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[Bojan]

I have an 3.0 V6, running on LPG. Usually I drive on lpg, but from time to time i do some 50-100km on petrol, in order to prevent petrol injectors from getting choked.

today was one of those days. I was driving around, on petrol. noting extreme, reving to 3000 rpm usually. when i first switched to petrol, i've noticed that the engine became a bit noisier -> when accelerating, there is a periodic louder sound, like one cylinder is missfiring, and in idle is a bit rougher. The sound is something like blown exhaust gasket (i have tought that it is, untill i got new lpg injectors -> from that moment, on lpg, it runs and sounds nice and healthy).   

So, i drove around for 10-15 km, and then came home, and while reversing back on the driveway, I have noticed a noticeable amount of smoke coming from exhaust. Car was smoking while under some load, but in idle too. I couldn't see what color was the smoke (it is almost night), but it wasn't black smoke, that's for sure.

My first reaction was A MASSIVE PANIC ATTACK!!! and instinct switching to lpg, after which the smoke stopped in few seconds, and it didn't reappear after i gave it a short drive around.

So, what could cause this?
Could a petrol injector have some residue on it, preventing it from 'closing' completely, and, therefore, enabling a petrol to pour into the manifold all the time, and, thus, creating too rich mixture in that cylinder? I was thinking about this before I noticed the smoke -> too rich mixture will not burn entirely, so it would 'explode' in the exhaust manifold, and create a sound similar to cracked exhaust gasket?

Thanks in advance!

[gsizoli]

I haven't got experience with LPG cars, but If you have no significant oil loss (in this case the smoke would be grey colour) I wouldn't worry about it. Try to determine the colour of the smoke, if it's black then you are on right way with this injector, or too rich mixture issue.
If the smoke is grey then you have a problem...I know...

[Bojan]

I have checked oil level, and it seems that there is no significant loss. But, I have drove only for 5-10 km.

There is no smoke anymore, thought. So, I can't see what is the color of the smoke. And I really do hope that an opportunity to establish it WILL NOT occur

In case that it is a dodgy injector, is there any chance that some of the 'fuel injector cleaning additives' (like liquy moly) could help cleaning it, or is the 'ultrasonic cleaning' only solution.

[TheBoy]

If you had a stuck open petrol injector, it would still be injecting petrol even when on LPG...

[Bojan]

I've spoke to a mate, he had similar thing on his astra, due to the poor spray pattern -> engine didn't run perfectly smooth at low revs and smoked a bit sometimes.
He got his injectors ultrasonic cleaned -> one had residue on a nozzle, causing poor petrol spray pattern.

Basically, my engine runs fine, both on petrol and lpg. But, on petrol, there is that sound (similar to broken exhaust gasket), a bit rough idle, and MAYBE a slight hesitation in acceleration on low revs.

Just to mention, most of people would say that my engine runs perfectly. But I am a very nit picky person (I think that is the word), always noticing small things like this, and than worrying about them.

[omegod]

Not doubting you but the V6 blows steam from the exhaust like Thomas the tank engine, espescially noticable when reversing into a cloud of it. I thought my HG was toast when I first noticed it, just a thought! 

[Bojan]

that would be a good explanation during cold days.
But it was very warm that day. And it had a strong 'chemical' smell  :-?