Lambda sensors for LPG and Carburrettored engines

[Martec]

Hi,

I have asked a few questions in the past for which you have been very helpful, this is a general question so look forward to your replys.

I have a 3.8 ltr MkII Jaguar running on LPG for over 10 years (replaced the gas tank a few years ago for the certificate and rebuilt the vaporiser), it has the usual nozzle rings infront of the carb mouths and is run by a Leonardo ECU with input from a lambda sensor.

My only real problems over the years have been failure of the lambda, I have tried cheap ones and a few years ago a friend in a scrapyard gave me a handful of second hand ones from ford escort and mondeo, the reason being that I wanted a sensor with a plug on it that I could get a ring spanner over to remove the sometimes tight ones. half were Bosch and the others NTK (NGK). With test runs on our local motorways and the laptop plugged in I could see when on an incline in 4th gear overdrive (2500rpm) each of the bosch sensors would reduce the gas and backfire (last time in holland if blew out the exhaust joint!!). The NTK increased the gas (as I opened the throttle to climb the incline) and no back fire.

I am using an Canems ECU and coil pack with switchable maps for LPG and petrol so it starts and runs on LPG all year round and petrol is only used when we can't find LPG (1200 miles in Scotland this summer), but each time I have to replace the lambda sensor as it gets sooted up (I assume).

I have run out of free sensors so I have a choice of

NTK 1890, NTK 0135, NTK 91312, NTK 92739

All have the square ford connection, length of lead is unimportant, the first is the cheapest on ebay. I have asked NTK which sensor they would recommend to put up with LPG and occasional petrol from a carburrettor (hence often rich) but no reply, so before I buy the first one as stock (my last free one in now) can anyone suggest a suitable sensor please, easy enough to change the terminal plug in the car.

Best wishes

Brian

[Gilbertd]

I run the Ford sensor that was intended for the 1.8 Dual Fuel Focus to drive my Leo but can't find the number at the moment. I worked on the principle that if it was good enough for both fuels on a Ford, it would be equally good enough on my Range Rover (the original LR sensors are 5-0V Titania and, although the Leo will work with them, the mixture is permanently slightly rich) so I have one in one downpipe solely to drive the Leo. That has a small round plug with tiny little pins but I cut that off and fitted my own plug.

[Oldskool]

Brian, I'm a bit of a novice with this stuff so this might be rubbish but I think it could be worth considering where you have the lambda located as compared to where it was designed to go. The one I've been using in an attempt to monitor my open loop mixture was originally screwed into a cast iron manifold but I've mounted it into my down pipe. Initially I did wonder (stupidly as it turns out) whether it would get warm enough, but I found it comes online very quick and I believe it's actually ending up significantly hotter than it was in its original application.

I don't know whether that might compromise longevity; I just know haven't cooked it to death yet. However I have noticed that when the engine gets right up to temperature the top end of the lambda output (by which I mean the rich end) drifts down a bit, in other words it reports a less rich mixture (still rich but not as much). I can't say whether this affects the other areas of the response so "lambda 1" might still be accurate but at least at the rich end I'm pretty sure it is behaving differently from the way it would have been in the donor car.

Secondly, (and I speak as a former '65 Jag owner) I'm wondering whether you use an octane booster or other lead substitute type thing in the petrol? If so could that be harmful to your sensor? Just a thought.

Steve

[LPGC]

Running on petrol with carbs will probably have caused your sensor to get sooted up..

Would think a heated sensor (usually white wires for the heater) mounted in the top part of the downpipe would be fine, just can't picture your manifold... If it's rather big that would mean the probe is sited further away from the exhaust ports.

Instead of paying for a new one, why not go back to your mate or another scrapyard and pickup some more lambda sensors? Most with 2 white wires, a grey and a black will work, ideally of course with the Ford plug but not a big deal to swap plugs if you can get a probe for free or very cheap.

Around here, if I went to one of the very well known scrapyards for a probe, they might charge £25 depending on spec but some of the 'old skool' scrapyards sell them for £5, remove yourself and get the lambda plug too.

Simon.

[Martec]

Gilbert and Steve,

Thanks for the replys, I think the sensor you refered to is NTK OZA659-EE76 1670, our early MkII has two 3 into 1 cast iron manifolds (angled back) and the sensor is in the down pipe just after the bend.

Simon,

I've looked at pictures on the NTK site and my old dead sensors look like oil contamination, but suspect soot is the final straw. My friend was forced out of scrapyard ownership due to the punitive council charges (a licience for everything), but It is a good excuse to go scrappy hunting at other local yards.

Thanks for your replies.

Brian

[LPGC]

One of the biggest UK scrapyards is only a few miles from me. I remember when it was an old skool scrappy where anyone could go in and walk around removing bits and bartering a price on the way out, just a couple of jack the lads behind the counter etc...

These days they've moved to new, very clean premises with cars on racking on concrete (rather than piled up adhoc fashion in pools of oil and mud) and loads of parts pre-removed on racking inside. Girly telephone operatives, reference numbers, what's your reg so we can check part compatibility, etc. Problem is, you phone them requesting a part and they reply 4 hours later saying 'sorry no stock' or 'yes we have 2 here, one still on car, one on shelf, (but will cost you 3 times as much as our old prices). Sometimes when they say 'no stock', you know they must have the part really! This happened recently when I needed 2 Chrysler electric fan relays (one for my own car, one for a Jeep - and not really relay but a little transistor pack that outputs fan current based on inverse voltage input)... 'Sorry we have no stock' (reply from the girl in telephone sales). So I just turned up there, explained to the fella at the front desk what I needed (and that the same part would be on all V6 GV's and Jeeps of a certain year range), they recognised me and let me go for a wander on one their golf carts, turned out they had about 20 of the part I needed and I got 2 for £20! Same part on Ebay is around £40... Sometimes they revert to old skool mode (a part is worth as much as it looks it's worth to the layman - advantage if it's a small part), that's usually for the better!

Simon

[Gordonjcp]

it would be equally good enough on my Range Rover (the original LR sensors are 5-0V Titania and, although the Leo will work with them, the mixture is permanently slightly rich)

Bugger. So that's why it whangs the LTFT right to the end stop after a mile?

[Gilbertd]

Yup, if you look at the Leo software, the output ranges from about 4.6V (lean) to 1V (rich), never getting much lower. The Leo is adjusting for an average of 2.5V, but the mid point isn't 2.5V, it's around 3.3V. So 3.3V is correct, Leo sets for 2.5V which is on the rich side of correct. Not enough to make it run rough but enough to affect the fuel consumption and make the LTFT try to adjust to get it back right again.

Mine had always had a separate 0-1V sensor in it but after I drowned it (flash flood on the M2 after a downpour that looked like a big puddle but turned out to be over a foot deep, interesting at 50 mph....) so I had a path from heater to output making it run very lean, I connected to one of the factory ones (knowing that you had yours connected like that and it was running OK). Then noticed that the fuel consumption had gone up so started to investigate.

[Martec]

Hi Simon and Steve,

All our old cars have unleaded heads so run on 98 octane petrol, so no addatives to upset things.

I have been visiting our local yards for the last 40 years, and make a point of chatting to the owners. Many is the time I've gone in for a pile of plastic or rubber bits to told 'just take that rubbish out of our yard' (free). Our old cars don't have expensive 'original' bit put on them but parts from the scrappy (original quality) that I can modify to suit.

I always accept the price they ask as I've already researched the parts new and know they are not ripping me off, and yes they are still the old fashioned style, but now only two cars high and will often lift cars for me to remove parts from. I am lucky up here to have access to these two remaining yards, Its a shame there are so few Jaguar S types in our yards as I'm salting parts for the early cars away.

I'm thinking of resurecting my old Wide Band Lambda measuring tool to reduce the petrol usage a little to help the 4 wire lambda. Its was probably silly to hope that there was a lambda sensor that would work with carburrettors!

Brian

[Gordonjcp]

I was going to go for the separate sensor idea, but found that the reason LR chose titania sensors is that they have no vent hole and are thus more immune to wading through muddy holes.

I wonder if some sort of preamp to drive it to properly 0V would work?

[Gilbertd]

Should do, and if you made it adjustable you'd be able to fine tune the mid point if needed. You'd be sending the Millennium a simulated signal much like it is capable to doing for the petrol system only rather than just generating it, you'd be doing a bit of level shifting on what was coming from the sensor.

[LPGC]

Hi Simon and Steve,

All our old cars have unleaded heads so run on 98 octane petrol, so no addatives to upset things.

I didn't mean lead contamination (which would of course break a lambda probe), I meant soot will damage the probe - Running on carbs there could be a lot of soot in the exhaust.

Simon

[Martec]

Hi Simon,

That was a reply to Steve (oldskool) about addatives.

I'm begining to think even if I could get the carbs tuned accurately (some hope) it would still be too rich and soot up. The old saying of carbs throw petrol in with a bucket and injectors use a metered syring comes to mind. Even Our Marina with modeo head and fuel injection is set up too rich and sooting the plugs (12.5:1 air to fuel ratio for max acceleration), I need to lean it off to about 14 for cruising, hence refit the 'Innovate' wideband lambda.

The reason I fitted the innovate lambda was to see what the old HS4 carbs were doing! Rolling road tuned needles 30,000 miles before and all over the place.

Looks like an other sensor each year after a tour on petrol, so scrapyards here I come.

Brian

[Oldskool]

Off topic but I've got a NOS S-Type hubcap if you want it. Never been on a car

[Martec]

Hi Steve,

I'm assuming they are the later round centre with a round badge on it? If you would like to PPM me with a an email address and a contact phone number plus what you want for it, then I can advertize it with on the Jaguar forum for you. If we exchange email addresses and a picture it will go easier.

Brian

[Oldskool]

Not bothered about ££ if it goes to a good home.
Don't think it's ever had a badge on it, will PM you.