But what's a good voltage?! Different mods produce different airflows. No Subaru dealer I've seen here is knowledgeable enough to know an under-reading MAF when they see one. They just wait for it to either fail, or engine to go bang!


And why wont AFR tell you whether it's under-reading?! If it's under-reading, less fuel is put in.

If you don't notice a difference with a replacement MAF, you don't have a problem. Last car I mapped had 248ps with only mod a decat downpipe - car drove noticeably better than any other similarly modded car, because MAF was under-reading causing a leaner mixture. New MAF made the car bloody horrible to drive...until the remap of course

Richard

Edited to add: must read posts fully before replying...sorry You're right, an idle gas test will tell you nothing - car is in closed loop fuelling at this time.


[Edited by dowser - 12/4/2002 8:09:56 PM]

 

That's my point Matt - you can normally tell a failing MAF story as; cars gets faster, and faster, and bang In reality, you *should* feel the performance drop of knock correction wiping 5 degrees of ignition off, but it's still dangerous - mostly to those with stock cars I'd guess.

Does anyone know whether there's a CEL once the MAF starts under-reading sufficiently? Does it just stay on briefly? I did a car recently that had a historic code, and MAF was definitely under-reading, but the owner hadn't seen any CEL's.

Dean - spark related? Have the coil packs been done? Maybe email Bob R. for confirmation, but I believe a quick test is to reduce spark plug gap by .1mm - if problem goes away, buy new coil packs.

Richard

[Edited by dowser - 12/6/2002 7:00:40 AM]

 

As above, What do i need, What settings Volts Etc should i get, & how can you tell if the probe is Fine, Allowing the replacement of the circuit board Etc that is around £60.00 & not the whole unit.
MY94 UK Turbo, No cats, BLitz induction, 15 Psi Boost Etc.

Many thanks

Dean

 

Only real way is to check AFR - in general they either fail completely (you'd know if this happened!), or slowly start under-reading. The more they under-read, the less fuel gets put in. This will actually improve performance...up to the point that det starts....

What makes you think it's failing? Probably best to swap yours with someone who has the same year and see if the fault is rectified.

Richard

 

why not take the complete car to a garage and get the exhaust emissions checked, that will give you a full gas analysis and definately show you if anything is not reading correctly,it beats probing wires or sensors and possibly creating more expense than you have already .

 

Cheers,

Just have to find someone willing to loan their Maf for a few days.

Dean

 

Find a friendly Subaru dealer and put it on the Select Monitor (or use a volt meter to monitor the MAF output voltage). What you really want to know is if it's under reading on full throttle. A Gas analyser on idle won't help much.

Sometimes you can't feel the difference and swaping it for a difference MAF you might not be able to tell the difference, leading you to think that your MAF is fine.

Matt

 

Richard,

You forget to mention one important issue caused by a underreading MAF: the ECU takes lower load sites, that means more advanced ignition. This in combination with leaner mixture is, of course, very dangerous.

Mark.

 

 

I've been in a car which felt fine to drive but when put on the Select Monitor, it was running very lean and would probably have gone pop if left for too long.

If the MAF is a little damaged then it can be impossible to feel that. It's only when it's properly damaged you can feel the difference which is better because at least you know something is wrong!

You're right though, knowing what is and is not a valid reason can be a problem in itself. Perhaps if you're going to go to a dealer and get it put on the SM, you put the standard airbox back on first? Then you'll know if the reading is correct or not?

Matt

 

Have had it on the select & subaru said the O2 sensor was cream crackerd, replaced this & no real difference (to the butt dyno anyway) Have also swopped the MAF with two second hand units no difference again (2nd hand units leave you wondering if they were O.K in the 1st place)Car seems to fall into a hole at low revs & v little throttle also hesitant at low speeds. Power doesn't seem to be consistent changes daily. Perhaps its just me but i think a bit more investigating is worthwhile.
Cheers

Dean

 

MAF lights up the CEL on my 02WRX.

CEL lit up, took it into dealers, they plug in the Select Monitor and say the fault code is for the MAF sensor, not in stock so they order one in.

The car ran just as before, no sign that anything was wrong.
Car has a FULL de-cat including Up-pipe, and also has an ITG panel filter. The dealers were happy to replace under warranty as they said it hadnt been affected by the mods. I even asked if the ITG had anything to do with it, and they were certain that the fault was NOT caused by the ITG and was "just a faulty MAF sensor"

Bob