Another odd thing is.

She's not registered on the LPG register.

Which is odd, as she's listed as Gas/Bio on the V5 and Gov site.

Probably because it was converted in the days of the paper certificate rather than the register. If you have the certificate you can scan that and your V5 and it will be added to the register, if you haven't, tough.

Gilbertd wrote:

I bet the injector nozzles are in the upper inlet manifold and not down near the petrol injectors like they should be. That'll give you poor throttle response.

Not only will that give poor response, theres the added downside of it being very easy to get banks mismatched like that due to the design of it. So you could have 2 cylinders on one bank and 2 on the other wired to a single petrol bank. You should be able to tell that by following injector wiring, but it may need reference to the software as well.

You'd probably benefit from getting hold of a lead for the lpg ecu and finding out what its objecting to as a first step, once you've cleared up the reason for it failing to switch over it may be worth seeing if you can switch a few cylinders over and monitor what happens with the engine when you do so, I'd suspect some will show up running much worse than others do (as one cylinder will get a double dose of fuel, while the other one in its pairing will get none at all in that state). If they are in the top bit of the tracts, once you know its working it would be an idea to improve the location of them anyway.

My Thor with multipoint has a 75L usable LPG capacity tank, and depending on what kind of driving I'm doing, I get between 210 and 250 miles out of it. I've been hammering the motorways this month, and usually when there isn't loads of traffic, so been getting around the 240 mark most of the time.

I modified some Hana Gold 4 way injector rails to fit right down under the bananas (most Thor's get the injectors fitted on top and either plumbed in the upper manifold or the hoses run through the bananas to the lower manifold) so my injector feed pipes are pretty short.

You should definitely be getting more than 150 miles out of it though. Definitely sort the MAF and get the petrol running right before anything else. Also, spend the extra and get a genuine Bosch MAF - the aftermarket ones are not quite there when it comes to the tolerances and still throw the fuel trims out after awhile (as me how I found that one out!! and it wasn't even a 'blue box' special!)

Agree on the MAF - The Thor I've got (though its a Disco rather than a p38) had some noname MAF on it when I first had it, and it was noticable that it was running rich, the proper Bosch replacement MAF made a noticable difference though had to change a few other things around the same time prior to that (both lamdba sensors being amongst them). I get around 300 miles to approx 95 litres of gas out of it, but the Disco is a bit lighter than the p38 is due to the lack of extra toys on it. I could get around 19.5 mpg on a motorway run on petrol using cruise control for the most part, if that helps compare (measured by filling tank and resetting trip, then filling again and calculating how many miles against fuel used when refilled)

I ran her out of pez once, spluttered into a station.

Brimmed the tank £134 IIRC.

And got 380mi from it.

£50 of Gas would get me 90-150 depending on the cars mood lol

It was cheaper for me to run it on petrol lol.

I'm thinking a complete system refresh a new BRC system perhaps.

I'm not entirely happy with the line routing and wiring TBF.

Wish I hadn't looked lol

BRC?? Trying to make matters worse?

Petrol tank holds 100 litres so 380 miles is only 17 mpg. Unless you were clogging it up to the red line all the time that's pretty pants too. Sort the runing on petrol and the running on LPG will improve as it is slaved off the petrol system.

No never slogged it upto redline.

What's a Thor supposed to get realistically.

I thought anything above 14mpg was a bonus.

If you are using it on longer runs, you should be looking at over 20 but obviously if just using it for short, low speed runs, then it might be correct. As for the LPG system, it will be far cheaper to correct the existing installation than replace it. BRC had a reputation, much like Prins, if installed correctly but it isn't really user friendly and would probably give no better results that what you have now. If your existing system is installed correctly and calibrated then it should be fine. As Brian mentioned, the intake tracts on a Thor cross over so if the nozzles have been put in the upper manifold it is almost certain that the wiring is crossed.

I've seen 22mpg on mine on petrol, when I first put the new engine in and did a long motorway run in it.

Since my Trip computer was reset when I had all the dash out a couple of months ago, I've done about 1700 miles - mostly on LPG and the average MPG is back up to 19.2

Previously over about 8000 miles on Trip 2, which was a good mix of motorway speed and around town driving, I was seeing somewhere around 18.6mpg

I do run mine on petrol at times just to keep the injectors running some fuel through etc, and also the keep the fuel trims in check, as even though the LPG setup now seems to be pretty good on mine, they do drift a little bit.

On a Thor, a Bosch MAF and Bosch Lambda sensors are the most important parts - aftermarket just don't work properly, and will cause it to pull the fuel trims out, which then will give bad mileage, and also rough running, bad idle, and almost stalling if the trims get pulled so far to the end of their range.

I had a Bearmach MAF on mine when the original one decided to fail the day I picked the RR up... it ran fine, but at idle was showing about 30kg/hr airflow instead of the normal 20-25 - so the ECU was constantly thinking there was more air going in, so was richening the mixture up, and pulling the fuel trims out constantly. It would then run really rough at idle. You could hook the Nanocom up and reset the fuel trims, and it would instantly come back to running smoothly - for another few weeks.

Once I had the money, I bought a genuine Bosch MAF, fitted it, reset fuel trims, and it's been fine ever since - well, until the O2 sensors failed and cause bad readings at the other end... But again, I know people who have had aftermarket sensors on the Thor, and they don't read quite right a lot of the time, so they then report too rich/lean in the exhaust gases, so the engine ECU compensates based on that, and again you get the rough running etc.

But ideally - with a combination of longer runs, and some around town driving you should be seeing 17+ on a Thor, on petrol. But definitely get the petrol side sorted properly and so it's happy before trying to get the LPG tuned - as already mentioned - the LPG system is slaved off the petrol system, so if that isn't right, then you're just pissing in the wind with the LPG side.

Hmmm, my trip computer says 13mpg average!
I can get about 70 litres into the LPG tank from empty and usually get about 180 miles from it*. I think that's just the price of commuting over B roads :(

• 2.57 miles/litre on the OB scale.

StrangeRover It sounds like it's time for a new system. If the lines are all in the right place and can be re-used it should save some time. I'm guessing your tank is getting a bit long in the tooth but if it's in the wheel well I can't imagine it needs replacing? I honestly don't give any extra for a car that has an LPG conversion. Even if it runs it's probably worn out anyway. The maths still works on a new install, it'll definitely save you money.

BRC isn't really a good option if you want to DIY it as access to the software is difficult, though not as bad as Prins - Simon would be best to ask on this point, but my impression is the kit isn't particularly good in the mapping side either. Might help to replace some of the bits of your existing front end (we know its a stag ECU, but not what other bits have been used with it?) as well as address installation issues at the same time. But get petrol working correctly first or reassure yourself it is working as it should do.

Might help to check though, the split intake pipe you mention right at the top of the thread - has this been replaced or fixed in some way? If its split after the MAF you won't get anywhere until you seal it again somehow (ideally replace it with a decent hose) as you will have unmetered air getting in. A fault like that will only get more noticable on gas as it will generally throw the petrol ecu trims out, which the gas ecu will then compensate for, which in turn will throw them out further still till you get to a point where it won't run well if at all. Add the possibility of any install issues on the lpg side into that, and you can have both systems trying to correct what the other is doing which just will not work.

Yep, the best choice is to switch off the LPG and forget about it until it's running properly on Petrol. With multipoint you're adding a new injection system on top of the existing one so any fault on petrol (apart from petrol fuel pressure, I guess) is going to affect the LPG side. Single point can mask/survive petrol side issues because it's a separate system, but it's not a great choice for a Thor as described up-thread.

It has OMVL Dream injectors.

A 2007 made tank in the boot.

The lines are routed outside the NS chassis rail.

Wiring is iffy..

If I was to replace the system, what is the best one to go for?

You should be able to get good results on LPG with the parts you've got as long as they're not worn out or broken. I can't remember reading what reducer you have fitted and don't know if the OMVL Dream injectors are oldskool metal bodied or later 'Superlights' but OMVL's are well suited to P38s and Superlights are very reliable. Could swap the ECU but little point if it works OK, just tidy the wiring up.

Like others have said, if you can't get good results on petrol you're unlikely to get good results on LPG. Sort the petrol running first, then see how it goes on LPG. If it was running right on petrol I'd sort any problems with the LPG in no time and would expect to be able to re-use most or all of the bits.

Edit - Just read Profess... So your ECU will be Stag, which should be capable of giving good results on a P38, not worth swapping it, even if it's broken would just plug another Stag ECU in. Also expect injectors will be OMVL SL (since Profess haven't been around long enough to have fitted metal OMVLs). But do the SL's have nozzles fitted (are brass bits visible on injector outlets if you pull the pipe off?) What reducer (would expect Stag again!) ?

They're plastic bodied injectors

According to the invoice.

Lpg system is listed as "AC STAG PREMIUM"
The Reducer is OMVL

The installation in 2013 was £1879

In 2015 it had what seemed to be a £704 service.

Bit string imo!!

Going back a step or two, I've had a decent run today. Mix of 70-80 mph motorway, country roads and M25 traffic. 205 miles on 55.9 litres of LPG. Ok so it only works out at 16.6 mpg on LPG but at 63p a litre that 205 miles cost me less that £36. Just to prove that what you are getting is pretty dire......

Yer.

What I get is terrible.

6-8mpg is what I think she averaged on LPG.

StrangeRover wrote:

They're plastic bodied injectors

According to the invoice.

Lpg system is listed as "AC STAG PREMIUM"
The Reducer is OMVL

The installation in 2013 was £1879

In 2015 it had what seemed to be a £704 service.

Bit string imo!!

If you mean steep, then I'd agree yes it is. Are they these injectors (yours will be a bank of 4 not 3 like these, but Tinley don't have them listed anymore)
https://tinleytech.co.uk/shop/lpg-parts/injectors/injectorsrails/omvl-injector-rail-3-cylinder-dream-xxi-sl-904527-no-ts/

If they are those, they are the SL type - Which are capable and decent injectors. You can just see the nozzles fitted to the ones in the photos, I've got a Thor 4.0 running on 2 sets of them without a problem (and without nozzles fitted as per Simon's advice).

You really need to get a lead to look at whats wrong with it as it stands, Luckily Stag uses one of the common leads so if you do go down the route of swapping kit, you could probably reuse the lead (or swap pins around to reuse it otherwise)