Classic cars forum & vehicle restoration.

[Rick]

Just after a spot of advice, and I know a few others here are thus equipped.

Mine has an occasional misfire when on gas, probably after 6-7 miles into a journey, ie warmed up. It tends to splutter after accelerating away from coasting, or sometimes on bends. Fuel level doesn't make any difference. It doesn't always do it, it tends to rear its head when under load, again not always. You can plough along a motorway and rarely if ever have a problem.

Dad's had LPG cars and mentioned the importance of plugs and leads.

What specific plugs and leads do you recommend? Mine is a 3.9 Disco II.

Thanks, RJ
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[ukdave2002]

I ran a Vauxhall Omega for 150k miles on an Lpg conversion many years ago. LPG forces a higher HT voltage to fire the plugs, so HT components must be considered as consumable. Plugs lasted 10k miles max, ignition leads, 50k miles and I had to replace the coil packs twice in 150k miles.

Still worth the conversion price

Dave

[emmerson]

Rick, I've used LPG V8s for around 15 years now, and can confirm UKDave's comments. Use genuine OE distributor cap, rotor arm and leads, with Bosch coil, and replace them every two years, or every second plug change.
Also make sure the vapouriser is clean. There should be a drain plug at the bottom to drain out the so-called "heavy ends" to keep the liquid gas (if you see what I mean!) flowing.
And its worth checking your coolant temperature. if the vapouriser isn't getting hot enough the gas won't flow.
I'd go for ignition first though.

[ukdave2002]

Running LPG the ignition system has to cope with voltages some 25% higher than it was designed for. NGK produced a range of plugs designed for LPG , may be worth checking if they still do?

There are better leads available; in the 80's Bosch produced its CD ignition system as fitted to the Porsche 911 at the time; the CD ignition system was designed to work at a much higher HT as such the leads were a different spec, fitting a set of these will help.

In my expirience when something in the ignition began to fail, if ignored it just got progressively worse, to the point where I would get a backfire in the induction system .....now the Vauxhall 2.0i L X20XEV engine uses a "hot wire" in the air mass meter, it basically changes resistance with air flow letting the engine management system how much air is going into the cylinders. Its also quite fragile and the induction backfire used to destroy it
As the LPG system on my Omega was a simple single point mixer, loosing an engine management sensor wouldn't affect LPG running and to be honest it still ran ok on petrol, but would have the engine management lamp on permanently until I replace the air mass meter, after this happened a couple of times I just soldered a resistor in place to fool the engine management system. However had I had had one of the more complex LPG conversions they use info from the sensors so this wouldn't have been an option.

When I sold the car I removed the LPG system and sold it to a chap who fitted it himself to a Ford Galaxy , I believe its still going, the system must be 14 years old now!

Dave

[Rick]

A change of spark plugs sorted the (under load) misfire ok, for a while anyway. A much more violent cutting out while on gas crept in, plus a worsening petrol leak from the smaller replacement tank, led to me taking it to a specialist last week.

A new solenoid sorted the cutting out, and raising the pressure slightly has helped general running also.

The bad leak on the petrol tank is down to it rotting out, so it's away having a replacement fitted as I speak.

RJ
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[D4B]

[Rick]

[ukdave2002]

I sold an old 1982 911 SC years ago, it had stood idle for a couple of years, the chap I sold it too took it to a local supermarket to fill up, basically the bottom dropped out of the tank with a really neat line around the tank

Dave

[emmerson]

Rick, just as a matter of interest I had my Range Rover engine rebuilt and slightly modified recently. It was fitted with new plugs and leads as a matter of course. I replaced the new leads after only 2500 miles to cure a persistent misfire. I used Land Rover supplied leads. It would appear that a lot of the so-called "performance" leads just look prettier because they're brightly coloured!

[Rick]

New tank now fitted, the original was actually fine inside (to my surprise), but it had rotted from the outside in, once the powder coating had let moisture in beneath it. It was in a very bad way, with several pinholes easily visible.

RJ
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[Keith D]

I know that LPG requires a 60% better spark than petrol, but I've never had to use special components to keep things running OK.

I currently have a 3.5 litre V6 OHC Mitsubishi Magna and a 4 litre push rod OHV Jeep running on LPG and have had no problems. It is accepted that LPG will give less mpg and less power than petrol. but having large engines I never know what I am running on unless I look at the position of the fuel changeover switch!

There are two types of gas induction here in Australia. The "cheap" way is for the gas to be injected into the air cleaner and the "expensive" way is for the gas to be injected into the cylinders (like the petrol). Both my vehicles use the "cheap" way and the one thing I have to be very careful about is never to have the engine backfire on gas because if it does, it blows the side out of the air cleaner.

Keith

[ukdave2002]

[emmerson]

Just as a matter of interest, my RR runs on a basic mixer set up, but I'm gathering bits together to fit a BLOS lpg carburetter as an experiment. This works like an SU carb, with a variable jet.
I've heard glowing reports of the BLOS so watch this space.

[Rick]

I was somewhat startled to spot that the large bracketry that holds both my underslung LPG tanks had badly rotted, to the extent that it wouldn't have been long before the assembly gave way completely Needless to say, the Disco's gone in for new mountings to be fitted to the tanks. I took it to the place that replaced my badly-rotted petrol tank last year, the smaller size type fitted at the time of the original conversion in 2005.

There appears to be a theme here.

If your LPG conversion is a few years old, have a good look at the securing brackets holding the tanks in place ... many have straps that secure the tanks, mine has an all-in-one cradle type affair.

RJ
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[Dipster]