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Vanorak
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Originally posted by Baxter Baxter wrote:

As Aidan says, the engine can be working fine on gas but the Lambda sensor is seeing a uber lean mixture, so as far as the ECU is concerned it is richening up the petrol mixture to compensate, it's only doing what it's told (the injectors are however switched off by the gas system, so not actually injecting any fuel)
You flip it to petrol and the injectors are switched back on they are stupidly rich because the lambda sensor has been telling the ECU to run rich, result is a engine that runs like a bag of shit.
Turning the engine off, then back on again will reset the ECU, by which time the exhaust gas has settled down and everything is behaving.
 
I hope that makes sense!

Makes perfect sense, except...
 
Quote I would try making the LPG system richer, similar to that of petrol and see if the transition between the 2 is better.

That's the way it's been all along. It's the way Steve set it up and the way it is now.
 
Quote I think this is one of the limitations of the cheap end of the LPG systems, and the fact that the VW injection systems of the era wasn't the best.
Unplugging the Lambda sensor would work and give better transitions as the ECU is not seeing a over rich or over lean mixture as the lambda sensor is taken out of the equasion meaning that when you flip the switch the default map is already running and it's not being corrected in leiu of exhaust gas composition.

Yep, all of that Smile I'm on the fence about this, really. Steve has suggested unplugging the lambda and leaving it that way, and I can see the reasoning. I'm an obstinate bugger though and would prefer to get it running with the lambda if possible, if only because it's the way VW intended the engine to be run. Er, on petrol anyway LOL
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Originally posted by Baxter Baxter wrote:

There Seb, it's fixed.
 
1. - Richen the gas.
2. - Live with it.
3. - Buy a more expensive gas system.
 
LOL

4. - Unplug the lambda and turn my SS into a DJ. Sort of.

Tongue
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And another one, if I'm feeling particularly flush: 

5. - try a Bosch lambda in place of the Beru. Seems to work for Aidan...
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being we are on the techy side of gas and everyone seems to be listening i have a question.
 
when you are setting the mixture on gas are you useing the pef factor on the machine you are useing.
 
now everyone i`ve mentioned this to previously has just gone all quiet so i expect more from you lot. in the mot manual it mentions that when testing a car on gas the readings must be " multiplied " by the "pef" factor which in my machines case is something like 1.179. i cant really remember now.  i think this is a miss print because if you actually did this then there wouldn`t be a gas fuelled car on the planet that would pass.
 
so when setting gas up to advised co reading do you include the pef factor of the machine or not. are the settings designed to take in to account the pef factor or not.
 
i persued once in the past but got little sense so i gave up.
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Originally posted by ..lee.. ..lee.. wrote:

being we are on the techy side of gas and everyone seems to be listening i have a question.
 
when you are setting the mixture on gas are you useing the pef factor on the machine you are useing.

I'm sure Simon will know about this, but the way I understood this is it only applied to HC? CO's CO, after all. Or perhaps not...Confused
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Never heard of that, I don't know as much as I should regards LPG and it's years since I tested.
I know my anylyser has settings for lpg, cng but never used them, if I do mess with anything I sort the petrol side and leave the gas well alone.
 
This Pef factor, is that in regards to the lambda reading, e.i multipy 14.7:1 (Lambda 1) by 1.179? or is it the CO?
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Vehicles which run on more than fuel (eg petrol and LPG) should be tested on the fuel they are running on when presented.
There is a slight difficulty with LPG vehicles: the hydrocarbons are propane rather than hexane. So the HC reading obtained must be divided by the propane/hexane equivalency factor (PEF) marked on the gas analyser. For example:
An LPG vehicle gives a HC reading of 700 ppm.
The PEF marked on the machine is 0.48.
So the actual MOT value is
700/0.48 = 1458 ie fail.
Some exhaust gas analysers have an automatic facility for doing this.
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Assess the colour of the exhaust smoke.

2. Exhaust Gas Analyser Test

Follow the analyser manufacturer s

instructions and carry out the full test

procedure to determine the proportions of

carbon monoxide (CO) and

hydrocarbon (HC).

On LPG vehicles the HC result obtained must

be divided by the PEF

(propane/hexane equivalency factor) marked

on the analyser to obtain the

figure required to assess the test result. Some

machines do this automatically.

Residual hydrocarbons, which are indicated

by the analyser when it is sampling

clean air, must be deducted from the HC

reading for the vehicle.

If a vehicle meets the CO requirement at its

normal idling speed but fails the

HC check, recheck the HC level at a high idle

speed of 2000rpm. If the HC

reading is then 1200ppm or less, the vehicle

will have met the CO and HC

requirements. Light pedal pressu
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thats the bumf  its only hc so doesnt matter much when setting up.
 
said it was a while ago.


Edited by ..lee.. - 13 Nov 10 at 23:01
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Well, I learnt something....
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sime in box full.
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Originally posted by SebRogers SebRogers wrote:

And another one, if I'm feeling particularly flush: 

5. - try a Bosch lambda in place of the Beru. Seems to work for Aidan...
I can't see that making a shit of difference TBH.
I think if you bought a Lambda meter thing and drove around with it you would be able to physically see what was happening.
Didn't Silver bullet build his own?
Theres a thread on 80-90 I think.
 
The fault could work the other way, the gas could be very rich, and the lambda sensor is telling the ECU to lean right off, then you flip to petrol and the ECU is supplying next to no fuel, engine throws a wobbler.
 
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Originally posted by ..lee.. ..lee.. wrote:

sime in box full.
On purpose!
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thought so
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Originally posted by Baxter Baxter wrote:

Originally posted by SebRogers SebRogers wrote:

And another one, if I'm feeling particularly flush: 

5. - try a Bosch lambda in place of the Beru. Seems to work for Aidan...
I can't see that making a shit of difference TBH.

Yeah, I know it doesn't make any sense, but it seems to work for Aidan. Otherwise either my gas setup's wrong (don't think so - Steve checked it, twice, and it runs beautifully with about the right mpg and the right emissions), there's something else wrong on the petrol side, or trying to get open loop lpg to play nicely with closed loop petrol is just asking for trouble. Trying a different brand lambda is the only thing left I can think of.

Quote I think if you bought a Lambda meter thing and drove around with it you would be able to physically see what was happening.
Didn't Silver bullet build his own?
Theres a thread on 80-90 I think.

Yep, I thought of that. Might be a bit more faff than I'm prepared to get into, not sure yet.
 
Quote The fault could work the other way, the gas could be very rich, and the lambda sensor is telling the ECU to lean right off, then you flip to petrol and the ECU is supplying next to no fuel, engine throws a wobbler.

Yeah, thought of that too. The weak link in all this is the gas side doesn't make use of the lambda and the petrol does. So taking the lambda out of the equation is one way to make it work...


Edited by SebRogers - 14 Nov 10 at 12:02
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Connect the lambda sensor through a relay do its disconnected during use on LPG?
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Originally posted by Baxter Baxter wrote:

Connect the lambda sensor through a relay do its disconnected during use on LPG?

I wondered about that too, but I wondered if the ecu will only recognise the lambda on startup? if that's the case it wouldn't solve the problem...
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probably difficult to do effectively as the signal lead is only running less than 1v and low amps and is screened to prevent interference because of that, relay would probably cause interference itself

and yes it does a system check on start up and after 30 secs, if no lambda it'll go to default map, that's why when they fail and you get the overfuelling and black smoke undriveability if you stop and turn off and disconnect lambda when you restart it's ok
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think you have to confirm that the lambda probe is flat lining first. then the question, why? needs to be asked. possibly get in touch with bosch technical and see what there take on lambda with gas is.??
there`s a few posts on youtube about gas and lambda. looks like the lambda is switching with their systems.

Edited by ..lee.. - 14 Nov 10 at 14:05
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Originally posted by ..lee.. ..lee.. wrote:

think you have to confirm that the lambda probe is flat lining first. then the question, why? needs to be asked. possibly get in touch with bosch technical and see what there take on lambda with gas is.??
there`s a few posts on youtube about gas and lambda. looks like the lambda is switching with their systems.

No mystery. The lambda simply responds to the amount of oxygen in the exhaust gases. On petrol the ecu is constantly tweaking the mixture between just lean and just rich (at idle, anyway, I'm not quite clear what happens under load?), hence the lambda's variable output. On an open loop gas system the only lambda variation is with throttle position IIRC. There's no attempt to vary the mixture second by second on any given throttle position and so only a constant output from the lambda. It's behaving exactly the way it should.

Next step up would be to have an lpg ecu hooked up to the lambda, engine temp and (and this is the problem with the SS and MV engines) the throttle position switch and controlling a stepper motor to vary gas mixture accordingly, a bit like the way the system works on petrol. Only there isn't a TPS on these engines Confused
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