Fitting LPG to an Audi S8 D2...

[SyncroS8]

I'll start this thread off now although I haven't fitted the LPG system yet.

I'll be posting as I go along so you can see my progress.

I just bought a BRC LPG kit from an Audi S8.

I was able to see the car running, witness it switch over to LPG and back to petrol (at tickover as well as revving) and am happy that everything is functioning as it should.



It's a BRC Plug&Drive FLY SF system which is a Multipoint, ECU controlled LPG system.

Obviously, having seen it run and it having come off another Audi S8, I know that it will fit my car and work without having to worry about initial setup, tuning etc although I will be buying the software and lead to plug into it and read the ECU.

The one part about fitting this LPG kit which is of a concern to me is fitting the injectors to the inlet manifold.

Having removed them from the inlet manifold, it was obvious that they have been fitted without removing the manifold... i.e. whoever fitted it did not remove any aluminium swarf so it definitely went through the engine when it was next started up.

To me, this sounds nuts!!

Ok aluminium is soft and is less likely to do major damage to the valves, pistons or bores but I still hate the idea.

The biggest problem I have with doing this the proper way, is how to get to the swarf after you've finished drilling, tapping etc.

I have read in the Audi Tech sheet that the inlet manifold is not supposed to be taken to pieces.

Has anyone stripped one down? Any ideas why you can't take the top off?

The tank is a toroidal 70ltr tank so an effective filling capacity of 56 litres. Not as much as I'd like and I know that it's possible to get a 90 litre toroidal tank in there but it'll do for the moment.

Components include ECU, Tank, Vaporiser, Loom, BRC indicator (doubles as fuel level and manual overide button and current status indicator), Fuel Cut Off Valves, Fuel rails, injectors, fuel pipes (lots of them!), water pipes inc T-pieces (they T into the heater matrix circuit) for the Vaporiser and other bits which I'm sure I've forgotten to list.

Having removed the system myself, I found it interesting that the injector wiring actually gets cut into rather than just taking a feed from... i.e. the original injector wiring on the car gets cut, then the feed runs to the lpg injectors and then back to the Audi injectors. So... if the LPG injector goes down and loses continuity, you lose the feed to the petrol injector too. It's obviously meant to be this way as the LPG wiring has two sets of wires, orange and purple which are numbered. If they were ok to run just by using the injector feed as a trigger, they'd run an earth on one of the wires instead.

The Vaporiser runs a vacuum hose up to the fuel pressure regulator vacuum pipe so works in the same way as the Audi FI does in that respect.

I'll be monitoring fault codes on the VAG system very closely once this is up and running. Hopefully the same misfire detection will work when running on LPG as well as Petrol.

I will put the filler nozzle inside the fuel filler flap as I don't want to drill holes in the body or have ugly LPG fillers slapped on the bodywork anywhere.

I have to run some wiring to the tank for both the shut off valve and level sensor and this means removing some of the interior. Similarly, I'll have to remove some of the dash area to wire in the loom there and fit the Indicator etc.

As I'm running the car daily, I'll do this bit by bit and the last bit will probably be fitting the injectors to the manifold ( ).

I've seen other cars that run LPG bringing on the engine check light regularly due to the sensors being setup for petrol emission checks.

I've also read a bit about changing the spark plugs to run on LPG.. arguements seem to be both for and against this. More research to be done!

The last thing I'll say here is that I'm planning on running the LPG kit under the stock covers. I don't want ugly extra bits stuck on top. It's got to be neat.

MG

[SyncroS8]

Thanks to Nollywood for pointing me in the direction of this thread which has photos of the inlet manifold in pieces.

I'm happy enough to remove the top section, fit the LPG nozzles and refit it now.

Inside Inlet Manifold

MG

[richyb66]

I'll be interested to see how you get on with this. I've got lpg on my S6, it's a Bigas sytem with a similar 70 litre torroidal tank (so range is around 200 miles). This only equates to maybe 17mpg, despite whtever the DIS shows (around 25mpg on average) although to be honest, I'm not sure how accurate the gauges are on the pumps and I know they cut off based on pressure which seems a bit variable depending on where I fill up and the DIS can only base it's figures on how much petrol it would be injecting.

As you say, I do get the check engine light on pretty well most of the time and if I clear it, it usually comes back on after 100 miles or so. I'm not sure whether this is down to the set-up of the lpg system or the fact that it now appears that my cats are on the way out. Hopefully after the weekend I'll have a better idea once I've swapped the cats and fitted new pre-cat lambdas.

I didn't fit my system but I've had a good look around it and the actual wiring seems pretty minimal, and as far as interconnections between the lpg ecu and the petrol ecu goes, it's really only the injector wiring.

My petrol injectors have had the harness disconnected from them, this is then connected to a link harness that goes up to the lpg ecu and then back down to the petrol injector. This allows the lpg ecu to prevent petrol from being injected and that's about it as far as I can tell. No doubt there's more wiring somewhere, but if there is it's well hidden.

My airbox has been also removed to allow the vapouriser to fit and I've got an ITG foam filter which means the secondary air injection doesn't now feed air into the inlet. I'm not sure of the implications of this, if any and whether this could be causing some of my check engine light issues. Again, fitting new cats might provide more answers.

When it's working properly is very good, noticeably smoother on lpg but also noticeably more powerful on petrol. I can easily cope with less power for the 95% of the time I'm just cruising around. One problem I have had has been blown air flow meters - 2 so far. This has happened on both occasions when I've run it round to the red line on lpg. It brings the ABS and ESP lamps which are classic signs of blown AFM although the driveability doesn't actually seem affected.

Finally, a bit of a daft question - is the inlet manifold aluminium? I tried using it as an earth when doing some electrical diagnostics and couldn't get an earth reading off it! I also tried a continuity test across 2 areas of the inlet and got nothing, it clearly is metal and even if it was mag alloy it would still expect to get a reading so I'm a bit puzzled!!!

[Ricky22buk]

Do most people on here have the same issue when running gas...... their management lights come on ? Surely that could be rectified by some sort of calibration ? Yes / No ?

[Conan_the_Librarian]

I ran a Prinz system for almost 80k and only got one fault. It was a PF though so only one set of Lambdas.
I had the same issue with the injectors. Mine were fitted profesionally and it wasn't until I cam to swap the inlet manifold to a different engine I realised that the manifold had been drilled without being removed. I know this as one of the injector tubes blocked the removal of a manifold nut! However, were I to fit a system myself I would remove the manifold to drill.

With regard to the injector wiring, you can get connectors that sit between the cars wiring harnes and the injectors that re-route the injector pulse via the LPG ECU. That way you don't have to cut into the wiring.