52 Fuel System Troubleshooting TP-6903 5/16a
3.6. Hesitation, Sag, or Stumble
Definition: The engine has a momentary lack of
response when accelerating. The condition can occur
at any engine speed. The condition may cause the
engine to stall if it’s severe enough.
Figure 3-8 Hesitation, Sag, or Stumble Troubleshooting
Checks Action
Preliminary Checks None.
Fuel System Checks
Check the fuel pressure.
Check for low fuel pressure during a moderate or full throttle acceleration. If the fuel
pressure drops below specification, there is possibly a faulty fuel pressure regulator or a
restriction in the fuel system.
Check the TMAP sensor response and accuracy.
Check shut-off electrical connections.
Check the fuel pressure regulator, air-fuel mixer and throttle body for proper installation
and leakage.
Ignition System Checks
Check for proper ignition output voltage with a spark tester.
Verify that the spark plugs are the correct type and properly gapped.
Check for faulty spark plug leads.
Check for oil-fouled spark plugs.
Additional Check
Check for manifold vacuum or air induction system leaks.
Check the alternator output voltage.
Check for air intake system leakage at all connections between the air-fuel mixer and
throttle body.
Check for charge air cooler leaks on turbocharged engines.
Check for sticking of the turbocharger wastegate.
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