Diagnostic Lambda oscillations - Advice required

[trendytramp]

Hi,

Checked the old boy's TVR quickly at the weekend with the Diagnostics software as he'd had a problem with it hot stalling. A local garage had upped the idle to get him home - too much I might add - it now idles c.1900rpm. The vehicle

No faults are registering but I'm getting consistent high frequency Lambda output oscillations on both banks. Now I presume that at 1900rpm and 20-22% throttle the fuelling is still closed loop controlled? I find it odd that this is also happening on both banks!

Do you think this is a lambda failure on both banks or a PCM issue? The former would seem a coincidence but has it happened to anyobe here?

I have screen shots of the recordings etc. but not here. Adapatives were 4% and 6% at this speed but I forgot to get the adaptive maps.

When I'm next back I was going to try and drop the idle down and check again at a lower engine speed.

Any advice greatly appreciated!

Thanks,
Rob

[trendytramp]

Here's the recording screen capture

[GreenV8S]

Don't see the screen shots. A closed loop lambda control system using narrowband sensors would normally osscilate at 1-2Hz if it's working correctly. If it's happening at a much higher frequency I'd wonder whether there's either a cyclic variation in the engine behaviour (perhaps one cylinder running rich/lean) or something else adding noise onto the basic lambda signal.

[methodwares]

at that RPM, the engine is hitting the 'not so good' part of the map and as such the lambdas will probably be all over the place. the ignition timing seems to be taking hits as well, not sure that is right

[trendytramp]

thanks for the responses guys

methodwares said:

at that RPM, the engine is hitting the 'not so good' part of the map and as such the lambdas will probably be all over the place. the ignition timing seems to be taking hits as well, not sure that is right

i noticed also the changing timing which i thought was odd - could be a PCM issue...

i'll drop the idle when i'm back next and see what's going on then and report back

Thanks again,
Rob