zhastaph

3 phrases, "MY99/00", "MAF" & "Blown Up Engine" seem to be repeatedly cropping up round these parts

Owning an MY00 Wagon and days away from picking up an MY99 Type RA I'm starting to get really jittery on the whole subject.

1. Why do they fail? Is it just bad use of air filters etc, or do they just go?

2. Do you get any warning that they are on their way out, or do they just fail?

3. I'm in the understanding that the MAF consists of little more than a piece of wire. I see that they can fail when they get coated in oil. Am I being daft in asking this, but cannot they just be wiped clean? Or do they physically break?

4. I'm in the understanding that when the MAF goes the idle becomes erratic, how noticable is this? Linked to this, I thought the Lambda was used to calculate fueling on idle, if this is the case then how can a failed MAF effect idling?

5. Is it worth changing the MAF as a preventative measure?

6. Am I being daft and getting worried over nothing after having read too many horror stories on here? It's got to the stage where I stare intensly at the needle whenever she's idling - in fact it's almost become obsesive

Many thanks for any input

dlehtihet

Hi,

Having owned a my00 turbo before (without problems) i was really surprised when my new STI 8 just died while i was in second gear, doing 15 mph (with no steering or brake assistance). It was the MAF failing. It is supposed to be a better design than the "old" cars, but i doubt it very much. I got no warning either, it just died...


Subaru MAFs are crap if you ask me.

(strictly original car without any filter mods, etc).

Kind regards

Daniel

ustolemyname??stevieturbo

iTrader: (1)

They may be crap, but AFM failure isnt limited to Subaru. A lot of modern cars suffer the same fate. Vauxhalls, VW's are also notorious.

dowser

Main issues;

- Vibration related shocks from a poorly secured induction kit causes total failure (and a very loud bang plus back smoke if it goes at 5k with WOT ). Not very dangerous, and the newer MAF's seem more resilient to vibration failures.

- Contamination from over-oiled cone (or panel, for that matter) filters. This causes MAF to under read, meaning you're running less fuel and too much timing (MAF is used by ECU to calculate load) - a bad combination which can lead to det and a failed engine.

- General age related death - over time some start to under read. Risks are the same as the above (ie; very dangerous ). This affected around 30% of the classics I remapped in the last 12 months - I always have MAF's in stock, and was very glad when they started selling just the single item!

I reckon the MAF has a bad name - it's a great way to calculate load and allows the ecu to self adapt to smaller mods by itself (assuming the load maps are stretched enough). MAP based systems require more care - just changing an exhaust system can require a remap (anything that changes VE is missed by MAP based systems).

If you're unsure whether your MAF is good or not, either get it checked over by a tuner with DeltaDash (they'll know what sort of voltages should be seen for a given set of mods and boost), or buy a knocklink to detect the det before it causes damage (protects you against more than just MAF issues).

Given that you're buying a car mapped for Japanese fuel, a knocklink would be a wise investment, as would an EcuTek remap

Richard

Andy McCord

My sti5 was mapped in october by Bob rawle with no apparant prob with my maf, i dont really use my car that much & lately the revs will just fall slowly below tickover then rise back, it doesnt do this everytime i slow down but usually after the first 5 miles off being dragged out of the garage, i have a knocklink fitted & its indicating no significant knock, can i assume all is well with my MAF purely by keeping an eye on the K/Link??

TIA
Andy

Soapy Sam

The MAF can start to fail and the ECU will learn and compensate (to some extent). This means you may not be aware there is any problem (unless you have a knocklink, then you'll know if it's going lean)

I only found out I had a failing MAF (on my MY99) when I had a remap done and the software showed up erratic inputs to the ECU from the MAF.

If you have any erratic idle or running issues, try a ECU reset. This will kill any learnt compensation and if the idle is worse, get a new MAF.

In fact, if the MAF has never been replaced on a MY99, I'd replace it anyway. I believe that all MY99 MAFs in the states are being replaced on a recall.

£70 for peace of mind, I'd just do it....

zhastaph

This too is my feeling, I have no suspision at all that the MAF is going, I'm just concerned that one day I'm gonna get bitten by it in a nasty way, particulary as I'm going to a JAP import that's already gonna be close on the fueling/detting side.

Also on the car I'm selling, I'd feel totally gutted if I sold it on and the poor bugger who bought it had a MAF go 2 months later that takes half his engine with it.

greasemonkey

No single authoritative answer to that; there are a number of contributory factors, not least oily/gunky air filters, poorly mounted induction kits and so-on.

What does seem to be pretty clear is that the design originally used on the MY99 and MY00 cars seems to be more prone to premature death than the other models of Impreza, although as the answers you've already received indicate, failures aren't confined to these MY's, or indeed to the Impreza or Subaru as a marque.

The plus side of the 99/00 cars is that replacement sensors are a quarter of the cost of the units for other model years, and the newer version does seem to do a better job.

It's not failures you've got to worry about. If you get one that literally breaks (i.e. the ECU can't read it at all), the Check Engine light will come on and the ECU will drop into safe mode.

The real problem is that the sensors normally degrade, and under-read before failing completely. Under these circumstances, the ECU will continue to work on the (incorrect) airflow readings, and if the sensor degrades enough, the resultant lean running can blow your engine before the MAF sensor itself actually expires, which can mean another blow-up if you leave the degrading sensor on after the rebuild.

...Or a piece of heated metal film.

[quopte] I see that they can fail when they get coated in oil. Am I being daft in asking this, but cannot they just be wiped clean? Or do they physically break? [/quote]
Sure, there's nothing stopping you trying to clean it, but the problem then is how do you know whether you can trust it? Can you be certain that it's now reading correctly? Without a method of calibrating/checking its readings, you can't rely on it.

No, that's one of the symptoms. It doesn't always happen and it's probably not really noticeable until the sensor is underreading by a margin.

In any case, because of the way the sensors deteriorate over time, the symptoms like this are hard to spot because they develop and worsen gradually.

Yes, the lambda sensor is used in closed loop mode, but that doesn't mean that the MAF sensor isn't.

Yes, if only in as much as the sensors currently being sold by Subaru UK for the 99/00 cars are a newer, more resilient (we think) design.

No. As you've read here, MAF sensor degredation does happen, and it can cause blown engines, so it's something to be aware of.

Forget that idea. It'll make you paranoid and probably won't actually alert you to a failing sensor. If you want a solid, reliable method of picking it up, fit a KnockLink and an AFR meter.



[Edited by greasemonkey - 1/28/2004 2:17:15 AM]

SoNiCa

a little contribution to this topic