Thread: how to install lambda on 1998 4.6 hotwire

Originally Posted by pibby

Hi all,

I have a 1998 discovery v8 petrol efi which has had the 3.9 motor replaced by a 4.6. it is still using the standard 14cux and 5am afm and is dual fuel but I use lpg 99.9% of the time. on my to do list it is to invoke a feedback loop by installing lambda sensors. I am hoping this will improve fuel economy and general engine performance.

I have summised what i believe needs to be done but am hoping someone out there has already been down this path and can confirm/correct me.

What tune resistor? From what I have researched so far about this, the 14cux has about 5 fuel maps in it and the enabled map is determined by the tune resistor under the dash which varied according to the market the vehicle went to. To get the catalyst map the resistor should be 3.9k ohms

What oxygen sensors? Haven’t seen it definitively written but I am guessing the sensors are narrow band and that generic three wire sensors will do. What would happen if wideband sensors are installed – will the ecu keep properly adjusting fuel using the lambda feedback and simply log an error?

Where to install the oxygen sensors? Where the exhaust pipes each side of the vehicle reduce from 2 to one and mounted from the top to avoid condensation issues.

How to install oxygen sensors? From what I’ve read the land rover sensors are 12mm thread whereas most other sensors are 18mm thread. Drill a hole at the appropriate place in the exhaust and weld on the appropriate thread size nut which the sensor will screw on to.

What wiring has to be done? The car has no wiring loom in place for lambda operation. from what I have read there is a wire to heat the sensor which goes from the sensor to the fuel pump relay. There is the signal wire from the sensor which go to pins 23 and 24 (one for each sensor) on the ecu and should be run in a screened wire to minimize any electrical noise. There is an earth from the sensors which goes to the chassis nearby I guess. There is also a screened earth from pins 23 and 24 but I’m really lost here how this is wired in.

Without trying to confuse this any further, I have also read that the appropriate air/fuel ratio for petrol is 14.7:1 and the appropriate air/fuel ratio for lpg is 15.5:1. however, “Lambda is a ratio of ratios and is 1.0 exactly at the stoichiometric point for any given fuel” and at this point will always be 2.5volts. is this just another way of saying that it doesn’t matter what fuel I am driving on ie lpg or petrol, the ecu will be adjusting fuel correctly to aim for lambda 1.0?


Look forward to any help here.

Ps I live in Hobart and spoke to JC who thought philipA had already been down this path.

Thanks,
brett.

OK I can help you with fitting an oxygen sensor to the LPG side, that is straight forward and I have done it plenty of times. The petrol side is a complete mystery to me!

The use of wide band sensors requires the ECU to be programmed for it, they can't be read by a simple voltage measurement.

First you will need an oxygen sensor, I use a narrow band heated (3 wire) one as fitted to EA to EL Falcons. You will need a harness plug off such a Falcon, I usually cut one off at a wreckers, easy to get at as it just below the brake booster. Solder and heatshrink a 3 wire harness to the connector long enough to get from the exhaust "Y" junction to the spot for your LPG processor. Drill a 19mm hole and weld a sensor mount to the pipe just after the Y. You will be able to drill across under the transfer case for a reasonably protected position. It is the same thread as old spark plugs, namely 18 x 1.5mm. You could cut a mount off a donor pipe, many cars use this thread.

Fit a LPG processor to suit your system, most use TPS input (0 to 5 volt approx) and oxy sensor (0 to 1 volt) output. The sensor black wire will be green/blue (?) in the harness plug, you must earth the processor to the engine block. The other 2 sensor wires are the heater, they are not polarity sensitive. I connect them to a 12V ignition supply and a suitable earth.

I can't say which processor I recommend unless I know what LPG system you are running.

PhilipA has done it. Have a look at this thread:

Fuel economy 3.9 with O2 sensors

You may have to PM him for the details as a PDF. Can't recall seeing it posted.

cheers, DL

hi bee utey - the gas system ecu is one of those sequential vapour injection thingys (elko brand) which is a slave to the 14cux. all the gas ecu does is take the injector opening time (as determined by the 14 cux) and does a calc on that to either increase/decrease or leave the injector opening time as is. that's why i am trying to run the lambda install through the 14 cux as the gas ecu has no lambda function.

thanks for the tip on the falcon sensors and install. never used lambda sensors but read they have a limited life km wise so better off buying new ones? $?

brett.

Originally Posted by pibby

hi bee utey - the gas system ecu is one of those sequential vapour injection thingys (elko brand) which is a slave to the 14cux. all the gas ecu does is take the injector opening time (as determined by the 14 cux) and does a calc on that to either increase/decrease or leave the injector opening time as is. that's why i am trying to run the lambda install through the 14 cux as the gas ecu has no lambda function.

thanks for the tip on the falcon sensors and install. never used lambda sensors but read they have a limited life km wise so better off buying new ones? $?

brett.

Gas injection! I should have guessed. Yes, its all up to the petrol ECU so I leave that to the experts.

However you can use an oxygen sensor and a Jaycar kit to read mixtures, then the results of any other method you have of tuning the ECU's output can be seen easily.

Lambda sensors can run for 150 000km happily in a new car, I tried used ones for a while but now I use only new ones. Mainly they respond faster when new, they can get sluggish with age and cause embarrasing lean out just after starting, until they dry out. Never had a problem with new sensors fitted horizontally, I suppose the heater helps.

Suggested part number for the NTK sensor: 0ZA23-D2. Last one cost me $77 trade. It's cheaper than a universal sensor, and being able to unplug it helps installation a lot.

I wanted to post this stuff as a thread, when I do another one I might take a few pics.

thanks for the tip on the falcon sensors and install. never used lambda sensors but read they have a limited life km wise so better off buying new ones? $?

You cannot use Falcon O2 sensors with a 14CUX.
Falcon sensors are Zirconia sensors and Rover sensors are Titania sensors.
They work completely differently. FYI they are also a different size thread 17MM Zirconia and 12MM Titania.

Zirconia generates a voltage , but Titania changes output voltage from an applied voltage by changing resistance.

Rover uses Titania as they are not susceptable to errors from being immersed etc.
Regards Philip A

Some more info on closed loop and the 14 CUX:

Closed loop 14CUX RRC 3.9

Closed loop was standard spec on US vehicles back then, so it's not like inventing the wheel. Should work controlling your injectors.

Will probably look at getting bee utey to update the gas system on my 350 later in the year, sounds like he knows his shiz.

cheers, DL

Originally Posted by PhilipA

You cannot use Falcon O2 sensors with a 14CUX.
Falcon sensors are Zirconia sensors and Rover sensors are Titania sensors.
They work completely differently. FYI they are also a different size thread 17MM Zirconia and 12MM Titania.

Zirconia generates a voltage , but Titania changes output voltage from an applied voltage by changing resistance.

Rover uses Titania as they are not susceptable to errors from being immersed etc.
Regards Philip A

I have met then on a P38A, I know what you mean. Where I fit LPG injection that's fine. When I fit a mixer type LPG system I fit a zirconia sensor to run a LPG processor. I must say that immersion doesn't happen to most of my customers but its something I need to be aware of.

For those of you now interested the project write up was posted 26/4/2008 in projects and tutorials.

Its name is "Finally the V8 3.9 O2 project"

Regards Philip A