How does fuel system work... Please explain
Thread Starter
Teching In
Joined: Feb 2002
Posts: 49
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From: Music City
How does fuel system work... Please explain Can someone explain how the fuel system works. I am looking into going with a custom setup in the future and need to get and idea of how the whole thing works. Please tell me if I am right.
Here is what I think is happening... Fuel pump is constatntly pumping fuel. Car is on and the pump is on. The computer is not adjusting the output of the pump at all, just on or off. Fuel then is pumped to the filter (just before), and back to the pressure regulator which keeps the fuel pressure constant. The actual line to the rail would just be a long extension of the fuel rail. Then the computer is adjusting the injectors to supply fuel to the motor.
Therefore, the only way to adjust the fuel pressure is to go with a bigger pump (pumps more fuel) or change out the pressure regulator for one that allows a higher fuel pressure (assuming the pump can handle the higher pressure). The computer is not looking at the fuel pressure specifically, and only assumes that there is enough fuel (pump and regulator) for the injectors based on what the programming is for the injectors. Changing out the pump, regulator, and fuel lines will not effect the computer as long as they are supplying enough fuel for the injectors.
Am I missing anything???
Here is what I think is happening... Fuel pump is constatntly pumping fuel. Car is on and the pump is on. The computer is not adjusting the output of the pump at all, just on or off. Fuel then is pumped to the filter (just before), and back to the pressure regulator which keeps the fuel pressure constant. The actual line to the rail would just be a long extension of the fuel rail. Then the computer is adjusting the injectors to supply fuel to the motor.
Therefore, the only way to adjust the fuel pressure is to go with a bigger pump (pumps more fuel) or change out the pressure regulator for one that allows a higher fuel pressure (assuming the pump can handle the higher pressure). The computer is not looking at the fuel pressure specifically, and only assumes that there is enough fuel (pump and regulator) for the injectors based on what the programming is for the injectors. Changing out the pump, regulator, and fuel lines will not effect the computer as long as they are supplying enough fuel for the injectors.
Am I missing anything???
Re: How does fuel system work... Please explain Computer does a lot of math and uses some tables
of data that embody assumptions about fuel
delivery vs. injector pulse width etc.; this in
turn includes the fuel pressure.
The regulator is back by the tank somewhere. This
makes the rest of the forward run an unregulated
pressure drop that varies with fuel flow and with
acceleration (weight of the fuel if you stood it
on end, over line area, fights regulator head
pressure. This is like 2PSI at 1g acceleration.
As to the line drop, I don't know. But it's
common to see 5-7PSI drop at the engine.
The tables are all just "fudged" to incorporate
all of this, as the regulator is not manifold
pressure referenced or injector-rail-pressure
aware.
Bigger pump will not change fuel pressure except
where the pressure was falling below regulator
blow-off point due to flow-pressure capacity.
This capacity can also be limited by power supply.
Bigger lines will improve fuel pressure forward
drop, which is the primary pressure loss
downstream of the regulator, I think. If you went
to an engine-mounted regulator and return line,
you could "null" all of the flow- and acceleration-
related drops (but then would be fooling the PCM
by making the fuel delivery too solid). But that
might be a good problem to have.
of data that embody assumptions about fuel
delivery vs. injector pulse width etc.; this in
turn includes the fuel pressure.
The regulator is back by the tank somewhere. This
makes the rest of the forward run an unregulated
pressure drop that varies with fuel flow and with
acceleration (weight of the fuel if you stood it
on end, over line area, fights regulator head
pressure. This is like 2PSI at 1g acceleration.
As to the line drop, I don't know. But it's
common to see 5-7PSI drop at the engine.
The tables are all just "fudged" to incorporate
all of this, as the regulator is not manifold
pressure referenced or injector-rail-pressure
aware.
Bigger pump will not change fuel pressure except
where the pressure was falling below regulator
blow-off point due to flow-pressure capacity.
This capacity can also be limited by power supply.
Bigger lines will improve fuel pressure forward
drop, which is the primary pressure loss
downstream of the regulator, I think. If you went
to an engine-mounted regulator and return line,
you could "null" all of the flow- and acceleration-
related drops (but then would be fooling the PCM
by making the fuel delivery too solid). But that
might be a good problem to have.
Re: How does fuel system work... Please explain all of the above is correct, set up stock the computer is tuned for ~55psi wot and ~58 at idle to land it around 0ltrims.
if you run a vaccum/boost referenced regulator then you can take the slope of the fuel injector constant graph down to zero.. this is where mine is.
you can run as much pump as you like as long as your return line and regulator can handle the flow and still not have to change the tune (because the fp didn't go up)
if you run a vaccum/boost referenced regulator then you can take the slope of the fuel injector constant graph down to zero.. this is where mine is.
you can run as much pump as you like as long as your return line and regulator can handle the flow and still not have to change the tune (because the fp didn't go up)
Thread Starter
Teching In
Joined: Feb 2002
Posts: 49
Likes: 0
From: Music City
Re: How does fuel system work... Please explain OK, here is what I have in mind. Add a new line from in tank pump to rail. Pressure regulator after rail and then back to the tank using the old fuel line. Now, how do I make that work with the computer. Is it just a matter of tweaking the fuel tables to get enough fuel throught the injectors... Assuming you go big enough on fuel pumps, rails, and regulator setting. The only changes made are getting o2s to .9XX using standard tuning procedures. In other words, adding more fuel pressure, pump power, etc. does not create a problem for the computer when everything is clicking (even if the computer thinks the stock components are there). The only thing that causes problems is if you don't have enough fuel pump/pressure for your power/acceleration needs when the computer thinks you do, which would not be an issue with a regulator in the engine compartment.
Re: How does fuel system work... Please explain You will have to modify your fuel rail. It does not have return line like the V6. I have seen it done by cutting the ends off the fuel rail, install some fittings and a crossover line at the back of the rail. They say it works well.
Re: How does fuel system work... Please explain as long as you have the same injectors as the computer is programmed for (stock) and run stock fuel pressure.. and do not hook the regulator to manifold vaccum.. there will be no tunign necessary until the internal engine mods come.
