Questions about 1995 F-350 with EFI

General Discussion
#15

Please explain more about the PWM… I am currently building my first Gasifier and not ready to install… I am open to all suggestions as to how to harmonize it with a 1995 Ford EFI gas system

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#16

I have allways used a small rheostat but if anyone needs info on them there is plenty on the site . I just searched ( search icon top right of the page ) and there are about 50 threads that mention the pwm.

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#17

This is what I am using

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#18

So Michael Gibb would you put both the injectors and the fuel pump on the rheostat or just the fuel pumps?

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#19

Just the fuel pump.

When the fuel pump is turned off the engine dies in 1 second so there must not be much fuel getting sucked past the injectors.

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#20

So if I mount the rheostat right next to the switch that controls the front/rear tank switch and wire it into that switch… Then I’m in business and all I need is to build the Gasifier and hook it up? Thank you for the information very helpful

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#21

My son is a master Ford mechanic. Using the assistance of a $100 95 F250 wiring book from Ford he found a wire on the right side under the hood to splice into.

I believe the fuel tank selector switch only operates a mechanical valve and the fuel gauge and pump switches, but is not the power to the pumps

An easy test would be to open the fuel tank switch and listen to see if the fuel pump runs when the key is turned on.

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#22

You might be able too find the fuel pump relay if its easyer too get at and find book wire you want.

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#23

So I should have a switch that turns off the power to the gasoline pump, and the other line through (pwm) rheostat, which always controls the pump otherwise.
Excuse the hijacking Dave

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#24

Yes the power switch is in the same circuit as the PWM.

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#25

Thanks, Michael.
So you either have the pump switched off or control which flow you need for the moment

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#26

Hi Michael.
I was going to plug in my pwm, but did not have the schedule with me.
How did you connect your pwm?

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#27

Jan, there’s a good explanation by Carl Zinn and others, starting at post 270 on my Mazda thread.

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#28

I have one that Michael @mggibb recommends, this 4 pins, so the connection is different.

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#29

We use a 3 pin, If I remember correctly on the 4 wire you can’t use chassis ground on the motor side, ground has to connect directly to the fuel pump.

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#30

Al, I use the 3 pin too but shouldn’t the fuel pump be grounded already and fed only by a single +12V wire regardless? Or am I missing something?

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#31

Hi Jo, There’s something different on the 4 pin models. On here some where we talked about this, some one came up with a work around for the 4 pin model, because they don’t sell the 3 pin model any more. May be here; Pulse width modulation PWM of fuel pump updates?

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#32

Hope I can explain this correctly, the 3 pin model uses the neg to only run the pwm, not the pump. The 4 pin passes the neg through the pwm to the pump.

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#33

Aha, so we’re talking about the pwm that does the pulsing on the negative side of the motor.
@Jan You may want to wait for @mggibb 's work around anyway.
As usual I should have kept my nose out of things I don’t understand. Sorry about that.

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#34

I have only ever used the four pin type. That was on a Dakota. The ground and the power for the fuel pump come from the relay and you just cut them both and run them into the pwm. If you want to have a second toggle switch on the system you have to switch both the hot and the ground.

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