So, Ive been told somewhere to understand that my S4 will only start firing the fuel pump after three revolutions of the engine via the flywheel sensor, when you start it.

Rogers SE here..will fire up after 12hrs sitting, simply touching the key it seems.

Now, of course I dont know what the fuel pressure is after 12hrs, but..I would be shocked if it was still at 50psi, and it can start that fast and run waiting for the pump to come on.


??

 

I don't recall seeing a 3-revolutions requirement to set the fuel pump relay. Must be related to when the EZK decides that it "knows" the position of the crank as it rotates, but that should take no more than 1 revolution for the CPS to 'see' the key/missing tooth pass by. Or does it look at the Hall sensor on the cam too? That could mean up to two cranskshaft revolutions. Someone more knowledgeable than I...

My old CIS cars would start in a fraction of a revolution. Fuel pressure as soon as the key goes to ON position, fuel flow as soon as airflow was detected at the intake. Also easy to flood if it didn't start quickly, and was somewhat generous with fueling at most part-load conditions.

 

I don't think that is accurate. I can tune my car to start with just a bump of the starter if I increase the fuel cells on the starting map, or I can have it crank for 30 seconds by lowering those cells.

Dan
'91 928GT S/C 475hp/460lb.ft

 

That's an interesting observation Dan.
Since I found it easy to flood the warm (room temperature) engine, I lowered the cranking pulse width from 4.2 ms to 3.2 ms. That cured the flooding once and for all but did not reduce the "delay" it takes to fire up. What pulse width did you set for "instantaneous" start ?

Kurt
____________
90S4 satin black metallic
OC charter member

 

Interesting - both the 87's I've owned take a few more cranks to start than my '89. I put it down to different compression, but have no real clue as to why exactly (89 is actual 10:1 compression, up to mid-88 have different shape pistons with a bigger dish and around 9.3:1).

SE has the high compression pistons.

 

The '89 I had for nearly 7 years, that was a to, from, and on track car ALWAYS started within the first revolution of the engine, even if it had not been started in a month. On the other hand, the '94 that I still have seems to always require 2+ revolutions to start - even if it's only been a few hours since last operated.

I'd love to get the GTS to start like the '89 did!

Gary-

 

I am not sure how fuel supply could be the variable in the "delay".

From what I have seen when the fuel system was opened and not bled completely or when the Temp II doesn't work correctly, the normal result is that the cylinders will catch on more or less one by one during cranking.

During the normal "delay" there is nothing and then all fire at once - and as Gary said, regardless of how long the engine car shut off.

Kurt

 

On my 1990 S4 the fuel pump runs for a fraction of a second when i turn the ignition on. Then the pump does not run again until the engine is cranking. I suspect this initial fraction of a second of pump running just with ignition in the on position is enough to pressurize the system so that it 'catches' as soon as the starter turns the crank.

Starts instantly after a month or more of non use.

Maybe differ ent fuel pump relay electrics in the relatively later cars.

Much conjecture on my part.

Dave

 

Dave

strange, if it varies between MYs, our 90s should behave in the same way, then?!
Maybe it's what makes the cars individuals, just like different owners need more or less time to get out of bed in the morning

Kurt
____________
90S4 satin black metallic
OC charter member

 

Dave, what you are hearing is the PSD pump priming its self.

 

Hmmm I have a 91 brain with an 87 block. 3rd turn and on, always. ruh-ruh-rev.

 

Reading through all the 928 literature and Probst book on Bosch fuel injection about the LH, there is no mention of any delay. Simply that the pump is energized by the ignition switch in the START position and the pump will run for a few seconds, stopping if it does not get a signal from the CPS that the engine is turning above a certain RPM (indicating it is running).

The check valve does not retain fuel pressure forever. The test spec is 0.5 bar loss in 30 minutes. Most I have tested barely make that spec if even that. So, it usually takes some time (a few seconds) to build up fuel pressure.

Most of the time my car starts after a few cranks. Occasionally it has surprised me and started instantaneously.

 

I think that what Bill says makes sense. If your fuel system holds pressure well it starts quicker.

Start the motor after a fuel rail outage and it takes a few good cranks to fire the motor. I am used to the motor firing up after a couple of cranks or should I say what I perceive to be a couple.

Regards

Fred

 

Hi Sean, maybe. Next time I'm home I'll get someone else to turn on the ignition while I listen for fuel pump or PSD pump energising. Could swear it is fuel pp, but I've been wrong before!

Dave

 

FWIW my 83 CIS car does NOT run the pump at ignition on - having tested the pump by jumping the relay, I know what the pump sounds like. All the Rover and L-R cars I have had ran the pump briefly at ignition on - all Bosch EFI systems, both L and LH.
jp 83 Euro S AT 55k