ENGINE DETONATION/LIGHT THROT. INSTALL NEW EGR SOLENOID

1982 HT4100 ENGINE DETONATION

Some 1982 HT4100 equipped vehicles may experience spark knock or detonation under light to medium throttle operation.

Replacement of the 1982 EGR solenoid with a 1983 EGR solenoid, which provides slightly higher amounts of vacuum under some operating conditions, may correct detonation. The recommended GMWDD part usage is as follows:

EGR Solenoid Part Number

1983 HT4100 1997634

To diagnose and correct detonation on 1982 HT4100 engines, the following procedure should be used:

1. Read DFI diagnostic codes and repair any codes before proceeding.

2. Check base spark timing. Timing should be set at 100 BTDC. Reconnect the set timing connector and verify that timing advances occur.

3. Check for proper Thermac and EFE operation.

4. Check for vacuum leaks and proper routing of vacuum lines.

5. Check for correct spark plugs.

6. Check for proper oxygen sensor operation in closed loop. Observe parameter (.0.7) for a normal swing during detonation conditions. A persistent lean fuel condition should be corrected (refer to code 44 trouble tree), even if the code may not yet be set.

7. Check EGR operation using DFI chart No. 7 on page 8D1-110 of the 1982 Service Manual.

On vehicles where the EGR system is functioning properly and steps 1-7 have not corrected a detonation condition, verify that the vehicle contains a 1982 solenoid and, if so, replace with the 1983 EGR solenoid listed above. The 1982 solenoid is zinc (silver) colored and is distinguished from the 1983 solenoid which is black in color.

If EGR solenoid replacement along with steps 1-6 above do not correct detonation, perform the following additional steps:

A. Check for proper tip-in enrichment as shown by an increasing TPS reading of parameter (.0.4).

B. Check MAP (.0.2) and BARO (.0.3) parameter readings with ignition on, engine off. Readings should be within 2 kPa of each other. Cases where the MAP sensor is 2kPa lower than the BARO may justify further investigation or replacement of the sensor.

C. Check parameter (.0.4) for proper coolant temperature. Coolant temperature should be between 90-95 DEG C with a warmed up engine (except during extended idle). The coolant system should be analyzed, since overheating may cause detonation.

D. Check operation of the air management system.

E. Check fuel pressure under conditions during which detonation occurs.

F. Check for proper compression.

G. If an internal carbon build-up is suspected, remove carbon with GM top engine cleaner. Follow instructions on can.

H. Remove engine front cover and check camshaft timing as described on page 6A8-23 of the 1982 Cadillac Service Manual.

For warranty purposes, use labor Operation No. T6070 at .3 hour when performing steps 1-2. When completing steps 3-7, add .5 hour.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.