Back firing on lpg

[larry gray]

I have a xv 2001 on gas. What causes it to back fire from time to time and how can it be fixed. Thank you.

 

[lowandslow]

Too rich i think it is.

 

[gossie]

Too lean.

 

[EYY]

Forget the mixture for the minute. I'll ALWAYS be either too rich or too lean because its a simple mixer system. It'll have the perfect mixture at only a small range generally at around 2500-3000rpm but that's about it. Luckily, lpg runs well either rich or lean, and theres a large margin for error either side of stoich.

You need to be looking at intake leaks and a weak ignition system. The wasted spark system these use doesn't help when running on lpg.

 

[delcowizzid]

If it hasn't had plugs and leads for ages its time .you'll want to check the intake pipe and joiners for splits after backfiring and make sure no hoses have popped off the throttlebody etc

 

[larry gray]

Thank you for your input. Will try some new HT leads and see what happens. If that doesn't work then I'll find a car gas mechanic.

 

[larry gray]

Thank you for your input. Will try some new HT leads and see what happens. If that doesn't work then I'll find a car gas mechanic.

Went to a gas mechanic and got new leads and plugs and he put in a spring loaded backfire plug in the box. Now runs like a dream. No backfires.

 

[jeepster]

Forget the mixture for the minute. I'll ALWAYS be either too rich or too lean because its a simple mixer system. It'll have the perfect mixture at only a small range generally at around 2500-3000rpm but that's about it. Luckily, lpg runs well either rich or lean, and theres a large margin for error either side of stoich.
You need to be looking at intake leaks and a weak ignition system. The wasted spark system these use doesn't help when running on lpg.

On a VX it would have an exhaust sensor to keep mixture correct (on average). The simple mixer would pass the emission regulations in 2000 because burning propane/butane is cleaner than petrol or diesel. But there are situations where it will fail, for example one approaches a red light coasting with closed throttle for several seconds, then plant your foot, and you will momentarily get too lean and it doesn't fire. The LPG then ignites in the hot exhaust manifold. Occasionally this happens when exhaust and intake valves are both open and the flame sneaks through to the intake manifold which is full of gas, so bang. It seems the GM Ecotec was worse for this than than Ford's Barra.