bob r

iTrader: (46)

What causes the 99-00 mafs to fail so easily?

I bought my RB5 16 months ago and after 4 months the maf went. I got a new one and now that one has failed.
I don't have a CAIK and only do 3-4k a year so I can't work out why it has broken so easily?

Do they come with 12 months guarantee?

andyxros

over oiling aftermarker air fillters can have a factor so after beingin same boat and buying a couple of these a year inow use standard air fillters so have no proplems....they are a bit soft though

Ste RB5138

What air filter do you have? It you have a induction kit, it could be causing it to vibrate which is another thing that makes them fail, as well as filter oil.

Splitpin

The short answer is "because of the design".

The long answer is that, inside the sensor body, the metering element is connected to the processing circuit board by eight or so absolutely minute wires (thinner than a human hair kindof thin). The entire PCB, and the wires, are covered in a thick non-drying silicone potting compound to try and protect them from vibration and moisture, but even then, the wires can, if subjected to enough shock load for long enough, either fracture or become detached, either at the PCB or element end. Because they're held in place by the silicone they still make intermittent contact, so you end up with a situation where the sensor still sends out enough of an output to make the ECU think it's still working, but an output that soon becomes totally unrepresentative of the quantity of air going in.

As the others have also said, excess oil leaking back from the filter (or microscopic bits of rubbish going through it) can cover or burn off on the element, covering, carbonising and eventually degrading it - so there are two distinct failure modes.

All that said, the "green stripe" revision currently sold by Subaru dealers is far more robust than the earlier green spot and original designs. I suspect JECS have, over the years, either changed the size of the wires (or their soldering/welding technique), or used different silicone to stop the vibration killing them so easily.

The green stripe one is much better, and the Bosch one used by BMW and Porsche, among others, supposedly better again, but they do have a reputation for this. When you say it's broken, can you tell us exactly how? Has it thrown a CEL, or have you suddenly noticed your car running lean, getting loads of KnockLink activity, or something like that?

If you bought it from a main dealer you could ask them nicely, but, knowing car dealers...

T4YLOR 83

iTrader: (2)

not trying to hijack the post but is there any other maf's you can use ie ive seen people on here with a nissan 200sx maf does this work on the 99 or due you have to get it mapped or something

Splitpin

You'd need to remap for the Z32 sensor, and I think it has a different connector too so wiring loom changes ahoy. I've had an intent to try the Bosch manufactured one for some time as this should be a 100% compatible drop-in replacement (the "Subaru" sensor is a licence-manufactured copy of the Bosch original design), but the green stripe one I've had for the last couple of years is still going strong.

Bosch is unsurprisingly expensive if you buy it from a BMW or Porsche dealer too, nearly three times the price of a Subaru one. I doubt it'd be three times more reliable, so pending finding one at a more reasonable price, and establishing with certainty that the voltage/airflow curve is the same, genuine is arguably still the way to go.

Ste RB5138

Good information Splitpin

Beastie

iTrader: (2)

Not sure what symptoms you are getting, but it is unlikley with low use that the MAF has failed after 4 months. Was it a new one or second hand?

Please note that the lamda probes also fail on these cars about the same time and will also throw up a CEL.

I had my RB5 for 7 1/2 years and in that time replaced the MAF and Lamda once.

bob r

iTrader: (46)

The maf was new around 12 months old and was not subjected to any oiling or CAIK as my first post states.
It was bought from Cheam Subaru so it's a genuine item.

Splitpin

Again, can you tell us exactly how it has failed?

Certainly worth asking the dealer if they'll warrant it, the worst they can do is say no. Provided you're running the standard airbox and filter assembly, it's all mounted on the standard rubber bushes and you're using the standard dumpvalve, there's no good reason why it should have expired within a year.

Oh - have a look at the sensor mounting flange and see if you can see either alphanumeric codes in white ink, or a stripe of green paint. If you can, tell us what you see.

bob r

iTrader: (46)

Ahhhhh! dumpvalve. The car has Forge VTA.

I was aware of CAIK's causing MAF failure but not aftermarket dv's.

The car cut out and would not start, then after a couple of minutes I managed to start it but then the same again. After a few more minutes it started and I drove it home the short distance.
The CEL check shows 2-3 so MAF failure.

Splitpin

The conditions by which an aftermarket DV can influence the airflow sensor are quite limited, primarily if the spring is too tight. If you lift off and it doesn't dump, you get shockwaves (albeit small ones) going backwards up the inlet and into the airflow sensor. This vibrates the sensor head and, over a period of time, gets to those little wires.

It's unusual, though, to actually see a CEL with a failing sensor so in some ways you got lucky, much better this than driving around for ages with the car running lean. I'd also be more tempted to go back to the dealer you bought it from and complain under the circumstances. If you got a CEL, there's no question that it's bust...

Ste RB5138

Home come you rarely get a CEL off A MAF failure?

Splitpin

Because they rarely fail in the dictionary sense (i.e. stop working completely). Most often they simply misread or start to drop out, and under these circumstances the ECU can't throw a CEL because it still gets an input, and because there's no internal closed loop monitoring, it has no way of knowing whether that input is accurate or not so it assumes the sensor is working.

So, in practice most of these things degrade to the point where they're, to all intents and purposes, knackered enough to damage the engine, while still working in the absolute sense. Therefore, no CEL.

rookymatt

iTrader: (15)

I can vouch for that on bmw bosch units, 318i (m43 engined) and m5 (s62 engined) mafs suffer from not the meter failing but the car getting gobbldygook readings from them i.e massively high multiplicative readings and pathetically low additive readings. Never do the fault codes ever show meter faults, you have to know what to look for!!

thamuff

This is the main reason I got a Simtek ECU for my RB5..

bob r

iTrader: (46)

I disconnected the battery yesterday and reconnected it today. I then took the car out for a drive and it seemed ok. I then did the CEL check which showed no faults?

So is the MAF knackered?

fireblade37

iTrader: (1)

What gave you the impression that your maf was knackered?

Splitpin

See post#11. Bob - as mentioned elsewhere there's no simple way of checking whether the sensor is "good" or not. We're not in a position to answer the question, only you have a chance of doing that, as only you have access to your car and the (potentially) damaged bits.

In an ideal world you'd pull the sensor out of the car and test it on a flowbench. You can't do that, but do you have some means of third party monitoring in the car? A knock monitoring system, AFR meter or select monitor emulator will all help you diagnose a degraded airflow meter.

If you can't diagnose it in any more detail, the way to go is probably to assume the sensor is broken and replace it as a precaution. How about going back to the dealer you bought the sensor from and asking them nicely whether they'll plug it into their Select Monitor? Even if it costs you a few quid it'd be worth the peace of mind.

bob r

iTrader: (46)

It was bought in a group buy off P1WOC 13months ago. I think from Cheam [which I think is a Subaru dealers] wherever that is. I very much doubt they would consider any form or refund.

bob r

iTrader: (46)

Update..................................

Well I disconnected the MAF and battery overnight and then reconnected them the following day. I took the car out for a drive and it seems fine. I then did the CEL check and no faults found?

Anyway, I have rigged up a switch in an easily accessible place, to check the CEL faults. I will try the swich daily just in case.

Splitpin

That's good to hear Bob. Fingers crossed it lasts but keep a really close eye on it. Switch (linking the black plugs?) is a good idea but this won't tell you whether the sensor is misreading, and it's misreads that will kill an engine quicker than outright failure.

Only way to monitor "properly" is with something that looks at AFR, knock, sensor output in real time. If you don't buy a new MAF now it'd be worth putting the money in the direction of something that'll give you some feedback.