hello everyone im new to the site hoping someone can help ive recentley bought a rangerover p38 96 4lire v8 on lpg , it drove home 250 miles on lpg swapping to petrol throwout the journy it seemed fine till we got to a flyover and blow the airbox off sinces then ive had new plugs leads and k n fillter coil pack and alterator . the lpg is an early unit single point which you have to change over manully 4 green lights appear but for some reason now when you change over and reach 2000 revs theres a small click down by the passengers footwell the lpg green lights go out showing one red light and it chugs along when you stop the green lights comeback on run fine on petrol any help would be really appreciated
mark 4x4
Active Member
my old one used to do that too, it drove me mad till the petrol pipe came off and caught fire lol best thing that could of happened to it !
got one now that i fitted a prinns multi point system to and never have any problems
check the wiring ? some kits are very badly fitted, i have seen some right bodges
got one now that i fitted a prinns multi point system to and never have any problems
check the wiring ? some kits are very badly fitted, i have seen some right bodges
RangeRoverBreakers
New Member
You need a toilet seat fitted between the maff and the plenum chamber. This will stop the lpg building up in the airbox and causing the thing to go bang! So many systems dont have these fitted and as a result we sell loads of airboxes!! 
mark 4x4
Active Member
You need a toilet seat fitted between the maff and the plenum chamber. This will stop the lpg building up in the airbox and causing the thing to go bang! So many systems dont have these fitted and as a result we sell loads of airboxes!!
my old one even distroyed a k&n !
v8hotrodboy
Active Member
Stupid question but has it run out of gas? The click is the solinid opening the gas supply. When they run out of gas that's when they back fire and blow the air box off. As said before you need a fart flap in the inlet pipe to the plemnim chamber. They are about 30 quid on ebay. You will get used to the feel when they run out its just like running out of fuel. Switch back to petrol when you feel it and it won't back fire. Also check all the vac pipes are still connected as mine blows some off when it does it.
I had this on a single point system i had on a Classic....it run out of gas and backfired through the plenum and air intake....it is a common problem when low on gas as there is not enough to keep the engine running so the lack of induction vacuum doesn't suck all the gas into the combustion chamber quick enough and the vapour goes bang in the plenum instead of the cylinders....
To decypher the vernacular used above....a toilet seat or Fart Flap is a one way valve that looks like a toilet seat that is fitted between the plenum chamber and the MAF. if the lpg system backfires in the plenum, the 'toilet seat' closes and usually exhausts through a safety valve instead of destroying intake pipes and the rather expnsive MAF.
The multi-point systems don't suffer this problem as the gas is directly injected into the combustion chambers, much like the petrol would be, so the gas can't build up in the induction system....whereas a single point system introduces the gas into the induction airflow into the plenum...hence why singles are a little less efficent and more prone to backfire than the multi's...
To decypher the vernacular used above....a toilet seat or Fart Flap is a one way valve that looks like a toilet seat that is fitted between the plenum chamber and the MAF. if the lpg system backfires in the plenum, the 'toilet seat' closes and usually exhausts through a safety valve instead of destroying intake pipes and the rather expnsive MAF.
The multi-point systems don't suffer this problem as the gas is directly injected into the combustion chambers, much like the petrol would be, so the gas can't build up in the induction system....whereas a single point system introduces the gas into the induction airflow into the plenum...hence why singles are a little less efficent and more prone to backfire than the multi's...
theres plenty of gas in i filled up yesterday but its hard to tell with the lights not responding it would only take a fiver worth, ive got a fitter to have a look tommorow , and ill order one of those flaps for the intake let you know how i get on thanks for the help fellas regards brusboy.
LPG systems are particularly sensitive to poor quality ignition components.
Check the condition of the plugs/leads, coil packs etc as weak components will not ignite the gas efficently and cause a slow burn which will still be burning when the intake/exhaust valves are opening hence the backfire.
This will be more evident at faster RPM's as the valve opening times will be closer to the gas burn rate....i.e. the valve will be opening whilst the gas is still burning...hence the backfire.
Also a weak mixture will cause a backfire too....some people looking to increase MPG, weaken the mixture to inject as little gas as possible, but this has the effect of raising combustion temperature and again slowing the gas burn rate due to too much air and too little gas.....
Get your guy to setup the mixture and check ignition components as these are, in my opinion, the most common causes of LPG backfire.
Check the condition of the plugs/leads, coil packs etc as weak components will not ignite the gas efficently and cause a slow burn which will still be burning when the intake/exhaust valves are opening hence the backfire.
This will be more evident at faster RPM's as the valve opening times will be closer to the gas burn rate....i.e. the valve will be opening whilst the gas is still burning...hence the backfire.
Also a weak mixture will cause a backfire too....some people looking to increase MPG, weaken the mixture to inject as little gas as possible, but this has the effect of raising combustion temperature and again slowing the gas burn rate due to too much air and too little gas.....
Get your guy to setup the mixture and check ignition components as these are, in my opinion, the most common causes of LPG backfire.
Just having a think about the relay click and shutting down the lpg system you are hearing.....
My single point system on the Classic used a signal from the coil LT side (the same one the ECU used) to tell if the engine is running or not....each time the coil fired a signal was sent to the Engine ecu and the LPG system to tell it the engine is running.....
Not sure how yours works, could be similar, but when the engine gets to 2000 rpm, the engine running signal isn't getting through to the LPG 'brains' and it thinks the engine has been shut down, hence the gas supply relay closes the solenoid valve to cut the gas supply....this sudden reduction in gas will cause a backfire due to rapid weakening of the mixture causing a slow burn in the combustion chamber that will backfire into the plenum.
It could be a bum-steer, but you never know....!!!
My single point system on the Classic used a signal from the coil LT side (the same one the ECU used) to tell if the engine is running or not....each time the coil fired a signal was sent to the Engine ecu and the LPG system to tell it the engine is running.....
Not sure how yours works, could be similar, but when the engine gets to 2000 rpm, the engine running signal isn't getting through to the LPG 'brains' and it thinks the engine has been shut down, hence the gas supply relay closes the solenoid valve to cut the gas supply....this sudden reduction in gas will cause a backfire due to rapid weakening of the mixture causing a slow burn in the combustion chamber that will backfire into the plenum.
It could be a bum-steer, but you never know....!!!
Hi.
I don't know where you are, but when I had LPG problems I eventually got them sorted out by going to an absolute genius of a bloke, Simon at 'Yorkshire Autogas' - www.lpgc.co.uk. They are between Wakefield and Doncaster.
I'd been back and forth to a local 'LPG specialists'(!!!?) in Halifax umpteen times, been fleeced for several hundred £s - if not a grand or so.... As he randomly replaced perfectly good parts at my expense. I eventually saw the light when he suggested a whole new system at a cost of another £2,000....!
Simon at Yorkshire Autogas got the problems sorted in a couple of days, at very reasonable cost, and all was well until I hit the standard P38 overheating issues.... but I digress.... if you are even vaguely within striking distance, I'd book it in with him, or at least have a chat with him.
For the record, I have no connection with the company other than as a very satisfied customer.
I don't know where you are, but when I had LPG problems I eventually got them sorted out by going to an absolute genius of a bloke, Simon at 'Yorkshire Autogas' - www.lpgc.co.uk. They are between Wakefield and Doncaster.
I'd been back and forth to a local 'LPG specialists'(!!!?) in Halifax umpteen times, been fleeced for several hundred £s - if not a grand or so.... As he randomly replaced perfectly good parts at my expense. I eventually saw the light when he suggested a whole new system at a cost of another £2,000....!
Simon at Yorkshire Autogas got the problems sorted in a couple of days, at very reasonable cost, and all was well until I hit the standard P38 overheating issues.... but I digress.... if you are even vaguely within striking distance, I'd book it in with him, or at least have a chat with him.
For the record, I have no connection with the company other than as a very satisfied customer.
Khryztal
New Member
has the timing been set to run lpg?
Are ALL ignition parts good? As for the flap get two. As mentioned a lot the single point system is renowned for back fire. Mine has destroyed 2 valves so far in less than a year.
Low LPG and heavy throttle are a big cause of it. thats not just caused by lack of LPG in tank, but if one of the gas flow valves is sticking or the evap unit is not hot enough etc can cause same fault
Are ALL ignition parts good? As for the flap get two. As mentioned a lot the single point system is renowned for back fire. Mine has destroyed 2 valves so far in less than a year.
Low LPG and heavy throttle are a big cause of it. thats not just caused by lack of LPG in tank, but if one of the gas flow valves is sticking or the evap unit is not hot enough etc can cause same fault
