General Description; Diagnosis Procedure - GMC SYCLONE 1992 Service Manual Supplement

6E3-2 4.3L TURBO (VIN Z) DRIVEABILITY AND EMISSIONS
ALL NEW GENERAL MOTORS VEHICLES ARE CERTIFIED BY THE UNITED STATES
ENVIRONMENTAL PROTECTION AGENCY AS CONFORMING TO THE REQUIREMENTS OF THE
REGULATIONS FOR THE CONTROL OF AIR POLLUTION FROM NEW MOTOR VEHICLES. THIS
CERTIFICATION IS CONTINGENT ON CERTAIN ADJUSTMENTS BEING SET TO FACTORY
STANDARDS. IN MOST CASES, THESE ADJUSTMENT POINTS EITHER HAVE BEEN
PERMANENTLY SEALED AND/OR MADE INACCESSIBLE, TO PREVENT INDISCRIMINATE OR
ROUTINE ADJUSTMENT IN THE FIELD. FOR THIS REASON, THE FACTORY PROCEDURE FOR
TEMPORARILY REMOVING PLUGS, CAPS, ETC., FOR PURPOSES OF SERVICING THE PRODUCT,
MUST BE STRICTLY FOLLOWED AND, WHEREVER PRACTICABLE, RETURNED TO THE
ORIGINAL INTENT OF THE DESIGN.

GENERAL DESCRIPTION

This section applies to engines with "Port Fuel
Injection" (PFI) fuel delivery systems. PFI engines
have a fuel injector in the intake manifold near the
intake valve for each cylinder.
PFI engines have controls that reduce exhaust
emissions, and maintain good driveability and fuel
economy.
The Electronic Control Module (ECM) is the heart of
this control system. A network of sensors provides the
ECM with information about engine operation and the
various systems it controls. Details of basic operation,
diagnosis, functional checks, and on-vehicle service
are covered in Section "C," component systems.
The ECM has the ability to do some diagnosis of
itself, as well as other parts of the system. When the
ECM finds a problem, it lights a "Check Engine" light
on the instrument panel and a trouble code is stored in
the ECM memory. The "Check Engine" light does not
indicate that the engine should be stopped right away,
but that the vehicle should be checked as soon as rea-
sonably possible.
INTRODUCTION
The following sections are written for specific
engine applications and are clearly identified. Be sure
to use only the section which applies to the engine
family being diagnosed.
Before using this section of the manual, you should
be familiar with the information and the proper
diagnosing procedures that are described in Section
"6E." If the proper diagnosis procedures are not fol-
lowed, as described in Section "6E," it may result in
unnecessary replacement of good parts.
T r o u b l e t r e e c h a r t s i n c o r p o r a t e d i a g n o s i s
procedures using an ALDL "Scan" tool whenever
possible. Using a "Scan" tool saves time in diagnosis
and prevents the replacement of good parts.
The key to using a "Scan" tool successfully for
diagnosis lies in the technician's ability to
understand the system he is trying to diagnose, as
well as having an understanding of the "Scan"
tool's limitations. See Section "6E" for more
information.

DIAGNOSIS PROCEDURE