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 Post subject: Tuning
PostPosted: Sun Feb 18, 2018 8:48 pm 
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Does anyone use an LM-2 analyser like this one : https://www.ebay.co.uk/itm/Innovate-LM- ... .l4275.c10

I'm wondering if one of these would be the most accurate way to tune an lpg system?


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 Post subject: Re: Tuning
PostPosted: Sun Feb 18, 2018 9:11 pm 
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At £270 it's about £250 more expensive than a basic OBD reader that will do the same job. Don't forget that the Air Fuel ratio on LPG is different to that on petrol too so it is likely that it will suggest things are right when they aren't.

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 Post subject: Re: Tuning
PostPosted: Mon Feb 19, 2018 10:46 am 
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On the majority of vehicles (that run closed loop fuel injection with narrow band lambda probes fitted) an LPG system should be tuned so fuel trims remain similar when running on LPG to when running on petrol. Tuning by monitoring fuel trims is a more accurate method of tuning for closed loop conditions than tuning using an EGA because emissions will remain the same while-ever the closed loop fuelling system of the vehicle is able to adapt by steering fuel trims and fuel trims usually have a range of adaption of about 40%.

Still, on such (majority of) vehicles an EGA could be of limited use in helping set calibration for high load high rpm open loop conditions, only very limited use though because tuning of the LPG system for such conditions will already have been mostly covered for lower rpm nearly same throttle opening closed loop conditions while the part of the LPG system map for both conditions will be nearly 'flat' (so if the map is right for say 2000rpm high load closed loop conditions it won't be far wrong with same values in map for 6000rpm high load conditions). Not only that but at high load high rpm conditions fuelling for LPG might want to be slightly different for LPG than petrol, LPG will usually make peak power at a slightly leaner mixture than the overly rich petrol mixture where petrol makes peak power (still rich on LPG, just not quite as rich as petrol). So we can take the map set under closed loop conditions and modify it slightly just on seat of the pants for max power... The only use an EGA could have here is to make sure the mixture isn't too lean but it won't be lean if seat of the pants gives anything like peak power.

Many more recent vehicles have wide band probes fitted as standard anyway (no reason to attach another wide band probe), we can use an OBD live data scanner to see mixture measured by the vehicle's own probes and calibrate on fuel trims... Such vehicles run closed loop even at high rpm high load so the live data scanner method makes even more sense than an EGA on these vehicles than it does on vehicles equipped with narrow band probes.

Many examples of people thinking they're going one step better than the pros when calibrating LPG systems by using external EGAs but they usually make less than ideal calibration by paying too much attention to the EGA instead of fuel trims and (as Gilbert implied) confusing stochiometric ratio of petrol and LPG (petrol is 14.7:1, LPG 15.4:1 but correct stoch ratio on LPG will still read as 14.7:1 on an EGA because they are calibrated for petrol not LPG).

If an EGA is useful for tuning any LPG system it will be of most use for tuning single point open fuel loop systems (usually carb equipped vehicles) but, again, on such vehicles best results are likely to be achieved using conventional tuning methods... but if the owner really wanted accurate fuelling they could add closed loop functionality to the LPG system for little expense (even on carb vehicles where closed loop wouldn't be possible for petrol).

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 Post subject: Re: Tuning
PostPosted: Mon Feb 19, 2018 7:22 pm 
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Thanks for your comprehensive answers, I won't waste my money then :-) I can't even get my interface to work at the moment so best I get that issue sorted first!


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 Post subject: Re: Tuning
PostPosted: Sun Feb 25, 2018 11:24 am 
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Joined: Tue May 12, 2009 7:29 pm
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LPGC wrote:
On the majority of vehicles (that run closed loop fuel injection with narrow band lambda probes fitted) an LPG system should be tuned so fuel trims remain similar when running on LPG to when running on petrol. Tuning by monitoring fuel trims is a more accurate method of tuning for closed loop conditions than tuning using an EGA because emissions will remain the same while-ever the closed loop fuelling system of the vehicle is able to adapt by steering fuel trims and fuel trims usually have a range of adaption of about 40%.

Still, on such (majority of) vehicles an EGA could be of limited use in helping set calibration for high load high rpm open loop conditions, only very limited use though because tuning of the LPG system for such conditions will already have been mostly covered for lower rpm nearly same throttle opening closed loop conditions while the part of the LPG system map for both conditions will be nearly 'flat' (so if the map is right for say 2000rpm high load closed loop conditions it won't be far wrong with same values in map for 6000rpm high load conditions). Not only that but at high load high rpm conditions fuelling for LPG might want to be slightly different for LPG than petrol, LPG will usually make peak power at a slightly leaner mixture than the overly rich petrol mixture where petrol makes peak power (still rich on LPG, just not quite as rich as petrol). So we can take the map set under closed loop conditions and modify it slightly just on seat of the pants for max power... The only use an EGA could have here is to make sure the mixture isn't too lean but it won't be lean if seat of the pants gives anything like peak power.

Many more recent vehicles have wide band probes fitted as standard anyway (no reason to attach another wide band probe), we can use an OBD live data scanner to see mixture measured by the vehicle's own probes and calibrate on fuel trims... Such vehicles run closed loop even at high rpm high load so the live data scanner method makes even more sense than an EGA on these vehicles than it does on vehicles equipped with narrow band probes.

Many examples of people thinking they're going one step better than the pros when calibrating LPG systems by using external EGAs but they usually make less than ideal calibration by paying too much attention to the EGA instead of fuel trims and (as Gilbert implied) confusing stochiometric ratio of petrol and LPG (petrol is 14.7:1, LPG 15.4:1 but correct stoch ratio on LPG will still read as 14.7:1 on an EGA because they are calibrated for petrol not LPG).

If an EGA is useful for tuning any LPG system it will be of most use for tuning single point open fuel loop systems (usually carb equipped vehicles) but, again, on such vehicles best results are likely to be achieved using conventional tuning methods... but if the owner really wanted accurate fuelling they could add closed loop functionality to the LPG system for little expense (even on carb vehicles where closed loop wouldn't be possible for petrol).



Simon can I just check I am understanding this correctly, using a standard narrowband lambda and air/ fuel gauge (all calibrated for petrol) should I be aiming for 15.4 or 14.7 - will the gauge show a true ratio irrespective of fuel?
Thanks


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 Post subject: Re: Tuning
PostPosted: Sun Feb 25, 2018 4:17 pm 
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The gauge doesn't read ratio, it reads the output of the lambda sensor and turns that into a number. So if it sees a correct reading from the lambda sensor it will assume running on petrol and display 14.7:1 even if you are running on LPG and the actual ratio is 15.4:1.

_________________
'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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 Post subject: Re: Tuning
PostPosted: Sun Feb 25, 2018 8:42 pm 
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Brilliant that's what I thought but then I started to doubt myself!


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