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[zirk]

1.4 Tigra with Multi point runs sweet as a nut on gas but when switched to petrol runs a bit lumpy at tick over and seems to running on 3 and a half pots, so to speak, up to around 2k (feels like a start of a missfire but not quiet there yet).

So the fact it runs fine on LPG, sort of rules out electrical and probably any air leaks, so thinking ICV first followed by petrol filter then injectors?, anything else I might be missing here?

Will start with some Injector treatment this afternoon.

Typical, MOT time in a few days, and what a pain in the backside just to change a Headlamp bulb on these!

Cheers Chris.

[albitz]

I think your diagnonis is probably on the right track Chris.Try your ideas and if they dont work,ask for more opinions, I suppose.

[henryd]

1.4 Tigra with Multi point runs sweet as a nut on gas but when switched to petrol runs a bit lumpy at tick over and seems to running on 3 and a half pots, so to speak, up to around 2k (feels like a start of a missfire but not quiet there yet).

So the fact it runs fine on LPG, sort of rules out electrical and probably any air leaks, so thinking ICV first followed by petrol filter then injectors?, anything else I might be missing here?

Will start with some Injector treatment this afternoon.

Typical, MOT time in a few days, and what a pain in the backside just to change a Headlamp bulb on these!

Cheers Chris.

I wouldn't worry about the mot,if its presented running on gas they will test it that way

[feeutfo]

How old is the install? Iirc you've had the car a while?
Imle it sounds like a build up of fuel trim on gas that cant adjust as quick as switching to petrol, so it runs rough until the fuel trims adjust back to normal, which it never will on cold starts alone.

On dbw omega clearing the codes also clears fuel trims. Which instantly means petrol runs fine but gas is then lumpy, until the trims adjust the gas fueling and the rolls reverse again.

Might mean adjusting injector nozel size, once rich or lean gas fuelling is established. If no dash light is on then fuel trims will probably be within limits set by the petrol ecu. In which case your probably looking at an internal lpg injector nozel size adjustment of only 0.10 or 0.20 of a mill.

See what others say but i'm sure Lazytinker can sort it with a bit of diag. Might need to aquire more nozels though if they need to re drilled smaller.

[Kevin Wood]

What he said. ^

The way to diagnose it is to run it around on petrol for a while without using LPG and see if matters improve.

Bar a clogged injector, fuel pump, filter, etc. there isn't much that wouldn't also mess up the running on LPG, so I'd say the LPG system needs calibrating, but might also need a new set of filters and/or an overhaul of the vapouriser if the system's not been serviced for a while.

[zirk]

Thanks Albs and Henryd

if its presented running on gas they will test it that way

Yea tried that one before, but my local MOT man works on the basis that if it works on Petrol then thats what He'll test it on, think it might be more of the case that He doesn't know how to work He's magic on his LPG sniffer.

  

[zirk]

Chris and Kevin,

Had the thing for about year and a half now, LPG came bundled with it, think I understand what your saying about the trims, ie, ECU learnt is way due to running mostly gas?

Car gets its regular normal service runs, but might admit never done anything on the gas side as its never moaned at me on gas, do remember the previous owner spent a fair bit on the LPG system prior to selling it to me, probably more than the Cars worth tbh.

Wont be able to play with it too much before the weekend, so, as suggested,  probably give a good blast run on petrol before then and see what happens. think I can probably afford that being a 1.4!

Thanks Chris.   

[PhilRich]

Zirk, if you tell the MOT Station you want it tested on LPG, then they MUST test it on LPG (provided the gas system is working properly of course )

[Kevin Wood]

Zirk, if you tell the MOT Station you want it tested on LPG, then they MUST test it on LPG (provided the gas system is working properly of course )

Yes, in fact, they must test it on the fuel on which it is presented for the test. They are not allowed to switch it to petrol.

[henryd]

Zirk, if you tell the MOT Station you want it tested on LPG, then they MUST test it on LPG (provided the gas system is working properly of course )

Yes, in fact, they must test it on the fuel on which it is presented for the test. They are not allowed to switch it to petrol.

Agreed,thats why I mentioned it earlier,its also easier for the tester as its a pretty basic sniff test

[feeutfo]

Leave it to switch over as normal. From cold it should be fine anyway.