Surges/Chuggles
Definition: Engine power variation under steady throttle or cruise. Feels like the car speeds up and slows down with no change to the accelerator pedal.^ Have driver read explanation of Transmission Viscous Converter Clutch and A/C compressor operation in Owner's Manual.
^ Perform careful visual inspection as described at start of Symptoms. - Visual/Physical Underhood Inspection
^ Check for intermittent open, or short to ground, in circuits #420 and #422 (VCC); #424 (HEI Bypass); and #423 (EST).
^ Check parameter ED12 for erratic vehicle speed reading from VSS.
^ Check for proper operation of EGR.
^ Check for restricted exhaust or catalytic converter.
^ Check ignition timing. See Emission Control Information label.
^ Check fuel supply system for water in tank and proper pressure. Fuel pressure should be 40-50 psi (276 to 345 kPa) at key "ON," engine "OFF." With the engine running, fuel pressure should be 32-38 psi and should increase under engine load. If fuel pressure is below 40 psi at key "ON," engine "OFF," or does not increase with engine load, see Chart A-4B. A-4B Dynamic Fuel Pressure Check
^ Check in-line fuel filter. Replace if dirty or plugged.
^ Check ignition secondary scope pattern with the vehicle in drive, brakes firmly applied, drive wheels blocked loading the engine against the brakes to obtain a 90 kPa MAP reading. (A cracked or intermittent plug or wire may be difficult to detect, even on an ignition scope. If any plugs are suspect, replace before continuing diagnosis.)
NOTICE: Total running time during which engine is loaded against brake must not exceed 20 seconds.
CAUTION: Brakes must be applied at all times.
^ Verify transmission for proper operation in all ranges. Verify that VCC engages and disengages properly and at the correct speeds. See Transmission and Drivetrain.
^ Check for exhaust system restriction by using backpressure measurement tap J353 14 with a 0-15 PSI pressure gage (J2965 8 or equivalent). Block the driver 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 running 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.
^ Decarbon the engine using top engine cleaner. Follow the instructions on the can. If top engine cleaner improves or eliminates the chuggle condition then diagnose for cause of flow restricting deposits in the heads.
^ Remove spark plugs. Check for proper heat range and type. Check for cracks, wear, improper gap, burned electrodes, or heavy deposits. Also check condition of distributor cap, rotor, and spark plug wires.
^ If signs of oil consumption are present (i.e. oil fouled plugs) repair cause of oil consumption and replace plugs.
^ Check for vacuum leaks in the upper intake manifold, the lower intake manifold, or the engine and body vacuum circuits.
^ Drive the car and note the engine RPM (Parameter ED11) at which the chuggle or surge occurs. In neutral, increase engine RPM to the value noted during the road test. If the surge feel is dependent on RPM and is evident in neutral, check for out of balance accessories such as generator or air conditioner.
^ Check for other rotating imbalances such as torque converter, drive axles, wheels and tires - See "Vibration Conditions and Correction."