Mazda Speed 6. Manual — part 2

01 ENGINE

10

Direct Injection
Diesels were the fi rst engines to use direct injection, but they use compression ignition
rather than spark ignition. Direct injection works just like PFI Port Fuel Injection. The
main differences are:

Fuel injectors are mounted inside the combustion chamber like spark plugs

Fuel is injected directly into the cylinders

Fuel pressure is much higher: 410 to 1885 psi

Fuel atomizes completely into a stratifi ed charge

DISI

2 fuel pumps

In-tank electric pump 60-71 psi

Camshaft driven mechanical pump 410-1885 psi

Direct injection allows complete atomization and the fuel vapor
provides a cooling effect, improving the loading effi ciency of the fuel
mixture
Allows a high compression ratio of 9.5:1, while resisting knock even
with turbocharging
Ignition timing is delayed without misfi re, decreasing exhaust
temperatures below NO

X

production temperatures

Catalyst lights off quicker: within 40-seconds of starting, the HC
conversion of the catalyst is nearly 100%

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01 ENGINE

11

DISI Fuel System

Fuel pressure from the in-tank pump is controlled at two voltages; low voltage for idle
when less fuel volume is required and high voltage for high volume required during
higher engine speeds. Voltage and volume change but pressure is constant.

In-Tank Low Pressure Fuel Pump Operation: Low voltage Idle operation

01 ENGINE

12

In-Tank Low Pressure Fuel Pump Operation: Battery Voltage Off Idle

Fuel pressure is inspected in the traditional manner in the engine compartment
before the high pressure pump and should be approximately 65 psi. You can also
use WDS to monitor the high pressure fuel rail pressure sensor before the engine
is cranked. Key on engine off, the in-tank fuel pump pressure is displayed. The fuel

pump resistor is located in front of the drivers side strut tower.

01 ENGINE

13

High Pressure Fuel Rail

High Pressure

High Pressure
pump

pump

Fuel Rail

Fuel Rail

Pressure Sensor

Pressure Sensor

High Pressure Fuel Pump
The PCM maintains pressure by monitoring the fuel rail pressure sensor

Pressure is modifi ed by opening the spill control solenoid
Fuel pressure on the high pressure rail can only be inspected using WDS or
equivalent to monitor the fuel rail pressure sensor
The PCM energizes the spill control solenoid to control fuel pressure

High pressure fuel is dangerous. Fuel pressure must be released prior to
service by removing the fuel pump relay and cranking the engine

Spill

Spill
Control

Control
Solenoid

Solenoid

Pump

Pump

Low fuel

Low fuel
pressure

pressure
return line

return line
from rail

from rail

High

High
pressure

pressure
outlet to

outlet to
fuel rail

fuel rail

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