Bonneville V6-231 3.8L (1984)
Knock Sensor: Customer Interest
Engine - Poor Driveability/Fuel Mileage
Number 84-6 (Gasoline)-42
Date 6/84
Subject:
1982 4.1L, 1983-1/2 3.8L AND 1984 3.8L POOR PERFORMANCE, DRIVEABILITY, FUEL MILEAGE
ModelsAffected:
1982 GRAND PRIX, BONNEVILLE, 1983-1/2 GRAND PRIX, BONNEVILLE AND ALL 1984 GRAND PRIX, BONNEVILLE,
If subject condition is encountered on above listed vehicles the warm driveability work sheet should be completed as well as the CCC circuit diagnostic
check to determine if any codes are present. Any items found in those tests that are out of specifications must be corrected first.
If all functions are within specifications, and no trouble codes are stored, the condition may be a detonation sensor picking up noises from the engine or
transmission which will retard the timing as much as 19 degrees. To determine if it is occurring, the following diagnosis should be used:
Diagnosis with ALCL Scan TOOL, All With ESC Except 1983-1/2 Grand Prix, Bonneville (Single Board ECM) and All 1984 3.8 L Buick Produced
Engines:
Drive the vehicle at normal city and highway speeds with the scan tool in the knock retard mode, and monitor the degrees of retard. "O" degrees of retard
should be seen on the scan tool (with no spark knock). lf reading other than "O" is seen on the scan tool (up to 19 degrees) and no spark knock is present,
disconnect the detonation sensor, and road test the vehicle again at the same speeds as before. If no retard is seen on the second test, the detonation
sensor is picking up noise from the engine or transmission.
Diagnosis with ALCL Scan Tool for 1983-1/2 Grand Prix, Bonneville and All 1984 Buick Produced V-6 Engines:
If 1983-1/2 Grand Prix, Bonneville or 1984 Buick produced V-6 equipped vehicles exhibit this condition, different readings will be seen on the ALCL
scan tool in the knock retard mode due to Internal ECM data stream changes.
These readings are no longer direct degrees of Retard and are best explained as counts. Figures or counts as seen on the scan tool may be any figure
between 0 and 255. If the number on the scan tool stays constant (the same number) then the engine has 0 degrees retard.
However, if the numbers seen are continually increasing such as (example) 60, 90, 118, 150, 195, 230, 10, 40 indicates that the ECM is seeing a signal
and is retarding the timing in large amounts (19 degrees) which will usually set a code and is most likely an electrical disconnect to or from the ESC
module. Small number increases indicate smaller or very little retard is taking place.
To locate the noise causing spark retard, the vehicle should be run on a lift at the speeds the most count changes were seen, and listen closely from
underneath to the engine and transmission for any unusually loud knocks, pecks, or buzzing, such as, rocker arms, lifters, trans-front pump pressure
regulator valve etc.
Diagnosis without ALCL TOOL Including 1983-1/2 grand prix, Bonneville:
Perform CCC circuit diagnostic circuit check to determine if any trouble codes are present. lf any codes are present, use of the appropriate diagnostic
chart and correction is required before proceeding.
If no trouble codes are present, drive the vehicle to determine if a performance condition exists (compare with another known good-like vehicle for
comparison, if required). If a driveability condition does exist, Code Chart 43 voltage at ECM terminal "L" low, should be used first. If no trouble is
found, using the Code Chart 43, disconnect the detonator sensor, and drive the vehicle again. If improvement is noted, the problem could be engine or
transmission noise being picked up by the detonation sensor.
To locate the noise, the vehicle should be run on a lift at the speeds the performance was at its worse, and listen closely from underneath to the engine
and transmission for any unusually loud trans-front pump pressure regulator valve buzz, etc.
If a performance condition still exists with the detonation sensor disconnected, engine timing may still be retarding due to a false signal on wire from the
knock sensor to the electronic spark controller. Rerouting wire away from other wires, such as spark plugs, etc. is required.
The following components should also be checked:
distributor shaft end play, camshaft timing, spark plug wires and distributor cap.
