The Subaru SVX World Network - MAF sensor swap question

The Subaru SVX World Network (https://www.subaru-svx.net/forum/index.php)

- Technical Q & A (https://www.subaru-svx.net/forum/forumdisplay.php?f=5)

- - MAF sensor swap question (https://www.subaru-svx.net/forum/showthread.php?t=63429)

Re: MAF sensor swap question

the problem is the limits of the fuel trim. it may seem like a small amount but the fuel trim is probably not capable of compensating for the difference. I would run with unplugged before using the wrong maf. you will always be in open loop so you will run a rich mixture based solely on engine rpm and ect. I have never torn down an svx motor that had issues with this but I have torn down motors because the maf was bad and the pitting on the pistons can be significant.

Re: MAF sensor swap question

Quote:

Originally Posted by oab_au (Post 740645)

There is a need to clear this up before it becomes "Internet law".:)

The graph the Michael showed, has the two curves for the two Mass Air Flow units, they are very similar, slight different at full voltage readings.
The voltage rises as the air flow increases, the ECU uses this to set the fuel and the spark settings, when the voltage signal reaches maximum reading, the ECU goes to the full throttle settings that apply max fuel and spark setting, for a fully loaded engine.

http://www.subiechips.com/posts/vqComp.gif

The point that people are missing is that the max. voltage reading for the two units are at different air flows. The 3.3 unit reaches full voltage when it is passing 3.3 lts of air. the Legacy reaches max voltage when it passes 2.2lts. of air. So when you fit the Legacy unit to the SVX it goes into full fuel and spark settings when 2.2lts is passing, it then holds this same voltage setting while the last 1.1lts is passed.

So it won't run lean, it will actually run the same full throttle settings as the SVX unit does, only doing it 33% earlier.

Of course this will only happen at full throttle, when in open loop, at normal driving in closed loop, the Svx will use the O2 sensors to use the same settings as it does with its own MAF fitted.

Thanks Harvey for the graph objective data. This confirms what my wideband O2 sensor has been showing me with a Legacy MAF in my SVX. No evidence of a too lean AFR ( never see anything greater than 11.2 at partial/WOT conditions and that is the max. spike , never steady state). This is with 2 new Os2 sensors. If anything, my SVX is running a more correct N/A AFR than with the OEM SVX MAF which was putting out numbers in the low 10's..."we run rich".

Re: MAF sensor swap question

I posted that graph in a different thread where I was asking the person who was promoting the use of the legacy afm if someone had obtained the data necessary to properly compare the meters or not. It doesn't sound like anyone has. The translation tables only show the shapes of the air flow meters responses. You need to know the scales to multiply those values by to make comparisons.

I'll be happy to do the math and post it with an explanation if anyone decides they want to get the injector flow data. If someone sends a legacy injector and SVX injector to be flow tested at the same time and provides me the flow test data I can use that data to determine what fractions of the K constants in each car's firmware relate to the scaling of the meters and make accurate comparisons of the meters.

Re: MAF sensor swap question

I've been running my SVX with Legacy MAF for some 4-6 months and for me, it feels more responsive with it. I do lot of WOT overtakes and have had no problems.

I'd also like to note that there's a little choke on the legacy MAF housing so could it be that electronics are actually identical and the measured difference is caused by the choke?

http://www.subaru-svx.net/forum/pict...0&pictureid=59

Re: MAF sensor swap question

Nobody knows the "measured difference." If somebody does they haven't provided the information to the rest of us.

I extracted the translation table from a car I believe uses the meter being promoted as a substitute and provided that graph so that the similarities/differences in the shape of the translation curve would be known but you still need to know the scale to multiply the readings by to make any comparison. 2v on one meter could equal the reading at 5v on the other. If it was that far off one of you would have blown your cars up already but still you have no real idea how they compare yet because nobody has bothered to put in the work.

Another method that could be used to obtain the necessary data is to plumb one meter right after the other and log the readings out of both meters at the same time. Or even just get one measurement from each meter at a reasonably high air flow. Tape one to the end of the other installed in the car and have one person hold the revs up and steady while another measures the voltage out of the meter with a multi-meter.

Re: MAF sensor swap question

I've been searching Ebay and came across this seller for the MAF sensor. He's much less expensive than a dealer and it's a NEW MAF not rebuilt/reconditioned. It still costs more than MAF sensors for other Subaru models but it is specifically a SVX sensor. So far my car has responded well and no more stalling/restarting. I'm more than satisfied w/seller and the sensor so if anyone needs a MAF sensor check this seller: http://www.ebay.com/itm/400949068391...%3AMEBIDX%3AIT