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[Craig_R]

Hiya Chaps Been doing some checks with my hand held LPG Tester kit mainly want to make sure I have the Mixture set right

When At Idle the Tester shows the voltage going from 0.4v to 5.0v ie going from Rich to lean

Ok Here is my Question Does the lambda switch off when your driving at speed or does it still measure the O2 in the Exhaust gases and if it does what should it read 2.5v half way ?

Any help would be great as i am driving all the way back to the Northeast tomorrow and I think its been running far to rich on gas and i dont want to be paying as much as petrol.

Thanks  
Craig

[Matchless]

The lambda sensors are fairly slow to respond, iirc they will switch between rich and lean at 1 or 2 times a second when mixture is correct.
And they are control the fuelling under all conditions except cold start and wide-open-throttle (wot)

[theolodian]

I don't know what the voltages are.  The lambda sensor is always giving a voltage, but unless wideband only accurate around lambda 1.  Therefore, ECU ignores it unless aiming for lambda 1.  Later non-turbo petrol engines have wideband by law and therefore monitor AFR at all times, but don't think pre-2001 miggys are part of that group.

[Craig_R]

Only the 2 litre engines have a 0v to 5v lambda the others have a 0v to 1v

its swapping from 0.4v to 5v about twice a second at idle, but when i am driving it does not it says 0.4v rich when over about 30mph.

Craig

[Kevin Wood]

Is this running petrol or LPG?

I'd say if it stops switching during cruising, it may be because the base fuelling is too rich or too lean and it would require too much correction to bring it back into range.

It will go out of closed loop during hard acceleration (it should always read rich), when the throttle has recently moved (acceleration and deceleration enrichment / enleanment will take over if the throttle position sensor detects this), when not fully up to temperature and some systems disable it at idle or at least below a certain engine speed.

Yours switching around idle sounds like it's in closed loop. It could just be that the idle is around the correct mixture and it keeps spiking above and below stoich though.

Kevin

[Craig_R]

This Is all on Gas I am trying to find out about as the petrol system is fine.

I guess ill find out on my 250 mile trip today how the MPG go

[Marks DTM Calib]

Sounds to me like the gas ECU is not controlling mixture very well.....

[Kevin Wood]

Well, if it's sticking on either rich or lean during cruising I'd say that's an indication that the fuelling is way out at that particular speed and load.

I assume the hand held device allows you to change the fuel map? If so, you can use what the Lambda sensor is doing as a guide and adjust the fuelling until it's in the middle of the range where it swaps from rich to lean. That'll get you pretty much there. If it's permanently rich at speed I'd say it'll still be a bit thirsty.

I have got a wideband Lambda sensor. Great bits of kit. Took it off the car because I was always looking at the Lambda display and not where I was going!


Kevin

[Craig_R]

Because my LPG system is a mixer setup the handheld tester will not change the fuel flow bugger it has to be done by a screw where the gas gos into the mixer which takes 70 to 90 percent of the fuel flow and the other 10 to 30 percent gos in the other side of the mixer through a duty flow solenoid which changes the flow of gas from information from the LPG ECU on information like throttle position and lambda readings.


The other thing that can change the flow rate of the gas is a hex screw on the Vap/Reducer this controls the pressure of the Gas

I am starting to think something is up with the Duty Solenoid and or the Vap/Reducer. Ill see how she does on Gas on the Way back to the north and if she is really bad ill have to book her in to see a LPG person who understands all these things


Craig

[Kevin Wood]

It sounds like a fairly crude setup. Maybe it's not designed to be able to run in closed loop over the whole range of speeds. Could be just at idle to keep the MOT emissions happy. Given that the fuelling appears to be set by mechanical means and not in the ECU, it's obviously not lost the main fuelling settings, unless there are settings related to how it controls this solenoid valve? So it does look more like a problem with the system or an adjustment required.

Sounds like it really needs to be looked at by a specialist.

Kevin

[Craig_R]

Well after a 250 mile run on LPG I think she is running fine

LPG up here is 41.9 pence a litre and she drank 49 litres

so it was about 20 pounds to do 250miles works out at about 7.5p a mile

So Thats what she used to drink about before the LPG ECU was reset so i am happy with that. So looks like she is bang on

[theolodian]

Well after a 250 mile run on LPG I think she is running fine

LPG up here is 41.9 pence a litre and she drank 49 litres

so it was about 20 pounds to do 250miles works out at about 7.5p a mile

So Thats what she used to drink about before the LPG ECU was reset so i am happy with that. So looks like she is bang on

OK, so LPG gets about 22mpg vs. ??  Say 30mpg, that means you use about 50% more LPG than petrol in terms of mpg?  Does the C02 go up as well, because if it does then I would expect the taxes to go up soon?