Thread: Discovery 2 V8 hesitation on downshift

I'll double check on the Nanocom it shows fuel trim on bank a and b fluctuating from 0.96 to 1.01 I'm not sure what that means.

1.00 means air/ fuel mixture is running at stoichiometric, which is what you want.

I shouldn't have read this thread....my D2 got the vibe and is now throwing a P0155 code for 02 sensor....having said that I just filled up again averaging 14.7l/100k of mixed running and the voltages look good on the Ultraguage. Will keep an eye on them. Cheers

Originally Posted by biggin

1.00 means air/ fuel mixture is running at stoichiometric, which is what you want.

If his o2 sensors are steady on 1V or more, they are stuffed.
They should/must vary constantly between .1 and .9
The o2 sensors drive the stft's, which constantly strive for stoichiometric.

the whole tuning setup of a thor is driven by o2's. they dont care that you are tring to overtake a semi, or taking off from a set of lights halfway up a mountain.

remember why carbies had power jets and second barrels?

thors dont care.

Exactly right, but he was talking fuel trim ratio not O2 voltage.

Originally Posted by Pedro_The_Swift

If his o2 sensors are steady on 1V or more, they are stuffed.
They should/must vary constantly between .1 and .9
The o2 sensors drive the stft's, which constantly strive for stoichiometric.

the whole tuning setup of a thor is driven by o2's. they dont care that you are tring to overtake a semi, or taking off from a set of lights halfway up a mountain.

remember why carbies had power jets and second barrels?

thors dont care.

I think I found this read out on the nanocom today they varied from about .05 up to .89 from memory. So I am assuming that they are working and if I have a small vacuum leak the o2 sensor will add fuel to achieve the correct ratio.

One of your fuel trims shows 50% - top image. Which one is that?
If that image is correct then that is a command to increase fuel.
A command to increase fuel is a vacuum leak.
Recheck that figure I mention above.
A serviceable narrow band O2 will oscillate from around .3 to .8 at a steady frequency during cruise. On accel they should both go high and on decel both should go low.
If either O2 sensor is stuck at a steady value then you have either continual lean, continual rich, or unservuceable sensor on that bank.
Do not change your O2 sensors until you nut out the fuel trims - work out the underlying cause of the problem first, recheck that the O2 sensors oscillate in voltage and respond as above to power on or off. If they are OK then move on methodically to continue the diagnosis.
There are heaps of info on O2 versus fuel trims on utube.

if needed,, buy genuine only..