Hi Wigan Pier
I might not be able to help you but I've had a problem a little bit similar. I think it might be useful if we compare our situations. I'd like to know a bit more about what happens to you, eg, do you start on gas and then a few minutes later it cuts out? Or do you start on petrol, change to gas and then it cuts out? How do you restart the engine? Wait and start on gas? Switch to petrol, restart and switch to gas? Then it cuts out? Have you tried changing back to petrol before it cuts out? A bit more information, please?
I'll tell you what happened to me.
I ran out of gas on the M5, switched to petrol and the engine began mis-firing. Pulled into the next services, did nothing useful but started the engine after about ten minutes. On petrol. It started easily and ran perfectly. A few miles later, not many, left the motorway at Taunton and filled up with gas. Back on the motorway and, with a little trepidation, changed to gas. No problem – it ran perfectly on gas.
Near destination, changed to petrol (in an investigative spirit) and the engine ran rough. Left overnight the engine started perfectly on petrol and ran perfectly.
This set a pattern. The engine ran perfectly on gas or it ran perfectly on petrol. Changeover from petrol to gas went well but changeover from gas to petrol never went well. So, I would stay on gas and if I felt a need to change to petrol then I would make it last thing in the evening so the engine would rest overnight and be fresh for anything in the morning. It always started perfectly.
I did track the problem down to wet plugs in Nos 3 and 4 cylinders but could find no reason for them to be wet because of the changeover. It was maddening.
After three months away I got back here and started serious research. But to no avail because the problem has righted itself! Maddening. Honestly, I can find no cause for the problem. It has left me, however, a little worried every time I change from gas to petrol.
The only possible reason (as far as I am able to reason) for the problem has to be that my problem was self-inflicted. That somehow I was making a mess of the changeover or, possibly, the little computer that manages the changeover was making a mess of it. That somehow, the computer or me, were trying to make the engine run for a little while on a mixture of petrol and gas, that the plugs became wet because of this and, somehow – I don't know why – refused to dry out unless I left the engine switched off for a while.
If you, or anybody, can shed any light on this then I'm grateful. I did ask an LPG installer for advice but I couldn't make myself understood. He kept talking about having to empty the float chamber before it would run on gas. I couldn't make him understand that the float chamber was already empty because I was on gas and wanted to change back to petrol. I don't think he actually had an answer for me and just didn't want to admit it. And of course, the problem had cured itself so I was unable to reproduce it. Nevertheless, an unsuitable mixture of petrol and gas truly does seem to have been at the root of my problem. And maybe yours too?
But, my problem seems to be over. If anybody can help explain it, I'd love to hear. Wigan Pier, if you feel able to explain your problem at more depth, I'd like to hear that too. For my own understanding as much as a wish to help you.
This is the sequence of changeover – for those who don't know, but would like to understand before helping.
Running on Petrol
1.Switch off petrol. (Engine carries on running on petrol in float chamber)
2.Engine stops running because float chamber empties.
3.Switch on gas. (Engine starts and runs on gas)
Running on Gas (with the system I had before this)
1.Switch off gas and switch on petrol at the same time (only one movement on the switch)
2.Engine stops running Float chamber fills and engine starts (Now running on petrol)
Running on Gas (with my new modern system)
1.Operate switch (I think this switches off gas and switches on petrol but engine keeps running – must be on gas.)
2.Engine hesitates and this is my cue to operate switch again. I think this switches gas off completely leaving the engine running on petrol.
The sequence of events changing from gas to petrol is a bit confused, don't you think? Even writing this confirms me in my opinion that this petrol/gas mixture sometimes goes wrong. For me it now seems to have come right. I do hope my problems are over.
Don't let it put you off LPG. Apart from this one little hiccup, I've had pretty well ten years of trouble-free experience of using it.
Tom
