i am really having probs with my uk 99 turbo impreza.i have a prob with the lambda sensor that sits on the downpipe right near to the turbo.i think its the o2 sensor. when the computer is plugged in it is not reading the sensor.when you reset the ecu it comes on line and starts reading but after a few seconds it stops reading again.i have tried another ecu and it does exactly the same.i have tried another sensor and it does the same. i have carried out tests on all the wires from the ecu side and the sensor side and they are fine.i have tried a third brand new sensor in and it is the same.the computer has been tested on another impreza to make sure it is not a fault with the software and that was working fine.
so if it not the wiring, not the sensor and not the ecu what else can be causing the fault. the car is very tempremental some days will drive fine then others showing loads of actvity on the knock link.
i am at my wits end and could do with some ideas to help me find the prob.please help of you can.

thanks Phil

 

This could be total cr@p but...if it's std 3-wire sensor, could it be an earthing problem? relying on the screw thread fitment for an earth.

When I replaced mine, I went for a 4-wire.

Faulty MAF sensor causes crap running & knock too. Apparently a common thing on MY99 & MY00

 

Probably the MAF.

Sounds odd but they do have an influence on each other (02). I had this on mine. If you look at the MAF reading on the computer you are using, it will probably count up and up and up at idle.

Be very careful and replace it ASAP. About £80 from the dealer of somewhere like Xtreme scoobies.

MB

 

PS - Noticed you are new, so will tell you the MAF is the Mass Air Flow Sensor. If you look at the air box on the front left of the engine bay, theres a black cylindrical tube coming out of it, quite big.

The MAF plugs into the side and you will see the connectors coming out of it. You will need Torx security tool to get it out, but a very easy job.

MB

 

MB,
Could the MAF account for the signal loss on the lambda sensor too?

 

Yes, if the MAF has failed and reading lean (which they generally do) - as the ECU uses the MAF signal to calculate engine load.

The ECU only knows whether its in open / closed loop by engine load from the MAF. The signal from the MAF to the ECU is turned into an assumed airflow - then uses a lookup table to assume a correct AFR.

If the MAF is showing less air than it should, it will give a low AFR - thus the reading on the lambda is lower (which is real)

I had to ask this on 22B a while ago. I was seeing it on my old UK MY99, but couldn't work out how the 2 sensors were interlinked.

MB

 

thanks for the reply, i have a knock link and general running about under 4000rpm if fine no activity at all but after that when you nail it big red light. it is very on and off though some days it will run fine. i will give the above mentioned a try thanks a lot.