p76rangie Posted July 18, 2011 Share Posted July 18, 2011 You will always have problems tuning a open loop (non-computer controlled) LPG system. Based on experience you cannot tune it for all conditions so everything is a compromise. On a hot day it will run rich, on a cold day it will run lean. Up in the mountains it will run lean. If you have it running rich it loses power, if you have it lean it loses power. Also remember that 99.9% of people fitting LPG to the vehicles do it to save money. Therefore they do not want to spend money in doing it. As a consequence, virtually all LPG systems are cheaply made and are certainly not refined. A closed loop system will keep the thing in tune no matter where you are driving. Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted July 18, 2011 Share Posted July 18, 2011 ... and the strobe shows timing of around 6 degrees AFTER TDC. I think I must be a tooth out on the distributor drive gear. Is there a reason why you cant just turn the dizzy until the timing is correct?... Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted July 18, 2011 Share Posted July 18, 2011 It seems that the consensus of those actually using MJ with single point LPG is that backfiring is not a problem if everything is set up and functioning correctly. <br> <div><img src="http://forums.lr4x4.com/public/style_emoticons/default/smile.gif" alt="" class="bbc_emoticon"></div> Quote Link to comment Share on other sites More sharing options...
duncmc Posted July 18, 2011 Author Share Posted July 18, 2011 Is there a reason why you cant just turn the dizzy until the timing is correct?... Yeah, I tried, but there was not enough adjustement available, the vac unit hit the water pump. This evening I took the distributor out. Fitted the new vac unit and refitted the distributor and managed to get it set at 6 deg BTDC with the strobe. Took it for a run, it was better but still low on power. So kept moving the dizzy a few times and now it feels much better. I haven't got to the pinking stage as yet, but I have again run out of adjustment. What is irritating is that this is on petrol and of course I will need to advance it more for LPG. So looks like I will have to move the dizzy again! Oh well getting quicker at it now. Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted July 19, 2011 Share Posted July 19, 2011 Move all the plug leads round one position in the direction you want to turn it... Quote Link to comment Share on other sites More sharing options...
duncmc Posted July 19, 2011 Author Share Posted July 19, 2011 Move all the plug leads round one position in the direction you want to turn it... I have done that already. Suppose no reason why I could not do it again though. Quote Link to comment Share on other sites More sharing options...
Quagmire Posted July 19, 2011 Share Posted July 19, 2011 It seems that the consensus of those actually using MJ with single point LPG is that backfiring is not a problem if everything is set up and functioning correctly. <br> <div><img src="http://forums.lr4x4.com/public/style_emoticons/default/smile.gif" alt="" class="bbc_emoticon"></div> I agree! I have only ever had two backfires on LPG ever- neither attributable to ignition, but to weak mixtures from running empty. Megajolt transformed my motor and gave me around 35,000 miles of trouble free LPG motoring. Only problem I have had has been a couple of failed coilpacks- but considering they were both £5 secondhand off ebay and had done god-knows how many miles previously I don't think that much of a problem. Megajolt has now been removed and Squirt is in its place, fuel injection here we come! Then maybe LPG injection later... Quote Link to comment Share on other sites More sharing options...
p76rangie Posted July 19, 2011 Share Posted July 19, 2011 I've been running single point LPG on 3 different GEMS V8s. The only times I had backfires, it was due to another, mechanical problem (bad HT lead, vacuum leak...). I certainly can't see a reason to retrofit with a sequential system, though I might opt for one if starting from scratch. I agree! I have only ever had two backfires on LPG ever- neither attributable to ignition, but to weak mixtures from running empty. Weak mixture cuts flame speed to the extent that there is a flame path back into the manifold at overlap around tdc of the exhaust stroke. It would appear that those that disagree with me have actually had the issue I was raising. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 19, 2011 Share Posted July 19, 2011 I'm not sure what that has to do with coil packs? LPG + Weak mixture gives backfires on dizzy systems as well, boy do I know that one Quote Link to comment Share on other sites More sharing options...
Quagmire Posted July 19, 2011 Share Posted July 19, 2011 :blink: :blink: Quote Link to comment Share on other sites More sharing options...
Quagmire Posted July 19, 2011 Share Posted July 19, 2011 From my understanding, megajolt does not use a distributor but uses coil packs like on the later GEMS motors. This makes them unsuitable for single point LPG systems. As the sparkplug in each cylinder is fired when not required (with 2 coils each cylinder is fired 4 times per cycle instead of once with a distributor system) it fires often when the intake valve is open. This can ignite the LPG in the intake manifold and cause a bad backfire. This is why most reputable shops will only fit injected LPG systems to these types of motors. I am not saying that it will happen all the time and some people get away with it not happening at all. However, the risk of a backfire is many times higher if you run a single point LPG systems on such a motor. The damage that a backfire can cause is usually not worth the risk. I was replying to that one. Quote Link to comment Share on other sites More sharing options...
duncmc Posted July 20, 2011 Author Share Posted July 20, 2011 I have now fixed the backfire and tickover problems. I serviced the vaporiser which was really dirty on the low pressure side, replacing the diaphrams. Also I changed the hose that was being crushed by the bonnet.. No backfire under full throttle and kickdown...YEAH! AND I haven't fitted the new Ignition amp yet or the better quality plug leads, so that will do for now. Brakes next. Thanks to all who gave advice. Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted July 21, 2011 Share Posted July 21, 2011 I also ran single point LPG and Megasquirt'n'EDIS (exactly the same as MegaJolt on the ignition side) with no problems at all. I think you'll find quite a few LR4x4 members are running exactly this setup, and I've not seen anyone reporting this problem. For me, switching to this ignition system got rid of backfires. Quote Link to comment Share on other sites More sharing options...
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