Rough at steady speed

[prj]

Try driving a bit and see if the issue is gone without lambda before replacing it.
If it definitely goes away, I guess you need to replace it. These things have a limited lifetime anyway.

[20Vcqdriver]

Try driving a bit and see if the issue is gone without lambda before replacing it.
If it definitely goes away, I guess you need to replace it. These things have a limited lifetime anyway.

Will do, Was only changed last winter but wondering if the 50% methanol mix at WOT has fooked it up as not been on RR yet to set it all up properly...

[prj]

I doubt it has, but your car is going to run pig rich if spraying a lot of meth anyway.

[20Vcqdriver]

I doubt it has, but your car is going to run pig rich if spraying a lot of meth anyway.

Hoping to get it on the rollers before the SORN starts so Paul can maybe tweak the ecu to get it a bit more optimised. Place here gives full AFR and boost graph as well as power and torque which should be interesting.

[s2quattroking]

Had exactly the same symptoms with my 3B would idle fine then when cruising felt like different cylinder's would be misfiring, changed everything on the ignition side, fault still remained. Changed the fuel pump to an uprated one and hey presto, instantly run as sweet as a nut.

[prj]

Yea, I wrote before that it could be the fuel pump on the way out...

Too bad you can't get a fuel pressure gauge into your cabin...

[20Vcqdriver]

Fitted an uprated 044 pump 18 months ago, though I feel I need to deal with the wiring as it looks a bit on the small side even for the standard version.
Ran to work today with Lambda disconnected and ran much better though seems to be a bit down on grunt... am I right in assuming that the ign is altered when lambda not working

[UrS4boy]

....Ran to work today with Lambda disconnected and ran much better though seems to be a bit down on grunt... am I right in assuming that the ign is altered when lambda not working

Most likely since it can't get an adaptive signal, the ECU will likely use a base map and dial back timing, etc.

Here is some G39 Lambda (O2) sensor info:

http://forums.quattroworld.com/s4s6/msgs/21012.phtml

[20Vcqdriver]

Drove out at midday, re-attached lambda and reset ecu and instantly got my rough 'missing' running back at any steady speed. So a new Lambda on order .... hope this one lasts a bit longer....
Anyone remember what the thread size is as might need to put a tap down the hole as took me an hour to get this one on last time as thread on top of bung looks pretty knacked.

[prj]

Most likely since it can't get an adaptive signal, the ECU will likely use a base map and dial back timing, etc.

Sorry, but you are wrong.
ECU does absolutely nothing when the O2 sensor is disconnected, except for disabling O2 closed loop and throwing a code.
Your timing won't be affected, the reason it was down on power is probably because OP has boost- or vacuum leaks or his MAF is old and needs to be replaced.

[20Vcqdriver]

Sorry, but you are wrong.
ECU does absolutely nothing when the O2 sensor is disconnected, except for disabling O2 closed loop and throwing a code.
Your timing won't be affected, the reason it was down on power is probably because OP has boost- or vacuum leaks or his MAF is old and needs to be replaced.

Making my own boost leak adaptor so once it comes off the road it'll be one of the first jobs I do.
PS MAF less than 2 years old too

[UrS4boy]

Sorry, but you are wrong. ECU does absolutely nothing when the O2 sensor is disconnected, except for disabling O2 closed loop and throwing a code.Your timing won't be affected, the reason it was down on power is probably because OP has boost- or vacuum leaks or his MAF is old and needs to be replaced.

Okay, explain to me why these boost/vacuum leaks/MAF issues only show up when the Lambda/O2 sensor is hooked up. Your explanation doesn't make sense otherwise.

[prj]

Okay, explain to me why these boost/vacuum leaks/MAF issues only show up when the Lambda/O2 sensor is hooked up. Your explanation doesn't make sense otherwise.

Please re-read what I wrote.
I wrote that when the O2 sensor is disconnected, the vacuum leaks are going to be more prominent, because ECU relies only on MAF, which is going to show less air going into the engine than there really is, and since there is no O2 feedback, the mixture will go lean.

In short: OP said his car was down on power with O2 disconnected, I said the O2 might be masking leaks, because his car can't maintain a good afr open loop.

[UrS4boy]

Please re-read what I wrote. I wrote that when the O2 sensor is disconnected, the vacuum leaks are going to be more prominent, because ECU relies only on MAF, which is going to show less air going into the engine than there really is, and since there is no O2 feedback, the mixture will go lean. In short: OP said his car was down on power with O2 disconnected, I said the O2 might be masking leaks, because his car can't maintain a good afr open loop.

Maybe you wrote that in another thread but you didn't write it here or at least not as well as you have now. Thanks. Hopefully the OP will find the leak(s) and the issue will be solved.

[prj]

Maybe you wrote that in another thread but you didn't write it here or at least not as well as you have now. Thanks. Hopefully the OP will find the leak(s) and the issue will be solved.

Uhm, what's this then?

Fitted an uprated 044 pump 18 months ago, though I feel I need to deal with the wiring as it looks a bit on the small side even for the standard version.
Ran to work today with Lambda disconnected and ran much better though seems to be a bit down on grunt... am I right in assuming that the ign is altered when lambda not working

And my reply...

Sorry, but you are wrong.
ECU does absolutely nothing when the O2 sensor is disconnected, except for disabling O2 closed loop and throwing a code.
Your timing won't be affected, the reason it was down on power is probably because OP has boost- or vacuum leaks or his MAF is old and needs to be replaced.

Is it clearer now?