AFM's

[nickmcgill]

Good day to all,

Here is my rant about AFM\'s that I\'ve been simmering on for awhile now. I will put a TL;DR at the bottom.

Vehicle is a 2000 BE5 AT.

I\'m about to go onto either my 5th, 6th or 7th AFM within about 5 years, I have actually lost track.

All of them have seemed to have failed within the 12 month "warranty" period.

First of all to clear some things up some of you will be thinking oh this guy\'s a douche and running a pod filter which will be breaking them.

Believe it or not I\'m not! I have a standard air box with genuine supplied filters from Armstrongs/Stubaru

At one point I was running a K&N panel filter which I found pretty quickly killed the AFM\'s and I moved back to paper ones.

Even so K&N have a "Consumer Protection Pledge" that it won\'t damage your parts found here : http://www.knfilters.com/MAF/

My current AFM has been in since January and has been degrading slowly over the last few months.

Symptoms include loss of power, excess fuel usage resulting in black smoke under load and 1-2 seconds gap between automatic gear changes. (Which feels as rough as hell)

I have been able to prove it is the AFMs causing this issue by swapping it out with a brand new one for 48 hours (Thanks Stu!) and testing this.

I have also swapped out the TCU, ECU and O2 on more than one occasion to test this issue.

I took my car into Armstrongs to get tested to attempt to do a warranty claim for the part.

They tested it and checked out my setup to confirm that it had a paper filter and standard air box etc.

Leighton came and reported to me that the air/fuel correction ratio is only between 3-6% and the threshold for error is 10%.

A week later I then contacted Subaru NZ directly to attempt a claim through them.

They called Armstrong\'s to get the details of what was done for the diagnostics and then called me back later that afternoon.

The chap I spoke to was really helpful don\'t get me wrong however he said that they rarely do replacements of these units normally less than 1 per year.

He suggested that it might be something else with my car causing the issue being either electrical or mechanical.

The only thing I could think of that would cause that would be the air coming from the inter-cooler through the BOV back down into the intake and going back out past the AFM.

If this is the case then I would have thought this would have been a design flaw and would have been corrected on future models but it seems not.

TL;DR

Why do these units fail so often and are known for having a high failure rate in the Subaru community.

Does anyone know if they are able to be reconditioned to save the $200 odd for another one ?

N.B I found using AFM cleaner makes them worse not better.

Hoping this generates some interesting discussion.

[rslegy]

Link it and then u can remove it and never worry about it again

[Steveo]

I\'ve had similar issue\'s done a MAF in my 2000 Legacy E-tune, and put it down to the age of the car. And going to have to do one in my 2004 WRX STI, which I\'ve put down to having a BOV venting full with no plumb back (on the car when I brought it) and a K&N panel filter (same deal already in the car).

Got a dry type HKS on order, and changed it back to stock BOV so hopefully no more issues, at least for a few years anyways.

Was lucky enough to get my car plugged into a really awesome scan tool, that does a live read out and checks pretty much everything and my MAF was out by quite a bit, hot and cold. Going to replace the filter and attempt to give MAF cleaner a go (nothing to lose really) and he\'s agreed to re-check for no charge.

As far as replacing 6 or 7 thats crazy there has to be something else going on surely.

[nickmcgill]

 rslegy said:

Link it and then u can remove it and never worry about it again

Requires single and manual conversion you should know better!

[madmike]

I wonder if the OP has a wiring issue going on here...

It\'s strange that its killing so many AFM\'s.. you need to look deeper into the problem dude, something else is causing these AFM\'s to die.

[Steveo]

Just had another thought, you don\'t have any leaks / splits or such in your intake. I know mine had a small split that could have been letting dust in on my Legacy, which I replaced as soon as I noticed it.

Also can a dodgy O2 sensor kill a AFM, just wondering if that might be causeing you issues.

Another silly question, doesn\'t have a aftermarket BOV (wouldn\'t have thought so being a auto)?

Keep us posted if you uncover anything, as AFM definatly seem to be a weak point on pretty much all Subarus. Haven\'t been game to price one for my V8 yet, as I think it will be pretty expensive.

[Guest]

Just throw a kink in I had the same issue V5 non sti which use the same afm went through 4-5 iirc. Now I gave a away a couple to people on the basis of may work may not because I was a bit sus. Turns out they were fine but the only way I could get rid of the issue was to swap out the afm to a new unit. All genuine also.

[nickmcgill]

 Steveo said:

Just had another thought, you don\'t have any leaks / splits or such in your intake. I know mine had a small split that could have been letting dust in on my Legacy, which I replaced as soon as I noticed it.

Also can a dodgy O2 sensor kill a AFM, just wondering if that might be causeing you issues.

Another silly question, doesn\'t have a aftermarket BOV (wouldn\'t have thought so being a auto)?

Keep us posted if you uncover anything, as AFM definatly seem to be a weak point on pretty much all Subarus. Haven\'t been game to price one for my V8 yet, as I think it will be pretty expensive.

To my knowledge there is no splits or leaks, I\'m pretty anal about the engine and keep a tight eye on it.

It\'s basically stock other than a Zerosports joiner between the airbox and the air intake that goes in under the manifold and silicon hoses between the turbo and the intercooler.

The issue was persistent long before these were applied.

It could be a dodgy O2 but it\'s also less than 12 months old so I\'m not too sure.

Can you explain a bit further how the O2\'s can kill the AFM\'s ?

I\'m aware that those two plus the other flow meter in the exhaust work together but unsure how they would damage each other.

The whole engine was also overhauled in January with a new long block due to BeB and I\'m pretty sure anyone in Chch would swear by Richards work so I\'m fairly sure it won\'t be anything to do with that.

[rslegy]

Nick is very anal about a lot of things lol

[Guest]

I had new O2 and maf at the same time both genuine. Never had a code on O2 but half of my maf threw a code other half just wouldnt idle/ran lumpy.

[Marky]

My first BH legacy killed 3 or 4 AFM\'s, it was the reason I sold it as it drove me fricken insane. That car was mechanically 100% stock apart from a muffler and de-cat (and every time the guy at suby dealers was like "ohhhh you must have a pod filter on it" - no I don\'t stop asking)

My second one I think nerfed 4 all up? (Maybe 5?).

One of those I can pin to contamination - got wet (torrential rain plus no inner guard...) and came right with a clean up. The rest just died mysteriously. Never used an oiled filter since it\'s meant to be such a touchy thing for them.

Sometimes they will only go out of calibration - like poor idle but fine to drive with - and sometimes they would die outright but not throw a CEL, just start to drive badly all over the show. And then sometimes they just randomly go "F this" and the CEL light comes on and you have to unplug the AFM just to be able to get home again.

Google has told me that the ones with a green mark on them are "supposed" to be a factory revision of it which is meant to be a bit more robust. Take that with a grain of salt I guess. Seems to be just this one model of AFM, which to the best of my knowledge no other car maker used, and subaru went away from using within what, 3 years of production? (Rev ABC legacy - V5 and 6 WRX and forester - that\'s it?)

All cars have their faults I suppose - this is just a very common one and seems to be a case of some particular cars kill them more than others do.

Mine killed them with good 02 sensors, with both vented, stock recirc, and no BOV at all, seems to make no difference.

Remember that the AFM is purely a sensor at the front of the "system". Anything downstream shouldnt affect it - it is purely just measuring air coming in. If your 02 sensor is shagged there\'s no way I can work out it could have an impact on a sensor before it. The only way a BOV "could" impact your air flow meter is if it\'s not venting much, if you got air chuffing back out the intake you could be putting a bit of an oil vapour onto the sensor itself - it might over time get it filthy the same way an oiled air filter would.

Other than that, F knows. People often say "Vibration will kill them" - the stock airbox vibrates quite happily so I don\'t think they are *that* touchy on how rigidly you fix them to the car.

[gotasuby]

Wild stab in the dark here but is there a ripple or something on the 12v feed that\'s slowly killing them or a faulty ground?

[Guest]

Isnt the V7- the same design? Havent seen one but similar denso insert style. Completely slipped my mind what brand the nissan/sub one is we\'re talking about its been one of those days.

[Marky]

No, they\'re a different unit completely

Still an insert-type but almost everything is these days

[madmike]

 gotasuby said:

Wild stab in the dark here but is there a ripple or something on the 12v feed that\'s slowly killing them or a faulty ground?

That....

[Steveo]

Sorry ignore the O2 Sensor comment I made, while a O2 sensor can cause issues your right it won\'t effect the air flow meter at all.

Priced a genuine AFM today and was quite surprised apparently they have come down in price and are $352 Inc GST.

I know this money could be put to better use getting a link, or similar. Biggest issue is my location deep south, no one down here I would really trust.

[Guest]

V5/6 rev a/b/c, sf5 are more like $176rrp $130odd trade. Genuine not aftermarket.

[Steveo]

Yeah sorry I was talking about V8 one, I got told to expect well over $500 so I was quite surprised with it being a lot cheaper. Just thought it might have been some random info someone might have liked to of known.

[nickmcgill]

 gotasuby said:

Wild stab in the dark here but is there a ripple or something on the 12v feed that\'s slowly killing them or a faulty ground?

This is actually quite possible.

I\'ve put a new battery in within the last fortnight as the last one was getting a bit dated.

Previous to this I did have issues with dirty/corroded contacts on the battery causing the inside lights to flicker etc until I had tracked it down to the battery terminals.

Other than that finding a ripple or a bad earth would be a fairly difficult task would it not ?

[Rosssub]

+1 For bad earth or electrical fault killing your AFM\'s. The ECU gets 12v then feeds out normally 5v to sensors (just variable resistors) which then feed a lower voltage signal back. I.E Subaru AFM\'s get 5v from the ECU then at idle give back 1-1.7v, at full rev\'s (air flow) 5v.

Looking in the wiring diagrams below the AFM also has its own separate earth which could be worth finding. Maybe on the guard near AFM branching out of loom.

http://www.clubsub.org.nz/forum/index.php/topic,6444.0.html

[Rosssub]

Also in that wiring diagram the AFM,MAP and TPS are all getting the same feed so a ripple (surge) would effect them all.

With a new battery, maybe over charging (voltage regulator) killed the old one as well as over amped your AFM\'s, put a multi meter on the battery and give it a rev and make sure the volts don\'t go above 14.6 ish?

[nickmcgill]

Just had a quick look for the earth for the AFM but the wind in Christchurch this afternoon is so crazy the bonnet almost took off.

I\'ll have a good look tomorrow.

[Guest]

Mine was charging fine.

[gotasuby]

You will need an oscilloscope to check for ripples but will show straight away

[nickmcgill]

If anyone has one of these in Christchurch feel free to yell out!