Range Rover 2002, L322, Vogue, 4.4 V8 petrol (LPG converted)

Hi,

I was starting my car this morning and upon starting it was very noisy, sounded like a belt slipping and engine sounded very weak like it was only running on a few cylinders. A message came up on the dashboard that said "engine misfire."

There is an existing LPG misfire, but this only happens on LPG and never petrol.

Turned the engine off and on, engine started fine, no misfire, no rattly belt slippy noise, nothing. Drove 32 miles to work totally fine. I have noticed there is an intermittent 'squeek' in the mornings when I start the car, but this goes away after I drive it. Turned the engine off and on 4 or 5 times this morning when I arrived at work, started with no issues.

Any ideas gentlemen? Help is appreciated. Thank you.

Your squeak may well be the belt slipping on the alternator pulley.
Not that unusual on start up as the alternator is under greater load after the drain on the battery for the start & an indicator that the belt is worn/requires adjustment.

Other than LPG will detect weak components - plugs/leads/coil packs - can't offer any suggestions for the misfire other than a diagnostic

It’s called the L322 virus some times they go into full shut down mode and will not start and die slowly on the driveway but some like yours have a little cough and feel weak for a few mins before making a remarkable and full recovery. You must have the latter

LPG requires a better than good ignition system, which would explain the misfire starting on LPG and then eventually progressing to the petrol side..
Check the coils and expecially the sparkers..

Another thing to consider is the LPG system slaves off the petrol injection system, if there is a fuelling issue on petrol it'll cause the LPG to go up the swanny aswell..

worth plugging in a diagnostic device and checking live data..

Thanks for all your replies chaps, I dropped her off at the mechanics this morning and received a call about an hour ago. They haven't managed to fully diagnose the issue yet as they haven't managed to strip it down so far (apparently they have a big job with a Q7), but they suspect it is a vacuum hose. No idea what that means, but hopefully it's not too expensive a job! I don't think the catalyic converter is bad (famous last words), as when I put my foot down the car is rapid, and there's no dark fumes coming from the exhaust. Will keep you all posted!

UPDATE: Link to a video I took of the engine on start up this morning... Immediately stopped doing it after I switched it off and back on again ->

GOOD NEWS! It is fixed. Turns out that the misfire was caused by two problems. The engine misfiring on first start was due to a vacuum leak, pipe changed by a mechanic for a reasonable price has fixed this issue. The LPG misfire was due to faulty LPG injectors, which were originally installed in 2002... So the fact they've lasted for 18 years is pretty good! All in all the car is now driving beautifully

Well done