Lack of Power/Sluggish/Spongy/Stumble

Definition: Engine delivers less than expected power. Little or no increase in speed when accelerator pedal is pushed down part way.

^ Check for blown or missing injector fuses (7.5 A) #4 and #5 in fuse center.
^ Compare customer's car to similar unit. Make sure the customer's car has an actual problem. Was the customer's old car much more powerful?
^ Remove air cleaner and check air filter for dirt, or for being plugged. Replace as necessary.
^ Verify that both the primary and secondary throttle valves are opening fully. Repair as necessary.
^ Check ignition timing. See Emission Control Information label.
^ See Ignition System for "Intermittent Operation or Miss" in HEI System.
^ Remove spark plugs. Check for cracks, wear, improper gap, burned electrodes and/or heavy deposits.
^ Check for restricted fuel filter and improper fuel pressure. If fuel pressure is not between 40 and 50 psi at key "ON", engine "OFF", see Chart A-4B. A-4B Dynamic Fuel Pressure Check
^ Check EGR operation for being open all the time.
^ Check for restrictions in the MAP sensor vacuum fitting or the upper intake manifold MAP port. Check for vacuum trapped in the MAP sensor. Tee a vacuum gage into the vacuum hose at the fuel pressure regulator. The gage reading and parameter ED02 should be approximately the same and respond quickly to changes in engine load. Clean out or repair the MAP port at the upper intake manifold or replace MAP sensor as necessary.
^ Check for an exhaust system restriction by using backpressure measurement tap J35314 with a 0-15 PSI pressure gage (J29658 or equivalent). Block the drive wheels, firmly apply the brakes. Place the vehicle in drive and load the engine against the brakes to a steady 1600 RPM. Measure exhaust system backpressure.


NOTICE Total time during which engine is loaded against brake must not exceed 20 seconds.


CAUTION: Brakes must be applied at all times.


Compare the backpressure readings taken on the customer complaint car to a known good car. If the backpressure reading taken is 1.0 PSI greater than the backpressure reading of a known good 1987 ALLANTE, then diagnose for cause of restricted exhaust system or catalytic converter.
^ Check for intake manifold or throttle body to intake manifold vacuum leaks.
^ Check fuel supply for water in tank.
^ Check engine valve timing and compression.
^ Remove rocker covers. Check intake manifold bolt torque. Check for bent push rods, broken or weak valve springs. Check cam lift. Repair as necessary.
^ Check transmission operation for downshift as designed and for proper torque converter operation. See Transmission and Drivetrain. Transmission and Drivetrain
^ Decarbon engine with top engine cleaner. If top engine cleaner improves the Lack of Power a condition, diagnose for cause of flow restricting deposits in the heads.