Disspelling the MAF MIFF

[scuzzy]

myth, rather.

I don't aim to slam this down and go "YOU ARE WRONG", nor is this an attack on Nico in his thread, but we need to do some more research into this soon.

So my day was fun and eventful, I have a Compaq Presario 1200 series laptop with an AC adapter that outputs 19 volts DC. I was about to test this MAF theory

The theory goes that removing the backing plate in the rear of the MAF allows air to flow at significant more levels across the MAF wires, the effect is that it takes more air to affect the same resistance change in the lines - more air to generate the same voltage in the MAF as with the plate.

Allright, back to the first story. I was about to test the theory - I turned around, heard a crackling/sizzling noise, turned back to find my AC/DC inverter literally on fire, smoking like nuts. no clue what did it. laptop is fine.
After trying to find a new inverter, I experimented with the laptop, and it now runs directly off the battery (blah blah voltage spikes will kill it. yeah. I know) The upside is that when cranking the car, the laptop stays running (versus cutting off with the inverter) - so I can see cranking events too and all sorts of neat stuff.


Now, this perticular plate sits atop two metal pedestal's, to which it is affixed by two very tightly secured phillips screws. Remove it and you'll notice there's a nice shaft infront of it (behind the sensor) extending both directions. air is meant to flow around the plate.

So I took before and after readings of my airflow signal at idle and at 1500 rpms. Sorry, no 4000 rpm idle ups, and keeping track of the signal while trying to drive is a pita.

My idle is 700 rpms, verified with the scantool.

0.92 @ 700
1.34 @ 1500

Without plate:
0.87 @ 700
1.28 @ 1500


Personally, these numbers are within a reasonable error percentage - but it does look like there could be some slight improvement.

How much? I don't know yet, we'll have to wait for someone else's experiences as well.


but at idle, the difference is negligable.

[NICO]

yes sir i told you, you can do all the test you need.

what me and paul did at neetronics is stamped in subaru legacy turbo history.

no need to swap out our overly well made maf sensor just remove the plate in the back and the jdm turbo ej22t 22b motor starts to show its secrets.

[Legacy777]

Looks like I need to build a MAF testing rig

Damn.....I really want to do this now. I'm more concerned with how the air flow is flowing past the sensor, if there's turbulence, and if the data read is repeatable.

Also....to add, you really shouldn't remove the plate if you don't alter your fuel trims because you'll probably be running a little on the leaner side.

When I get time to test I could check before & after data with my wideband.

[scuzzy]

Looks like I need to build a MAF testing rig

Damn.....I really want to do this now. I'm more concerned with how the air flow is flowing past the sensor, if there's turbulence, and if the data read is repeatable.

Also....to add, you really shouldn't remove the plate if you don't alter your fuel trims because you'll probably be running a little on the leaner side.

When I get time to test I could check before & after data with my wideband.

I'm running an EJ22T on an EJ22 NA computer, safe to say, I'm a little pig rich

[NICO]

josh test it out its worth it, all i seen before the plate was a dead spot nothing past like 10psi. then i opend it up and he siad it did not max out no more so we turned the boost up and i seen how it did not go even near the end of the table. he siad you have room for like 20psi now.

[scuzzy]

Allright I have interesting results to report today, stay tuned. I've got to do one more uphill pull and compare that then I'll post it all here.

[scuzzy]

Allright, here we go.

I did these tests with the car warmed up to 180-200F in every situation.

First off was with the maf plate

Code: Select all

Engine Speed:	700	AC: OFF	Airflow: 0.92V	Load:	52
Engine Speed:	850	AC:  ON	Airflow: 1.20V	Load:	65
Engine Speed:	3000	AC: OFF	Airflow: 3.24V	Load: 	255
Engine Speed:	4.2K-6K	AC: OFF	Airflow: 4.08V	Load:	255

I repeated the test with the maf plate off. These are the
results:

Engine Speed:	700	AC: OFF	Airflow: 0.82V	Load:	43
Engine Speed:	850	AC:  ON	Airflow: 1.14V	Load:	61
Engine Speed:	3000	AC: OFF	Airflow: 3.26V	Load:	255 
Engine Speed:	4.2K-6K	AC: OFF	Airflow: 4.20V	Load:	255

Here are some other things I noted.

Promptly after removing the plate, I took the car around the block, gave it some revs, drove it in low rpms (lugged it) drove it hard through first and tried to see if it was going to ping. I didn't notice any pinging via the scantool, the engine sounded ok and didn't hesitate.

After the plate removal, however, she started to idle really rough when coming off of an engine load, no stalling, just a little rough running. It's cleared itself up since then (I'm still running with the plate off) I also wanted to note that after plate removal, my usually rich idle of 0.85V O2 dropped
to 0.00 and hovered, it came back up after letting it idle for a little bit and the scantool reported the ECU had a fuel trim of approx +5%

As of late, the fuel trim has settled to -1% to +1%

Timing correction stands at +3* when idling, +2* with AC on

My cruise timing advance, with a TPS signal of approx 4 volts, load of 100 (of 255) and airflow of around 1.5V is 45 degrees BTDC

Idle timing is 20 degrees +/- 1 degree

WOT O2 signal is 0.88 to 0.75V (rich)


All values observed must include a +/-0.05V deviation for factors that cannot be compensated for in a real world environment (IE: This isn't a lab, so it's not 100% accurate)

[scuzzy]

so no responses yet, I suppose everyone else is just as confused as I was.

I hope someone has something to say, my loud exhaust gave me a hell of a headache doing all this testing that I didn't get rid of till about 11PM

[not8player]

Interesting results, but hard to draw any conclusions from them. By removing the plate you would expect the voltage values of the MAF to be by a factor lower thru out the entire range.
An interesting test to setup would be to put two maf in series one with the plate and another without and log both MAF voltages and RPM. Then swap the order and log again.

[Legacy777]

I will tell you this after my own experience with trying to read info from the select monitor/scan tool.....it's not always that accurate.

I was reading voltages above 5v from the select monitor. To truly get accurate and repeatable data, you either need to tie into signal leads going to the ECU, or setup a test jig where you can control the variables and accurately measure readings in a steady state environment.

[vrg3]

You have a lot of hidden variables when you test it this way. When you alter the MAF signal, you alter the ECU's fueling, so you alter the efficiency of the engine, and in turn alter the actual quantity of airflow.

What you should do is like what not8player is suggesting - leave your car's MAF sensor where it is, and install a second sensor in line with the existing one. Run +12v and ground to the extra sensor and read its signal under several test conditions. Then remove the second sensor's plate and read its signal under the same test conditions.

[not8player]

I was thinking a little more about the experiment and found a cheap DAQ system. Has anyone played with one of this http://www.dataq.com/products/startkit/di194rs.htm I am only familiar with LabView and there DAQ boards (which are mucho $$)

But then how would you go about recording RPM??? I guess you could record throttle position just to get a reference to where the engine is at and use the idle switch as the start and end of recording

[vrg3]

I don't know what Remove Event Marker Control means, but maybe you could use that input for RPM?

To make sure you're at the same load site, you'd need to make sure RPM, manifold pressure, and intake air temperature were the same. But you don't actually need to be at the same load site, do you? You just need the same mass air flow. So if you have two sensors (one to run the engine and one to test), all you need to do is continuously record the signal from both sensors and go for a non-boring drive and you'll have plenty of data.

[not8player]

I just pickup the
DI-148U Starter Kit
I think it might become handy for something sooner or later.


At the end of the day RPM is not that important, nor throttle. The only thing that we would be looking in this test is to get a sense if the sensor without the plate reads lower Voltage than the stock one with plate. And if there is a constant relationship between the two.

But I think it would be a more useful test to compare the EJ22T sensor against a MAF sensor that the Values are known for. (E.g. WRX MAF) But that’s deviating from the original thread.



PS. in regard recording RPM maybe Voltage-to-Frequency Converter LM2917 or something similar.

[azn2nr]

how bout this. if i get some sti injectors installed and then see if the car is driveable with the plate off??

[vrg3]

And just ignore everything Nico said about having his ECU recalibrated for the sensor and injectors?

[azn2nr]

bascily

there has to be a way to mechicnaly compensate for fuel

[Splinter]

You can do limited compensation using a rising rate pressure regulator

But you really need electrical control.

[NICO]

when you stick the sti injectors in and just use them, it revs like shit.

[rightandtight]

hey i've got my MAF housing on my desk in front of me, searching the forums for the best way to clean the little wires. but that's besides the point...

if you take off the backing plate, assuming that air speed over the wires brings about higher voltage reading, then scuzzy's lower readings make sense i think.

with the backing plate on you would have a higher air speed over the wires because air speed increases at the smallest part of the system. so the plate creates a sort of bottleneck (or a controlled environment as i'm sure subaru would call it).

not really sure about the readings at higher rpm...just some thoughts

[douglas vincent]

I log using the SMT6 Perfect Power all the time. And I have logged the JECS, the metal Maf with the plate, and the metal Maf without the plate.

Plain and simple, the JECS wins hands down, and even then it needs to be modified.

http://bbs.legacycentral.org/viewtopic.php?t=28039

The metal Maf sucks. Removing the metal plate does NOTHING to remove the suckiness. 10 psi hits 5 volts fast. 13 psi hits 5 volts faster and my max recording is almost 5.6 volts!!!!! Using the Perfect Power I clamp the MAF signal to 4.98 but still run lean sometimes.

NICO, I call bullshit. I can post proof via logs that I hit these numbers. Get Neetronics to post some logs and personal experience please.

I say do the JECS mod and be happy.

[Splinter]

I say convert to MAP readings

[NICO]

i need vrg3 on this one becuse i wont make any cents to you douglas vincent.

i am not using a piggy back nothing thats why you hit those numbers you say, its a burnt chip no need to clamp or mess up the signal of my ecu to fool the ecu and the chip its running. there tuneing equipment (made in japan) cost +20grand, the perfect power cost 600bucks piggy back (made in america) they use what the japanese use standard to tune factory chips for all japanese cars like what we have.

that reminds me i am booked in for this month at neetronics i got to call them to see when i am in next, i will get print outs of my work.

91turbo legacy "GC8impreza" is the car
ej22t block
ej20k heads
sti 550cc injectors
tdo5h 18g @ 19psi

[douglas vincent]

Your ECU, your Chip, whatever, has NOTHING, absolutely NOTHING, to do with the MAF.

Unless you are using a "japanese" special maf, then your maf should read just like our metal mafs, crappy.

[Legacy777]

Ok.....little lesson time.

The MAF simply takes a supplied input voltage from the ECU, runs it through a metallic strip that is heated to a specified temperature. When air blows across that strip, the metal cools.

A certain amount of voltage is inputted to keep the strip at that specified temperature. The amount of voltage required is what is sent back to the ECU, and is what is used to determine the airflow.

Irregardless of reference voltage, piggy back, modded chips, etc. The sensor has a certain range it can accurately measure. I have not done any testing, and cannot comment on the metal plate, but I can say with 100% confidence that any "special" tuning can not change the range of the sensor.