Q:  What's a "pulsation damper"?  Why do I smell fuel everytime the engine is running?  What caused my engine fire???

9 times out of 10, the pulsation damper is the culprit on these fuel leaks which can turn into expensive engine fires.  1986-1988 Zenki FC3S models seem to be more prone to these pulsation damper failures versus the newer 1989-1991 Kouki FC3S models.  The later Kouki pulsation damper has been redesigned, but don't let this give you a false sense of security.  Kouki FC3S and even FD3S models have also had pulsation damper failures that have caused fuel leaks; the FD3S uses a very similar designed pulsation damper in the 1989-1991 Kouki FC3S.

We are currently trying to launch a recall campaign with the NHTSA in the U.S.  "NHTSA" stands for the National Highway Traffic and Safety Administration and has the autonomy to launch independent investigations of safety complaints on all mass-produced automobile vehicles in the U.S.  If the NHTSA finds a valid safety concern, it can force an automotive manufacturer to trigger a safety recall which will ultimately protect the consumer.  Engine fires can cause extensive damage which can easily cost an owner thousands of dollars to fix; a successful campaign for a safety recall can force the automotive manufacturer to reimburst those huge expenses.  Please follow this link and log a complaint if you've gone through an engine fire or a confirmed pulsation damper failure: 
NHTSA online complaint form

Major signs of a pulsation damper failure are signs of gasoline puddling under the car and major gas fumes smelled when the engine is running.  The fuel tends to leak toward the rear of the engine on the passenger side.  Fuel leaking from the failed pulsation damper puddles on top of the engine right next to the lower intake manifold.  You can sometimes shine a light under the intake manifold and see the fuel puddles by the primary fuel injectors.  After overflowing from this area, it tends to trickle down the back-side of the engine, where the exhaust system starts from the turbo or exhaust manifold (non-turbo).

Here is a pic of the location of the pulsation damper as located on a Zenki turbo model.  Kouki turbo models are similar.


What actually happens in a pulsation damper failure is that the internal (rubber?) diaphram tears.  A long-standing myth is that you can epoxy over the screw that falls out of the Zenki pulsation damper, but this just makes the problem worse.  The screw typically falls out of the Zenki pulsation damper, but it's not a sure sign that the pulsation damper has failed.  Below are GIF animations of the Zenki and Kouki pulsation dampers under operation.  It is obvious viewing the GIF's that epoxying the screw in place causes more strain on the diaphram.  Cranking down on the screw also can cause the diaphram to tear, so even that is not a good idea either.


1986-1988 Zenki FC3S pulsation damper		          
1989-1991 Kouki FC3S pulsation damper
Animated GIF's originally designed by Blake Qualley.


What exactly does the pulsation damper do?  The rotary engine uses a pair of primary fuel injectors that are usually the only pair firing the majority of the time the engine is running; the secondary fuel injectors do cut in under heavy load conditions (above 4,000 RPM) like in WOT situations.  Due to the alternating firing of the primary fuel injectors, there are significant pulsations induced in the (primary) fuel rail from the primary fuel injectors opening and closing alternately.  Theoretically, the fuel rail pulsations would affect fuel delivery at the fuel injectors.  Hence, the pulsation damper was designed to damp these pulsations for a more consistent fuel delivery.

How does this fuel leak cause an engine fire?  Ultimately it looks like the leaking fuel hits the hot exhaust system that ignites the fuel itself.  Puddling fuel under the intake manifold is easily ignitied next, which ends up burning a lot of expensive components under there.  Remember I had mention "thousands" for such a fire?  For an FC3S to go through an engine fire, this is what usually gets burned:
  • fuel injectors - ~$300/each from the Mazda dealer, 4 total
  • fuel injector seals - o-ring, upper grommet, lower grommet; ~$15/set from Mazda dealer, 4 sets total
  • engine harness - ~$1,000 from the Mazda dealer
  • oil injectors - ~$30/each from the Mazda dealer, 4 total
  • oil injector lines - ~$20/each from the Mazda dealer, 4 total
  • pulsation damper - ~$150 from the Mazda dealer
  • oil injector vacuum splitter - ~$30 from the Mazda dealer
  • miscellaneous rubber vacuum hoses
  • miscellaneous rubber fuel injection hoses

    • And that's just a minimal list!  Check the Mazdatrix web page for their write-up on pulsation damper fires.  Once you add up the above list, you're looking at an easy couple thousand dollars just in parts; add another easy thousand for labor, and this whole mess turns into a minimum $3,000 repair job!

    Now that you know about the hazards, what are you options?  Some people will tell you it's a preventive maintenance item that should be change every couple of years - I find the requirement to change a part that could possible kill you due to being a fire hazard is downright wrong.  You could go changing your pulsation damper every other year.  Zenki FC3S owners seem to like to change over to the more failure resistant Kouki FC3S fuel rails (the Kouki pulsation damper is welded onto the primary fuel rail), but this still doesn't totally eliminate the chances of the pulsation damper failing.  We've done quite a few conversion of totally eliminating the pulsation damper with a metric banjo bolt; obviously, this will only work on the Zenki FC3S with the cast aluminum primary fuel rail and screw-on pulsation damper.  Summit Racing carries the Earls banjo bolt/parts, and I have listen them below.  Kouki FC3S owners can only do this banjo bolt conversion if they convert over to the cast aluminum Zenki fuel rails.

    Pics Description Earls part number Summit Racing
    part number    		 Summit Racing
    Price
    12mm x 1.25 banjo bolt and crush washers 997591ERL EAR-997591ERL
    (new part number)    		 $10.39
    Summit Racing - http://www.summitracing.com/


    There's an extensive thread on the RX-7 Forum about this problem:  PD thread on RX-7 Forum






    Questions?  Comments?  Send mail to:  reted(at)fc3spro.com

    02/19/2008