clintmeyer

For the last 6 weeks my 2001 A8L with 135K has been cranking without starting, I replaced the battery because the CCAs were well below spec and the problem did not go away.

I took the car to a foreign car mechanic (fancy type). They said that the fuel pressure was low and bleeding off and that I needed a $1900 fuel pump replacement but the would give me 10% off if I signed up for their car care club for $39. WHAT A DEAL

Does this problem sound like a bad fuel pump? Why would a bad fuel pump leak pressure over time? I have seen some videos online and read some resources concerning the replacement of a fuel pump and it seems like a fairly involved job. However as always it seems there is a much cheaper path to fixing it than $1,900. It seems I can get the part for ~$150 and it might take a couple hours of labor. It seems tricky to get the assembly in/out and replacing the pump inside the assembly. Tricky but doable.

I just want to double check that leaking pressure is not something simpler like a hose or something.

clintmeyer

Let me clarify......my A8 is cranking a long time before starting but it ALWAYS starts and runs great once started. It will crank for 2-3 seconds sometimes longer. Sometimes if I let it crank for 2 seconds then turn off it will start right up. Sometimes it starts and idles around 1K and then stalls.

Sorry for not being clear in my original post

Kneale Brownson

If it continues to run, it's probably not the fuel pump. Try spritzing the ignition wires after dark with some water. See if you get a light show of misdirected sparks. How old are the wires/plugs/coils?

Prospeeder

Why not? Fuel pump check valve bleeds all the fuel pressure back so it takes forever for it to refill the rail and pressureize it and start the car. See it all the time from old old audi/vw to newer ones.

clintmeyer

I have owned the car for 2.5 years, and put 35K miles on it. I have not changed the plugs/wires/coils.

I seriously love the car/platform (such a great vehicle), but sadly am going to sell it to buy a truck (need to tow an ATV). I just need to fix this issue. I would prefer it to be plugs/wires/coils but my gut (and its a substantial gut) says its likely to be fuel pump. But hey i will check the plugs tonight.

silverd2

No need really to ever change the wires or coils in this car...change a coil when it goes out...they generally work or do not. You'll know when a coil goes...you'll loose that cylinder (REALLY rough idle and running) and get a constantly blinking CEL.

35K miles on the same plugs? ...change em. Not necessarily your problem, though...wouldn't hurt.

You need to read the codes, if the fancy mechanic hasn't already..just to make sure it's not something like an MAF, which alone can cause stalling, especially in combination with old bad plugs.

There are other things that can commonly cause fuel pressure to bleed off...like a leaking injector...only takes one with a little dirt in it. Some have cured this with a bottle of Techron through a partial tank of gas. In A8/S8, the fuel pump check valve (not changeable) is RARELY the problem with fuel pressure bleed off...maybe on some older VW's, in my experience.

A correct fuel pressure test is done under the hood and includes checking pressure and bleed-off on both sides of the pressure regulator...this can point backward to the fuel pump or leaking line or forward to the injectors. A leaking injector common causes extra cranks at start up.

All the above is just long distance guess, going on your description alone.

Does it continue to stall once running or just once maybe shortly after starting?

If extra cranks are the only symptom, don't do anything rash yet...you could drive it forever like that...and in a D2, NOT generally the symptom of a pump going.

P.S. If you ended up changing the pump, DO NOT buy anything but the correct VDO Siemens pump....ALL others are a scam and lead to problems or no start at all. Most members here buy the pump from a VER dependable UK source...World Parts I believe...check back here.

Audi mechanics and most indy mechanics in the states only change the entire housing with the pump...totally unnecessary...thus the high price quote.

Again, don't jump to any expensive conclusion yet...unless the car becomes undrivable.

clintmeyer

Will do.

I have run the codes, there was nothing relevant. P0430-Catalytic Converter Efficiency below Threshold and P1569 Cruise Control Switch. I messed up the airflow when i reassembled it after fixing the cooler pipe 2.5 years ago (thanks for the help then silverD2), and this is much different than that situation. The car runs beautifully after it starts.

I bought 2 bottles of Techron and dumped one in my 1/2 tank. They were on sale and while it said to wait until the tank was empty and then add it with 12 gallons, i figured i would dump one in now and then run one through when i go for my next fillup.

I do put in cheap gas. Is that a bad thing?

This is what the receipt says. Should I bug them about how they tested the pressure?

"Checked fuel pressure-good at 50-55 PSI at idle. Checked residual fuel pressure (car shut off) at .5 bar (approx. 7 PSI). Recomend replacing fuel pump and filter."

It starts up like a dream if I turn it off and then crank it. This morning there was barely a stutter when starting after sitting overnight.

Here is a video of it starting this morning, like I said this was an especially good start after sitting overnight. I will make another video when i leave for work and upload if it shows a different behavior.


One other odd thing, i opened the hood after taking it back from the mechanic and there was a shiny razor blade in the engine compartment sitting on the fog light assembly. I found it odd that they had a use for a razor blade. Should that concern me? And if so what should I do?

aduggs

Sounds like you are losing fuel pressure, so there must be a leak in the line somewhere. Does not sound like a fuel pump issue.

The fuel lines are designed to stay under constant pressure. If you are loosing that pressure as the car sits, then the pump is needed to re-prime the lines every time at start-up. This explains why it takes a few cranks to fire. You will have to trace the fuel lines to find the leak (could be a worn fitting/seal somewhere).

Apart from wasting fuel, the leak isn't much of a problem. You do not need to crank the engine to prime the fuel lines. Just turn the key (do not start) wait a few seconds and then turn the engine over. The fuel pump starts when the key is turned on, so that will prime the fuel line (don't put extra wear on your battery and starter by cranking the engine for longer than needed).

Kneale Brownson

A leak to the outside would be pretty apparent. A leaking injector would not.

Is it true that newer Audis turn on the fuel pump with the ignition without cranking? I know that applied to older Audis, but I thought the ECU now has to get a signal from a sensor that the engine is turning in order to activate the fuel pump.

silverd2

The running pressure was good. The residual pressure is bad...it should still be at 2.5 bar or better 10 minutes after shutting off the car/pump. BUT if the final step was not carried out, they didn't pinpoint which area to look for the unwanted bleed off...they likely would not have printed this, even if they did it. Hard to say with out getting an honest answer out of the mechanic who did the test.
The correct pressure test gauge has a lever that shuts off the pressure line back to the pump...if there is no bleed off when this is closed, it indicates the "leak" is on the engine side...unsealed injector or bad fuel pressure regulator...more likely injector leak.

By "cheap" gas, if you mean low octane (below 91), it should cause actual problems...just lower power, esp at higher rpms...engine retards to prevent knocking (pre-detenation), therefore a loss of power. Some disagree, but I personally NEVER use low octane...always 93 around here. The engine was designed to run best with highest available. It will "run" on low octane...and I could eat dogfood, instead of cheeseburgers

Dirty gas is likely to be cleaned up by your filter, but hard to say if micro grit or bad chemicals from questionable sources could eventually cause an injector(s) to stick slightly open (wouldn't take much to bleed off pressure quickly) could lead to this...possible(?)

Your best bet is continuing to clean the system.esp if you see ANY improvement...if so, I'd run even some more through there...well worth it if it's helping and a good indicator that the problem could be sticky injectors.