Commodore Backfiring and shudder-help

[burnsy16]

Hi Everyone

Ive got a 2001 VX berlina that has recently been put on gas. It ran fine for a month apart from the engine cut off when going around corners so the mechanic tweaked the mixture and now yesterday whilst driving, not accelerating just casually driving the car backfired, It runs fine on Petrol still but the car has a very strong shudder when accelerating, i thought it would be the air intake/box was blown up but it seems intact. Im unsure now as to what it is?
Could anyone please help me with this problem as to what it could be
Thanks

[Dr HaxZaw]

sounds like it could be the plugs and leads... that would be where i start

[gotham.r]

try looking over the usual, fuel filter, oil levels, coolant, spark plugs, has it had a service recently other than the gas conversion? I doubt your air box would be blown, may be something not plugged in properly, does it have a hissing noise at all?

[burnsy16]

No it has no hissing noise, but i havnt tried running it on gas since then though, and yes it has its regular service 2000 ks ago where most of the gasket heads were changed, the gas was only fitted 1300 ks ago and the gas service was 2 days ago now, but as i said i think he tweaker the mixture and made it too rich which is what may have caused the backfire? Would the spark plugs cause shuddering though?? im mainly just stumped as what the shuttering is. Its sounds like the engine is losing power and not enough fuel is being pumped into it now.

[petergl67]

Plugs I think I had the same prob. Leads could do it as well. I'd try leads first use the bosch gas ones.

[m1lky]

Sounds like it could be coils to me.they usually fail at low rpm first. Try on petrol to labour the engine and see of you can get it to shudder or backfire, to eliminate the gas system

I'd check the gap and clean the plugs and change leads first. Much cheaper than coils.

The shuddering will be the fuel not igniting and the car not running on all 6 cylinders.

Chances are plugs, coils or leads are to blame. Doesn't gas run hotter than petrol?

[burnsy16]

Sorry for the Confusion, after it backfired i changed it straight to petrol and since then it hasnt backfires but still shudders really bad, on petrol that is.

[m1lky]

I'd bet money it's coils. Does it shudder at low rpm under load?

[UW1SH]

it would most likely be your plugs because when u run on gas you need a special spark plug (literally).. my old friend drove ex taxi on gas and she changed the spark plugs and it ran like shit then changed them back to normal and it ran good... so get spark plugs first that will suit gas and petrol and see how it runs

[jarred_gates01]

I had same problem with my vr, i had to replace the fuel injectors, one of them had a snapped tip, may be the problem if you've tried everything else, does it splatter and backfire heaps when cold and not so much after the engine has heated up???

[burnsy16]

It shudders and has power loss, especially in the lower Revs but isnt affected by if the engines hot or not. Running on Petrol it doesnt backfire, it only backfires on gas

[burnsy16]

HI everyone, Thanks for all your help, just to let you know it was the SparkPlugs and Coil, Thanks again!!!!!!