Hello good morning everyone, I am having a problem with the first start of my s4 87, I describe what happens, I have observed what happens when the fuel rail pressure drops in several hours or from one day to another, the question is that when I am going to start it I have to insist more than necessary with the starter or cut off the ignition with the key and that is when I hear the fuel pump running, then after that and already having pressure on the fuel rail it will start without problems, any ideas? Thank you very much

 

The correct fuel pressure in the rail is needed to get the thing to start. If you do not have fuel pressure it will not start- plain and simple.

If the fuel pressure has been lost in the rail it will typically take about 5 seconds to get it there. Some examples hold pressure well, some less so and then there are the ones that have an issue- a leaky injector, a faulty check valve on the pump or maybe a faulty FPR or dampers. When all these elements work as they should then the motor will usually fire up promptly assuming there are no other issues lurking like faulty earth connections or poor wiring harness condition.

 

So is it normal 5 seconds of starting from one day to another?

 

If the rail is not holding pressure and going completely flat then yes- it will take several seconds to fire. A system that is well sorted will take a second or two of cranking to fire up

 

I have checked the rail pressure and it is correct, but when I start it overnight or lower the rail pressure after several hours it takes approximately 5-6 seconds, I understand that it is correct, any video of the process?
I understand that starting is not practically instantaneous as in current vehicles.

 

As the system cools off some degree of pressure drop is normal- the WSM indicates what pressure drop can be expected and then it should more or less flat line and thus hold until the car is next cranked. If there is a leak the pressure will completely flatten and may even drain down partially or maybe even totally and thus if such happens it takes a finite amount of time for the system to be flooded and correctly pressurised. Sounds as though you should be looking for what is bleeding pressure out of the rail.

On the positive side, at least you managed to get the thing firing up which is more than some manage first time.

 

The system pressure is correct both at idle and with the relay bridge of the engine fuel pump stopped, there are no leaks since the pressure is stable and practically does not drop after 20 minutes.

 

The fuel pressure will always drop over time. Until it pumps back up, the car will not fire. My starting procedure has always been, turn the key to ON and listen for the pump for a couple seconds. Do that twice and then turn toSTART position. Car always fires right up. Don`t compare the older 928`s to a modern car when stating.

 

That would be the correct boot process? Wouldn't it be harmful to the starter?

 

The 928 s4 does not carry a fuel preload system before starting is not it? So what is putting the contact in the on position? It is no use as I understand.

 

Given your well-described symptoms, there is nothing wrong with your car.

 

Early cars have a different fuel pump relay. They have a 'priming' feature that runs the fuel pump for a few seconds when the key is first turned on. It pressurizes the system so that the car starts quicker.

Your S4 does not have this. The LH needs to 'see' the motor turning from the crank sensor before the fuel pump will kick in. It then has to build pressure before it will start up.

For the fuel pressure to leak down overnight is normal.
For it to take 5 sec or so of cranking to fire up after the car has been sitting overnight is normal.

 

Yep. Your fine. WSM test for fuel pressure is that is holds for 20 minutes. Overnight, your car is not expected to hold pressure. My S4 takes 3-4 seconds to fire up after sitting overnight.
On a side note, the CIS and early L-Jet cars fire up with a quick flick of the key....because the pump comes on as soon as you turn the key, as noted by Wis. Joe.
-Jason

 

Ok, thank you very much for the clarification and I remain calmer, there would be the possibility of incorporating the fuel pre-system of the previous models? I suppose that in that way, by facilitating a faster start, the starter will be less punished.

 

I have talked with owners of other s4 and gt with a more immediate start, why that difference?. Would it be possible to adapt the first 928 relay for a more immediate start or do something?