Thread: LPG conversion '94 Discovery 1

i recently got my disco converted to lpg (sequential injection) my gas fitter summed it up - the ring mixer is for grandma going down to the shops (not suitable for off road driving in general) and it can create problems from back fires etc - the carby type mixer is not bad if you dont plan on taking it off road as again it can cause problems, fuel starvation etc. he recommended the injection system for off road use and i 110% agree with him, it has not even given a hint of a problem, if anything it has made it smoother to drive, also with the injection destructive backfires are near on impossible as the fuel is injected right into the port not in the intake piping, so you dont have an intake path full of combustible fuel mixture ready to ignite if it does back fire, therefore you wont be replacing any costly air flow meters etc

to keep the cost down and because i dont use the back area for storage a whole lot, i had a 72L useable cylinder installed behind the back seat which has taken up 1/2 of my floor space

the price i was quoted for twin under body tanks was ridiculously expensive ($6500 compared to $3800 for the single cylinder) and also they can be damaged if you take it off road into rough terrain

i just thought about another pro for injection - the fuel consumption is pretty much the same as petrol where in the more basic systems it can be up to 50% higher

whichever system you choose, filling up for $40 is the best thing of all

and about the oxygen sensor, i have a wideband sensor installed in my exhaust but that is for my megasquirt tuning, the gas fitter used its output to tune my lpg but AFAIK it does not get used when the lpg is switched on

Thanks Jazz, much reassured!

I hear that the ignition system needs to be top end, to get the best out of the LPG? Magnacore leads etc. Do you think I need to go there from onset, or do so afterwards. The engine was rebuilt recently (before I bought it) and it runs very well, as is.

We were recently quoted 3700 for twin underbody lpg tanks on our 3.9 EFI 1990 RR. We would be supplying our own sill tank which we already have, hence saving a few hundred dollars there. a sill petrol tank is often $200 seacond hand--do not know the new full price.

Originally Posted by Adrian

I am the recent owner of a 1994 Discovery , 3.9L V8 in very good condition and am planning to convert it to LPG. The system of choice is sequential gas injection, with 70L underfloor tanks (manifold) and a 35L petrol aux. The petrol injection system is a open loop system. An option seems to be to install a oxygen sensor in the exhaust manifold to feed back to the LPG controller. I have been advised by some gas mechanics to install the ring vapouriser and to avoid the sequential injection. Any rationale for this? Would a ring vapouriser be adequate? Can backfire and damage to the airflow meter be avoidable with the latter system?

I had a venturi ring system on my previous RR - no problems with destroying the AFM as it didn't have one - the EFI computer had been replaced with a Haltech system which used a MAP sensor.

I had the same system on my current Rangie but back fires detroyed a very expensive MAF sensor and two expensive airboxes. It was noticeably less powerful on LPG so I would swithc back to petrol on hard climbs.

That was eventually pulled off owing to continuing backfires. My wife refused to drive it on LPG as backfires would blow hoses off the engine and she wouldn't know where to look to refit them.

I now have a sequential vapour injection system. You cannot tell when it's on LPG vs petrol. No backfires, either.

Re tanks - if you are fitting an under floor system and removing the main petrol tank, I suggest it may be cheaper to fit two larger cylindrical tanks. Manifold (scuba) tanks are expensive and have little usable capacity. Re the 70 litres quoted, is that water capacity or usable capacity?

70 litres WC gives about 54 litres usable - that's what mine is and it's a pain in the proverbial having to refuel every 250km. I'm considering cutting out the floor and fitting two larger tanks.

The underfloor tanks are 70 ltr useable and about 88 WC and are not manifold tanks but 2 separate tanks plumbed together with a single filler/outlet, in my RRC i would normally get around 74 ltrs in and was good for 350-370 k's.
Sequential is overkill and overpriced for a D1 as it will cost half of the value of the car (or more) save your cash go the venturi sytem, save the SI for the more complex D2's and P38's.

Agree with loan Rangie.

I have a D1 and put 3 tanks on back floor.
If the gas fitter is any good, he will advance timing to 10 degree, use right plugs, seperate leads to eliminate back fires etc and hopefullt like mine, I never had a single backfire.

Sloght loss of power but just switch to petrol on climbs, also with fuel tank still inplace, you have a proper touring range.

Where you live?

Here in SA is a guy, cost me $200 dollars after the rebate.

Great value.
The 3.9 is a fuel gazzler.
I get 200k's in heavy city and close to 300k's on open road with around 55-60 litres of gas.
cheap to run.

Best of luck

I also agree with loanrangie.

Vapour injection will give virtually the same power and economy as petrol, but is an expensive option on a D1.

I have a D1 with the underfloor tanks and sill petrol tank. Always can get 75L into the LPG tanks and get around 350km start stop in town. The sill petrol tank will only get around 150km. This is a great setup for town driving as you still have a full boot to load up, but no good for touring as the range is just not large enough.

The power is marginally less on LPG, but not enough for me need to change to petrol up hills etc. The biggest difference in my car is initial response when you put your foot down, lpg takes longer to respond to the throttle, but never a problem just a difference compared to petrol.

On petrol the sound is also deeper from the exhaust, sounds like the lpg is more sort of blowing through the system.

I have also never ever had one backfire from the lpg system, so if it's tuned right I don't think backfires should be a problem.

Originally Posted by Adrian

Thanks Jazz, much reassured!

I hear that the ignition system needs to be top end, to get the best out of the LPG? Magnacore leads etc. Do you think I need to go there from onset, or do so afterwards. The engine was rebuilt recently (before I bought it) and it runs very well, as is.

i dont know too much about the stock ignition side as with my megasquirt conversion, i also fitted EDIS-8 coil packs and now have a more powerful spark, and my timing is variable right through the rev range as i no longer use the distributor. one thing i do know is that lpg will magnify your ignition weaknesses so if there are any parts in your system that are breaking down under load etc, you will notice it on lpg