Really strange idea of the day!!!

[jim_in_dorris]

I was talking with my son tonight, and according to him, all the new toyota's, and dodges pulse width modulate the fuel pump itself to control fuel pressure. If a 747 class ecm had a spare PWM output, is it possible to write a routine to control fuel pressure based on load and rpm? No more adjustable fuel pressure regulators. Just putting this out as a discussion item. What does everyone think. My 355 build will require #80 injectors at 20 psi or #61 injectors at 34 psi. How nice it would be if you just told the pump how much pressure to supply (like a vacuum referenced FPR except much more accurately).

[gregs78cam]

A few years back when I was working on a friends 300ZX (the one in my avatar) we learned that the fuel pump in that was controlled by a module. We ended up bypassing module control so it would put out constant pressure. I don't know if it is similar to what you thinking, but it sounds possible.

Just did a quick search, and it seems like the module runs the pump at 2 speeds depending on load. So yea it would be something to look into. And you meant '7427 right?

You would also probably have to give the PCM feedback on fuel pressure. And you would probably have to come up with another way to bypass the excess flow(like an inline restriction on return), or just dead-head the TBI.

[1project2many]

Your son's correct. The strategy today is to use a returnless fuel system which reduces vapor formation in the fuel tank with pump pressure controlled electronically. Although you could implement a non-feedback based pump control strategy you leave yourself open to problems if actual pump output doesn't match the model used for development. Better approach uses a fuel pressure sensor. Once you have fuel pressure as a variable controlled by ecm you have a lot more dynamic range for a set of injectors so larger cams and boost will become easier to tune from idle to full power.

[EagleMark]

Don't think there is extra PWM circuit on 1227747 which I believe Jim runs. But if he did a 16197427 conversion that does have a PWM circuit for the E trans which could be first part of the puzzle?

[RobertISaar]

keep in mind you wouldn't be able to directly run the pump off of the PCM, way too much current draw. you would need to setup a solid-state relay or some transistors to handle all of the load.

[jim_in_dorris]

Okay, after reading the replies, and thinking about it, I came up with the following;

Robert-- I wonder if the fuel pump relay can handle PWM

I was thinking about setting the fuel pressure regulator at a maximum pressure, then if something goes wrong, it won't go over that pressure. If I was to use say an EP377 pump which IIRC is rated at about 45 psi, I would set the regulator at 35 PSI, then build a table to drive the fuel pump. I would most likely use multiple settings like:

idle -2000 rpm 33%
2001 - 3000 rpm 66%
over 3000 100%

Then include 3 different values for flow rates depending on my injectors.

Having a closed loop feedback system would be the best route, but I am trying for a minimalist approach here at first. If that doesn't work, increase the complexity a little at a time. Also, if the FPR looks stock, it's one less thing for the smog nazis to object too.