ECU Lamda Log File?

[davidn]

I'm getting a fault on Lamda 2, looking at the log file shows it's doing something but I wondered should both sensors be doing the same thing at the same time or should they fluctuate, i.e one full rich one full lean. Some of the time they are in sync. some of the time they are wildly different but both go closed loop in sync. above 4,000rpm. I,m thinking I might have a blocked cat or 2 neither has been changed in 24,000 miles.
Any pointers appreciated.

Cheers
David

>> Edited by davidn on Saturday 1st October 13:43

[mikesr]

At 4000rpm the target lambda map is set to 0 which disables the closed loop lambda control. (unless someoe has been fidding and fitted a modified EPROM in the ECU) The sensors are not wide band so can't give reliable readings at wide throttle openings.

If the lambda is showing a fault then it needs investigating. The ECU raises a lambda fault when the voltage from the sensor is outside its upper/lower limits (0V and 1.73V IIRC) at which time it uses a default value. If its an intermittent fault (MIL light on intermittently) then I'd suspect connector corrosion/damaged wire etc

If its a permanent fault then broken wire or duff sensor

I don't believe a blocked cat would cause a lambda fault to be logged - AFR fault possibly if the adaptives go wild trying to compensate for the blockage?

[davidn]

Thanks for that Mike. The lamda's show 1.2 above 4,000rpm which I understood to be full rich, is this right?
I do get an intermitant MIL and this corresponds with a fault log for lamda 2, the sensor was changed prior to buying the car as the MIL light came on intermitantly through my test drive. Doesn't seem to have cured it though.
My adaptives are all over the place +40 to -35 in places which I know to be way out.
I've been reading through the help files which gives values for the ignition. The values stated (can't remember off hand) are these only correct at idle? I get massively different readings, double in places when the engine is under load - can that be right?
Blimey I'm going on a bit here but nearly finished, the reason I'm wondering about the cats is I've noticed a slight buzz/rattle from the centre of the car and some days the exhaust sounds muted and strangled this coincides with sluggish repsonse to the throttle, a quick blip and she stutters other days far nosier and lightning throttle response.
I guess it's time for the experts or bite the bullet and replace the cats.
Anyway thanks for the reply If you have any thoughts I'd be glad to hear them.
Cheers
David

[mikesr]

Don't think I've ever checked the lambda readings when above 4,000rpm. They still record a value but the ECU ignores it and just uses the base fuel map. I would expect if it was just a duff lambda once you hit 4k revs the engine would come to life as it were. Sounds as if its giving grief across the rev range so definitely something else going on. And yes those adaptive values are wildly out. I'd get someone in the know to check it over.
Mike

[mikesr]

BTW Ignition advance goes up to 60 mid throttle openings IIRC

[trackcar]

The muted exhaust / dull response thing sounds suspiciously like a cat blocking the exhaust then rattling free doesn't it? .. that *sounds* like you're on the right track.

cats dislike vibration and excess temperature, with misfires/unburnt fuel down the exhaust you get both these in large doses, one reason why cerbera cats have a limited life. The misfire could be caused by any number of faults, but HT related issues, faulty lambda feedback and valve clerance issues are all favourites with the cerbie engine.

I suspect you've hit the spot with what's causing yuor alternating power issue, but further investigation would be required once you'd sorted the ehaust restriction out to make sure that was all there was to it.

[davidn]

Thanks for the extra info and advice gents. I think I'll bypass the cats initially to clear up once and for all if they're causing a problem.
I've been following the recent thread on de-catting and am not sure that this is the way to go for me with a sports exhaust all ready fitted (unless someone round these parts cares to pursuade me otherwise ), so I guess it may be new cats and then a RR session to see what it's doing.
Cheers
David