4.0 Discovery 2 with Bigas has poor mpg. Ideas?

[Hedgesweep]

I recently bought a 4.0 Discovery with a bigas sequential multipoint system. I'm getting only 180 or so miles for 75 ltrs of gas.
I make that around 11 miles a gallon.
I've had the car checked by an autogas specialist who said that he could find nothing wrong with the emissions and therefore in his opinion everything is fine.
I've had three Range Rovers on gas before, a 3.5, a 3.9 and a 4.2 all on single point systems and they all gave better return than this Disco.
The only thing he did say was that maybe the injectors are sticking open intermittantly, obviously not while he had it.........is this likely?
Any help would be much appreciated.
Hedge

[Gilbertd]

I'm surprised nobody has come up with any suggestions but I agree your consumption does seem to be high. I get roughly the same as you did on your previous cars from my two. The P38 (4.0 litre GEMS engine) does between 180 and 220 miles on 66 litres while the LSE (4.2 litre old school Lucas system) can manage around the same giving between 170 and 210 on 60 litres. Both of these are running single point closed loop systems.

Like you, I would have expected roughly the same, if not better, mileage from a multipoint. Do you have the software to look at the mapping on the system or has it been checked? Checking the emissions will only tell half of the story, it needs the mapping checking too.

[tommo2009]

First of all, we need to know what the car is doing on petrol, not a guess as to what it is doing but what it is actually returning when running on petrol.
It could be a problem with the petrol side of things that are putting the gas out.
Just because the emissions are OK don't rule out that the gas system is not running correctly. Could be way out of tune and the cats are working overtime to clean up the gasses. This could result in an expensive set of replacement cats.
You need to get the vehicle checked over by someone who can read the bigas software and also has diagnostic capabilities so they can see the live data stream.

[Tubbs]

This can happen with the bigger engines if they hit the max injector duration too early. They just go open loop then. Where in the uk are you mate ? I can have a look at it for you. It could be to do with reducer pressure in need if adjustment and the map setting up accordingly. I would be expecting at least 14's ?

[fenair]

Hi There, i have had two disco MK2's both i converted my self using bigas systems, these are in my opinion a good user friendly system.

I would recommend you contact tinley tech, and buy your self a copy of the software and a lead, install it on a laptop and then view the live data,

do this by getting a competent person to read the data sitting in the passenger seat, find a 4 to 5 mile stretch of road which is without roundabouts etc dual carriageway is best, get out at night or early on a weekend day and do 1 run at normal driving on petrol, then do the same run at the same speed on gas, watch the difference between your injection timing (tnj) on petrol, and then on gas, you should be no more that + 20% extra injection timing on gas compared to petrol.

check your difference and then modify your trim timing on gas to achieve as near to the petrol as possible, forget O2 readings as your cat is modifying your emissions, its the quantity of fuel you are putting in the engine that is the key to performance, all you are doing is helping the ecu to achieve its programmed goal.

This all takes time, if you want to get it right, as every time you make an adjustment you have to stop and kill the engine and download your revised map to the bigas ecu.

Don't expect miracles though as the best i have had from both my disco's running "Thor" v8's is around 15 mpg combination driving 18-20 mpg motorway and keeping a legal or just below speed, i can squeeze 170 miles loaded at motorway ish speeds from 55 liters, sit at 15% above legal with the family on board and a boot full of camping gear, and expect to achieve 12mpg !!!!

your disco weighs 2.7 tons before you load it with people and luggage, people forget this and expect mondeo performance, you will get this with speed, but not mpg, LR did not make the disco with fuel consumption as a priority, its a serious go anywhere vehicle, pitch this against a Kia on the moors, or pulling a 4 ton load on a Ifor at motorway speeds and see which is best... horses for courses..

Do as the earlier post suggests, go to the pumps as soon as your petrol gauge light comes on put in 9 litres of petrol, reset your trip meter and drive on a open road journey at legal speeds and as normally as possible, until the light comes on again, record the distance and divide by 2 this gives the mpg.

Expect to have travelled about 35 miles, more than this your engine is in good tune, less than 30 and you need to be looking at, the whole car itself first before tinkering with the gas system.

Start with LPG grade plugs, (never used as 8 cost a fortune as most put in the cheapest ebay plugs, but these are bearly ok for petrol! and are for the old carb / gems v8) if the car has done more than 60k fit new leads, if you are mr suguar you might want to stretch to competition grade, my self i use LR or equal grade.
Change the engine oil, make sure your tyre pressures are correct for the weight you are pulling, are your brakes binding?? big vehicle like this can ride around power sapping issues, and all of things are common, as people can barely afford to buy a 4x4 so expensive FULL servicing really gets completed.

Once you have got the car performing on petrol, then asses the gas performance, buy a new set of lpg filters from tinley's, get the vaporiser pressure set properly, if you have the software you can see the pressure on the data..

If all of this is over your head, then find a reputable professional who is experienced in lpg servicing and engage his services along with your laptop if he has not got bigas, and you will be sorted..
Once again Tinley tech may be able to point you in the direction of a engineer close to you, call them ..

Good Luck
regards

Pat..

[Gilbertd]

Start with LPG grade plugs, (never used as 8 cost a fortune as most put in the cheapest ebay plugs, but these are bearly ok for petrol! and are for the old carb / gems v8) if the car has done more than 60k fit new leads, if you are mr suguar you might want to stretch to competition grade, my self i use LR or equal grade.

The correct plug is an NGK BPR6ES which are fine if you close the gaps up a touch (set them to around 0.8-0.9mm) which aren't too expensive. Alternatively you can fit Iridium which are better and will also last for up to 50,000 miles. You can either spend a fortune on the NGK 'special' LPG plugs or get the Iridium equivalent to the standard plug which is the NGK BPR6EiX which you can get for under £50 a set if you hunt around. I've not actually been able to find any difference between the LPG plug and the standard Iridium plug other than price......

[Tubbs]

I thought the LPG plugs where silver and the iridium plugs where well iridium ? Never seen much point myself tbh, as you say just gap the buggers down and you are away. However i do know silver is a better conductor according to the periodic table anyway. If you sort them in terms of electrical conductivity then silver is way better than iridium or plantinum. Well thats what i persuaded myself when i came to service my shogun and its stupid plugs ! I dont even want to think of how much they where, I bought some brisk silver lpg/cng plugs and the car has been absolutely faultless ever since. I dont think they where expensive either maybe 4 quid a piece. Unlike the magnecor leads, man they make your ass twitch !

[Gilbertd]

The NGK LPG plugs are Iridium but with a Platinum pad on the earth electrode see http://www.ngkpartfinder.co.uk/files/LPG_info.pdf. Whereas the standard Iridium plugs have an Iridium centre electrode and a platinum pad on the earth electrode.......

So what do you get for the extra tenner a plug?

[fenair]

An Extra tenner a plug??? !!! i'll tell you what you get .... about a month out of the pub... lol

pat..

[Gilbertd]

It's right, how about this http://www.ebay.co.uk/itm/NGK-Laser-Lin ... 43a2464385
compared with the same thing with a different number on it http://www.ebay.co.uk/itm/NGK-IRIDIUM-I ... 335f3a6724

No brainer really......

[Hedgesweep]

Hi All,

Thanks for your advice, it looks like I'll need to chat with the bank manager whatever route I take !!

When I've got a spare moment I'll review the situation and have a look, probably invest in software and leads first.

Cheers

p.s.
I'm on the Norfolk/Suffolk border, Thetford area.

[tommo2009]

you won't need a chat with the bank manager, what you do need is to take it to someone who can look at the gas system and has the ability to look at live data. all this talk about spark plugs is nonsense until you can see what is actually happening.

As for iridium or silver plugs, go with standard NGK copper core, they work just fine and as they are not that difficult to change on the rover V8 it doesn't justify the cost of iridium or silver. The shogun on the other hand is a nightmare to change the plugs so that is worthwhile.

Set of 8 standard NGK should not cost any more than £25 if you do decide to change them, but as said earlier this is a pointless excercise until you know what is happening.

[Hedgesweep]

Cheers Tommo,
I think I'll start by giving it a service, oil & filters, plugs etc., then see what it's like on gas and petrol.
Then I'll get leads and software to check the gas system, if only because I'd like to learn more about it anyway.

Thanks All

Hedge

[binder4]

Had iridium plugs in mine, ran like a dog. Got rid of them and replaced them with el cheapo NGK's and it ran like a train. Mechanic told me that iridium plugs dont like our gas, they glaze over after a while and start miss firing.

[Tubbs]

Hi All,

Thanks for your advice, it looks like I'll need to chat with the bank manager whatever route I take !!

When I've got a spare moment I'll review the situation and have a look, probably invest in software and leads first.

Cheers

p.s.
I'm on the Norfolk/Suffolk border, Thetford area.

Got a good mate in cambridge, just down the road from tinley tech. He will be able to get to the bottom of it for you. Pm me and i will give you his number.

[Sir Henry]

As it takes a full day to change the plugs or plug leads on The Old Girl I bit the bullet and bought a set of the NGK Iridium plugs. She's never run as well or as quietly as she has since I fitted them. Fortunately I got them for a significant discount by getting them through eBay. Without this resource I couldn't have afforded to get her through the last MOT as the parts needed would have cost close to £2K (and far more if I hadn't done virtually all the work myself) compared to the actual £800 I eventually paid. A lot of that figure was having to purchase a pukka top and bottom overhaul kit for a track rod end and even they came from an official stockist who lists them slightly cheaper on eBay than on his own website.

Considering that she's already 35 years old and has just 95K on the clock I shouldn't have to disturb them in my lifetime.

[Hedgesweep]

Thanks guys for all your help,

I've managed to get it up to 210 miles per tank, purely by leaving it running on petrol for another mile or so when cold, ( quite a difference I feel )

The last decent run I had, I got 215 miles for 75 litres and the first 70 miles was fully loaded and towing !!

When I've got time I'll service the old girl , (money and wife permitting), and I'll let you know, however, it's still not going to be anywhere near as good as the old V8's on single point.

Is this an emissions thing?

Hedge