Hesitation, Sag, Stumble

Condition defined as momentary lack of response as accelerator is depressed. May occur at any vehicle speed, usually most severe when moving away from stop. Check the following:

1. Incorrect fuel pressure or contaminated fuel.
2. Air leaks between manifold and throttle body. Fouled spark plugs or faulty secondary ignition system components.
3. Binding or sticking TPS. TPS voltage should increase at steady rate as throttle is opened.
4. Incorrect ignition timing. Check initial adjustment, EST and ESC, as equipped.
5. Improper charging voltage.
6. Poor HEI system ground.
7. Improper canister purge operation. Refer to canister purge valve diagnosis chart.
8. Improper EGR system operation. Check EGR valve operation and if satisfactory, refer to applicable diagnostic chart.




*** THIS PROCEDURE HAS BEEN UPDATED BY TSB # 86-T-186, dated 9/86

Some 1985-86 S/T vehicles equipped with 2.5L and 2.8L engines may exhibit a stumble or hesitation while making a turn. This condition usually occurs when the truck has less than 1/8 of a tank of fuel. This condition may be caused by fuel "sloshing" away from the fuel pickup during a turn. This condition can be corrected by installing a new fuel tank.

P/N 15598520 with (20 gallon tank).
P/N 1559852 with (13 gallon tank).