Andy_LR90 Posted February 22, 2008 Share Posted February 22, 2008 Hi I just aquired a 1986 90 with the 2.5 petrol engine. It has a LPG conversion which works very well. The previous owner said he ran on LPG full time but I read somewhere that this is not a good thing, I tried switching it to and from LPG /Petrol but this causes much coughing and spluttering. my question is can you run on LPG full time? if not I'll need to sort out the stuttering, secondly when running on LPG should I disconnect the fuel tank pump to save it running all the time? Quote Link to comment Share on other sites More sharing options...
Guest WALFY Posted February 22, 2008 Share Posted February 22, 2008 I had a 3.9V8 Def 90 running solely on LPG and I know of another RRC bobtail running the same setup. No probs what so ever. As for the in tank pump running all the time. That should be turned off by default of the LPG running. In such that when you run 1 system the other is efectively dead and when you switch over, apart from the small time span of going from LPG to petrol 1 system is redundant. I'd check the wiring and make sure it is all correct. Is the system certified? If not then get a grown up local to you to give it the once over. Quote Link to comment Share on other sites More sharing options...
Diff Posted February 22, 2008 Share Posted February 22, 2008 HiI just aquired a 1986 90 with the 2.5 petrol engine. It has a LPG conversion which works very well. The previous owner said he ran on LPG full time but I read somewhere that this is not a good thing, I tried switching it to and from LPG /Petrol but this causes much coughing and spluttering. my question is can you run on LPG full time? if not I'll need to sort out the stuttering, secondly when running on LPG should I disconnect the fuel tank pump to save it running all the time? You can start and run on gas 100% of the time with no problems. Sophisticated modern gas injection convertions are supposed to start on petrol until warm up because 'some' types of gas injectors can suffer from liquid gas freezing in the tips leading to damage. This is not a problem for your mixer type conversion. You will get misfiring and stuttering on change over if you are trying to run on two fuels at once, or if one fuel has been used up in the pipes before the other fuel has come through. To explain: The carb has a float chamber full of petrol when running on petrol. To change to gas, you must switch the petrol off (middle position on changeover switch) and keep driving while the petrol in the carb is used up (can take a few minutes). WHEN the engine falters, switch to gas and it will pick up on gas. To change to petrol from gas, you can change the switch straight from gas to petrol, but the engine won't run properly until the float chamber has had a chance to fill up with petrol, this may take a while. So it is often best to stop somewhere safe before switching from gas to petrol. If you have an electric fuel pump, the float chamber will fill up quite quickly with the ignition on. If you have a mechanical petrol pump, the float chamber will only fill up whilst you are cranking the starter or while the engine is turning whilst moving in gear, say down a hill or under its own momentum. Electric pump can be shut off via a relay, or can be left running. It is a matter of personal choice. A solenoid closes the fuel line, so the unused petrol will return to the tank. IF you leave the pump running, it is important to keep at least 1/4 tank of petrol so that the in tank pump doesn't pack up from lack of lubrication. Hope this helps, Regards, Diff Quote Link to comment Share on other sites More sharing options...
hattymender Posted February 22, 2008 Share Posted February 22, 2008 I,ve a 2.5 on LPG. When I got it (a long time ago) it would only run on LPG, if you switched it to petrol it would die. Eventually I tracked it down to the carb. It had dried out and behind the brass inlet boss a lump of crud like concrete had formed. You need to run petrol once in a while to keep the carb going. I run on LPG 90% of the time but it is easier to start on petrol on cold mornings then switch over. It's a bit of an art learning how far you can go in switching mode before it runs out of fuel. About 300 yards depending on throttle setting. I've done it so long I now know which road sign to which lamp post gives the smoothest change. Much quicker LPG to petrol, about 50 yards. I run petrol at MOT time. They can test on LPG but it's not common and it causes confusion/work for the tester. Best not to p#ss off the MOT man. Running LPG all the time will pit the valves. It did on mine anyway. While I had them re-ground I had .080" skimmed from the head which ups the compression and helps performance (Performance? On a 2.5?). Best thing I did though was fit a Maplin 'electronic' ignition unit (about £8) and a Lucas Gold Coil (about £17). You need the Maplin unit or the coil will fry the points. LPG likes big sparks. Starting on LPG is easy enough but there's a routine. On mine I switch on (red lights), wait until I hear the tank valve switch and then give it a quick flick to 'prime'. Off again, wait a second and then another flick. It should start. Most of the time. I also find it's much better on LPG off road. But if towing or for big hills switch to petrol. I get about 17mpg on LPG (but I drive like a granny) so don't expect too much. But LPGs works out at about 50% of the price of petrol so it's not too bad. Rich Quote Link to comment Share on other sites More sharing options...
Andy_LR90 Posted February 23, 2008 Author Share Posted February 23, 2008 Thanks for the replies, given me something to think about, LPG system needs a once over as the fuel pump does run all the time and switching fuels on the LPG control doesn't turn it off. Also may consider upgrading to electronic ignition. Quote Link to comment Share on other sites More sharing options...
TomG Posted February 23, 2008 Share Posted February 23, 2008 With carb LPG conversions, if you switch the fuel pump off there is still fuel left in the float bowls which takes time to use up. If you switch from Petrol to LPG too quick you'll be running on both fuels at once (very rich) and the engine will cough and splutter. Likewise switching from LPG to Petrol, the float bowls take time to fill up, if you switch too quick the engine will cut out due to lack of fuel. When my 90 was on LPG with carbs it had a switch wired in series (mounted on the panel by the handbrake) with the fuel pump, there was a bit of a knack to switching from one to the other - preferably done on a downhill or at speed on a straight bit of road. It was also a handy anti-theft device as you could flick it to petrol and switch the fuel pump off.. should delay the average oik for a bit Quote Link to comment Share on other sites More sharing options...
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