Engine - Surging, Hesitation, Rpm Hunting at Idle
Group: ENGINE ELECTRICALNumber: 94-36-004
Date: OCTOBER, 1994
Model: 1993, 94 SCOUPE
Subject:
SCOUPE DRIVEABLITY DIAGNOSIS
DESCRIPTION
This bulletin provides diagnosis check points for driveability conditions such as "surging", "hesitation" and "rpm hunting at idle" for 1993 and 1994 distributor equipped Alpha engines.
NOTE:
These conditions may not appear until the vehicle has been driven at least 20 miles. Therefore, it is important the vehicle is thoroughly test driven before returning it to the customer.
CAMPAIGNS
Make certain all campaigns related to the vehicle have been performed. The following campaign TSB's apply to the 1993-94 Scoupe:
93-01-001 (All)
93-01-002 (Cal)
94-01-006 (Cal)
94-01-009 (Fed)
DIAGNOSTIC TROUBLE CODES
Use the MUT tester to check for diagnostic trouble codes. Repair as necessary.
FUEL
Fuel and fuel filter quality are directly related to the overall driveability of the vehicle.
1. Check fuel for contamination and fuel filter for clogging.
2. Check the fuel pressure and verify the readings are within specification.
If the measured value is out of specification, refer to the service adjustment procedures for Fuel Pressure in section 31 of the shop manual for further diagnosis.
IGNITION SYSTEM
1. Perform the Ignition Coil campaign 93-01-001 (if it has not already been completed.) If it has, make certain the ignition coil cable is routed to the correct position.
2. Inspect the high tension leads from the ignition coil to the distributor cap and from the distributor cap to each spark plug, and check the resistance of each lead.
3. Replace the cable set if there is any signs of cracking, corrosion or wear due to contact with another engine component
4. Make certain there is sufficient space between all the cables to eliminate the effects of electro-magnetic fields (EMF) generated by each cable on the adjacent cables. Move any cables a minimum of 2 inches away from the engine wiring harness.
5. Inspect the distributor cap and rotor for excessive wear, pitting or corrosion.
6. Check the timing and verify that it's steady. If it is not steady, this may indicate a poor connection of the throttle position (TP) sensor connector or knock sensor malfunction. See Throttle Position (TP) Sensor below or Knock Sensor for diagnosis.
THROTTLE POSITION (TP) SENSOR
Use the MUT tester to view service data information of the throttle position (TP) sensor (item No.23) and verify the readings are within specification.
If the values are erratic, try the following:
1. Clean and tighten the female pins of the TP sensor
2. Apply a light coat of dielectric grease* to the pins
3. Fasten the connector to the TP sensor and make certain the connection is secure.
4. Recheck the data.
If the data remains out of specification, perform the component inspection procedures for the throttle position sensor described in section 31 of the shop manual.
* Dielectric grease prevents corrosion and allows the passage at electromagnetic fields but does not conduct the current.
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
Use the MUT tester to view service data information of the engine coolant temperature (ECT) sensor (item No. 24) and verify the readings are within specification (MUT data should correspond with actual engine coolant temperature.)
If the values are erratic, try the following:
1. Clean and tighten the female pins of the ECT sensor
2. Apply a light coat of dielectric grease to the pins
3. Secure connector to the ECT sensor
4. Re-check the data.
If the data remains out of specification or is erratic, perform the component inspection procedures for the engine coolant temperature sensor described in section 31 of the shop manual.
GROUNDS
Good, clean grounds are essential for proper engine control management Poor or dirty grounds can produce false sensor signals to the ECM that can result in driveability problems.
1. Remove and clean the three ECM ground bolts on top of the intake manifold. Apply dielectric grease to the bolts and ground terminals.
2. Remove the negative battery cable to the engine block mounting bolt. Clean the threads and cable contact surfaces, apply dielectric grease to the cable ends and bolts then reinstall.
KNOCK SENSOR
The knock sensor effects ignition timing. When a knock signal is detected, the ECM retards the timing which will reduce the power of the engine. Correct knock sensor torque is critical to its proper operation. If the torque is too high, the knock sensor may pick up false signals.
1. With the engine at operating temperature, measure resistance between pins 1 and 2 of the knock sensor connector (component side). Resistance should be between 4.75 and 5.0 M ohms. If resistance is not within specification, check knock sensor torque.
2. With the engine at operating temperature, loosen the knock sensor from the cylinder block and re-torque to 12-14 lb.ft.
If re-torquing the knock sensor does not remedy the problem, re-route the knock sensor wiring to prevent EMF induction. See TSB 93-36-012 for complete diagnosis of the knock sensor.