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Hesitation, Sag, Stumble

DEFINITION: 

Momentary lack of response as the accelerator is pushed down. This can occur at any vehicle speed. It is usually the most severe when first trying to make the vehicle move, as from a stop. Hesitation, sag, or stumble may cause the engine to stall if severe enough. 

CAUTION: Before diagnosing this condition, check service bulletins for PROM updates.
HESITATION, SAG, STUMBLE - DIAGNOSIS PROCEDURE

Step Action Value(s) Yes No
1 Were the Important Preliminary Checks performed? - Go to Step 2. Go to Symptom Diagnosis .
2
  1. Check the fuel system pressure. If the pressure is not within the value specified, service the fuel system as needed.
  2. Inspect the Throttle Position (TP) sensor for binding or sticking. The TP sensor voltage should increase at a steady rate as the throttle is moved toward Wide Open Throttle (WOT).

Is the problem found?		 310 kPa (45 psi) Go to Step 3. Go to Step 4.
3 Repair or replace any components as needed.
Is the repair complete?		 - System OK -
4
  1. Check the Manifold Absolute Pressure (MAP) sensor response and accuracy.
  2. Inspect the fuel for water contamination.
  3. Check the Evaporative (EVAP) Emission Canister Purge System for proper operation.

Is the problem found?		 - Go to Step 5. Go to Step 6.
5 Repair or replace any components as needed.
Is the repair complete?		 - System OK -
6
  1. Disconnect all of the fuel injector harness connectors.
  2. Connect an injector test light between the harness terminals of each fuel injector.
  3. Note the test light while cranking the engine.

Does the test light blink on all connectors?		 - Go to Step 8. Go to Step 7.
7
  1. Repair or replace the faulty fuel injector drive harness, the connector, or the connector terminal.
  2. If the connections and the harnesses are good, replace the Engine Control Module (ECM).

Is the repair complete?		 - System OK -
8 Measure the resistance of each fuel injector.
Is the fuel injector resistance within the value specified (the resistance will increase slightly at higher temperatures)?		 11.6 - 12.4 Ω Go to Step 10. Go to Step 9.
9 Replace any of the fuel injectors with a resistance that is out of specifications.
Is the repair complete?		 - System OK -
10 Perform an FUEL INJECTOR BALANCE TEST .
Is the problem found?		 - Go to Step 11. Go to Step 12.
11 Replace any restricted or leaking fuel injectors.
Is the repair complete?		 - System OK -
12 Check the fuel system pressure after a cold start or during moderate or full throttle acceleration.
Is the fuel pressure within specifications?		 310 kPa (45 psi) Go to Step 14. Go to Step 13.
13 Repair the restriction in the fuel system or replace the faulty fuel pump.
Is the repair complete?		 - System OK -
14
  1. Inspect for fouled spark plugs.
  2. Check the ignition system output on each cylinder with a spark tester.

Is the problem found?		 - Go to Step 15. Go to Step 16.
15 Repair or replace any ignition components as needed.
Is the repair complete?		 - System OK -
16
  1. Check the generator output voltage.
  2. Repair or replace the generator if the generator output is less than the value specified.
  3. Check the Exhaust Gas Recirculation (EGR) valve operation.

Are all checks and needed repairs complete?		 12 - 16 V System OK -
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