For fuel injected pumps, are they internally pressure regulated to some degree? Do they run continuously, or switch on/off during operation?

I've installed the external pump and adjustable pressure regulator on the 65 vert project. I haven't run the fuel system yet, and am curious as to what I'll get when I finally turn the key to the On position. My recollection of fuel injected cars is that the pump should kick on, build pressure, and then turn off until that pressure is bled off. That would indicate to me that it has some sort of internal regulating capability.

 

good question .. my stock unit on my truck seems to stop after it builds pressure .. i turn on the switch .. hear a few seconds of pump buzz then it loads up and stops ..

 

The pump runs continuously. What happens when a key is turned on in a Stock Fox Mustang is the pump is turned on for a bit to pressurize the system. It then turns back off, after a second because there is no oil pressure. Once the car fires and oil pressure comes up, the pump is fired up again.

The fuel continuosly flows throughout the system. No matter how much fuel is used, the flow is constant. It is the flow of fuel that cools the pump.

Regulation is done by the fuel pressure regulator mounted at the fuel rail.

With aftermarket pumps, it just depends. A Holley red does not need a regulator (good carb pump) while a Holley Blue comes with a regulator when you buy it. Then you must decide whether to do a deadhead, or a return line.

Does that help?

 

I know the newer ones have the ability to increase their pump amount to a certain higher percentage of their max duty cycle most times during cruising they only use about 10-12% of their max duty cycle. at least that's the way I understand them.....but this is on newer mustangs, the old ones pumped full time all the time and the regulator would close off the return line a set amount to increase your fuel pressure.

 

Phil, you are speaking about the pumps that came on the 99+ stangs with a returnless system. They vary voltage to the pump based upon fuel needs determined by the FPR on the rail.

They are a different pump than the return pumps, in fact if you install a return pump on a 99+ stang it will burn out in a short time.

 

that's what I was saying, on the newer model mustangs....the older being the return style....or was it not making sense the way I said it?

 

Now that I'm wiring the A9L computer that came with the injection system, I'll have to open a debate here. I don't believe the A9L has any knowledge of oil pressure. There are no interfaces between the computer and the oil pressure sender or the gauges. It certainly knows RPM. I would guess it's looking at the RPM signal to control the pump.

But you helped in answering the question. When I turn the key, it better run for a second or two and shut off. When I start it, it should kick back on and stay running as long as the car is running.

 

Do you have a Fuel pressure gauge?

 

I didn't know how "new" you were talking about. It's not so much as increasing the pumps ability or duty cycle as a function of voltage to the pump.

Anyway, you were correct in your thought.

 

Nope, no debate. I was mixing the A9L and a regular electric pump that should be wired into the oil pressure switch so that there is oil pressure or it shuts off (think accident).

I am not a 'puter guru, but I can sure find out. I think you are right that there must be some sort of "RUN" indication to turn the pump back on and have it stay on.

 

Thanks Ralph. The A9L system (or at least the custom system I'm installing that uses the A9L computer) comes with a separate inertia switch to turn everything off in case of an accident.

I'll let you know when I'm ready to fire this thing and we'll make an event out of it.

 

Yep, on the Fox bodies, that switch in in the rear.

I am so wanting to see/hear that DFI unit.

 

Sounds interesting. I'd like to be there for the firing up, Maybe I can bring the seats over then as well.