Disco 1 V8 3.9EFI cats and O2 sensors

[Jbdisco]

Hi all

I have a question regarding my 1995 Disco 1 3.9V8 ES. I live in Zimbabwe, so no worries about MOT checks or anything like that. My vehicle is fitted with catalytic converters, with O2 sensors both sides, ie before and after. The light for the cats has come on on the dash, unfortunately the plug in computer diagnosis comes up with nothing. The suggestion here is to just remove the cats. My questions are, is this possible with the O2 sensors? Will they need to be removed? Will that affect consumption/ computer controlled fuel injection? Can this be resolved by changing the tune resistor?

Sorry for the long question, wanted to try and cover everything :-)

Thanks in advance :-)

[BogMonster]

Change the tune resistor, disconnect the O2 sensors and forget about the cats unless they are actually blocking the pipe.

[Jbdisco]

Thanks,

Which tune resistor would you suggest? Green?

[Jbdisco]

Thanks BogMonster

Which tune resistor would you suggest?

[BogMonster]

I don't have the info to hand but from memory there are a few types of resistor listed in parts books, among which is a non cat low compression and a non cat high compression, choose whichever you need for your engine (probably high comp, if it had cats)

[Jbdisco]

Thanks again,

I have looked a bit more, can't find any reference to a different resistor depending on high or low compression. Seems a green, 470ohm resistor is for UK, europe spec, and a red tune 180ohm for Aus etc. So I will try green and see how I go.

Thanks

[Jbdisco]

Hello again, changed the resistor easily enough, but now wondering about the o2 sensors, where should I disconnect them from?

[James NZ]

Hi there,

if you are doing away with the o2 sensors then just unplug them from the loom. From the exhaust pipe follow the wiring from the sensor to the plug and disconnect there. You may want to remove the sensor's and fit blanking plugs.

For what it is worth I run my V8 with the white tune resistor and the o2 sensors connected. I did away with the cats when they met with a large rock! With the green tune resistor fitted you will need to tweak the afm to set the idle.

Here a two links that may be of help -

http://www.g33.co.uk/fuel_injection.htm. I use the Rovergauge software hooked up to my windows tablet.

http://www.britishv8.org/articles/rover-14cux-efi.htm

Cheers

[Jbdisco]

Thanks James NZ

I dunno why I never noticed this before sorry about that!

I have changed to a green resistor, but haven't noticed any changes, well it's better, but I haven't adjusted the afm..

I found the rear set if o2 sensors weren't connected anyway. Front ones were looking challenging to remove and wasn't in a mood to look further that day.. One dat though

[Jbdisco]

Thanks again! The link really helped! Still reading, but I haven't come across this page before! Thankyou!

[Disco-Ron]

Found this thread through searching about tune resistors...... I need a green non cat one, but no one can get it..... Is it simply a case of getting a 470ohm resistor and swapping it for the existing one??

[Jbdisco]

Sorry Disco-Ron, been out of comms for a while. There are some good Youtube videos by MrBeamerdave regarding the resistor. All I did to remove it was cut it out and solder a new resistor with appropriate resistance in. I never checked to see if the fuel map actually changed with diagnostics, but I am sure it did. I kept the original and have actually just switched back to it as I believe it is more adjustable. Unfortunatley one of the O2 sensors is bugered and has to be imported from UK, but anyway. Sorry for the delay