Please advise! A8 d2 4.2l no-start after battery dying

[Mikaric]

Hello all. I hope this is the correct area for this post. I am a long time casual reader of this and other forums but this is the first time I am reaching out for help.

Car is a 2001 A8L 4.2L Quattro in Canada. This car was given to my grandfather by a friend, who then gave it to me. I put it on the road for my dad. Odometer 280,000km.

Here is what happened as an account from my dad.

Car was driving fine. Red battery light came on above the tach. He was afraid to shut it off incase it wouldn't start.

After 5-15 minutes, larger yellow battery icon appears in center of dash.

Shortly after, car dies.

Decides to tow it home. Tow truck driver manages to start it on a booster pack of ours but it won't "idle up" and runs like poo.

Once home, I try to start it. It does one of two things. Either it starts and runs great, for 1-5 seconds, or it starts and runs for much longer but only at ~400rpm and does not respond to throttle.

Took battery into work and tested it. OEM battery rated 850CCA, measures in the 300 range, but tester passes it as low on charge and not failed.

Slow charged all day and retested, cranked out 815CCA.

Now when I try to start, all it does is crank and crank, barely hiccups randomly every 3-10 cranks.

Took intake hose off and sprayed brake cleaner and then quick-start into the intake directly, I don't think it changes.

Inspected ECU for water intrusion because the day before this event, my dad pressure washed it and focused heavily on the cowling area is what he says.

Also car has a history of battery dying. Radio is in safe mode and I don't have the code, and it has had to be boosted a few times in the last few years.

To further complicate things, all we have is the valet key, and in the midst of this all, the trunk popper button is dodgy at best, regardless of battery charge.

So basically originally I was thinking alternator went. But I thought once I charge the battery then it should at least start and run until battery discharges. I need advice, I have no VCDS, no bentley manual, no wiring diagrams, and it's not my car and I don't know if I can justify the budget for these items.

Any help would be extremely appreciated!

Edit that I have also checked resistance of all the fuses in the passenger footwell (both the panel behind the wood and the one that isn't), and all the fuses in the ECU box area. And also that, according to the manual, with a new battery hookup I did wait in accessory position for the 5 seconds prior to restarting. Also I have checked the junction box in the pass side wheel well. It is packed with grease and so therefore I do not believe there is corrosion in there.

[somedude]

I am a bit confused here. I want to do this blow by blow. Red battery light came on and it eventually ran out of electricity.

Tow truck driver jumps it and it runs but will not rev above idle

Charged batery but car will not run. Above 400rpm even with new batery it will not run. What happened when you used starting fluid? If spark and valve timing is good you should be able to get it to run on starting fluid spraying directly into the throttle body. The maf will probably have to be disconnected for it to run like this.

If it will run on starting fluid or brake clean or whatever you are using then you have a fuel issue. Check to see if you have fuel in the car, then check fuel pressure.

[somedude]

Short story but the way you described the way the car runs is exactly how my 01 a8 died when i ran the bastard out of gas. I found out my fuel gauge does not read properly. It ran perfect the. Died. Then it would idle at 400 to 500rpm. Then would briefly fire on crank and die right away. It is easy enough to throw a couple gallons of fuel in it just to play it safe.

[Mikaric]

Somedude thanks for the reply. Thursday I will be at the car and will plan on spending an hour or two on it between other projects.

First of all, yes what you described is what appears to have happened from my second hand account - battery stopped charging, eventually died, then wouldn't really run well. He was carrying the booster pack with him because this car had a history of needing a boost.

He swears there is fuel in there and the gauge is around a half a tank but I agree that I should try to put some fuel in there. Originally I did suggest this when I first looked at the car but he was very sure there was premium fuel in there.

As for the starting fluid - I am not sure if there was much of a difference in how it cranked, but the MAF was plugged in. I wasn't aware that would make a difference but I'm assuming if the MAF doesn't see airflow then the car wouldn't spark or would reduce spark? I think my plan now is to throw two gallons of fuel in there. If this does not work, unplug MAF and liberally spray starting fluid directly into intake.

Next update will be Thursday.

[somedude]

Somedude thanks for the reply. Thursday I will be at the car and will plan on spending an hour or two on it between other projects.

First of all, yes what you described is what appears to have happened from my second hand account - battery stopped charging, eventually died, then wouldn't really run well. He was carrying the booster pack with him because this car had a history of needing a boost.

He swears there is fuel in there and the gauge is around a half a tank but I agree that I should try to put some fuel in there. Originally I did suggest this when I first looked at the car but he was very sure there was premium fuel in there.

As for the starting fluid - I am not sure if there was much of a difference in how it cranked, but the MAF was plugged in. I wasn't aware that would make a difference but I'm assuming if the MAF doesn't see airflow then the car wouldn't spark or would reduce spark? I think my plan now is to throw two gallons of fuel in there. If this does not work, unplug MAF and liberally spray starting fluid directly into intake.

Next update will be Thursday.

in theory it really should not make a difference on initial startup. if my memory serves correctly the maf is not used during startup but is used after startup which could be a reason it does not run well after it fires on starting fluid or brake clean or whatever you are using.

MAF plugged in with no airflow will make the car run horribly or not at all because actual and measured values are so far apart, while a unpluged maf will go to default values and will usually run just fine for diagnostic purposes.

[Mikaric]

Ok finally had a chance today to look at the car. Put 10l of 94 octane in and the gauge moved approx an 8th which i think is roughly correct. Wouldn't start. Opened airbox, unplugged maf, removed all hose up to throttle body. And...she starts! As in, she instantly starts, super strong with no delay! So now it will start and rev excellently with any combination of the maf being plugged/unplugged and the intake tubing connected or not (I tried all four combos, can't notice difference with a quick rev). So voltage at battery and directly off alternator (using ground beside greasy junction box in wheel well) is the same, around 12v. So I think alt is defective. I removed alternator and I'm looking closely at the voltage regulator since some posts mention it as common failure. The brushes have tons of extra material left but all of the metal on other areas is green corroded. I've never had an alt off a car so not sure what to look for. Would like to take it to bench test it. Reg is transpo brand and alt is Bosch, I wonder if this indicates it's been rebuilt before, car does have 300km

[Mikaric]

Basically this is a free-car-zero-budget kinda thing, I enjoy trying to fix things using the least amount of money possible. Regs look cheap online and I'm not ready to fork out on an entire slt until I know for sure, but if we do need to spend a few hundred or whatever then we will

[somedude]

Ok finally had a chance today to look at the car. Put 10l of 94 octane in and the gauge moved approx an 8th which i think is roughly correct. Wouldn't start. Opened airbox, unplugged maf, removed all hose up to throttle body. And...she starts! As in, she instantly starts, super strong with no delay! So now it will start and rev excellently with any combination of the maf being plugged/unplugged and the intake tubing connected or not (I tried all four combos, can't notice difference with a quick rev). So voltage at battery and directly off alternator (using ground beside greasy junction box in wheel well) is the same, around 12v. So I think alt is defective. I removed alternator and I'm looking closely at the voltage regulator since some posts mention it as common failure. The brushes have tons of extra material left but all of the metal on other areas is green corroded. I've never had an alt off a car so not sure what to look for. Would like to take it to bench test it. Reg is transpo brand and alt is Bosch, I wonder if this indicates it's been rebuilt before, car does have 300km

so i just want to recap this so I understand clearly. so you put gas in and now it runs perfectly? you removed maf and reinstalled and it makes no difference? I get that the alternator is not functioning but that should not effect the engine running at all if the battery is not dead or low voltage.

[Mikaric]

so i just want to recap this so I understand clearly. so you put gas in and now it runs perfectly? you removed maf and reinstalled and it makes no difference? I get that the alternator is not functioning but that should not effect the engine running at all if the battery is not dead or low voltage.

So when I added gas it didn't start, but after the MAF unplugged it did start. Now it starts.

Took the alternator to a place, bench tested it, failed. So they are going to fixer up. Hopefully this will be the end of this adventure and when I put everything back together I don't get a mystery no-start. Thanks for the MAF advice somedude!