When the technician reset everything for me today, he was able to use the LPG software firstly to look at the petrol ECU settings for injector timing, and then use this information to set the injector timings for LPG.
We then went for a drive with the laptop connected, and he was able to adjust the fuel trims at different engine speeds and loads.
When we got back to the workshop we switched between gas and petrol, and there were clearly problems in doing so. When switching back from gas to petrol the idle would fall away. There was a diagnostic function in the software, and this identified that the injector nozzles were too big. This meant that the new regulator was delivering too much gas. We changed the injectors for a smaller bore and tried again. There was a definite improvement, and it was possible to adjust the LPG fuel trims to give a better changeover to petrol. However, the diagnostic function again indicated that the nozzles were on the high side of correct, so we swapped them again for even smaller bore ones. This time everything worked out fine.
It could be that with your new installations, the regulator and injectors have loosened up a bit and just need re-checking.
The reasoning goes like this:
The petrol ECU runs the car fine on petrol. On LPG the O2 sensors detect that the mixture is rich and adjust the
petrol trims accordingly. However these trims are wrong for petrol so the cars runs poorly when next used on petrol, until the petrol ECU recalculates the fuel trims. These will be correct on petrol of course, but wrong for when the car is next used on LPG. So in effect, because the LPG is too rich, the petrol ECU keeps getting the wrong information and is always trying to compensate.
The answer is to make sure that the LPG fuelling is within the proper limits. If not then when you start the car cold on petrol, or when you switch to petrol from LPG, the idle will drop for a while, and then recover. On LPG you will get an oscillating idle.
It's possible to test and see if this is indeed the problem:
1. Start the car on petrol and let it switch to LPG automatically. The idle on LPG may well be uneven. Switch manually to petrol and the RPM may dip at first, then recover. Run the car on LPG for a few miles, the switch off. When you next start on petrol, the RPM at idle may be lower than usual - 750 or less, but the idle will be steady.
2. Start the car on petrol and let it warm up fully, then manually switch to LPG. It should idle OK on LPG. Run the car for a journey of several miles, and then for the last five minutes of the journey, manually switch back to petrol. The petrol ECU should have chance to recalculate the petrol trim. When you pull up, allow the car to idle on petrol. It should be fine with no dip in RPM.
Next time you start from cold on petrol, the RPM should initially rise a little above 1000, but quickly settle to around 900. The RPM should not dip.
What you're doing is trying to show that if the petrol ECU is allowed to recalculate the trims for petrol immediately after it's been running on LPG then the problem goes away.
If however the petrol ECU doesn't get a chance to recalulate the petrol trims afetr running on LPG, then it gets confused next time you start the engine on petrol, and this continues when the car switches automatically to LPG, which then causes the oscillating idle on LPG.
This trick of finishing every trip on petrol provides a short term solution and allows you to use the car on LPG some of the time. However, it's not good in the long run, and will probably cause the engine warning light to come on. The fault code will show a long term fuel trim problem. If you clear the code the warning light will go off, and the car will run fine on petrol. If you go back to LPG then the fault code will come back eventually.
The real answer is to get the system set up by someone who knows what they are doing!
If you're prepared to have a try yourself then this is the sort of kit you'd need, plus of course a lap-top computer.
http://www.ebay.co.uk/itm/Prins-VSi-...item53ed9a890d
The other thing to do may be to get in touch with Prins direct.
This is my own understanding of the system, I'm not an LPG technician so please understand that I might be bit wrong on some details! I do hope it helps a bit though.
Let us know how you get on.
Cheers
Jack