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MG MGB GT V8 Factory Originals Technical - EFI Lambda/O2 sensors

I am putting a "Hot wire" fuel injected 4.2 liter Rover engine in my 1974 roadster. I am not planning on using catalytic converters they are not required for 1974 vehicles here in California. Do I need to install the Lamda/O2 sensors as the ECU has the option of setting it up either with or without them? Are there any benefits to the ECU to fitting them without the cats?
Regards
Tony Bates
Tony Bates

I believe the tune resistor can be changed to account for a lack of catalytic converters, but not a lack of O2 sensors. Install a set of 3 wire heated oxygen sensors in the exhaust manifolds (close to the motor if possible) and you'll be ok. Go to the local parts place, and ask for the least expensive 3 wire sensor they have. Don't worry, it's still probably made by bosch, and it will work perfectly well with your system.


Justin
Justin

Justin,
OK, I understand, but the Range Rover Workshop manual states in Section 19, page 3 under the circuit diagram of the EFI sustem, "Lambda sansors fitted to catalyst vehicles only". This is why I am confused.
Regards
Tony
Tony Bates

I won't profess to knowing the inner workings of what rover was doing with these systems, but I've never seen one that doesn't use O2 sensors. I would think them to be a crucial sensor in this system.

Anyone else have a take on this?

Justin
Justin

Justin,

Not overly familiar with the EFI system you are working but in my experience the systems rely in the input signal from the Lambda sensor to adjust the fuel mixture so having that signal is an essential part of the feedback loop.
Witness what happens when an oxy sensor goes South and the engine runs like a dog.

If you can set up the system without ths Lamba sensor input signal as you mentioned in the first post then there is obviously a facility to run with and without the cat and oxy sensor arrangement.
Maybe Rover have markets where this is the case.

Sorry best I can manage.
Cheers, Pete
Peter Thomas

Put simply the later Hotwire EFI system can work in closed circuit mode where it uses its fuel map to determine optimum fueling at cruise speed (ie. not accelerating or decelerating) dependent mostly on airflow, or closed circuit mode where it uses lambda sensors to determine the correct mix at cruise by directly sensing the exhaust gasses. Choice of mode is dependent on a tune restistor fitted to the loom (plenty of info in the archives re tune resistors, can't remember the values off hand).

A warning, a number of people have said "just use any three wire sensor". Certainly for the UK market this is not necessarily true. The CUX uses Titania 3 wire sensors whereas 90% of cars use Zerconia sensors. The signal voltages are not the same and thus i'd guess that Zerconia sensors may not give the right tune.

Geoff
Geoff Richmond

I'm confused.

A web search shows that the titania sensor is a four wire device, but the schematic for my hotwire shows a three wire sensor. I had sensors from my older federal type fuel injection that I used on my hotwire without the heater, and when I connected them all that was in the Rover harness going to the O2 sensors was a signal, 12V for the heater and a ground. Am I missing something here? Would using the zerconia sensors be a problem with 90-95 hotwire?

Here's some details on the titania sensor

The lambda sensor is also referred to as the Oxygen (O2) sensor plays a very important role in control of exhaust emissions on a catalytic equipped vehicle.
The lambda sensor is fitted into the exhaust pipe before the catalytic converter. The sensor will have 4 electrical connections and it reacts to the oxygen content in the exhaust system and will produce an oscillating voltage between 0.5 volt (lean) to 4.0 volts, or above (rich) when running correctly.

Titania sensors unlike Zirconia sensors, require a voltage supply as they do not generate their own voltage. A vehicle equipped with a lambda sensor is said to have 'closed loop', this means that after the fuel has been burnt during the combustion process, the sensor will analyse the emissions and re-adjust the engine's fueling accordingly.
Titania O2 sensors have a heater element to assist the sensor reaching its optimum operating temperature. The sensor when working correctly will switch approximately once per second (1 Hz) but will only start to switch when at normal operating temperature. This switching can be seen on the oscilloscope, and the waveform should look similar to the one in the example.
If the frequency of the switching is slower than anticipated, remove the sensor and clean with a solvent spray and this may improve the response time.

From Pico Instruments web site.
Phil

Phil

Have look at this site: http://www.lambdasensor.com/. A generic 3-wire 12mm Titania lambda sensor is listed for the Land Rover Discovery; Range Rover, TVR Chaemera and Rover 800 2.0i (all of which use Lucas hotwire EFI). It seems that Titania lambda sensors come in three and four wire types as well as Zirconia.

Geoff
Geoff Richmond

OK, so for a Rover/Hot wire set up with no catalytic converter, what's the best solution, O2 sensors or not. Is it a performance versus emmissions issue? It looks like the general configuration is to use o2 sensors, if so, which tune up resistor do you use, "no catalyst" or "with catalyst"?
Regards
Tony
Tony Bates

If you want to run with O2 sensors choose the "with catalyst" tune resistor even though you have not fitted catalytic converters. That is the config I am using on my conversion. Not sure that there would be any significant performance difference because the ECU uses the fuel map to determine fueling under acceleration and the O2 sensor does not figure in the calculation.

I think that with O2 sensors and closed loop operation you could be more confident that mixture was precise during cruising (hence better economy and less emissions) in comparison to using a fuel map entry with no direct measurement from the exhaust gasses. Having said that the O2 sensors are pretty expensive compared to simply using a "no catalyst" tune resistor.

Geoff
Geoff Richmond

Tony -

A Green (470 Ohms) resistor will give a non-cat tune, and White (3900 Ohms) a cat tune.

Geoff -

Thanks for the great information - now I need to see if the old SD1 lambda sensors are zerconia or titania -they are almost certainly zerconia since they only have one wire and no heater.

Thanks again.

Phil
Phil

Maybe rover is different, but most EFI REQUIRE a o2, it is not an option to use or not. least not if you want it to run well. The O2 is the ecu's way of monitoring actual mixture and adjusting for best economy and perormance. If not using O2, might as well run carb'd, the ECU will be guessing how much fuel to use..
Larry Embrey

Tony, use green tune resistor and no oxygen sensor. This is the way the Hotwire system works in some MG V8's that I know of, and it's the way it works in mine; the wiring loom doesn't have a place for the o2/lambda control. My wiring loom came of a Rover 1991, this was a small period where the British cars were allowed to run without cats, but had the hotwire system (without o2 control sensor).

Frank
Frank de Groot

EFI systems run in two modes: Open loop (OL) and Closed Loop (CL). Only CL used O2 sensors. OL uses fuel maps in the ECU memory to control the injectors. The map is configured for a specific engine and vehicle combination. CL is used after the vehicle is warmed up and only during certain operating conditions, usually switching to OL when a specific load factor is reached, such as hard acceleration and WOT. Normally cruise, decel, and idle will be CL. The map will be close enough to give good driving and economy in OL, and CL will tune for minor variations. If you make large changes to the system such as a cam, headers, open exhaust, greatly decreased vehicle weight etc, this may take you outside the envelope for the existing fuel and airflow tables, and correction factors (the map), with unpredictable results.

Having said that, it is my understanding that the Lucas hotwire system is somewhat unsophisticated (flame suit donned) and can often be made to work by swapping tuning resistors around. My suggestion is to try the green tuning resistor as suggested by Frank and others, and if the results are not suitable, then fit an O2 sensor and see if that helps. Systems which use two O2 sensors generally default to one sensor if that's all there is. On Fords it's the left one. (Or is it the one that's left? ;-)
Jim Blackwood

>>>Having said that, it is my understanding that the Lucas hotwire system is somewhat unsophisticated (flame suit donned)<<<

In plain English the system is 'crude', which in these circumstances is a real bonus. Having a fair degree of experience with Hot Wire in various forms and contact to the guys who developed and made the systems I can confirm that tune resistor changes offers a degree of flexibility that would in todays systems normally need a chip change. The 14CUX being a fairly generic ECU with several built in operating modes, the appropriate one triggered by the controlling tune resistor. 14CU also seen on later Rover M16 16 valve 4 cylinder units (early ones used 12CU) and the cat equipped O series Montego.

Rog
Roger Parker

This thread was discussed between 21/12/2002 and 25/12/2002

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