The Red battery light of Joy
 

Driving the S8 this evening and having a great drive in a wonderful car.

On the way home the red battery light came on that is on the rev counter. Most odd I thought as the car is going well and its got a new battery in the back.

Stayed on and I was thinking hello is this an Alternator problem....

Driving through Cheltenham and more warning lights came on, dash dimming, battery light on the DIS, gearbox goes into limp and yes the poor old battery was clearly being drained and not charged. Luckily got it just to a friends house and parked it up and I can worry about it tomorrow. So its either going to be an alternator failing (was working fine) or its thrown the belt due to a grumpy tensioner.

I mean I cannot be too hard on the old girl it is 18 years old and done over 200k so the occasional old part is allowed to wear out!

First thing I'd check is the battery terminals to ensure they are fitted securely, and you don't even get your hands dirty.

Next would be a visible inspection of the connection block on the front drivers side chassis leg to see if there's a buildup of crud.

Failing that, await an answer from MJ :)

Beg, borrow, perhaps not steal a multimeter from someone, put it on volts and put the leads across the battery terminals. Start the car and check what voltage your alternator is putting out. Quick and easy test. Should be about 14.4V. If it's low, and I suspect it will be, I'd then repeat the test at the terminal box in the wheel arch but place the meter leads between the big battery cable and the chassis. You will have to probe around a bit on the battery cables because it is possible that a bad terminal box connection will give a poor result on the long cable going back to the battery and a good result on the shorter cable. This would actually be a good thing as it would indicate a bad connection in the box. An easy ish fix.

If all is well here then you need to be checking out the alternator. Could be poor connection's there or brushes worn-out.

Brushes are easy to replace, no soldering required but I am unsure if it can be done with the alternator on the car. Not sure if there is enough room to remove the rear cover and air duct to get access.

Thanks for that, yes have a multimeter as tested it a while back when I had a Yuasa Silver battery causing no end of problems.

Got the car back home tonight which is good news.

Put a spare battery in and started OK, still had the red battery light on the dash. Then the car was running rough and really rich, then it died...

.....and would not start again even after a period of time to see if was flooded :(

Called the RAC and said they would be about three hours!!!!!!!

This would normally be the end of the story but I disconnected everything, let is reset and then forced the car to start on LPG. Drove home no problems (red battery light still on of course).

Ahhh all in the pouring rain also.

Never mind, Hooray for LPG +++

You may have killed the fuel pump running it low on volts. I've seen that before when the alternator has died and the car was driven until the battery went flat.

The alternator does need to come off to replace the regulator so at that point its as easy to just fit a recon, although if you can afford to have the car offline for a few days a regulator is a cheap enough to try. If you buy a recon, make sure its for a V8, not a V6. A lot of places say they are the same, but the rear air ducting is different. The V6 alternator will bolt up but the ducting then won't fit.

It can be on the drive/ in the garage for a while so I agree I will take the alternator off and try a regulator first of all.

Then look at the fueling, it could well be the pump has decided to die at the same time just to help matters! I will give it a tickle with VAGCOM to see if it throws any light on the matter.

Does anyone have the part number for an S8 Regulator?

028903803e

Thank you +++

Nognar - I still have a V8 alternator [Bosch] rated at 150 amps sitting in my hallway. A replacement was obtained from Prestige and was fitted to my car after experiencing charging problems with, you've guessed it, a silver Yuasa battery. I'm convinced it was working before I foolishly replaced it but haven't tested it.

If it can be of any use, let me know either in this forum thread or a private message. The only possible caveat being that the S8 alternator is different to an A8?

V8 alternators are all the same +++

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.

Agreed, will drive it with a Jerry can in the boot and see.

Though it did die on petrol after the alternator/ battery died and before I replaced the pump. It would not start again with the 1/2 tank hence replaced the pump as a precaution. But could well be old pump died and new one had an airlock or no fuel as you say to suck up in the bowl.

Hello MJ, after lurking on this post and watching the developments, do you think it's worth asking my local garage (the one that fitted my replacement fuel pump within the last year) to refit the pump and pay special attention to this fuel return line? I'm still running out at about 1/3 capacity. I've attached a couple of screenshots from my ELSAWIN for reference.

The return pipe is the convoluted piece in the centre of this pic

https://www.audiworld.com/forums/att...a8-4.2l-4-.jpg

It needs to be tucked in to the fuel pump bowl. If its left loose it can cause the 1/3rd tank problem.

Low battery voltage can definitely kill fuel pump, I am no expert or physicist but will try to explain best I can. It is a bit counterintuitive as you think lower would not hurt, only higher but I have seen it happen before. The problem is that as volts drop current can increase and too much current can kill it. Now again this is not straight forward as normally current is voltage divided by resistance so lower voltage should be lower current. But the deal is that pump motor actually has very little what what is called resistive impedance so it draws a lot of current at startup but as soon as it starts turning the inductive and capacitive impedance goes up and adds to the resistive impedance so the total resistance goes up and and current reduces. If the voltage is too low to start the pump turning then capacitive and inductive resistance never come into play and pump is stationary with little resistance and a lot of current going through it and eventually it can kill the pump.

MJ - thanks for the real-life photo, as opposed to the sanitised Audi manual version.
Ainars - thanks for the explanation of the low voltage situation.

From what I understand of a possible shared experience with Nognar's issues mirroring mine (alternator was replaced in my case when it was actually the silver Yuasa battery at fault, and additionally a fuel pump replacement) it's all starting to fit together in my brain.

Armed with that photo, I can now approach the garage with some level of confidence that I might be able to get back to the heady days of being able to use a full tank again. The garage did have initial problems fitting it and was refitted after a complete seal kit was ordered.

Apologies for slight thread hijack but hopefully of some use to Nognar and others.

I also ensured the return pipe was in the right place. It’s one of the things I checked when fitting the pump for the second time was it poked down into the right place.

We may both be out of luck then, if my garage did it properly... I remembered that I saw a post by moltuae from a while back and I'm sure he had the whole tank replaced.

Found the post: http://forum.a8parts.co.uk/showthread.php?t=12072

I'm not sure I can stomach that expense right now so I'll keep my 5-litre can in the boot if the garage don't find anything wrong.

I did. With hindsight (and the right info) it was probably fixable but I'd had enough. 2 different garages, numerous mechanics and I think 3 (or maybe 4) attempts to fix it. I even had a go myself, which quickly turned into one of those 'I wish I hadn't started this' sort of jobs -- Spending a Sunday contorted in the boot, swearing and high on petrol fumes is not my idea of fun.

And to add to the frustration, with every failed attempt to fix it came the testing period and the embarrassment of having the car splutter to a halt, usually at the most inconvenient times, and then having to add a little petrol from a jerrycan to get me to the nearest petrol station.

Interesting article here on another owner with the fault.

https://www.audizine.com/forum/showt...mystery-solved

The implication there is that, assuming the pump is seated correctly, that the long bolt simply isn't tight enough and thus isn't compressing the D-shaped gasket and allowing air in to the pump. That would suggest some sort of lubricant is needed on the bolt thread which is compatible with petrol but which doesn't dissolve in petrol.

Its an interesting post but for me I ran out at half a tank before I changed the pump but after the battery/ alternator died. Though it could be pump died in the first instance, then when replaced it did not seat/ seal perfectly and its sucking up air.

Currently plan is to circle locally burning off fuel to see what happens, good news is an S8 on short journeys can be quite thirsty so it should not take long +++

Luckily the car is a "Hybrid" as its got LPG so I can swap over to get me home when it happens, also with a Jerry Can in the boot I also consider it a Range Extender.

Currently still circling in Sport mode locally like a Jumbo Jet burning off fuel to see what happens.

Previously the car stopped and would not start again with a little over half a tank of petrol.

As of now its running on petrol no problems with a little under half a tank so we will see!

Long drive yesterday and still going strong at now under 1/3 tank +++

Though of course it was all going too well...

Drove through a puddle and and the speedo died which is far from helpful, P0501 code on VAGCOM now with a failed Vehicle Speed Sensor. Never mind another job to do, I am assuming this is the one around the gearbox?

VAGCOM also confirmed no speed signal either is coming through.

ABS sensors all working and OK from each of the four wheels so I don’t think it’s that. Also without a working speedo, whilst everything else on the dash is OK it really upsets the fuel gauge without that speed signal.

Rather odd that the speed signal affects the fuel gauge :Confused: Its just a resistance driving a gauge.

The VSS might just be a wet connector. Its on the left hand side just above the output flange.

Thank you I will take a look.

Fuel gauge is fine at standstill then when driving it bounces up and down like a slow old fashioned VU meter on a hifi. My thoughts were it maybe needed a signal from the speedo to work out range and it was getting upset.

I may order a new speed sensor anyway, does anyone have the right part number?

The VSS is 01F409191.

The fuel gauge has a conditioning circuit to reduce its response time so it doesn't jump up and down as the fuel sloshes about so that behaviour is also slightly odd.

What are the interior lights doing while the car is running? Do they pulse at all or are they stable?

Everything else is ok and interior lights all ok.

I will leave it for a day or two to dry out and have a look, I will also order a new VSS also just to cover that.

Yep still bouncing when driving and putting on the brakes etc.

As mentioned it only started to do this after the Speedo died, though its driving Ok and not running out of fuel which is a bonus.

I will replace the VSS and then perform an Exorcism.

I wonder if part of the conditioning circuit does have a link with the VSS so that it slows the response time of the gauge when the car is moving? Perhaps if it is stationary the circuit is disabled so that you get a quick response when filling with fuel, and so with the VSS broken its just showing the fuel sloshing around.

It'll be very interesting to see how it behaves with a new one +++

Evening all and an update.

The VSS/ connector has clearly dried out and now the speedo is working again. With a working speedo I can confirm the Fuel Gauge works and remains steady. It does not move around as the petrol was sloshing about as I had before with no speedo.

Secondly the car has run into the petrol reserve with no problems which is good news.

I will keep an eye on it and make sure I always have LPG also just in case.

But to confirm this is what I think happened.

Regulator in the Alternator wore out and gave a red battery light, in turn this drained the battery and during this low voltage period it killed off or at least upset/damaged to some extent the old fuel pump. When starting the car again it drove for a short time then died on half a tank of fuel and would not start again. New fuel pump put in but still would not start though all connected, power was going to it and had half a tank of fuel. Refitted everything, checked it all and its seating etc to make sure and still no luck. I then topped the petrol tank up 100% and it started fine and has been driven and used a full tank of fuel with no problems at all.

So my thoughts are as suggested putting more fuel in allowed the pump to be primed/ filled the bowl/ pickup/ remove airlocks and at that point it worked fine.

So time to drive it more +++