951North

Okay, so it all started with.... sound familiar?... an annoying misfire under boost, turned out that was improperly gapped plugs. However during investigation I found gasoline in my KLR line. So I replaced the FPR because it's a lot less expensive than the FPD. Still get fuel in KLR line. Next I notice fuel seeping on the supply hose into the FPD. Replaced the supply hose with one of Lart's lines. At the same time I delete the FPD because I've determined it pukes Gasoline out the vacuum port. Fuel line works great so far, however I've noticed what I think to be one of the reasons for the FPD. There's other threads out there why you can or shouldn't delete the FPD so I wont go into that. This is my observation. At idle there is a pronounced NVH (noise vibration harshness) in the cabin now without the damper in place. Which among other performance aspects is probably why Porsche put a Fuel Damper in the FI system. Under the hood there is no noticeable difference audibly. If you touch the fuel supply line you can feel a pulse, however when you touch the fuel rail there is no pulse felt. I suspect the pulse felt in the fuel supply line is transmitted via the hard line to the cabin. In the near future I will look into getting a FPD likely from Radium or the like and plumb it inline on the new fuel supply line. As an aside, I deconstructed both the FPR and the FPD, internally they are very similar, the FPD has a port drilled into the side of the supply tube (inside the damper) and a slightly different diaphragm seal. The springs and diaphragm seem to be identical.

odonnell

On these cars, all 4 injectors are fired at the same time (batch fire). It makes sense that the system has an accumulator. That pressure wave can cause weird pressure spikes/drops at certain frequencies.

Droops83

Agreed, get a new dampener. Porsche didn't install it just for fun. Sure there are people who have run without one "without issues," but do you want to chance a fuel delivery issue at high load due to fuel pressure fluctuations?

Voith

So that's why 968 didn't come with one as it fires in sequential mode..

951North

Here’s the deconstruction of the FPD and FPR if anyone is interested.

Humboldtgrin

I’m pretty sure two injectors fire at the same time not all four. That’s why there are two fuel injector drivers in the DME. Injectors 1/4 and 2/3 fire in batch on intake and power stroke. When the injector sprays fuel on the back side of the closed intake valve on power stroke it helps cool down the intake valve and atomize the fuel, then on intake stroke the injector sprays again. Also you want to install a FPD as soon as possible with batch firing. FYI, if you changed to multi port injection then you wouldn’t need the FPD.

MAGK944

Fixed it for you

Humboldtgrin

My apologies, thank you.

Tom M'Guinn

Hmmm... check that... the two injector pins on the DME (pins 14 and 15) are connected inside the DME, so all 4 injectors are running off the same signal. Not sure why they used 2 DME pins, but presume it was to keep the wire gauge size down in the harness.

MAGK944

+1 all 4 fire at once, I’ve visually seen this with the injector rail off the intake.

Humboldtgrin

I was wrong on the cylinders batched together. The Motronic units have 2 injection outputs, and the injectors are arranged in 2 "banks" which fire once every two engine revolutions. In an example 4-cylinder engine, one output controls the injectors for cylinders 1 and 3, and the other controls 2 and 4. The system uses a "cylinder ID" sensor mounted to the camshaft to detect which cylinders are approaching the top of their stroke, therefore which injector bank should be fired. During start-up (below 600 rpm), or if there is no signal from the cylinder ID sensor, all injectors are fired simultaneously once per engine revolution.[5] In BMW vehicles, this Motronic version did not have a cylinder ID and as a result, both banks of injectors fired at once.

Tom M'Guinn

I gather you are talking about something other than the 944 turbo? The Montronic units on the 951 fire all 4 injectors at once, regardless of operating conditions. Although the DME has two pins for injector outputs, they are tied to the same driver inside the DME.