ever since I have had this rig about 5 months the check engine light has been on and it needs new 02 sensors ,I have the new ones and would like to put them in I have put about 3000 miles on it since I have had it , I just fueled up tonight and it was 95% highway , i got 505 kms and used 65 litres of fuel for my American friends it works out to 22 mpg. Would you change the 02's ?

 

I have a 97 D1 automatic and am enjoying about 14 mpg.... as are many others. 22 sounds like a dream.

 

Wow....22mpg...amazing! If it needs it, replace it.

 

Wouldn't touch a thing, unless you have emissions inspections.

 

I wouldn't touch a thing either, unless you have to. I think I would read the codes or get them read though, just out of curiousity and to make sure it wasn't something that really matters.

 

Well....doing a bit of math...

505 km = 313.8 miles
65 liters = 17.17 gallons

313.8 / 17.17 = 18.27 miles/gallon

So while you're doing well, it is not 22mpg. 22 is just too good to be true.

Anyway, upstream O2s send info to the ECU and that in turn is used to adjust air/fuel ratio. Over the long term, you don't want that system to be too far out of balance.

 

Since your mpg is a little higher than normal, might want to check - radiator fan clutch - when warmed up, and engine off, if it will spin "free wheel" more than 1 revolution, the fluid inside the clutch has weeped out, and you won't get the cooling you need at idle. You will get about 1 mpg or better boost with a worn out useless fan clutch.

 

Codes for the O2 sensors put the truck into a limp home mode that makes the engine run richer than normal. Also, it's tough to get an accurate determination of gas mileage off a single tankful. If you are certain the problem rests with the O2's and not something upstream from them, then most certainly install them. You already bought them.

 

Keep in mind that 95% of all O2 codes on a Disco are because you need a tune up.
But I would reset the check engine light and drive it and see if it comes back and what the codes are then and go from there starting with a tune up if you have not already done so.

 

Yes I will get the codes cleared and see if it comes back ,it has new plugs and wires I put in NGK BPR6ES instead of 5 ,it is a 5 speed and it has 221,000 kms. the fan clutch works well and I am going to install an electric Volvo one from a s70 which will help some as well. To the math expert here in Canada there are 4.55 litres per gallon our old gallon was 160 onces not 128.Now see what numbers you get .the last few tanks were 18.6 to 19 but they had a combination of city driving as well ,but the last tank was pretty much entirely highway so I guess that is why the higher number. thanks for the feedback.