Vin

Just to expand on my earlier thoughts about fuel varnish...

When you apply power to the pump, it will quickly heat up if the motor is seized. Do as Wally suggests and reverse the power. You'll probably find that no amount of effort will restore the pump if varnished fuel has seized it.

It's never to late to answer, i appreciate all reply.
As i said before i'm not in the hurry.
I will change the pump and not takes chance.
A friend of mine in montreal who have a 928 got one brand new.
He baught it last year but not fit on his car.
I look at the part number he gave me and fit on 1987 S4, i will take it tomorrow.
Got a spare fuel filter when i baught my S4 black.
I will buy fuel line.
I read around internal fuel pump this after noon and i anderstand that i must have wires to power it.
On Porsche plan «928 Fuel System Parts» i see internal fuel pump or strainer.
No wires on the car so i have a strainer on the fuel tank.
When i empty the tank fuel, the flow was very fast, tank is 3/4 full so it seems not blocked but do i have to dismont the strainer to clean it or it's waste time ?

Sounds like you are lucky to have a strainer. If it were me, I'd replace the pump & filter, fill it up, and give it a go. If it doesn't start, my next suspicion would be frozen injectors. I had this problem when waking an '85 from a long slumber. 6 of the 8 injectors were frozen, so I replaced them with working injectors from a 5.0 Mustang. I am not sure if your car used the same injectors. Just thought it was worth a mention.

I found my spare Fuel filter. It's a KL40 Mahle part 928 110 253 03.
If i'm looking in the PET, the part is 928 110 253 06.
Can i use mine, is it good ?
When i look at it it seems the same but the old one is wrote KL21 !