silverd2

Sorry, but cranking the engine (without outside help, like jumping the pump leads) IS indeed the best way to prime the lines with pressure. Thanks to the engine speed sensor ("crank position") the pump is only running (and always running) while the engine is turning...except for the 1st 2 seconds of ignition on...and that's ONLY on the 1st attempt, unless you reset the system by removing the key, locking/unlocking the car, reinserting the key and trying again.
When all is normal, that 1st and only 2 seconds is enough to assure enough system pressure for a quick start...BUT if you are well below normal residual pressure, it ain't always enough for a quick start.

aduggs

You would be surprised how much gas the pump can move in 2 seconds. Don't ask me how I found out

When everything is normal, no one waits the 2 seconds - the engine fires right up because there is residual pressure. So not sure what you mean by normally waiting the 2 seconds before cranking.

Anyway, it will take fewer cranks if you wait the 2 seconds even if there is no residual pressure in the lines. Agree, cranking is still required.

silverd2

[QUOTE=aduggs;24486948
So not sure what you mean by normally waiting the 2 seconds before cranking.
[/QUOTE]

Semantics...Rearranging my words changes the meaning a bit...the above is not what I stated.

The point being: If the residual pressure was down to .5 bar just after the running pressure test, that's a pretty fast leak. So trying to start this car, whether he waited the 2 secs or not, it was also leaking off pressure while priming. The proof? It wouldn't start until multiple cranks = apparent slow build up of pressure.

Years back, before I figured out the problem, I added a fuel pump button to a 77 Rabbit that had a bleed off leak at the check valve near the pump (replaceable). Actually only took a few minutes to put in a momentary button under the dash connected to the fuel pump relay...I had to be somewhere. I used this for a while and you could actually hear the point that pressure was built to the point of letting the car start...free spinning to a quiet hum. Even after being parked just a half hour or so, it took a few seconds to get starting pressure. I know...different car, different fuel injection system, but...just sayin.

Cheers

clintmeyer

Well, in the last 2 days I have only had 1 long crank start. It seems fine this morning. I doubt that the Techron is working after only 6 miles on it, but we shall see.

I am going to replace the plugs and run through this 1/2 tank, put in premium and another bottle of techron and report back.

I did call the mechanic and the front desk guy said they had their top guy on the job and that's why it was $250 of diagnosis so he is sure the leak pointed towards the pump ($1900 repair) rather than dirty injectors ($5 repair) but he would ask the mechanic what process he used and let me know.

Thanks for the help.

aduggs

Sorry, didn't mean to misrepresent your comment - just how I understood it. But a question arises: does the pump ALWAYS run 2 seconds with key on? I was under the impression that the pump will run only as long as the pressure is low. So normally the pump would only take a fraction of a second to restore correct pressure because a normal system would have virtually no bleeding.

silverd2

No problem..really

If you don't start the car, it will run the same 2 secs (approx) only on the first try. I've played with this before to satisfy my curiosity and help answer a past question. Seems to be on a set timer, to cover any normal start-up (slow or fast key turner)...obviously, with everything working perfectly, you don't need anywhere near a full 2 secs or any time at all(?)...just makes sure the pump is running a hair before the engine speed sensor takes over sending the signal.

Prospeeder

I dont see how dirty injectors are a 5$ repair. Sorry, but the over the counter "injection cleaner" stuff is a complete scam, there hardly any more "solvent" than gasoline, which is a solvent, and is full of cleaning detergents. If you injectors are truly sticking open from debris cooked on, then removal, and sending them to a FI re builder and have them repaired and sonic blasted is the fix, not some 5 dollar bottle of fix all. God 250$ for diagnosis, thats such a ripoff. Just have them put a pump in it, if it doesnt fix it, then dont pay for it. Why in the hell is it 1900$ for a fuel pump again, I just did one in an A8 and used a VDO/Siemens pump and the bill was like 700$.

Kris Hansen

Before replacing anything else, have you replaced the coolant temp sensor? When it does finally start, is it smooth and normal, or does it cough and sputter a little?

twentysevenlitres

The D2 A8 only primes the fuel lines with a 2 second burst on turning on the ignition with a cold start. The only other way to run the pump is during cranking and with the after-start relay - its a safety feature.

My hard start proved to be a torn high pressure fuel line within the pump housing itself.
I replaced the pump as well (World Car Parts is correct source for Siemens VDO pump).
Caused me some frustration until I learned the "trick" of how to position the two halves of the assembly!
The loss of pressure can only be a few things - injector leak, fuel line leak, pump non-return valve (non serviceable item, replace pump) .
The high cost of pump replacement is because Audi only sell the whole assembly for $1000!

Daumants

Techron has worked on an Audi and a Saab... the only way to tell that you have dirty ionjectors is when it runs rough at low RPM (starting and around town) but is fine at high RPM (highway)