LPG MISFIRE

[ffcgary1]

I Hope some one can shed some light on my problem, i have a 2000 jeep cherokee and is running a polish lpg system , which has developed a miss fire. it switches over ok and will run for a short time then starts to run rough and misfire.
It will run perfectly on petrol so i think it rules out the coil on plug rail. ( i hope)
I have replaced all the plugs and air filter. bUut the problem is still there.

HELLLLP.

[Rossko]

Using will run for a short time then starts to run rough as a clue ... it's probably safe to eliminate ignition, but how long is 'short time' - seconds, minutes?

Check the engine coolant level.
Be sure there is gas in the tank, don't believe the gauges.

[ffcgary1]

Hi there thanks for replying to my enquiry, a short time could be 1/2 mins or 10/15 secs who knows, some times it could be 5 mins all very strange.
I have checked coolant level and they are spot on, I am trying to find a local lpg specialist but they are hard to find near me who want to get involved with diagnostics on a polish conversion. Shame because when it was running ok it ran beautifully on gas.
Gary.

[RichardD]

It could be dirt in the gas injectors or a bit of moisture or, as said above, low pressure.

Fill it right up from a known good source and see if it still happens. The conversion, although Polish, is probably of Italian origin as LPG is very popular over there apparently. (I've done 3 conversion and most of the bits were Italian)

[Rossko]

Check that the car's oxygen sensor(s) are working, some gas systems will bale out if not.

Other than that, you are pretty stuffed without a connection to a laptop to see what's what. Some Polski systems have free software download, so you only have to buy a lead ; eBay is full of folk flogging cheap copies of maker's leads.