LPG on a 101

HELP!

In the interests of finding out why my fuel "economy" is crap compared to Simon I´s, I have fitted a lambda probe and a dash mounted mixture meter. The probe is a heated version, but its mounted in the T joint from the two banks (thanks for the tips Lee !), which on a 101 is a fair way from the engine, 4 feet on the short length, probably 6 on the long.

When we ran the engine and warmed everything up, as far as we could (10 minute run), the lambda meter showed we were running desparately lean - off the scale lean, except for the instant when you lift your foot of the go-pedal.

If it really was that lean, I wouldn´t expect to have any power, and I think I have decent power at the moment. I COULD make the sensor read by restricting the air filter with my hand, and then the reading was incredible sensitive to the incoming air flow, even at 2000 RPM.

So, is the heated probe STILL unable to read properly where I have had to place it ? Or have I done something else stupid !

Steve

Reply to
steve Taylor
Loading thread data ...

Your set up is similar to where I have my heated probe on the 110. I use a dmm and compared with petrol I run very lean. Can you run on petrol as a comparison?

My guess is the diffusers are wrongly sized so that it's OK at 3000rpm but weak all the way down to tickover.

AJH

Reply to
AJH

On or around Sat, 06 Oct 2007 16:44:29 +0100, AJH enlightened us thusly:

I assume the probe measures credibly on LPG?

I know there's some issue with LPG and emissions testing, but that's CO and HC not lambda.

Reply to
Austin Shackles

I´m not sure. I always run on LPG.

Its about a 2 years since I last had him set up by the LPG specialists near here, and I don´t THINK the power is too poor now. Trouble is I don´t have any references to go off.

Steve

Reply to
steve Taylor

So do I! Ordinary zirconium?? lambda sensors are cells that generate a voltage when they're hot and there is no oxygen on one side and air on the other, the voltage is caused by a migration of ions through the cell.

On LPG I see about .9V on tickover and then it drops to nought. On petrol I see .9V on tickover and as I accelerate and it drops off slightly on cruise.

Yes this is because LPG burns to a different proportion of H2O to CO2 from petrol on account of it having a higher hydrogen content, so the volume ratios in the exhaust differ.

AJH

Reply to
AJH

ZiconiA ? Its a ceramic membrane I think.

Steve

Reply to
steve Taylor

I think Si may have a fluke 101.

I averaged 9 mpg in Morph on the way back from the Unofficial last October. To be fair it was via the Llanberis pass back home towing out not light caravan. That was also on petrol and with the 101 loaded up too.

Lee.

Reply to
Lee_D

I tried to ring you back earlier steve but you musta been busy. Was getting some hassle from a 1 year old who had just learnt my name and was throwing stuff at me earlier! ;)

My probe is working fine in the same position as yours - however mine is a heated wideband one with a proper controller which is sold as working right at the tailpipe of an exhaust. I have some narrowband heated probes here but never had any luck with getting sensible readings off them - even when mounted right after the turbo on my turbod saab.

Is your gauge showing the air/fuel ratio or lambda? Cos stichometric is 14.7:1 for petrol and 15.1:1 for LPG apparently - so if your numbers are set for petrol then it should read a tad lean for LPG.

were you testing it when stationaryily revving or when driving?

Do you still have your airbox stuffed with teatowels like mine is?

i recon that the only way to find out if it is lying is to pop into a garage and get them to stick their exhaust probe in and see how it compares to your reading. Perhaps it is reading lean cos it is too far back and cant get it hot enough

Reply to
Tom Woods

My understanding is that there are a range of ratios over which the fuel will burn, they vary from lean for economy to rich for power. The figures you give are the stoichiometric ratios and they do differ as you say but burning the fuel totally at these ratios will give a lambda of 1 in both cases.

I didn't get to Wales this summer but I am still holding a gearbox for you, I think?

AJH

Reply to
AJH

Steve

It needn't be a long way out to see zero and still drive OK.

I have a Lambda sensor located after the two exhausts come together on my 110 V8 petrol - a heated one as its so far back. I don't know the type but it reads 0.0 to 1.0 volt. If you plug a laptop into the ECU you can watch it as you go along and if I let the ECU use it will try to adjust the fuel so the Lambda gives about 0.6 - but I usually set the fuel map manually so I can run it a bit leaner. I find that it only takes a small change in fuelling to drop it back to 0.0 - and the car still drives well. I try and get it down to about 0.2 ish - once I am down to zero I don't know how far I am off the mark. So you could still see zero and have a driveable motor - but it sounds like it would be better a bit richer. I find mine idles better if I avoid having it super-lean. Also when working the engine hard it is much better to have it slightly on the rich side - lean is not good when flat out (not according the Holley anyway - and they should know about old V8s).

Cheshire Steve

Reply to
Cheshire Steve

steve Taylor uttered summat worrerz funny about: .

You finished that Diesel lump for the Ambi yet?

:-)

Lee D

Reply to
Lee_D

This is a naturally aspirated ECU-less 101FC GS we are talking about Steve ! The idea is to see if adding a closed loop system is really worth it, to see if I can catch that jammy bastard Isaacs up.....;-))

My worry is the way the probe is wired. Its a 4 wire sensor, and the ground for the sensor and one end of the heater are made at the chassis by the sensor, the meter and reference ground are on the dash - I bet I am dropping a fair few mV between the two "grounds" and that´s my problem. Obviously, the answer is to sniff the signal from the probe at the probe and compare it with what the meter is actually seeing before I get into a panic.

Thanks for all the tips !

Steve

Reply to
steve Taylor

Off to Korea on Friday, then it looks like a trip to Venezuela, Arizona in November...when the hell am I going to find TIME :-( Steve

Reply to
steve Taylor

For some reason, running too lean seems to use more fuel, I spent ages playing with my setup to get it to run like that, plus I ditched the strombergs and stuck some SU's on it, much nicer carb IMHO.

-- "For those who are missing Blair - aim more carefully."

To reply direct rot13 me

bURRt the 101 Camper

formatting link

200TDi Disco with no floor - its being fixed at last! 200 TDi Disco, "the offroader" 1976 S3 Lightweight
Reply to
Simon Isaacs

On or around Sun, 07 Oct 2007 09:34:57 -0700, Cheshire Steve enlightened us thusly:

no, it's not. ISTR the MOT for the cat-things has to be lambda of 1.0, but that might be a requirement for the cat, not the engine.

last thing you want is it running lean under load, that leads to melted pistons...

Reply to
Austin Shackles

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.