Poor Fuel Economy - Mazda B-Series 1997 Workshop Manual

TROUBLESHOOTING GUIDE
FT
STEP INSPECTION A C T I O N -
l g l
Is OCT ADJ shorting bar removed and is a
modification decal attached to the vehicle indicating
that the OCT ADJ shorting bar was removed?
p p p - -
OCT ADJ shorting bar
If OK, go to next step
1
15
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POOR FUEL ECONOMY
7
10
11
12
DESCRIPTION Fuel economy unsatisfactory
STEP
/
INSPECTION
Is air leakage felt or heard at intake air system
components while racing engine to higher speed?
Is engine oil quality OK?
Verify test results. If OK, return lo diagnostic index to service any additional symptoms
Are any diagnostic trouble codes displayed during
Key On Engine Off, Key On Engine Running or
Continuous Memory inspection'?
-
page FT-71
MF1754-C2 6BUOFT-023
Yes
Check PID values of the following:
DPFEGR sensor
ECT sensor
IAC solenoid
LONGFTllLONGFT2
VPWR
VREF
I I - ~
page FT-74
Are PID values within specification?
p.ppp-p-
Perform Fuel Line Pressure Inspection.
a
page FT-150
Is fuel line pressure correct?
Fuel line pressure:
240-280 kPa (2.5-2.8 kgflcm2, 35-40 psi)
Diagnostic trouble code displayed
Check for cause (refer to Diagriostic Trouble Code
chart)
-
page FT-77
No diagnostic trouble codes displayed
Go to next step
Repair or replace poor connec1:ion in circuit or
component as necessary
I
Yes / G o to next step
I
Zero or low:
Check pressure regulator diaphragm
=
page FT-154
Check fuel pump circuit
I I - ~
page FT-151
High:
Check pressure regulator for high pressure cause
=
page FT-154
Check for clogged fuel return line
Visually look for fuel leakage at injector O-ring,
pressure regulator, and fuel line. Service as
necessary.
Perform Fuel Pressure Hold Inspection.
I I - ~
page FT-150
Does fuel line pressure hold?
Disconnect inertia fuel shutoff switch connector.
Crank engine for 5 seconds. Does pressure drop
more than 34 kPa (0.35 kgflcm2, 5 psi) by the end
of 5 second crank cycle?
I
Yes / G o to next step
I
Check pressure regulator diaphragm condition
=
page FT-154
If condition is OK, check injector
I I - ~
page FT-155
If condition is not OK, replace pressure regulator
Yes / G o to next step
I
/
Check resistance of injector(s) at PCM connector
If resistance is OK, check a:s follows:
* lnjector drive signal
* Injector flow rate
* PCM
If resistance is not OK, check for open in injector
,
circuit