Spectrum 3.0L GM - Before Using This Section; Fuel System Check; Visual and Physical Checks

36
FUEL SYMPTOM DIAGNOSTICS
Checks Action
Before Using This
Section
Before using this section, you should have performed On Board Diagnostic
(OBD) Check and determined that:
1. The ECM and MIL are operating correctly.
2. There are no Diagnostic Trouble Codes (DTCs) stored, or a DTC exists
but without a MIL.
Several of the following symptom procedures call for a careful visual and
physical check. These checks are very important as they can lead to prompt
diagnosis and correction of a problem.
Fuel System Check
1. Verify the customer complaint.
2. Locate the correct symptom table.
3. Check the items indicated under that symptom.
4. Operate the engine under the conditions the symptom occurs. Verify
HEGO switching between lean and rich (cycling of voltage).
IMPORTANT! Normal HEGO switching indicates the fuel system is
in closed loop and operating correctly at that time.
5. Take a data snapshot using the DST under the condition that the symp-
tom occurs to review at a later time.
Visual and Physical
Checks
 Check all ECM system fuses and circuit breakers.
 Check the ECM ground for being clean, tight and in its proper location.
 Check the vacuum hoses for splits, kinks and proper connections.
 Check thoroughly for any type of leak or restriction.
 Check for air leaks at all the mounting areas of the intake manifold sealing
surfaces.
 Check for proper installation and leakage around the Regulator and Throt-
tle body.
Check the ignition wires for the following conditions:
 Cracking
 Hardening
 Proper routing
 Carbon tracking
 Check the wiring for the following items: proper connections, pinches or
cuts.
 The following symptom tables contain groups of possible causes for each
symptom. The order of these procedures is not important. If the DST read-
ings do not indicate a problem, then proceed in a logical order, easiest to
check or most likely to cause the problem.