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[Arpy]

my 2.2 has recently started to idle very badly when first switching to LPG sometimes the engine manement light comes on this clears after a while.
If I switch back to petrol the engine ticks over fine
I dont notice the problem if the gas switches whilst I am moving and once its been on gas for a while it ticks over fine strnge one this any help out there!!

[Lazydocker]

A wild stab in the dark here (but with a little experience )

Does it do this when cool (but not too cold) and it switches over very quickly still? I'd say that the petrol ECU is still throwing some enrichment in which the LPG is copying (as it's a piggyback system) and doesn't need

Only solution is to turn the switchover temp and/or time up a little or make sure you don't leave it idling when you first start it in those situations

[feeutfo]

If the light has come on it's stored a code, might be worth checking what that is. Probably a misfire, and the set up is dropping out of it's LPG happy operational "window". This window is smaller than on petrol, so you need to make sure ignition system is up to scratch.

How long has it run on gas without issue? How old are the plugs? How long does it take to switch to gas from cold start up? This is a setting in the software.

[tunnie]

also worth looking at plugs as mentioned, LPG needs a stronger spark.

[Arpy]

sorry took so long to get back on this matter
I have had lpg now for well over 3 years and done 55k
gas usually switches within a  mile or so engine not that warm as always
I usually change plugs at every other oil change because I know they need changing more regulaly (but I will change them hopefully this week with oil)
so if it is an ignition problem how do I resolve this?

[Dodge]

I have been on lpg for some years now andd on 3 omegas. Sparg plugs are always the 1st not to mention cheapest option to change when you have a problem like this.  Make sure you get NGK plugs (BKR5EK) they are a bit more expensive than others but without doubt the best and will last at least twice as long!

[Lazydocker]

I have been on lpg for some years now andd on 3 omegas. Sparg plugs are always the 1st not to mention cheapest option to change when you have a problem like this.  Make sure you get NGK plugs (BKR5EK) they are a bit more expensive than others but without doubt the best and will last at least twice as long!

Afraid I disagree... After some 70k in 2 LPG Omega's I'd still recommend Vauxhall plugs bought on Trade Club for under £2 each, changed at regular intervals (say 20k) over NGK's I tried a set of NGK plugs in my last Omega and there was no difference whatsoever so why pay more?

If we were comparing them to other brands, however, NGK over Champion for LPG applications every time because I went through a set of Champion's in my LPG RR in under 5k

To the OP, if the plugs don't cure it you may have issues with the coil pack but you need to get the fault codes read before randomly changing parts Has the LPG system been serviced in that time?

[tunnie]

20k here on GM plugs, on gas. They had done about 25k on petrol before converted too!

For the money you can't go wrong, can't see the point in spending big bucks on plugs

[Kevin Wood]

I find bog standard GM plugs are fine on LPG. They get swapped at 40k and still have plenty of life at that mileage. By all means check the plugs but I suspect that this problem will lie elsewhere. If you are having problems with plugs failing on LPG, the chances are that the system is mapped too lean IMHO.

Whilst it's true that LPG requires a stronger spark, this will manifest itself when the engine is under heavy load. At idle a very weak spark will be enough for a stable idle, on LPG or petrol.

If the car is thoroughly warmed up on petrol, does it switch over to LPG OK without the poor idle?

If so, as Lazydocker says, it might be switching over to LPG a little soon after startup. The question in my mind is why it has started doing this when previously it wasn't an issue? Perhaps a problem with the temperature sensor on the vapouriser. Does it switch to LPG earlier after startup than it used to?

[Lazydocker]

I'm thinking that the LPG hasn't been touched for a while and needs a service (which includes a tweak of course) to get the calibration correct again. Or that the Vaporiser diaphragm has perished in time and may need a service

The trouble with the Omega (and most cars) is that on startup it enriches the mixture. This is not required for LPG and if it is switching too soon can manifest itself as a poor idle.

Just out of interest... What LPG system is it?

[Kevin Wood]

Yep, if it hasn't been serviced recently then it could well be that it's requiring a large fuel trim on LPG, hence my question of whether it switches over cleanly when warm or not.

A check of the vapour pressure and a quick tweak along with replacement of the filters, draining of heavy ends, etc. would do no harm, but will require the lead and software to talk to the LPG ECU.

[Dodge]

Well I guess the plugs is a matter of opinion then, but I have done over 750k miles on lpg and would not use anything other make even GM! Having said that, I only pay £3 for mine so hardly breaking the bank!
All the other points made are valid and with lpg it tends to be the same things that need changing, plugs, leads/coil pack, rocker cover gasket, o2 sensor etc it is just a matter of trial and error and eventually experience that tells you which one it is or when it is time to change them.
Which system will make a difference too.  Direct injection with its own ECU takes care of its self but my first system, some 10 years ago had to be re-tuned at regular intervals and like anything else........regular servicing is a must.

[TheBoy]

Another vote for GMs here, both my LPG Omegas use GM twins

Direct injection with its own ECU takes care of its self but my first system, some 10 years ago had to be re-tuned at regular intervals and like anything else........regular servicing is a must.

I think you mean fully sequential and mixer systems

[Dodge]

If you say so 

[Darth Loo-knee]

If the car runs fine on petrol does that not point to an LPG problem? I would think the car needs to run properly on petrol before it can possibly run right on Gas?
Would be idea to measure what voltage there is at the spark plug?
As for spark plugs, I have seen where people have bought these expensive specific LPG plugs which being honest did not last too long at all.