Miss fire

[edge]

My Vitara has developed a mid range miss fire and a lumpy tick over that gets worse when warm
I have replaced the plugs and coils but she still isn't right If you are gentle with the throttle there is a hesitation /miss if however you are heavy footed it rev's out no missing.
Its a bit like a over jetted rich carb that works only at full chat.
Can the gas trims go out to make her run rich?
Am I right in thinking the gas ECU follows the petrol in fueling ?
As you may guess I have no idea I used to leave it to TUBBS

[Brian_H]

My Vitara has developed a mid range miss fire and a lumpy tick over that gets worse when warm
I have replaced the plugs and coils but she still isn't right If you are gentle with the throttle there is a hesitation /miss if however you are heavy footed it rev's out no missing.
Its a bit like a over jetted rich carb that works only at full chat.
Can the gas trims go out to make her run rich?
Am I right in thinking the gas ECU follows the petrol in fueling ?
As you may guess I have no idea I used to leave it to TUBBS

First thing you need to work out is if it does the same on both petrol and lpg - if its just lpg it may be an injector playing up, or a tired vapouriser causing issues (the ecu shouldn't have lost its settings or anything as it still attempts to run, so that suggests something isn't quite right, but theres not enough info there to suggest what - maybe a sticky injector or a few other possibilities).

Start by seeing what it does on petrol - it might take a few miles on petrol to return to normal running if its thrown the trims off. It might also help to scan the petrol side with diagnostics and see if it gives any error codes if you have access, as these might give a clue which cylinders are the problem.

[edge]

Ok so here we are again only 7 months later!
after much faffing around and having the gas system"serviced " by a local mobile LPG gas techie
The vitara was not much better.
I was talking to a gent who recommended I get in touch with Phil Price of the Mid Wales Rally School he has a fleet of Scoobys on LPG and is a font of knowledge.
Anyway long story short a half hour drive round Welsh lanes with the lap top plugged in resulted in a smooth running engine with a mid range it never had before no missing or hesitation in short everything I was hoping for.
I was worried that the MPG might go up a bit with the new driveability but so far so good all in all RESULT!!!

[LPGC]

No surprises there tbh.

Mpg should be better, not worse.