Discussion
My car went onto the dyno today at Rapid. It's making an impressive 440hp at the flywheel; last time it made 520! It seems my O2 sensors are knackered (switching slowly or not at all apparently) and it's overfuelling. I don't know how long it's been like this but the consumption has rubbish for a while - 17mpg.
I thought they were supposed to last 70k miles+ and mines only done 22k. Makes me wonder how many other owners have/are experiencing this.
I thought they were supposed to last 70k miles+ and mines only done 22k. Makes me wonder how many other owners have/are experiencing this.
I'd have thought the car would be running open loop when maxing out on the dyno, so the lambdas would be irrelevant. I'm sure Ringram will comment if he passes by.
Lambdas are fickle things and can go lazy or peg out much sooner than 70K. Tuning mods, especially a blower, can hasten their demise.
Lambdas are fickle things and can go lazy or peg out much sooner than 70K. Tuning mods, especially a blower, can hasten their demise.
Correct O2 sensors have nothing to do with full throttle power control.
BUT before I forget, its been a long time since I used Long Term Fuel Triming, long term trims are built up over time and if they are wrong because of O2 sensors can cause issues as described.
Basically the long term trims are added to WOT fueling as a correction factor in case they are really needed and the base timing table is bad/lean.
Long term trims are learnt corrections to the tune based on o2 feedback, the more fuel the o2 sensors say is required at a certain load point the larger the long term trim will become. Kind of works to anticipate fueling to kick start the o2 feedback.
So yes things can go out the door big time.
Some of us run open loop (no O2 feedback), or short term trims only to avoid this type of issue.
A nice way to check to see if you tune or o2 sensors are fubar is to reset the PCM by pulling the fuse for a while to the PCM, then you power it back on the fuel trims will be zero. If the car drives much better then something is amiss either with the tune itself or with the o2 sensors.
BUT before I forget, its been a long time since I used Long Term Fuel Triming, long term trims are built up over time and if they are wrong because of O2 sensors can cause issues as described.
Basically the long term trims are added to WOT fueling as a correction factor in case they are really needed and the base timing table is bad/lean.
Long term trims are learnt corrections to the tune based on o2 feedback, the more fuel the o2 sensors say is required at a certain load point the larger the long term trim will become. Kind of works to anticipate fueling to kick start the o2 feedback.
So yes things can go out the door big time.
Some of us run open loop (no O2 feedback), or short term trims only to avoid this type of issue.
A nice way to check to see if you tune or o2 sensors are fubar is to reset the PCM by pulling the fuse for a while to the PCM, then you power it back on the fuel trims will be zero. If the car drives much better then something is amiss either with the tune itself or with the o2 sensors.
Edited by ringram on Friday 4th July 18:33
wormus said:
Wierd. Mark told me this afternoon when he switched them off the power went up but he wouldn't let me take the car with them disabled. Still making 500+ lbs torque but the power is way down on what I expect.
Yeah see my updated comment, I forgot about long term trims being added to WOT, mainly because I haven't used long term trims in years and remembered again why they suck 
t!Well you could ask him to run short term trims only. That in effect retains o2 feedback trims but without the learnt fudge factors.
It should keep it a little sharper.
IIRC short term trims can still add or subtract up to 25%.
Ultimately having it richer from long term trims is safer even if performance and fuel consumption sucks.
I just run short terms at the moment. Same as at the pod
It should keep it a little sharper.
IIRC short term trims can still add or subtract up to 25%.
Ultimately having it richer from long term trims is safer even if performance and fuel consumption sucks.
I just run short terms at the moment. Same as at the pod
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