Problem with LPG

[part_time]

Have had a problem with running LPG with Nissan Patrol 4.8lt,backfires sometimes.Any hints??

[ozscott]

leanness usually. It can be a host of things though. If she is running lean at times it could be the filter or a build up of crap in the covertor - although the latter assumes the older system. What system is it? Also backfire is much more likely on gas than pertrol if there is any weakness on the spark side of things.

[Roughasguts]

Tighten some hoses for a start might be a bit of air leaking in to the system

The fittings on some gas instalations are very ordinary quality wise.
Even the hose clamps are very ordinary and break easy.

[part_time]

Thanks guy's i shall try a few of those things out ,also would you know of a good gas mech on the southside,they seem hard to find.

[Dave]

I find with my ute that when it backfires it has been spark plug leads or spark plugs. I would check these first and also for any leaks.

Dave

[ozscott]

Cam thoroughly reccomend Peter Harris Auto Electrician at Smith St Capalaba. Very sneaky on gas.

[Mr__Bean]

Agree with the posts above about ignition leads, leaning out etc.

It must be remembered that modern EFI engines really push the limit on valve overlap and spark timing, they can do this as their design does not add the fuel until the last millisecond via high pressure injectors.

When we convert the engine to gas the inlet plenum is full of the fuel air mix all the time it is running and it sure is ripe for a backfire.

Another cause for backfire can be that the engine RPM is below a certain level, when the rpm gets this low it allows backburn as the inlet and exhaust valves are both open together for a short time, whilst at higher rpm it will not pose a problem but at low rpm it can ignite the fuel mix in the inlet plenum.

The low rpm can occur during petrol to gas changeover or during very low lpg fuel level due to starvation.

When does it usually backfire, under load or during start with throttle open?

- Darren

[part_time]

Darren,
Only sometimes it will backfire when you back off to turn a corner then put your foot down..always at very low rev's...-Gary

[ozscott]

Sounds like its leaning out - what system is it?

[part_time]

Pro gas,fitted since new 2001,melbourne....I will drop by smith st.
Thanks for the advice and the tips guy's..

[Dave]

Sounds like my ute when the plugs are due. Slowing down for lights they turn green put foot down to take off and bang. Wack a new set of plugs in first. Cheapest option too.

Dave