Thread: 97 disco 3.9ltr tuning

I have done LOTS of things to try to get better around town economy on my 3.9 Range Rover.
1 unichip
2 Thor manifold
3 modified head including 15thou shave
4 free flow exhaust
5 New injectors (Bosch 4hole)
I still get about 22L per100Km, admittedly in a very hilly area, Avoca beach , and short trips. On the highway I get about 14-15 at up to 115KMh, so I think there has been some improvement.
Of course I have LOTS more power, about 50% off idle and at least 20-40% across the range.

Next step is to fiit O2 sensors and fit the correect tune resistor. Have the sensors from USA ($80!!!), and the tune resistor ($10 from UK) and now trying to locate some of the little connectors that fit in the plug into the ECU. Anyone got a plug they do not want? I just need 3 connectors and about 10CM of wire on each.

FYI, the o2 sensors are unusual. They are Titania sensors which output a signal from 0.5 volt to 1 volt,compared to Zirconias which give 0 to 1 volt, and they are only 12mm,not 18MM as usual. but I found a couple of 12MM nuts and bolts which are the same thread. Now to weld the nuts on the exhausts.
Regards Philip A

Would you say it would be worthwhile for me to do that kind of retrofit to my flapper 3.5 Rangie? I think I have a short 3.9 I can use, maybe I should get the bits and build a complete engine ready to swap in.

hey Philip are you saying that you can retro fit 02 sensors? I have a 93/94 disco 3.9 that doesn't have them?

What difference would it make?

Cheers Blythe

I have got my car back at my local Land Rover specialist for them to have a look at as I was getting p!ss poor fuel economy any performance (around 25l/100km). I'll let ya know what they find/do to see if that helps you.

Originally Posted by blitz

hey Philip are you saying that you can retro fit 02 sensors? I have a 93/94 disco 3.9 that doesn't have them?

What difference would it make?

Cheers Blythe

I have seen it done. O2 sensors, correct tune resistor and run premium fuel. Feller with it done said fuel economy was much improved.

There is another thread on this.
Range Rov in Melbourne appear to do it, for a price.
I have checked the ECU, and it appears all the circuitry is there.
The plug does not have wires for the sensors or earth.
So it appears all you need to do is source the correct sensors, change the tune resistor, and wire them up.

What the result is , I have no idea as yet, but theoretically the sensors will make the ECU "closed loop" at 14.7:1 AF ratio. This should yield better economy at part throttle. I have checked mine with an O2 sensor and Jaycar kit, and it is running much richer than that, so there should be some gains.
Whether it all works on mine is also another question as I have a lot of mods.
Regards Philip A

Hey Grimace and Sam D,
before you try anything expensive to improve economy, try replacing your fuel cap. I was getting around 25/100 with my 3.9 and on an advanced drive day at Eastern Creek one of the other drivers in our group noticed fuel spill out of my filler cap. I went and got a new filler cap for about $30 and virtually over night got a 20% improvement in economy. I often wonder whether you get better economy on a trip just because you are not letting the fuel get a chance to evaporate. IMO best 30 I have ever spent.
Brett

Phillip is a wideband o2 sensor better ?