Thank you Johnny Quattro.

I have ordered the Regulator and will try that at the weekend, if no joy I will PM you in regard to yours.

Much appreciated.

Still working on this one but cannot get the car to start on Petrol.

Hence thought I may have broken the fuel pump as suggested by the good Dr.

Replaced the fuel pump (yep its damn fiddly to get in and out) and still will not start. To confirm there is about half a tank of petrol in the car and all was well and working before the alternator died.

To confirm:

Car will not start or run on petrol but runs on LPG OK
New fuel Pump fitted with no change to the above status
Fuel Pump relay replaced - No Change
Fuel Pump Fuse checked and all good
Old fuel pump tested on the bench and appears to work
New fuel pump can be heard working in place if I put a 12v probe onto it from the battery to the 4 pin connector

Looking at the 4 pin connector itself that attaches to the fuel pump it has 4 wires and using a multimeter I do get some volts but not many (3v) with the key out or in position 2.

http://forum.a8parts.co.uk/picture.p...pictureid=1414

Now does anybody have a wiring diagram so I can check the 4 wires or what I should be reading? I have also been going through the Fuel Supply systems test on the Service manual and not got much further with that also.

http://forum.a8parts.co.uk/attachmen...1&d=1604676543

When you switch the ignition on you should hear the pump running for a second or so, but it can be very subtle especially with a new one.

Pump power is on the large green & brown wires on that connector. The two small ones are for the level sender.

Thank you and appreciated +++

Its very hard to hear the pump hence I can only hear it when up close and kicking it into life with a 12v test probe.

I shall have another tinker with it over the weekend.

Are you saying that the car will not run on petrol at all? If so I'd be looking at whatever it is that inhibits the petrol injection system when you switch to lpg.

I don't know anything about lpg by the way, never worked on one. Just a punt.

Evening all, a fun day underneath the car tinkering with it.

Replaced the regulator in the Alternator, and indeed 100% fixed that problem so thank you for that. No red battery light on dash and well over 14v being put back into the battery when the car is running.

Can you tell which is the old one....

http://forum.a8parts.co.uk/picture.p...pictureid=1415

Though getting the alternator back in, lined up and bolts in is a little fiddly.

So back to the fuel problem.

To summarise, car was working perfect then the Alternator died which in turn killed the battery and the car stopped. Put new battery in and ran on petrol briefly then died, so got it home on LPG.

Checked today and there is 12v going to the Fuel pump, I can hear it running in the car also.

To be 100% sure I took the fuel pump out and checked everything, made sure it was all connected and working and put it all back and its seated properly.

So....

It will not start on petrol, fuel gauge shows 1/2 full. Works on LPG if I force it to start but dies when flicking back to petrol on the OMVL LPG button. I did get it running for a short period on petrol after revving the car to 4,000 rpm on LPG and flicking back to petrol but it shortly died again.

This is an interesting one really and could be many things, I am beginning to feel it may be earthing/ electrical so will check the amps on the connection to the pump under some form of load next to see what that does.

It could well be the LPG system has gone a little broken after the battery when flat. It may be now upset and its not switching properly, so I will look into that as its a really good point well made.

Without doubt petrol in it but as a wise man says put some more in and see, so will top it up at some point also.

I am sure it will be simple once I have worked it out +++

I presume the ECU is not reporting any issues in VCDS?

I think the ECU can switch the injectors as part of its output tests (although not sure how it would mitigate residual fuel pressure flooding a cylinder if an injector is opened?). If it will, then you should be able to hear them clicking in turn. If not then it does seem likely the LPG ECU is not relinquishing control of them. Do you have diagnostic software for the LPG ECU?

Yes nothing on VCDS and don’t have anything to connect to the LPG.

I may try pulling the fuse out of the LPG and see +++

Also thanks for heads up on just changing the regulator, saved a good few £££ though I am sure the old S8 could do with a visit to Devon at some point in its future.

Well poke me with a pokey stick...

Car has 1/2 tank of fuel in so as suggested went to the petrol station this morning and topped it up.

Car works fine on petrol now +++

Which is amazing news and thankyou and all back and working.

Though I need to work out why since the alternator died it no longer thinks 1/2 tank is enough. Before that it would go into the reserve no problem.

Progress anyway, alternator now working and battery charging fine and no codes on VCDS shown.

It could be that the fuel level wasn't high enough to fill the pump bowl when the new pump went in. Maybe carry a 5 litre can of fuel with you and run it down below half and see if it behaves now?

If not then the new pump may not be seated correctly, or the return line may be outside the pump bowl.