Quote:
Originally Posted by pmiulian
I`ve noticed something interesting when running on lpg.
It seems that I get better FE going 100 to 110 km/h than going 80 or 90.
I think that it is because the lpg ecu has some problems in the lower rpm. At 105 km/h the engine stays at about 3000 rpm. That is the peak torque rpm - so it seems that the lpg gets along better with the overall car configuration at that rpm.
If I run on gasoline, I get better FE at about 85-90 km/h.
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Reviving dead thread. I'm also LPG converted car driver. I have read a lot about properties of petrol and LPG. You are observing this phenomenon because LPG is burning slower on low to mid rpms compared to petrol and it needs more timing advance as high as additional 12 degrees. Otherwise flame front in cylinder never catches piston head. I also feel that my car revives around 4000 rpms on LPG. There are special devices to correct timing advance on LPG for nineties cars called Timing advance processors on Google. Unfortunately my BMW is newer and the only way to get correct timng is to make custom ECU remap. 7 years ago I eas driving Swedish brick 740 with dumb 2.3 liter petrol engine also converted to LPG basic system. I optimized it to run extra lean on light loads and normal on full load and advanced timing around 8 degrees. The effect was 2 liters per 100 kilometers less LPG consumption than petrol. There was no signs of premature engine wea.
Search on Google "lpg timing advance processor". You will also get graph of optimized timing.