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PostPosted: Sat Jun 24, 2017 7:29 pm 
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Been having this issue intermittently for the last 4 years and its now happened again and finally driving me crazy. Every few months I get a misfire and the lpg reverts back to petrol. Always Cylinder 8 error. Usually I turn the car off and back on and it runs fine again. Occasionally though this doesn't fix it and the car refuses to run on lpg on this cylinder. Today is one of those days.

Last time it happened I spent so many hours trying to fix it I finally admitted defeat and took it to a specialist. He couldn't get his head round it either as after trying a different injector, going through all the options and resetting up the software it was still the same. After taking it all apart and putting it back together, for some reason this fixed it and it ran ok again. This confused the hell out of him but after deciding three hours of his time was enough to investigate the fault and that it was running ok, we left it there. The car has been ok since apart from the occasional hiccup where restarting the car fixed it, but here we are again where cylinder 8 is proving stubbord again.

Today I've tried a different injector again, tried adjusting the fuel % for just this cylinder, checked all connections, hoses, looked for any frayed wires etc and all is fine. I have no idea what else would be causing this probkem. Any idea what else I could check before admitting defeat and setting this cylinder to just run on petrol from now on?


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PostPosted: Sat Jun 24, 2017 8:25 pm 
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What car is this? Reading like LPG switches back to petrol when it senses lack of injection pulse on cyl8, in which case it will be a vehicle that shuts off fuelling to a misfiring cylinder and the LPG system isn't at fault for switching back to petrol... but could still be causing the misfire.

Plenty more to check - ignition, LPG spud location and pipe routing, LPG wiring or ECU issue on the specific channel that misfires.

Simon

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PostPosted: Sat Jun 24, 2017 10:41 pm 
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Joined: Mon Jan 23, 2012 12:21 pm
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Location: Milton Keynes
If its the same vehicle as his historic posts its an L322 Range Rover with a Stag 300 system?


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PostPosted: Sun Jun 25, 2017 10:53 am 
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Hi both, yes its a stag 300 in a L322 Range rover. I also replaced all the plugs about a year ago so its not those causing it. All wiring and pipe routing has been checked too. No damaged wires or kinked pipes unfortunately.

Would there be any way to double check the wiring somehow by swapping the wiring to cyl 8 with another cylinder? I.e swap the wires 8 and 2 or whatever is in sync to see if the problem jumps to a different cylinder? I'm guessing this would askew the firing order but would this be possible just to rule out a wiring issue?

Simon, I'm also a little confused by your first part of your post. Does the car have the ability to cut the fuel to the lpg system but then reactivate it when it reverts back to petrol? Surely this would still indicate a problem with the lpg? I'm not getting any engine warning lights either when it misfires and swaps back to petrol which would indicate the car was to blame.


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PostPosted: Sun Jun 25, 2017 5:42 pm 
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KILOCHARLIE wrote:
Hi both, yes its a stag 300 in a L322 Range rover. I also replaced all the plugs about a year ago so its not those causing it. All wiring and pipe routing has been checked too. No damaged wires or kinked pipes unfortunately.

Would there be any way to double check the wiring somehow by swapping the wiring to cyl 8 with another cylinder? I.e swap the wires 8 and 2 or whatever is in sync to see if the problem jumps to a different cylinder? I'm guessing this would askew the firing order but would this be possible just to rule out a wiring issue?

Simon, I'm also a little confused by your first part of your post. Does the car have the ability to cut the fuel to the lpg system but then reactivate it when it reverts back to petrol? Surely this would still indicate a problem with the lpg? I'm not getting any engine warning lights either when it misfires and swaps back to petrol which would indicate the car was to blame.



Some Mercedes amongst others will drop a cylinder if enough misfires are detected (stop using it till engine is restarted). Its not a case of it cutting the fuel more it would cut the petrol injector pulse for that cylinder.

You should be able to swap 2 over yes, but where are you seeing the error? I'd take it from what you've said its in the lpg software rather than the cars own diagnostics. It might be worth a screenshot so the exact error is known?


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PostPosted: Sun Jun 25, 2017 5:51 pm 
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Joined: Mon Jan 23, 2012 12:21 pm
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Brian_H wrote:
KILOCHARLIE wrote:
Hi both, yes its a stag 300 in a L322 Range rover. I also replaced all the plugs about a year ago so its not those causing it. All wiring and pipe routing has been checked too. No damaged wires or kinked pipes unfortunately.

Would there be any way to double check the wiring somehow by swapping the wiring to cyl 8 with another cylinder? I.e swap the wires 8 and 2 or whatever is in sync to see if the problem jumps to a different cylinder? I'm guessing this would askew the firing order but would this be possible just to rule out a wiring issue?

Simon, I'm also a little confused by your first part of your post. Does the car have the ability to cut the fuel to the lpg system but then reactivate it when it reverts back to petrol? Surely this would still indicate a problem with the lpg? I'm not getting any engine warning lights either when it misfires and swaps back to petrol which would indicate the car was to blame.



Some Mercedes amongst others will drop a cylinder if enough misfires are detected (stop using it till engine is restarted) Though I don't think your L322 does?. Its not a case of it cutting the fuel more it would cut the petrol injector pulse for that cylinder.

You should be able to swap 2 over yes, but where are you seeing the error? I'd take it from what you've said its in the lpg software rather than the cars own diagnostics. It might be worth a screenshot so the exact error is known?


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PostPosted: Sun Jun 25, 2017 8:22 pm 
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As Bri says, some engines such as Mercs and BMWs will stop pulsing the petrol injector to a cylinder that misfires, the LPG system is designed to switch back to petrol if that happens. Switching back to petrol when when 'cylinder de-activation due to misfire' can maybe be prevented by setting 'Hemi' mode in LPG software but this won't prevent the cylinder deactivation, you'd still have to switch the engine off to get the engine to run on all 8 again.

Yes, if you swap wiring from cyl 8 to say cyl 7 (petrol injector cut loom and LPG injector plugs) this would prove/disprove a dodgy channel on the LPG ECU (and some of the LPG loom wiring).

Simon

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Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240


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