Vehicle & Technical > Range Rover
MPG on LPG
Rossko:
It's probably running rich - too much LPG. Clues being smell of unburnt fuel and low MPG. You can't tell from the look of the plugs, but you might have a slow/laboured idle.
It might just need adjustment, this really is best done with an exhaust gas analyser. Set up at around 3000rpm using the adjustment in the large gas pipe, looks like this is at a Y-piece. Then adjust at idle, but using the screw on the vaporiser. Go round again and refine settings.
That assumes it is an "open loop" system, i.e. no electric motor/valve in the large gas pipe (can't be 100% sure from photo). These don't use the O2 'lambda' sensor.
If its a "closed loop" system with electronic feedback control, you'll need to identify the brand of the control box (not the one visible in the photo) - it might need a laptop to set up. But first check the vehicles O2 sensor function. (Both these systems are "single point" systems - the LPG is introduced at a single point, whether it relies on vacuum or is adjusted electronically.)
If it just won't set up properly, you may need a new vaporiser. They do "go off" after some years, mostly rubbers hardening etc. but it's not worth messing with rebuild kits, just replace with new. You'll get the cost back in a few tankfuls. Have a sniff around the vapouriser when idling on LPG, if there's a big stink of gas coming from a half-inch vent hole the diaphragm is leaking.
cheers
Ross K
Yoshi:
OK, and what for those who dont have access to the exhaust thingy or the money to pay for a garage to look?
Rossko:
I dunno really, it's a bit like changing a wheel without a jack - do-able but maybe not the best way.
When its working right you should be saving about £30 a tank over petrol prices, maybe saving £5-10 a tank on LPG if its working right as opposed to working as badly as stated. Work out how long it'd take to be back in pocket after paying for some help or a tool. (not suggesting a Sun analyzer, but one of those £70 Gunsons CO meters should allow basic tuning with a little patience to allow readings to settle). Or try approaching a few local garages for a half-hour cash job on their analyser.
If its not worth doing, so be it.
Did it turn out be a manually tuned system, no electronic control valve in the vapour pipe?
cheers,
Ross K.
skip:
Get your multimeter out. I'm assuming that the rangie has a four wire sensor however the same still aplies to sensors with less wires just dissregard the colours you don't have. firstly find the wires coming from the sensor. try to get them away back from the zorst for obvious resons. Ignore the two white wires, these are for an internal heater one +12v one earth, test these if you wish to confim that power is there.
Next you have a grey wire and a black wire, now to test that this is working have The motor running on petrol at idle , if ive got this next bit the right way round the grey wire is earth and the black wire is the one you want to test, at any given revs the sensor signal should cycle from 0 volts(lean mix) to +1 volt (rich mix), it'll be easier to see on an analogue meter but still possible to read on a digital.
If the signal is only deviating from a given value mildly say 0.7 volts the sensor is probably goosed as it's not reacting quickly enough. if it is cycling properly try switching to gas and see what happens but bearin mind alot of the lambda controlled mixer systems don't control the mix at idle (pre injection type) so it defaults to a rich mix. so have somone handy to hold the revs at about 2000rpm, on this type of system the cycling will not occur as quickly as on petrol as the gas system cannot react that fast, modern lpg injection should.
I hope any omissions or mistakes will be picked up by others but I'm pretty sure I got it right.
Done it myself enough times 8)
Yoshi:
Just remembered that it stalls as well sometimes, so i will look at a standard air box next week :D
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