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post #1 of 9 (permalink) Old 11-11-03, 10:11 AM Thread Starter
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lpg backfiring

My Manual EBII is backfiring on gas when in gear, with my foot off the acclerator and only above about the 2,000 rev mark; like when gearing down. This only occurs on gas, virtually not at all on petrol.

If i give it a quick squirt at idle, it will drop back to below its usual idle point almost stalling, then come back to normal idle. Similarly, when returning to idle from 1500+ revs, (like any gear to neutral) when driving it will also do this, and sometimes stall completely when cold.

The backfiring seems to be going on in what i think is my slowly dying resonator, (about halfway along the exhaust i guess), which is getting a bigger and bigger hole in it.

Can anyone shed some light on this for me?

I have what i understand to be a craptacular 'landi' conveter. A mech i took it to seems to think that 'the secondary diaphragm plate needs to be drilled out'...to a bigger size.

Opinions on this?

I have read a lot of posts regarding this problem, most people seem to suggest a leads and plugs issue. I think the leads are fairly new, and i just put in a new set of plugs

Thanks in advance for the infinite wisdom....

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post #2 of 9 (permalink) Old 11-11-03, 02:12 PM
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Re: lpg backfiring

Hmm, when my LPG was backfiring, it was blowing the airbox off.. I spent a LOT of money at a garage where the people had no real clue. If I could do it all again, I'd just get a different converter, because it was to do with leaning out (probably your problem too), and the current converter on mine is too small anyway (probably the same for you).

On mine, they replaced the MAP, Oxy, LPG computer, tried using an "econovalve" (uses the manifold vacuum to determine gas flow), and in the end, got it running alright (it is now fine, leans out above 3500rpm, but doesn't backfire)... but that was about $1000 I could have spent much better :(

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post #3 of 9 (permalink) Old 11-11-03, 03:04 PM
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Re: lpg backfiring

have you reset the gas computer.. it might help.. if it is a landi 96 computer i have the landi sheets with reset and diag on them just email me and i'll send it to you

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post #4 of 9 (permalink) Old 11-11-03, 11:56 PM
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Re: lpg backfiring

depends on the type of convertor you have fitted... i think the landi has a mixture screw on the side.. turn it half a turn each way and see if it's any better.might be as simple as the balance line is off or as complex as a the convertor dying.. the new plugs and leads are for gas i assume so we'll cancel them out.. Can u hear any vacuum leaks?
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post #5 of 9 (permalink) Old 11-12-03, 12:06 AM
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Re: lpg backfiring

mine backfired heaps when the leads were dying.
had leads replaced and its perfect.
it almost stalled at idle quite a bit at one stage but that was due to the idle mixtures needing adjusted (was real lean)

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post #6 of 9 (permalink) Old 11-12-03, 04:00 AM
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Re: lpg backfiring

Stalling is caused by a balance line problem,that is a hose from the converter to the aircleaner box,check that there are no holes,splits or leaks.Also check all vacuum hoses.The backfiring on de-accelerating is the hole in your muffler,buy a new one.Find a different mechanic for a second opinion on the converter,if it is leaning out at high revs increase the gas mixture,most gas conversion places use the same converter on all Falcons regardless of engine size,so I would be very wary of anyone claiming the converter is to small and if you do need a new one a MGA converter is about $200 fitted and will handle a Falcon motor no problems.Don't be conned.

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post #7 of 9 (permalink) Old 11-13-03, 09:56 AM Thread Starter
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Re: lpg backfiring

hmm thanks all, ill follow these up and get back to you.
- has ZGR6B 11 plugs
- bosch sports super inductive core leads (sorry if its not enough info)
- not sure about model of converter, searched the web for a match but to no avail; has numbers TVPD 7029, 67R, E3, AGA4015, 22.5MPa, DGM46725, on it.
I will investigate other points made and get back....
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post #8 of 9 (permalink) Old 11-14-03, 02:51 AM
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Re: lpg backfiring

A friend of mine back in the uk (much less popular with lpg) had a Merc C36 AMG on gas, but it was a single unit - ie single point, for all 6 cylinders. Kept doing big damage to his airbox - got it sorted with a more complex system which involved a unit per cylinder - improved performance loads too. sorry for the lack of tech talk...
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post #9 of 9 (permalink) Old 11-15-03, 10:29 PM
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Re: lpg backfiring

Yeah, our ED I6 had backfiring issues too. It had new leads and plugs too. The problem with the backfiring was that it kept of blowing apart our air boxes. As a result i installed a pod filter into the engine. hope the filter wont blow apart when the car backfires.

Dunno if this is of any help except i understand the frustration.
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