Ford's answers to the NHTSA 6.7 Investigation

BenK wrote:

Can one assume that some of those shock waves enter the fuel pump piston chamber
while the one way valve opens into the common rail feed tube?

Diameter of the injector tubes is very small relative to the plenum / common rail, which in turn is connected by a slightly larger diameter tube -- have to wait for rick to post some pics to estimate diameter.

I can't speak to the shock wave --- but do note that one of the Bosch? patents is for a way to isolate the pump from engine heat (and possibly with that, vibration) as well.

• What does that do to the piston?
• The cam and follower?
• The PSI inside the piston chamber?

Anyone know the characteristics of those piezo injectors? Am assuming that there
is little to no hysteresis with their open/close cycle...or am I all wet there?

I have no info on that one.

Good that there is no return on this system, as think any return would just add
another layer of potential wrench in the frey


There is a pressure relief / sensor on the pump itself that lets fuel return to the fuel tank --- also note the Ford patent re fuel cooling in common rails cited above.

I cannot tell if the RHS common rail have a return / or just a sensor at the end.. it looks like a connector to a electrical device.


If/since no return, then it MUST have some sort of accumulator...otherwise that
piston pump would kill itself in short order pumping into a fixed volume chamber
with 'some' relief via injectors...but...it must not be, as then the PSI would
fluctuate too much.

The more I think about it, it has to have an accumulator or some compliant
reservoir (accumulator) somewhere...maybe they are using some rubber/synthetic
hose as the accumulator?

AFAIK, the hoses are metal, but we don't know what s inside the common rail and injectors.

Could there be some shock absorber in there?


Anyone know the injector working PSI range? vs the common rail PSI range? This would provide limited and a guesstimation look at their
hysteresis. On that, how does the injector close?

Can one assume that the common rail/accumulator HAS TO HAVE HEAD ROOM OVER THE INJECTORS?

To keep this from going too oblique...this train of thought has to do with the
shock back-feeding to that one way valve and then the pump piston

It would be an interesting simulation to see at what frequencies / rpm do standing waves get set up inside the system and can feed back to the pump piston.


Think that it is cavitation inside he pump piston chamber that creates bubbles
(either or both micro gaseous bubble, H2O micro droplet) that then tears apart
the softened DLC (via organic amines). That then has the DLC pit/flake/etc to
have the piston go metal on metal (those bubbles will have voids which has no
lube).

If that is the process, it would take time to work its way through --- and it is not really just a lubricity issue in fuel, but cavitation etc. That would explain it getting through durability testing on reference fuel (with less water / contaminants).


The injector/plenum/common-rail shock waves working on the one way valve only
exacerbate this or is an accelerating catalyst for this mess.

A very interesting, complex hypothesis.

Summing up your theory:

Shock waves / standing waves are set up at certain rpms / frequencies that can be transmitted from injector to common rail(s) then to pump via fuel line, to the valve and then onto the piston / pump chamber, weakened DLC coating (with amine reactivity) result in ablation of coating at far higher rate (as pressure pulse transmitted would exceed pump spec pressure).

Note your theory would not create an issue at the normally regarded point of maximum stress, which is the cam lobe / piston contact area.

Intriguing.