FSD or PMD function

[SnowDrift]

What does this little part actually do? First of all I'm curious, but second of all, I'm wondering due to the project truck I'm working on. What is the function of this part and if there is fuel present at the injectors, then is it safe to say it is working, or is it not that simple?

Lots of questions, I know.

 

[great white]

The fsd takes the signal from the PCM and basically amplifies it to drive the fuel solenoid on the injector pump. It does have a "feedback" function to essentially tell the PCM the injection event occurred and offered in the manner the PCM commanded.

That pretty much is in simple terms.

Essentially, its a signal amplifier.....

 

[SnowDrift]

If it isn't functioning, can there still be fuel getting to the injectors?

 

[JiFaire]

Nope. Well, maybe to the injectors, but not with enough pressure to get Past the injectors. Without the high-energy pulse from the FSD, the DS4 solenoid pump won't compress the fuel down the line.

Without highly-compressed fuel, the injectors won't 'pop'.

 

[Will L.]

Possibly, it can fail and cut all fuel; it can disable certain functions like cruise control; you could have intermittent fuel problems of all kinds. I've seen fish biting, shuttering, die for no reason at any speed,hard start, lack of power at specific rpm,over fueling at idle, and one time it made the truck idle like a top fuel dragster. The "dragster" had been doing that for 2-3 weeks but the driver and his passenger didn't report it because they thought it was cool and got upset when I swapped it out.

The rule of thumb is always have a new one with you. When something weird is going on, suspect ground wires first if not cleaned within last couple of years, and swap pmd second. This is assuming you don't see air bubbles in your clear return line coming off the ip.

 

[THEFERMANATOR]

Basically in the DS4 injection pump, the fuel solenoid in the end of the pump replaced the cable and mechanical throttle assembly internally with a solenoid that opens and closes to do the job of the cable opening and closing to control fueling. The FSD is what powers the solenoid to open and controls how far it holds the throttle inside of the pump open. So the pump cannot actually push fuel without the FSD since without it the fuel solenoid will stay closed and not allow the pump to actually push any fuel.