Unseen Pics: Inside the Fuel Pressure Damper
 

Just had a bunch of trouble with my fuel pressure damper and when searching I found that I could find no online pics of the inner workings....Until Now!!!!

Yes, here they are.

Oh, don't think of ever rebuilding this as it's very difficult to get the two halves apart, even when not concerned with preservation. And then the rubber diaphragm is sandwiched between the two halves so that is an essential seal.

Further info: The diaphragm has a metal center which is pressed against the the fuel inlet so any fuel flowing in will push against the diaphragm and of course any pulsations will be dampened.

Enjoy:









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https://cimg9.ibsrv.net/gimg/rennlis...4d98e8a65b.jpg

Cool photos.

Nice, what did you do about a replacement? Where did you get one? The only place I can find a new one they want over $400!

in EU they are also 300€ a piece. ordered from US with that price but a kit of two, oem. :)

I see pelican parts has a Bosch unit in stock for a reasonable price...never mind, when you try to buy they are out of stock.

Parts geek. Not the best prices but my experiences with the company have been OK. Check for your model/year
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Going through the FPD dilemma right now as I have one leaking...

QUESTION - what is the role of a vacuum line in this assembly? I don't understand how it could affect damper performance in looking at the design...I'm thinking that the vacuum line may just be there to remove any fluid that leaks past the diaphragm so it doesn't fill up and then hydrolock or cause a significant leak of fuel. Is that it?

@Jim H. : Not an expert by any means but I tried to do some learning about this when I went through a similar expensive-as-all-get-out replacement of the damper on my 928. From what I read, having the vacuum line present and attached makes it a rising rate damper system. If I understand how things work correctly, the vacuum on the damper will compress the spring and diaphragm, which should help to compensate for the increased fuel flow and overall vibrations/dampening needed as the engine increases RPM. Having the vac line attached also helps with general safety in the case of a failed diaphragm, as you point out.

Somewhat interestingly, the damper that I used to replace mine in the 928 explicitly said that the vacuum line should NOT be attached, and that a line should instead be run somewhere to dispose of the fuel safely away from heat sources. I put on a vacuum line because there's not good place in the engine bay to do that on the 928 (that I felt comfortable with).

Just my thoughts.

Cheers

Thanks. I guess I underestimated the strength of a vacuum through those tiny lines...but it does make sense now. An increase in vacuum will put more tension on the rubber diaphragm which should have an effect on the rebound and distention properties and therefore affect the dampening effect.

Fuel damper
 

Most engines run about 18-19 inches of vacuum at idle. As the RPM’s go up the amount of vacuum decreases. I’m sure that someone out here will have a graph showing that the amount of vacuum available at such and such rpm will be the inverse square of the piston travel in feet per second, or something. (LOL). It’s really due to the reason that the valves are open for a longer period of time as the rpm goes up. Hence, less vacuum. So, that must be one special spring in the damper to accommodate all of this as the vacuum level goes up and down. WOW!