Thread: New to LPG

Your converter is a complex converter, brand is Renzo Landi. Your mixer is a simple venturi, sometimes known as a "gas ring" mixer.

Backfiring is most commonly caused by the use of standard petrol spec plugs, leads and ignition timing. Simply put, for LPG I use Bosch spark plugs, type WR7DC+, gap 0.7mm, Bosch stainless steel spiral core (inductive core) leads (kit no. B8026i) and ignition timing set at 10 degrees BTDC at idle.

Below is a pic of a D2 with the type of air cleaner that will withstand a backfire far better than a plastic box. It was fitted to early 3.5/3.9 Disco's and RRC V8's with the same air flow meter as your vehicle. It will take a modest amount of work to mount in your model D1.




The next most common cause of backfires is a very lean mixture during start-up. There should be a relay or control box that allows a short period of petrol injection during starting. It should be adjustable for best results.

The last common cause of backfiring and rough running is a weak Lucas ignition amplifier, which can be upgraded/replaced as needed.

Hi Thanks bee utey thats great information Ill change the plugs and leads asap and check the timming. Just a couple of questions where would the ignition amplifier be and what do you upgrade it to? I dont think the mixture is lean as it only backfires when you accelerate from a long over run not when starting.

The inition amplifier is sited next to the radiator and is mounted with the ignition coil. There are two upgrades, one I developed for around $100:

Lucas ignition amplifier replacement by Bosch 024

Or there is the Scorcher distributor upgrade from Performance Ignitions at Nunawading Vic, cost over $600. Plenty of words to search on Scorcher dissy's here.

Both upgrades use the same Bosch amp. Failure of the Lucas amp can be gradual and casue poor running without stopping completely. Hard to predict exactly what the symptoms will be.

Originally Posted by bee utey

The inition amplifier is sited next to the radiator and is mounted with the ignition coil. There are two upgrades, one I developed for around $100:

Lucas ignition amplifier replacement by Bosch 024

Or there is the Scorcher distributor upgrade from Performance Ignitions at Nunawading Vic, cost over $600. Plenty of words to search on Scorcher dissy's here.

Both upgrades use the same Bosch amp. Failure of the Lucas amp can be gradual and casue poor running without stopping completely. Hard to predict exactly what the symptoms will be.

I have the complex converter (Landi) on my 95 3.9....no end of problems despite very good LPG leads, plugs, gapped down etc until the Scorcher came to town...then never a problem.

What I do find with both my 95 and my 02 is that the converters gum up pretty quickly and both of my vehicles will not run on gas when cold (and the converter is not icing up either at start up)...they require engine coolant temp of about 50 degrees plus to run. I suspect the idle circuit has some varnish. I have replaced mine several times on each vehicle over the years and each time they start and idle beautifully on LPG (although I generally dont do this because of risk of icing until coolant level is up) for a few months - then go back to no start on LPG but running very well when warm (which makes emergency starting on LPG a no go if you run out of petrol...).

With the last installation on my 02 which uses a Lambda control module, I tried installing a thermostat in my heater line just before the converter - there is research in the US to show that this reduced gumming up because the converter runs at proper temp, not overtemp and there is no further cracking of the LPG...doesnt seem to have worked because she wont start on LPG again... But I love LPG so I dont mind, and starting on petrol is standard procedure anyway.

Bee-utey - what do you reckon about this?
Cheers

Originally Posted by ozscott

I have the complex converter (Landi) on my 95 3.9....no end of problems despite very good LPG leads, plugs, gapped down etc until the Scorcher came to town...then never a problem.

What I do find with both my 95 and my 02 is that the converters gum up pretty quickly and both of my vehicles will not run on gas when cold (and the converter is not icing up either at start up)...they require engine coolant temp of about 50 degrees plus to run. I suspect the idle circuit has some varnish. I have replaced mine several times on each vehicle over the years and each time they start and idle beautifully on LPG (although I generally dont do this because of risk of icing until coolant level is up) for a few months - then go back to no start on LPG but running very well when warm (which makes emergency starting on LPG a no go if you run out of petrol...).

With the last installation on my 02 which uses a Lambda control module, I tried installing a thermostat in my heater line just before the converter - there is research in the US to show that this reduced gumming up because the converter runs at proper temp, not overtemp and there is no further cracking of the LPG...doesnt seem to have worked because she wont start on LPG again... But I love LPG so I dont mind, and starting on petrol is standard procedure anyway.

Bee-utey - what do you reckon about this?
Cheers

Gumming up is quite common in some areas. It appears to be contaminants dissolved in the LPG which come out of solution on evaporation and glue up the primary regulator seat. They are in the range of wax-like substances, softening point at least 20C. Generally when I get a "no start when cold" phone call the phone will ring all week until a batch of gas has been sold off through a retail chain, usually Mobil or Liberty. Morning air temperature factors heavily in non-starting. Boiling the kettle and pre-heating the converter by pouring hot water on it would allow customers to get going each morning until a clean-out was done.

Tests were done and it was claimed to be plasticisers from rubber hoses. Barrier hose was developed for vehicle use and it might possibly have alleviated it. But mainly in the past it has been a case of avoiding filling at the service stations concerned. My local BP has always been good, so I stick with it where possible. LPG sourced from the Longford plant in Victoria used to be bad quality, also that is the plant that blew up due to poor maintenance standards. PS I run straight gas and do not have to option of warming up on petrol, so I need to know where it is safe to buy LPG.

Cracking of propane in the converter is another problem entirely, the residue remains liquid and doesn't usually need more than an occasional drain out.

It is one of the reasons I stick with the Zavoli/MGA and Lovato converters, as their front cover comes off very easily for regular cleaning. Undoing the inlet junction and pouring in a hose full of carby cleaner can also assist in cleaning the valve seats.

Hi thanks alot you guys ive learnt so much about lpg and my system over this weekend and will change leads plugs and amplifier and give it to a local garage to give it the once over hopefully it will cure all ills . Just one last question I have seen an a&r ignition amp on ebay anbody have any info good or bad?.

mmej - i've got one of those a&r ignition amps. yes they work and are great for dual timing.

however - they (rpi in uk who make them) say they are made to work with the original oem lucas coil which is standard in uk. how do i know? well when i installed mine i queried them as it made bugger all difference. one of the mechanics there told me they had done their testing with the lucas coil so i would have to use one of them. can't say i was happy about it as it wasn't mentioned on their website it was a requirement. though, if you check their website now it does mention it.

so in a nutshell, you're on lpg so upgrade your electricals which means you shouldn't get the a&r amp unless you go get a lucas coil which kind of defeats the purpose of upgrading????.

do the upgrade recommended by bee utey. there's heaps of people on here who have done it and recommend it as one of the best bang for bucks you can do whether for petrol or lpg.

i had my dizzy regraphed for lpg by the mob who make the scorcher. done bugger all driving in it since so can't comment on how it goes.

Thanks very much Bee-Utey - really helpful mate as usual

Cheers