NDT

my STi4's been hesitating on really light throttle for ages now
cleaning the MAF sensor seemed to cure it for a little while, but it's come back, and cleaning the MAF a second time has made no difference...
It only happens after a good run, and gets worse after a thrash...

Can anyone tell me when the engine's setting the fuelling using the lambda reading?

if it's only at light throttle, I wondered if the hesitation was caused by a faulty lambda sensor - i.e. reading wrongly after getting hot?

Bob Rawle

Could be that, a faulkty lambda sensor will make the engine run very rich indeed, safest to replace it.

ECU uses closed loop ie lambda sensor off boost and up to about 5000 rpm (ish)

NDT

thanks Bob.

when does it switch to open loop?
is it based on MAP, MAF or throttle position?
I assume that on open loop it's fuelling based on a combination of MAF/boost/air temp?

Nick

NDT

one other thing - I had it rolling roaded 7 months ago (when the problem had started) and all the emissions looked OK according to the mechanic.
can lambda sensors develop intermittent faults?
Or can they temporarily overheat?

cheers
Nick

JDS

Funnily enough I have had the same problem start just today with my UK MY99. However, I have an air/fuel ratio (AFR) meter installed which looks at the output from the lamda sensor. Before today when I've noticed these hesitation problems, the AFR shows constant rich output when at wide open throttle and typically cycles itself between a lean/stoichiometric and then rich mixture.

However, as of today it has started sticking around stoichiometric and under WOT tends to lean out. I have obviously stopped using WOT until the problem has been sorted as I don't want to have any detonation problems.

Like you , I was thinking it was a faulty lamda sensor, however typically when these fail it results in a rich mixture, not a lean one. It could be I'm getting a fuel injector blocking?

James.

NDT

mine only does it on a light throttle - as soon as you give it a bit of throttle it clears.
I'll try to organise another lambda sensor to try....anyone know the price, or got a spare?

if the lambda's making the engine run very rich, it wouldn't show up on your AFR meter - as it would be under-rading anyway.

Nick

[This message has been edited by NDT (edited 09 July 2001).]

FrankM

Hi

I am fighting for 4 days now with such a similar problem!!

I have fitted a completly new MY99 engine with APS-Air Flow Cleaner + Intercooler, and a new IHI VF23 turbocharger after the old engine blowed up due to a whole in the 2nd piston.

The car runs like s+"§$%/" and seems to get no fuel and we can not find the failure :-((.

A very strange matter is the fact that we see absolutely NO signal of the lambda sensor.
We have replaced it two times - Nothing happens, no lambdasignal on the Subaru Select Monitor??
There are also no error codes in the ECU?

So we had done a CO test as well and the car runs absolutely lean if you just "look" at the throttle.

The MAF seems to work because it shows changing values but we will replace it with a new one tomorow as well.

Any ideas what I could do or where the failure could be?

I don't have any ideas at the moment...

Concerning the thought that a faulty lambda sensor is making the engine run very rich, I can say - in my case - that even if i cut off the lambda sensor, no error codes appears and the car runs the same bad (lean) way.

Fuel Injector blocking? Hmmm... Would I see the changing values for the injection time on the Select monitor? So I do...

FrankM

NDT

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by FrankM:
<B>
Fuel Injector blocking? Hmmm... Would I see the changing values for the injection time on the Select monitor? So I do...

FrankM[/quote]

I don't think so - surely the Selectmonitor can only 'see' the electronic pulse going to the injector, not whether the injector is actually opening or not.

good luck

Nick

Nigel Bowles

Mine was doing the same, lumpy and hesitant at part throttle and running rich on the lambda link.
Bought a new sensor from partco, much cheaper than subaru but has bare wires not plug. 10 minutes later .... same problem !!!
Did the normal thing of starring under the bonnet. I noticed an induction noise away from the air filter .... A BROKEN T CONNECTOR !!!!
Seems the connectors had got hot and brittle.
Replaced that and everything is back to normal.

NDT

cheers!
will check all hoses etc at weekend

Nick

FrankM

Hi

The engine is running fine again after changing the MAF sensor.

The MAF sensor was faulty and was perhaps that part that has caused my enginge damage.
Subaru will check the MAF as well.

Now I can see the Lambdasignal on the select monitor as well...
I am a little bit confused about this behaviour?
MAF Sensor faulty - Lambdasensor gives no signal... strange Scoobything.


BTW: Somebody told me that the MAF Sensor is the same as it is used in the MY99 and about the half cheaper...


FrankM :-)

FrankM

Sorry...now the complete phrase

...
BTW: Somebody told me that the MAF Sensor in the SEAT IBIZA is the same as it is used in the MY99 and about the half cheaper...
....

Frank :-)

NDT

Nigel - was your car an STi or import?
do you know the part number for the Lambda sensor?
does anyone know if it's the same for the WRX/STi?
questions questions......

Nick