The V8 Owners Forum -

My Rover v8 is fitted with the Hotwire injection system but with no cats.
I have the electrical sockets on both sides of the engine for the Lambda sensors and plugs in each side of the exhaust system to fit them.
Is there any advantage in fitting them?
I realise I will have to change the tune resistor.

I highly doubt there will be any performance advantage. There might be an emissions advantage though!

Chris.

Without cats the mixture can vary from optimal for maximum power (rich) to best for MPG at cruise (lean) A simple lambda sensor for a cat tends to keep it near constant.

DaveEFI wrote: ↑Tue May 03, 2022 9:01 am Without cats the mixture can vary from optimal for maximum power (rich) to best for MPG at cruise (lean) A simple lambda sensor for a cat tends to keep it near constant.

Well I don't think it's so much the cats as the Lambda sensors which adjust the mixture. OK, sounds like I'm being a pedant but the point I'm makins is I guess you could run Lambdas in the exhaust without having to also have cat's and you would then have a system capable of running closed loop which can adjust the fuelling.

As well as adding the sensors (and making sure all the cabling, fuses and so on are in place to power them) you would also have to change the tune resisitor to allow the 14CUX to invoke one of the closed loop maps and the program sections which implement this. This resistor is sometimes wrapped up in the loom so not always obvious.

However there is also the question "Is there any advantage in fitting them?". In the 14CUX system the Lambdas are narrow band so will only indicate a specific AFR, 14.7:1 in this case, and so closed loop can only be used under specific conditions such as idle and cruise unlike a wideband system which can target any AFR (in range). There may be an advantage in fuel consumption in these areas but not really for performance.

There may be the added benefit if the trim values calulated when in closed loop mode are applied even when running open loop. I don't know if this happens or even if it would be a good idea as this would be making the assumption that any deviation found would be applicable across the board as my car runs without Lambdas or closed loop.

Although it sounds like it may be a good idea I'm not too keen, if my system started to flow more or less fuel over time I'd like to know about it and find the cause although I guess a counter argument to that would be that if you monitored the trim values periodically this would alert you to any changes.

The purpose of a narrow band lambda sensor is to keep the mixture at near stoich for the cats. Can't see any practical advantage in fitting them with no cats. A wideband, a different matter. Assuming your ECU can make use of one, which I doubt the 14CU can.

With my MegaSquirt, the mixture varies between about 12.5:1 at full load, to about 15.5:1 at a gentle cruise.

I'd say Lucas chose not to fit lambda sensors to a non cat engine for good reasons?

DaveEFI wrote: ↑Fri May 06, 2022 10:09 am The purpose of a narrow band lambda sensor is to keep the mixture at near stoich for the cats. Can't see any practical advantage in fitting them with no cats. A wideband, a different matter. Assuming your ECU can make use of one, which I doubt the 14CU can.

With my MegaSquirt, the mixture varies between about 12.5:1 at full load, to about 15.5:1 at a gentle cruise.

I'd say Lucas chose not to fit lambda sensors to a non cat engine for good reasons?

That's pretty much the point I was trying to make Dave.
Bearing in mind the 14CUX is a early system I think the main (only) reason it had the facility to use lambda sensors was to allow the use of cat's and hence only narrow-band used. It wouldn't be possible to simply nail on a couple of widebands without writing a new algorithm and while that may be possible I don't think it would be practical and the 14CUX may not have the processing speed to handle it even if you did.

DaveEFI wrote: ↑Fri May 06, 2022 10:09 am
I'd say Lucas chose not to fit lambda sensors to a non cat engine for good reasons?

One and only reason. It's cheaper not to.

Even NB's if functional can improve economy etc on any engine. But most engines may be happier and feel more responsive running richer than stioch

An RV8 which never went richer than 14.7:1 would feel very 'flat' indeed. It's why modern engines use multi-valves and variable valve timing. And other tricks to get back the performance a cat dulls.

Thank you for your views.
Think I will leave as it is.
Cheers,
Andy.

Aussie spec series 1 3.9 Discos came with no cats or lambda sensors. Just adjust idle mixture value at AFM. Less to go wrong.