jpitman2

When I was in the hydraulic hose industry I was told there a NO, NONE, ZERO metric AC connectors. Is the OP sure the rubber is not just a sheath over a metal pipe? I seem to recall rear fuel pipes with rubb sheathing...
Fred said "10mm hose indeed has an ID of 9.5mm" - a rubber hose with 0.5mm walls ? Or is the OD not really 10mm, its just the name of that product?
jp 83 Euro S AT 57k

thepurpleblob

So (update)... I've temporarily replaced the rubber pipe under the rear wheelarch with a new bit to keep the car mobile. But it needs fixing properly.

Worse... I've realised that the fuel accumulator is completely missing. So it appears that somebody has (presumably) bypassed a leaking accumulator and the associated piping with a length of rubber pipe. There's clearly a bracket where it once was. Great!

The car starts and runs fine but needs a few spins before it fires. I suppose, at least, it gives the oil a chance to get around the engine before it fires

I have some thinking, research and sourcing bits to do.

FredR

Before you do anything it might be useful to understand why your model needs [needed?] a fuel accumulator and later models like mine do not.

As I understand they act to maintain constant pressure and dampen pressure spikes in fuel injected systems but why your model needs one and mine does not I have no idea as I have never studied your fuel delivery system. i assume your model has pulsation dampers like my motor has but i do not know that for a fact.

thepurpleblob

Well... that's an interesting point. I have no idea if it definitely had one. The parts diagrams from my year show the acumulator. From a small amount of reading I assumed that they all had one. Mine is the 16V "twin distributor" engine and does indeed have the pulsation dampeners in the fuel rail.

FredR

I suspect that Porsche engineers when developing the S4 back in the mid 80's and possibly armed with better design tools concluded that the accumulator was doing nothing except adding to the build cost and dropped it.

Move the clock forwards 30 years or whatever and then John introduced ST2 and its analytical software companion "Sharplotter" developed by Jim Corenham and al of a sudden mug punters like myself could see what was going on inside the engine as a consequence of the engine management system. Sharkplotter takes the measured data and plots it for both the EZK and LH operations and each data point is colour coded to reflect the AFR measured for that point. Lo and behold the S4/GTS systems exhibit a pronounced "leaning out" at three different engine speeds as I recall- one of them quite pronounced at around 3.9k rpms or so- this is a pure natural frequency resonance effect where the shock waves coincide with the engine speed. The trouble is that the problem happens over a very narrow band engine speed wise and even though each operating cell in the maps covers a range of engine speeds the disruption can cause issues. Richening the mix in that cell helps a bit but then all operating points outside the troubled band are then running overly rich.

I am guessing here but maybe deleting the accumulator made the unwelcomed difference we see and without such your motor will also experience this mystical leaning out condition leaving you with a flat spot. Thing is if you have never had your motor running the way it left the factory chances are you will not spot the negative aspects of not having such. Maybe Porsche were able to improve the damping characteristics with the S4/GTS such that they felt the residual negative impact was not worth the bother of trying to deal with it.

thepurpleblob

I think you've just placed enough doubt in my mind to forget about the damper. It works and, to me, it runs well.

I'd rather spend money on the rusty bits. Of which there are - shall we say - some.