MAF output question!

[FarFetched]

I could only get ~2.5V at 4000RPM. Does it mean MAF is getting weak or?I think I am heading toward MAF replacement!

[Q45tech]

Voltage depends on air flow. The only true test is to data log the MAF voltage during a WOT acceleration in 1st gear, Due to Consult memory time you only have 3 seconds worth so I start at ~~4,000 [30 mph] [and log thru shift [6500 rpm] [~~50 mph].

The VE is highest [gulp size per rpm] [amount of air the 4 cylinders allow in, to refill the cylinders] at 4,000 rpm [X] and drops by ~~20% at 6500 rpm but the rpms increase by 62%.........so......[X] x 0.8 x 1.62 =1.3[X].

What is critical is how the MAF behaves from 4,000>6,500 rpm.

Remember it takes 2 rpms [revolutions] to refill all 8 cylinders.

If you could see the shape of the MAF voltage RAW output [VVVVVVVVVVVV] before smoothing you could see each fill as the [each]valve opens...........~~ 460 refills per second at redline [6900/60=115 x4=460 compared to 46 at 690 rpms [idle].

46-460 Hz is in the audible range

[Q45tech]

Some approximations of a non Q MAF.

Since most engines [V8] produce less than 350 HP......MAF [dynamic range] tend to be selected based on displacement.100% of displacement divided by 2 x redline rpm gives 20% or more head room.

[FarFetched]

All that info is pretty impressive. I value your experience and knowlege. However, I need some real world info. I have worked arounf MAF systems, mainly GM trucks/vans. I graphed MAF sensors on our SUN machine. You could see MAF drop-outs or fuzzy response form MAF. Also, knowing veh history (we have detailed records for every veh in our fleet) help a lot. In my case I don't know full history on My Old LAdy (Y33 97). To me it seems that MAF drops out at sertain load/speed change. I don't have tools at home to verify if MAF and plot a graph. I work for state and cannot use state property for my purpose. I cannot either spend 120$/hr dor diag at Infiniti. Service writer said that if there is no MIL on, Consult woun't (in most cases) pick up anything!So if you have had any real world experience with MAF mulfunctions, please direct me on a right path!Thanks!

[Q45tech]

Ebay always seems to have inexpensive [under $100] volt-ohm-meters with high low memories. For a few hundred you can purchase a simple analog to digital convertor that would use the serial/parallel port of a laptop to data log a zero to 5 volt signal. with free software.

http://www.picotech.com/40_42_100.htmlh ... index.html

http://www.picotech.com/auto/w....htmlh ... /w...1.gif

http://www.bitscope.com/?c=565...644D9h ... lo...CB4EF

If you cannot afford a few hundred for dealer diagnosis...........most dealers are not very good at it.......takes too much time that they have a hard time getting paid for, then somehow you must acquire some test equipment. Or sell the Q or drive it like it is.

[DAEDALUS]

I think you already found your answer in the FSM. At 4000 RPM the engine is consuming about 80% of the max air that it does at redline--for best resolution you would want the MAF voltage as close to 5.0 V at redline as possible, with maybe a little pad built in. What this means is that 4.0 V is reasonable, and if you were between 3.8-4.2 I'd say you were probably fine. 2.5V doesn't seem normal at all. Are you backprobing the ECU connector to get this reading?

[maxnix]

1.) However, I need some real world info. 2.) In my case I don't know full history on My Old LAdy (Y33 97). 3.) So if you have had any real world experience with MAF mulfunctions, please direct me on a right path!Thanks!

1.) There is at least one extensive thread on typical voltages at RPM for the G50 on which Q45tech is an expert. Knowledge of FY33 is incidental from observing shop problems while he is there (not his job).

2.) Have your service writer at Infiniti of Kirkland print it out for you.

3.) Must read all previous posts by Q45tech.

[FarFetched]

I was backprobing at the connector.

[FarFetched]

I own a BluePoint multimiter (similar to Fluke 87) and have recorded min/max readings on the MAF itself (backprobing at MAF). Even when I redlined (almost) I didnt get more that 2.5-2.7V. It seems a little low, doesn't it?I don't suspect KS because when I had "free" run on Consult we didn't get anything at all. I also disconnected MAF and tried to drive w/o it. I felt the symptoms were (worse) similar to what I currently have with MAF attached. I think there is some kind of glitch going on with MAF. I am also looking through FSM PDFs. ALLDATA is good, but it is incomplete!Thanks guys!BTW: it is my first car with Mass Air Flow system. I know a bit more about Speed Density system (Chrysler). So don't kik me hard, I am learning!

[DAEDALUS]

KS can't impact the MAF readings directly. Voltage should be closely related to RPMs and nothing else, except for a bump up when the VTC solenoid kicks in. If the MAF is not reading right, though, the VTC probably won't kick in at all. I assume you've already tried to clean the contact points on it. If you have, then give the element a little blast of non-chlorinated brakleen. Any fouling will act as an insulator and throw off the readings.

[maxnix]

I am also looking through FSM PDFs. ALLDATA is good, but it is incomplete!

A lesson that everyone on this board has learned.

[Q45tech]

A 274 ci engine turning 4,000 rpm will consume [274/2...x 4000] /1728=....... corrected for VE [which on Q might be 90%]317SCFM x 0.9= 285 standard CFM

Same engine at 6,500 ~~= 360 Standard CFM due to lower VE [0.72] caused by valve restriction and shorter filling time.

I use standard CFM because we don't know temp or barometric or humidity.

Which can vary density of a CFM by 6% [1% per 11F] and baro by another 3% per thousand feet of altitude [plus variances]............the ecu expects that the MAF reading will be within 20% of what's in memory..........thus the fuel will be within 20% of normal.

WOT is much less critical as a 9.0-12.5:1 AF is acceptable in acceleration.The closer to 12.5AF the more power the engine makes [less cooling from excess gasoline] but also how you melt the pistons in high sustained loads.

Take a dyno torque curve [normalize peak torque as 100%, then look at the falling curve as rpm increases this shows the decrease in volumetric efficiency = how must less than ideal [274 ci] the cylinders fill with increasing rpm]...........not perfect but very close as friction [oil churning, etc] may increase slightly with rpm [4>7,000 rpm].

The problem is the MAF voltage is not linear [vs flow]..........the usual equation raise the voltage by the 3.5 power [exponent] plus a constant [inside ecu to arrive at a flow rate].

Now don't get confused here: The 1.2> 4.44 MAF output voltage represents a 600> 6500 rpm range and a from idle 10-15 gm/s to 220 gm/s.

Obviously the VE at idle is very low like 15% [only 15% of the cyliinder is filled with air, thus 15% idle fuel..........think how little HP is produced at idle just enough to overcome friction and maintain 650 rpm......turn the AC on and you need to produce 3-5 more HP.......more MAF voltage as more air needed.