Architectom

My 01' d2 was throwing a code that showed lean fuel trim/ shortly after I started having a problem with warm start, now I have no start. I threw a new coolant temp sensor in, no improvement- I'm waiting on a vagcom but am interested in trouble shooting- it appears that given the lean condition the Maf could be a cause, I am also reading the crank position sensor and fuel pressure solenoid are potential culprits-

silverd2

VagCom is the only logical next step in troubleshooting ... the code(s) will tell the story.

The only thing that won't throw a code of its own is a bad fuel pump (common failure at high mileage).

A bad engine speed sensor ("crank position" sensor) will throw a code, intermittent or failed ... A bad ESS will cut ground to the fuel pump relay and shut off flow.

Architectom

Thank you- not finding a shop locally that can fit me in immediately and am waiting on vag com not being able to track a person down locally with one... Other car is in the garage with engine on a stand- it's worthwhile for me to do the parts changer thing in effort to resolve this in the interim- would ess be a safe bet for $65 and 15 minutes? I know this isn't good or smart car repair but I need to work with my options

the_duke

There is no safe bet without proper diagnostics. If you're will to throw money and parts at it then go for it. My bet is on fuel pump.

twentysevenlitres

You can test the fuel pump easily enough.
There's a factory procedure buried in the bowels of my PC hard drive which is still packed away in its moving box...
However my version of it goes like this:
1. Arrange a way to hotwire the fuel pump. Some blokes take the cover off the fuel pump relay to manually operate it, or jump the fuel pump relay plugs (this could be done with a switch easily enough). The factory method is to run a wire from the fuel pump fuse to the pump directly to bypass the relay while keeping it fused and switchable via the ignition.
My method depends on having the boot (trunk) carpet out and the inspection hatch removed. From there it is very simple to directly wire the fuel pump main plug to the battery via a toggle switch.
2. Open the bonnet (hood) and find the fuel return hose after the fuel pressure regulator and remove it (it's a low pressure hose, so no danger of spray, but may leak, so have rags handy).
3. Place a piece of hose from the return fitting on the fuel pressure regulator into a container of at least 1 litre (or quart).
4. Now's the tricky part, as I can't recall how long to run it and what capacity you should expect, however I think you need to run the fuel pump for 15 seconds and you should get 400ml or more of fuel into your container.
If that happens, your fuel pump is fine.

DaytonCarCare

Is the timing belt fairly new?
Could it be it jumped out of time because the tensioner failed?

Reason I ask is the 99 A8 Q 4.2 I received a couple months ago had a crank no start issue like it wasn't getting fuel.
It did throw a code for a bad crank PS and misfire due to a bad ignition module. After I replaced but same symptoms. I pulled the valve covers and found a set of cams out of time because the belt jumped a couple teeth.
I installed a new belt, tensioner, and pulley, runs great now.

Though with yours it was running then gradually stopped. I would suspect fuel delivery. Not sure with your MY were to test for fuel pressure though with mine (4.2 32v) I checked where it connected at the rail, under the car at the filter, and directly at the pump by removing the line. Be careful of course because it will be under pressure.

Architectom

Ok- so I put the car on a vag com and produced a bunch of codes; o2 sensor, misfire, ... Anyway, it was the engine speed sensor, replaced it and had no problems, car ran like a top since. Last night I drove 90 miles, stopped, filled up, 5 miles down the road I started to have a retard where at ~65 I would suddenly have a brief loss of power /no throttle response... Shortly after this happened a couple of times the engine stopped. I was able to restart however there was extremely hard idle, no throttle response, and if I put the car into gear it stalled.

Architectom

Tbelt was supposedly replaced by the previous owner in 2015

Architectom

Next trick, I will test the pump and replace the filter while I was there- I did have a surging idle yesterday.

Architectom

removed fuel filter- fuel drIned from it is brown and has sediment. No fuel feeds from the pump