to rail & purged out some fuel....thinking maybe got some bad gas-but was all clean.
Car ran perfect ever since.
There are way more skilled & knowledgable people on here that have valid input's.
A little more maintenance is required,but catch can's may be a start to prevent gumming up inside the intake system.
Also a failing or clogged fuel system can cause it to go lean & even show mis-fires.

Gonna pick up a couple of pcv valves today just as preventative maintenance. I do recall when i had the upper intake manifold off the the chambers on the lower intake manifold leading to bank 2 had quite a bit of oil built up on them while oddly enough the chambers leading to bank 1 barely had any oil build up at all. Not sure if that indicates anything, but still the pcv valves on this car are the originals and the engine has close to 157,000 miles on it. As a side note i have run a couple of cans of fuel system cleaner through the tank before just on the off chance that there was a clog somewhere in the lines back when this all started, but didnt seem to help much