I've just put the RB5 back on the road after a 2 month lay off, and I need some advice on how its running.

The car is an RB5 WR version, with the follwing mods....
H&S downpipe
Magnex centre
TSL Group N back box
K&N induction kit
New MAF 6 months ago.

Anyway, at normal operating temperature, my Air-Fuel ratio meter is indicating lean, bordering on 'stoich'.

On boost, it is consistently dropping into the lean (hence not much on-boost driving), and at the most it only goes a few led's into the stoich.

Never does it go anywhere near the 'rich'.

Prior to being off the road the led's on the A/F meter would kind of "dance" about when at idle, or off boost, and when on boost it would go right round to the very extreme end of 'rich' but it hasn't been 'rich' since I've started using the car again.

I suspected imminent MAF failure but the MAF was changed not that long ago
The car has been idling a bit funny with the revs hunting occassionally at traffic lights etc, but never does it feel like its going to cut out.

Is my MAF dead/nearly dead?

Could my lambda sensor be suspect?

As far as I know, the car's boost is peaking as normal.

Would delta dash indicate/confirm MAF failure?

Any suggestions would be much appreciated.

Any tests I can carry out on the MAF?

 

sounds like lambda sensor, DD will confirm lambda failure by virtue of the oxy sensor voltage behaviour. its not running closed loop off boost hence the idle behaviour

bob

 

Cheers Bob. Are main dealers the best place for lambda sensor, or am I better off elsewhere?

Do you know of anyone in west of Scotland with DD?

Ta

 

I'd put my house on it being the lambda sensor. You can get them for about £25 from any Motor Factor. Subaru OEM will cost you over £100, and there's no evidence to suggest that they're any better than the universal. Mine (MY00) was replaced in October last year, after wiring up an AFR gauge and wondering why the display wasn't doing as it should. Anyway, 8 months on, and it's still working fine.

Regarding MAF checks, this thread might help...

 

You can also check the lambda sensor by resetting the ECU, and seeing how long it takes to display the all clear CEL. Or it might throw an error 32 at you. You could also try disconnecting it, and see if it idles/drives off boost any better...

 

When my Lambda failed, my car (another RB5) just ran very rich. On DD, it showed itself as a flat-line 0.3v

I would have thought a lean mixture would be down to MAF when on-boost.

Any Subaru Dealer with a select monitor should be able to see the voltages from both sensors. John Banks has DD, but he's in the East and you'd need to ask if he can help.

Other than that, there's the garage in Dunfermline that John recommended. Apparently they've equipment to diagnose cars, but you'd need to phone to see if this covers classic Impreza's.

Stefan

 

I have unplugged the MAF whilst idling and the car does not cut off, but continues idling.

Is this a reliable test to confirm MAF failure?

Is the lambda sensor located in the downpipe or manifold?

Is the sensor that motor factors supply a universal fitment or Subaru specific?

 

1) check the maf thread. think that disconnection of MAF when running should stall engine. may be worth resetting the ecu before running this test.

2) check maf thread

3) downpipe - by the turbo

4) motor factors ones have different/no plug on them. you will need to chop the plug off the connector on the car and join the new sensors wires on. don't think you can solder as the cables on the car (or it might be the sensor) are stainless. the subaru lambda plugs straight on but is about £80 more!

 

When you say it carried on idling, was there any change at all in the revs?

Forgot to mention above, has the AFR gauge stopped "dancing" at idle/part throttle?

Have you checked the link in my post above for other MAF tests...?

 

Judge,

The idle note changes VERY slightly, but does not even come close to staling when disconnected.

AFR does not "dance" at all any more, the way it used to go from one side to the other and back again

I've had a look at your other thread.....

As above, disconnection has little or no effect on revs.

ECU reset has been done via SECS unit, no noticeable change.

No 3 test is positive.

I haven't noticed any better performance.

I don't have a KL fitted atm.

I'm confused as some folk think lambda and others say MAF.....

 

Yeah, I'm confused as well to be honest. It seems only one of the MAF tests failed...

- The idle test would suggest MAF is failing.

- AFR problem is definitely failing lambda sensor.

- ECU reset would suggest MAF is OK.

- Throttle blip would suggest MAF is OK.

- No increase in performance would suggest fuelling isn't too lean, and so would suggest MAF is OK.

Have you tried disconnecting the lamdba sensor? If that's knackered and the MAF is OK, you should notice an improvement in idle and part throttle.

I'd also try resetting the ECU via the plugs rather than SECS, just to see if it makes any difference.

 

Right, just tried all the tests again!

1) MAF disconnected, engine continues to run with little change in engine note.
2) Car is not hunting as badly as it was of late, which is confusing me no end
3) AFR meter does not dance around, but basically sticks at the lean end of "stoich" (9 o'clock position on Autometer gauge)
4) On full boost, the AFR meter drops into the red (lean) around the 7 or 8 o'clock position.
5) The gauge has not been in the green (rich) since I put her off the road, 2 months ago.

 

UPDATE!

I've swapped the MAF for another that I had lying around, and it now cuts off when the plug is disconnected, suggesting that the MAF was failing.

When blipped to 3k rpm, the revs drops steadily to 800 rpm with a slight pause at 1200 rpm where they settle nicely.

The car is now idling fine, but the AFR gauge is still stuck in stoich near to lean and I assume it will continue to indicate lean on full boost, as it is not "dancing" around.

Lambda sensor it is then.

 

That's pretty conclusive. Failed lambda sensor, failing MAF sensor.

 

Cheers for all the advice guys!

 

No problem

A thought. You say you've got a K&N induction kit? I know that's supposed to be the "safest" induction kit, but I wonder if that was a contributing factor to your MAF sensor only lasting 6 months...?

 

Possibly,

I'll maybe re-fit the airbox, but I'll need to buy a new filter, as its an ITG in it and I've heard plenty horror stories about them.

Any suggestions as to best/safest brand?

I believe ScoobyWorld do an STi one thats quite good?

 

Yeah, that's what I use. To be honest, I don't think there's a great deal of difference between the STi/Green/K&N...

 

Sorry to jump on to the thread but it has also solved me problem here -

http://bbs.scoobynet.co.uk/showthread.php?t=341779

Did MAF test, all ok. So bought a lambda tonight and fitted and pretty lights all over my AFR

Just one query if I may, as I did not get an instructions with AFR could someone descibe how I should read ?

Took it out tonight for about 5-10 mins and they were dancing all over the place for a while. Went to rich under load then lean off throtle. Then were around stoich to rich at around 4000rpm cruising but still dancing a little.

Clive

 

Got my lambda sensor fitted and problem solved!

Big cheers to the Judge for the advice

Mad Hammer,

Your car should be "rich" when on boost in order to prolong engine life.

When at idle or off boost, the gauge's led's will dance about from lean to rich, but when booting it, it should always be in the green.

 

Thanks mate.

 

Hey Talizman:
Rather than refitting the airbox, have you considered the following:

1) Have you recently oiled your K&N? If so, the oil could have destroyed the MAF> They are VERY easy to over-oil.
2) what is the MAF mounted to at the moment? If not bolted to the airbox, you should have some sort of bracket that securly mounts it to the body of the car so it cannot vibrate with the engine. Vibration will kill the MAF.

 

1) No, have never oiled it. I'm aware that the oily content of the ITG panel filters is what contributes to their early demise, so for this reason I haven't lubed it at all.

2) The MAF is in the factory MAF housing which is in turn bolted to the header tank using the bracket provided. It is pretty solid with very little movement or vibration.

 

No problem. Glad it's sorted...

Just need to keep an eye on your MAF now. If you're going to revert back to your airbox and get a panel filter, might be worth getting a new MAF, just to be on the safe side...