LPG. Missfiring, rough idle and rough running.
A dual fuel engine has its own set of factors which may cause problems to deal with. First, and foremost, the ignition system needs to be in excellent condition to handle both fuels.
Running constantly on LPG, for long periods of time can cause some components in the carburettor to dry out and become unserviceable.
If after checking for vacuum leaks, faulty ignition components, freeing up any sticking carby linkages and running a carby cleaner in the petrol, the problem still persists, you have a few options.
You can do a carby kit change out, replace the carby with an aftermarket unit, or get it reconditioned. Once the problem has been fixed it is a good idea to start the engine on petrol, then switch to lpg, at least once a day. This will ensure that the carby components will be kept in working order.
The quality of the gas conversion plays a big part in how the engine will perform. I have found that some (not many) of the mechanics that do the gas conversion can sometimes use of inferior wiring connectors (scotch locks and cheap lugs), and also they may run poorly routed wiring and heater hoses.
Some mechanics also use pliers instead of proper lug crimpers when doing the conversion. This can cause high resistance joints and/or intermittent faults, and might also be a factor in making the engine backfire, which, in turn can cause more problems.
Routing of the electrical wiring over sharp metal, near the exhaust, or not securing the wiring properly may also result in short circuiting or open circuits. Also wiring that is under tension, has a knot in it or is flexing constantly can become open circuit. Sometimes it a can also be the cause of an intermittent fault.
Loose or poor quality spade lugs can develop a film of carbon under them. Although they may look okay it is a good idea to check them and use a pair of pliers to tighten them.
The cab heater hoses are often used to supply hot water to warm the mixer and prevent it from icing up and starving the engine of gas.
The use of "Y" pieces instead of "T" pieces at the junctions where the mixer heating circuit is piggybacked to the vehicle's heater is recommended, because they prevent cavitation, which may result in poor water circulation.
I have also seen problems caused by metal filings or swarf from the gas piping or from the service station get lodged in the gas components, such as solenoids.
There has also been a few cases where the solenoids and control components have failed.
The Diaphragm in the gas mixer can "go slack" over time, too so the mixture may need to be adjusted. I recommend taking the vehicle to a mechanic who can tune the engine properly.
Some relevant threads;
http://www.nissanpatrol.com.au/forum...t=idle+mixture
http://www.nissanpatrol.com.au/forum...t=idle+mixture
This is a scotch lock. An easy way to join wires, but they sometimes fail, especially if subjected to moisture and vibration.
I strongly recommend soldering all joints and then sealing them with heat shrink or brush on electrical tape.
