Spectrum 3.0L GM - Cuts Out, Misses

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CUTS OUT, MISSES
Checks Action
DEFINITION: A surging or jerking that follows engine speed, usually more pronounced as the engine load
increases, but normally felt below 1500 rpm. The exhaust has a steady spitting sound at low speed, or
hard acceleration for the fuel starvation that can cause the engine to cut-out.
Preliminary Checks None
Ignition System Checks
1. Start the engine.
2. Check for proper ignition output voltage with spark tester J 26792.
3. Check for a cylinder misfire.
4. Verify that the spark plugs are the correct type and properly gapped.
Remove the spark plugs and check for the following conditions:
 Insulation cracks.
 Wear.
 Improper gap.
 Burned electrodes.
 Heavy deposits.
Visually/Physically inspect the secondary ignition for the following:
 Ignition wires for arcing and proper routing.
 Cross-firing.
 Ignition coils for cracks or carbon tracking.
Engine Mechanical
Checks
Perform a cylinder compression check. Check the engine for the following:
 Improper valve timing.
 Improper valve clearance.
 Worn rocker arms.
 Worn camshaft lobes.
 Broken or weak valve springs.
 Check the intake and exhaust manifold passages for casting fl ash.
Fuel System Checks
Check the fuel system:
 Plugged fuel filter (if equipped).
 Low fuel pressure, etc. Refer to Fuel System Diagnosis.
 Check the condition of the wiring to the Shut-off Valves.
Additional Check
Check for Electromagnetic Interference (EMI), which may cause a misfire con-
dition. Using the DST, monitor the engine rpm and note sudden increases in
rpm displayed on the scan tool but with little change in the actual engine rpm.
If this condition exists, EMI may be present. Check the routing of the second-
ary wires and the ground circuit.