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[Itinerant Fred]

I'll start by saying Hi all and thanks in advance for any advice. Here goes.
I have a 1993 Cherokee Ltd. It runs on petrol as well as LPG. At times she starts up 1st crank and runs like a dream, whether on petrol or gas. I arrive wherever i'm going come back to the Jeep and it's a none starter. Doesn't matter whether i'm starting on either fuel, it just wont go. Sometimes it fires and starts but then the revs just die and she cuts out again. Sometimes it just wont start at all. Twice i've had it recovered and by the time its back on my drive and off the recovery truck she starts first time again.
I've had the coil tested ok, new disributor cap and rotor arm and HT leads. Plugs are fine, spark is fine and according to the nice recovery man, fuel is getting there fine. I though it may be the crank sensor so did the diagnostic check and get the codes 12 and 55. I have had the battery off to re-charge so expected code 12, i understand that code 55 means the end of the check. This indicates crank sensor is ok i presume.
I tried to start the Jeep on petrol again to no avail but she started on LPG first turn of the key. I let her temp rise and sprayed some carb cleaner in, this stopped the engine. I tried to start her again and after a couple of cranks she started ok. I let her idle for about ten mins and turned her off. I then tried to start her again and now she wont start again. She tries and fires but just wont start. If I go back to try tomorrow she will more than likely start again.
I'm at the end of my tether with it, any suggestions or advice gratefully received. I love my Jeep and am lost without it at the mo as she's my only form of transport.
Help Please.
Thanx Muchly.

[Panic mechanic!]

does your engine automatically switch over to lpg I had a similar problem with a lpg cherry I had and it was that the lpg system was set up running to lean, when the jeep was turned off it was running on lpg, it would then try to start using the lpg  but it couldn't do it cos the lpg wasn't vaporising properly due to the engine being cold.

Oh and is it sequential or single point lpg?

[isle of man]

I'm thinking cam sensor - basically your turning the ignition off/on could be the system configuring.

[Itinerant Fred]

Ta muchly for getting back to me. My LPG is switched on manually panic mechanic chap , went to start her earlier today on petrol fired up no prob and ran for about 30 secs then the revs just died again and she cut out. Tried to start on gas, yup first turn of the key left her ticking over for a while and gave her a bit of boot, still no prob. Turned ignition off and then tried to start again. Nope, turning over and attempting to fire but thats it again until tomorrow when she will no doubt start again fine.
Is there any simple way of testing the cam sensor isle of man chappy?

[Panic mechanic!]

have you got a manual? it will tell you in there some basic test methods,most  starting running probs seem to be crank position sensor ( cps) with cherry's and if you  use the search function on here , you will pull up loads of threads on the common problem

[isle of man]

If it's pumping fuel it will not be the CPS....

[bill99]

Some of my friends driving for a service company used to always switch over from LPG to petrol for a few minutes before switching off the engine; this was to help re-starting by priming the petrol system ready to re start.

Also next time when this is happening on petrol, switch off the key, then loosen the petrol cap and see if it lets it start, yeah I know it sounds daft but try it.

bill