Orlando Smith

so basically my car wont start when i park downhill. This is the second time that my audi a8 hasnt started for this reason. I narrowed it down to believe it wont start downhill. however im not sure if i can hear the fuel pump running or not. I have usually a smidget over a quarter of a tank left. not below 1/4 each time. the grade is fairly steep but not extremely steep. borederline e-brake worthy. the first time this happened i waited 30 minutes and it did start. the next day it drove fine until i turned the vehicle off on the slope. I towed the vehicle home, and the vehicle started right up on level surface. This is confusing, i believe it is the fuel pump but it may be something else. this is a 2006 audi a8l and i believe it has 2 pumps. a left and a right. how would i know which is the culprit. OBD shows nothing related to this. What about the fuel filter i hear that can cause this as well. and its cheaper. but at this point i want it fixed idc about price, i can do the installation.

Mister Bally

No fuel to engine does not give a fault code.

91quattro

Have you tried parking downhill on a full tank to see what happens? Does it matter whether the car is facing downhill or uphill when the problem happens? Any fuel leaks? Where are you located - what sort of climate?

ltooz_a6_a8_q7

This type of things happen to all types and make of cars. As I understand the fuel system, the gas pressure lines are sealed tight... therefore, the up/down hills doesn't matter. When the tank is low or full, if the system is air tight, it should start. I would check all the fuel lines for cracks or leaks at all the connection, gas cap also.
Just a thought. I've never changed fuel filter to fix any no start problems in all my life or change them even with 175k miles car and I use cheap gas. Don't introduce another fail factor into existing problems by replacing things.
Cheers,
Louis

Orlando Smith

so today i went to my brothers to test different slopes. it passed all the test, then however i did not crank again. on level surface. it sounds like maybe the right pump is workin but the drivers pump isnt. while turning the key to the on position he could hear 1 pump. i could not hear the pump pressurizing the lines. Why is it intermittent and only happens at times. I can come back to it later and it possibly will crank right up. I checked my abs sensor on the rear driver hub, it was dirty and had a light brown dry dirt looking substance inside the gaps. I ordered a new speed sensor however they sent me one for the opposite side even tho i requested the driver rear. So i have to return that item.

MP4.2+6.0

The erratic start symptoms by themselves--as opposed to the slope theory--sound as or more likely diagnostics. Could be basic crank sensor, which has erratic failure like this from a variety of posts over years. It also may not yield any codes from what folks have reported either. Search for more info.

Mister Bally

Is the problem no crank and thus, no start? Or, Cranks but no start when you have the issue? Need to know as there is a big difference when troubleshooting.

Are you using VCDS diagnostics or a generic scan tool ? Most generic OBD scan tools won't help with the actual starter circuit diagnostics.

Orlando Smith

no it definitely cranks, hey is that one guy 3dogsandmonkey i seen his videos before buying this car. he's awesome he hooked a tv tuner up that was amazing. Need more info on that...Anywho, yes it cranks fine. if i wait it seem to start again. yesterday i was on flat surface with over a half tank after driving it 45 miles with no issue i parked it. attempted replacing my abs sensor rear driver but somehow they sent me SU11918 and i needed 19. left vs right side. however it was filthy so i cleaned it up nicely and replaced it. And wait for the right one to be sent. Afterwords it did not start. I had my brother try it a few hours later and vroom. he said it started right up. Im not sure if its the crankshaft position sensor or the fuel pump, and which fuel pump. There is a flap in the rear of the trunk that seems to allow access to the pumps. i seen 2 big metal lids with 4 screws holding it in. i assume its a cover for access. hopefully i dont have to drop the tank. i dont have the pumps handy so im not touching it yet. I bought a fuel filter from autozone and it was the one with 1 line on both sides. basically a in and a out. well on my audi it has 2 in and 1 out or whatever. hmm. another epic purchase fail. theres 2 fuel pumps with 2 different part numbers labeled left and right im sure somehow i will get the opposite one. however how can i tell which pump or CPS sensor

MP4.2+6.0

Run VCDS scan and see if you have codes pointing at either fuel pumps or crank sensor. Sometimes yes you will, sometimes no you won't--among few places it's not definitive. But don't even bother with an OBDII scanner, or rather save the $ for beer since it won't show anything and you will be back where you began anyway.

Yes, you access fuel pumps on most newer German cars through floor/access plates rather than dropping tank. Obviously do it with fuel level down at least some and basic safety around fuel vapor--tool use, no electric switching (including shop lights), etc.