GDI - High Pressure Fuel Pump Control

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AndreyB
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GDI - High Pressure Fuel Pump Control

Post by AndreyB »

Direct Injection is giving us a completely new domain - now we need to control fuel pressure. There is the strategy of deciding on target fuel pressure based on load, RPM etc and there is the tactics of actually achieving that desired fuel pressure.

A relevant picture from Slack, this fuel entry solenoid is also peak and hold.
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puff
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Re: GDI - High Pressure Fuel Pump Control

Post by puff »

where is the fuel pressure sensor?
i'd love to see the circuitry for that one.

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Re: GDI - High Pressure Fuel Pump Control

Post by mck1117 »

puff wrote:
Tue Feb 04, 2020 10:12 pm
where is the fuel pressure sensor?
i'd love to see the circuitry for that one.
The fuel pressure sensor is on the fuel rail. They're not particularly exciting, actually: just normal linear analog pressure sensors with two outputs.

Here's a Ford Fiesta ST as an example:

Image

1. fuel pump
2. fuel injector connectors (injectors aimed straight down in to head)
3. fuel pressure sensor

edit: here's the video that's snipped from, showing disassembly of the DI system on that car:

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Re: GDI - High Pressure Fuel Pump Control

Post by puff »

and what's the nominal pressure? by any chance, do you have part numbers/pictures of those pressure sensor and solenoid valve?

I still have a similar challenge - build a cheap diy version of FrankenCIS, which has essentially the same concept: control fuel pressure (withstanding up to 150psi) based on coolant temperature, load and RPM using a certain type of fuel injector instead of a solenoid valve.
In FrankenCIS they suggest using megasquirt to control it - still not sure if it was P&H or the normal one.
Last edited by puff on Wed Feb 05, 2020 5:57 am, edited 1 time in total.

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Re: GDI - High Pressure Fuel Pump Control

Post by mck1117 »

Here are the tables that define the fuel flow/pressure controls on my 2013 Ford Focus ST.

Image

Observations:

- Injector flow is proportional to the square root of the pressure (within about 2%, this is true of all injectors). Roughly g/s = 0.142 * sqrt(kpa) for these injectors.
- Injection pressure is higher under higher loads and speeds (duh): around 250psi at idle, and 2000 PSI under load at speed

These two effects combine to give a pulse width that's relatively constant: it's always in the 1-5ms range, because for direct injection you have to. You only have limited time to inject fuel, so you have to get it done in a hurry, but waste a minimum of extra power driving the pump harder (higher pressure).

Another observation is that it always runs at high pressure (~2000psi) for about 30 seconds after engine start, at which point it switches to the table. You can audibly hear this happen outside the car, because the pump gets silent for around 1 second while the fuel pressure drops (being emptied out the injectors - the pump can only increase pressure in the rail).

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