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Hi guys,
Has anyone done much modifying of the dwell settings?
I'm running LPG on my LQ9 and am finding a misfire at medium to high throttle angles below around 2000 rpm. I've found that closing the plug gap to 0.6mm has massively improved matters but it does still stumble occasionally.
My thought is that increasing dwell between 800 and 2000 rpm at normal ignition voltages will give me a bit more spark energy where I need it... I just don't want to melt the coils.
stay below 6ms on stock coils. You'll need to reference multiplier table as well as the main dwell table to make sure multiplier doesn't go 5 x 1.4 = 7ms.
Many people have modified their dwell settings on these motors with little positive result. The factory ignition has enough current to fire almost anything if the AFR and plug gaps are OK without changing the dwell settings.
That “stock” answer doesn’t really help. I know the standard coils are powerful, but at standard dwell settings they aren’t powerful enough. I’m running lpg which requires a much more powerful spark than even a high boost petrol setup. This is demonstrated by the fact that closing the gap reduced the misfiring considerably.
Thank you to the chap who suggested 6ms as a safe limit. As it’s running a multiplier corrected 3.4ms in the area I’m experiencing misfire, I’ve got some headroom that should give me a vastly more powerful spark. I’ll see what happens.
As it’s running a multiplier corrected 3.4ms in the area I’m experiencing misfire, I’ve got some headroom that should give me a vastly more powerful spark. I’ll see what happens.
If that doesn't help, you may want to look into Redline coils. They put out about 4x the spark energy AND will safely run 8ms dwell. I run them on mine.
That “stock” answer doesn’t really help. I know the standard coils are powerful, but at standard dwell settings they aren’t powerful enough. I’m running lpg which requires a much more powerful spark than even a high boost petrol setup. This is demonstrated by the fact that closing the gap reduced the misfiring considerably.
Thank you to the chap who suggested 6ms as a safe limit. As it’s running a multiplier corrected 3.4ms in the area I’m experiencing misfire, I’ve got some headroom that should give me a vastly more powerful spark. I’ll see what happens.
Something is vastly wrong with your setup if LS style coils will not fire LPG at a .023" gap. Your assertion that LPG requires a much more powerful spark is simply incorrect. I do not know what the issue is, but increased dwell times or more powerful coils are only going to "maybe" bandaid your issue. I work with multiple LPG powered engines that are still running ancient 1970's era single coil ignitions that fire them off just fine. The only problems usually end up being due to worn out points, if that tells you how inferior these ignitions are.
Increasing the dwell to a multiplier corrected 4.5ms has pretty much cured the misfire. It's not a complete failure to fire on all cylinders, its a brief stumble at high load and low rpm. I'm prepared to accept that something is not right, but what? I have brand new plug leads, good earths and standard air and spark tables.
Gametech, I'm puzzled that you say LPG doesn't require a more powerful spark than petrol. 10 years experience tells me that it does. I have found that good, properly gapped plugs and heavy duty ignition leads are essential. A "dry" gas is more difficult to ignite than petrol vapour. Read any article about LPG vehicles and they will tell you the same. Again, I'm prepared to accept that may not be correct, but I'd need a reason why.
I know single coil systems can run LPG. I have done so in the past, that doesn't mean to say that problem with a multi coil setup aren't possible.
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Dwell and melting coils 
