TECH: The Fuel Pressure Dampener

[Cp1]

Well folks i was puttering around under the hood of my car and found a little fuel while feeling around with my fingers sure enough the top of the fuel pressure dampener was wet.

So seeing as i was now taking it off i thought i might as well take it apart too and see just how it functions. sorry for the crude drawing i dont have pics but it is just brazed onto the fuel inlet pipe and is comprised of only 5 components.

1: the upper and lower housings
2: Cup or 'piston'
3: spring
4: Rubber Gasket
5: Rubber Nipple



1st the purpose of why its there, it is basically there to reduce small variations in fuel pressure in your line by using the spring and cup to add a small amount of pressure when fuel pressure drops. such as when your secondary injectors first kick in or when you quickly boost up.

The benefit of the FPD only lasts a fraction of a second just long enough to provide a little extra 'kick' to the system. it does not regulate pressure nor does it guard against leaning out. if your pump is weak or insufficient the FPD will do nothing to protect you from blowing an engine.

the whole unit itself is just brazed onto the pipe which has two very small holes in the pipe that allow fuel into it. after discovering its construction it is easy to see why these fail at such an alarming rate.

the gasket inside of it is just crimped on where the two housings are bent over each other and then it simply 'rests' on top of the cup the spring it self is what seals it to the cup. this is where i noticed where it failed. the spring being a sharp or even rounded piece of metal that pinches onto the gasket over times pinches right through it in places thus allowing fuel into the upper chamber where the spring is housed. there is a little rubber nipple there to prevent any fuel from escaping the unit but it is also sealed up by the top of the spring to the upper housing. thats it!!! if your fuel pressure dampener is on the way out i have devised a very good test for you.

Turn the key to the on position to prime the fuel pump, you will have to have your upper intake manifold removed for this test however using a screwdriver but nothing too sharp, with your fuel system pressurized push slightly onto the rubber nipple if any gas leaks out (like mine did) you will need to replace or remove it altogether.

MY SOLUTION: after seeing how it is made and really what limited benefit it provides i opted to settle the argument for myself once and for all, so i took the fuel pipe with the now removed FPD and welded up the two small holes. i pressure tested my new "straight-pipe" in a bucket of water, re-painted it and have put it back on. One more thing i wont have to worry about on this car.

The debate over whether to remove or leave it on may still rage on but ive now made up my mind.

[Prometheus]

A few things.

It would be interesting to see fuel injector transition maps of a stock fuel delivery system before and after F.P.D. deletion.

It would nice to compare those transitional maps to maps of a modified fuel system. I assume the transition between larger injectors would be more radical due to their larger volume.

Steady fuel delivery means more perdictible tuning.

I'm sure a faulty F.P.D. has been the source of tuning headaches in the past, and will continue to be untill an alternative has been brought to the table.

Since the original design is pretty lame, we should devise a plan or test to manufacture an aftermarket F.P.D. or see if possibly adding more than one F.P.D. would help smooth out the primary/ secondary transition, if there is even a problem at all (which I'm sure there is)

[Cp1]

Originally Posted by Prometheus

Since the original design is pretty lame, we should devise a plan or test to manufacture an aftermarket F.P.D. or see if possibly adding more than one F.P.D. would help smooth out the primary/ secondary transition, if there is even a problem at all (which I'm sure there is)

I really dont see even an aftermarket option being a cost effective solution to a non problem. if your fuel pump is in good working condition and your pressure regulator is working properly you should not ever have such a condition that would call for the dampener. the miniscule benefit it may provide in my belief under transition is not worth the cost or development of a bigger/better unit, when simply plumbing your fuel system in "parallel" as opposed to in "series" would eliminate the need for it altogether.

I understand why mazda may have put it there in the first place but its benefit is very little on even a stock fuel system. sooner or later it simply becomes a hazard not to mention the most restrictive and weakest part of the whole system.

Btw since i first wrote this article my FPD has been eliminated and i have noticed no difference whatsoever. there is no lean or leaning conditions during injector transition that even my wideband datalogger could detect. I have no data suggesting that eliminating it has somehow affected any performance negatively or anything else for that matter. there is no problems, no difference i can tell and best of all no worries since i took it out.