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MAF Reading Higher During Humid conditions?


covertrussian
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Has anyone noticed MAF readings going a little wacky with CAI's and very humid weather? Happened to me two weeks ago, car became very rich (AFR's in the 9's) for half a week. I had to park the car for 1.5 weeks (while I was away). When I cam back AFR's are back to normal (I think after MAF/filter got a chance to dry out).

 

My cold air intake is high enough not to suck in water, but filter does get wet after car washing so I would assume rain water can do the same. As weather gets colder I guess I'll see if it starts happening more often again. This is on a new MAF (as of last October).

 

During the richness, 0psi would register as 1.50g/rev, while during normal operation 0psi is 1.15g/rev.

05 LGT 16G 14psi 290whp/30mpg

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

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I bought Denso 197-6040 but they actually shipped me a Subaru branded one. Has been working without a hitch since October.

 

I'm starting to wonder if one of my ground wire is simply showing it's age and starting to impact readings.

Edited by covertrussian

05 LGT 16G 14psi 290whp/30mpg

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

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https://nvlpubs.nist.gov/nistpubs/jres/15/jresv15n6p575_A1b.pdf

 

TLDR: Yes it makes a difference, but not as much as you were seeing. Sub 5%.

 

Bonus research paper showing the effect of ambient temperature: http://fluids.princeton.edu/pubs/Hultmark_and_Smits_2010.pdf

 

Edit: Well this has been a rabbit hole. The MAF sensor is self temperature compensating. This is the difference between old school single wire constant current units, and the newer two wire units. The "cold" wire acts as a thermistor that controls the gain of the current supply amplifier.

Edited by utc_pyro
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https://nvlpubs.nist.gov/nistpubs/jres/15/jresv15n6p575_A1b.pdf

 

TLDR: Yes it makes a difference, but not as much as you were seeing. Sub 5%.

 

Bonus research paper showing the effect of ambient temperature: http://fluids.princeton.edu/pubs/Hultmark_and_Smits_2010.pdf

 

Well if you do the percent difference between 10.5:1 and 9.5:1 it's about 9.5%. But still I don't think it's that alone.

 

Remember how my MAF tends to jump around a lot of different airflow mods (even header) or spark plugs? I thought it was a bad maf, but even new one has shown same thing (especially when I replaced spark plugs again recently). I wonder if that was foreshadowing to this issue (which fixed it self after car stood for a while).

 

I might try to reground the MAF, just gotta make sure it wont burn the ECU first.

 

With an OEM sensor the reading should not be effected as much as you are seeing (as utc says). All bets are off with the generic replacements. A finicky ground could deff cause an issue.

 

It's an OEM sensor even stamped with a part numbers from same year WRX/STI, Denso is just lazy sometimes and sends out a Subaru branded one vs denso "white label". If it was a denso stamped MAF I would be thinking the same too though.

05 LGT 16G 14psi 290whp/30mpg

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

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Well if you do the percent difference between 10.5:1 and 9.5:1 it's about 9.5%. But still I don't think it's that alone.

 

Remember how my MAF tends to jump around a lot of different airflow mods (even header) or spark plugs? I thought it was a bad maf, but even new one has shown same thing (especially when I replaced spark plugs again recently). I wonder if that was foreshadowing to this issue (which fixed it self after car stood for a while).

 

I might try to reground the MAF, just gotta make sure it wont burn the ECU first.

 

That paper shows a 1.8% difference between 20% and 70% humidity on wire power dissipation vs airspeed. The 5% I gave was conservative as I didn't go convert the heat transfer numbers to mass flow rate reading corrections. Air density actually drops as humidity goes up, so it may add a little to the error.

 

On your spark plug thing, replacing my plugs and coils due to misfires didn't result in any MAF scaling changes. Unless you’re getting turbulence around your MAF sensor, your theory of the MAF ground being suspect is sounding like something worth checking out. If you pull your new ground to the engine ground it should have any risk to your ECU.

Edited by utc_pyro
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I think the reason spark plug change would effect it is, it requires unplugging/removal of the MAF pigtail. Same applies to doing the header, turbo, inlet, all required me to unplug or stretch the MAF fire.

 

Did some testing today with the car idling when I got home from work. First thing I did is let the car idle for a bit and noted the idling MAF voltage, which was 1.28-1.30v. I then touched the MAF pigtail and car's fast idle kicked in and ECU started adding more fuel, the new MAF voltage became 1.20-1.22v. No matter how much I moved it around after that it wouldn't go above 1.22v. I took it for a spin, now AFR's were in 11.5:1 range instead of 10.5:1 that it was earlier today (what I tuned for too).

 

Next I took apart the MAF connector and checked the wires which looked fine, but the individual connectors were a little loose against their MAF pins. I used pliers and screw drivers to compress them a little, which made them be much tighter against the MAF pins. After reassembling the MAF connector took it for a spin, the AFR's stayed around 11.5:1 still.

 

What's interesting is, this made 0psi to now be 1.00 g/rev instead of the 1.15 g/rev that I thought was normal before. This can be seen in the MAP traces of boost vs engine load below.

 

Here is what the previous "good" was:

attachment.php?attachmentid=268102&stc=1&d=1534484004

 

Here is what the current one looks like:

attachment.php?attachmentid=268103&stc=1&d=1534484004

 

Here is what the map trace of MAF being really wonky looks like, I didn't floor it too much cause I didn't want to clog the cat since AFR's were hitting 9.50:1 by 2.00g/rev

attachment.php?attachmentid=268104&stc=1&d=1534484164

 

Moral of the story, as our cars age it makes sense for some wires/connectors to go bad, especially with how often I remove the MAF plug.

1622202002_PreviousNormal.PNG.49fee28860cc3dda777bd1f68f5ff566.PNG

651203658_AfterRecrimp.png.e90e177c98112a137f106bd73251937e.png

1616410936_MAFReallyOff.PNG.b276a36da942b8db5a08148a4e85385e.PNG

Edited by covertrussian

05 LGT 16G 14psi 290whp/30mpg

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

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So this brings me to the other question, the difference between my 2.40 and 2.70g/rev columns is only about .10 AFR. Thus that means there is some kind of other multiplier for fuel mixture. I want to find it so that I could REALLY smooth it out, because .15 g/rev calculation difference shouldn't richen the fuel by a whole AFR point.

 

Yikes. May want to replace the entire connector:

 

https://www.bmotorsports.com/shop/product_info.php/cPath/109_182/products_id/3236

 

$9 for peace of mind.

 

I'll keep an eye on it again, if it acts up again will definitely replace it with that. Plus they are fellow Virginian's :).

05 LGT 16G 14psi 290whp/30mpg

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

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Yes, the male/female wire connections actually "wear out". I cant count how many OBD connectors I have encountered with issues. I have replaced more than a few.

 

 

 

I have seen this happen on cam and crank angle sensors as well as coil pack connections and probably more that I have forgotten.

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  • 2 weeks later...

Been a few days, car is still running the same as after the connection recrimp. I actually had to go back to my factoryish MAF scale from the custom made one.

 

Car seems to be running great so far, but I haven't touched the MAF or done anything in the engine bay either.

05 LGT 16G 14psi 290whp/30mpg

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

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