EXPERTEC TSB (51-65-48)
Publication date: 1995-08-07Reference number: 51-65-48
EXPERTEC TSB
TECHNICAL SERVICE BULLETIN
SECTION 3 - DRIVEABILITY AND EMISSIONS CONTROL MODULE SYSTEMS - REVISED INCORRECT OR FALSE DTC 91-98 CYLINDER BALANCE FAULT
Model(s): 1994-95 Chevrolet and GMC Truck C/K, G, P3 Models
Bulletin No.: GMC 51-65-48
Date: 08/07/1995
MODELS AFFECTED
1994-95 Chevrolet and GMC Truck C/K, G, P3 Models with 6.5L Diesel Engine (VINs S, F, P - RPOs L56, L49, L65)
SERVICE INFORMATION
DTCs 91-98 Cylinder Balance Fault are intended to identify a specific cylinder. PROM modifications in 1994 and 1995 for cylinder balance DTCs may cause a cylinder identified in the Service Manual to be incorrect. A new diagnostic procedure using the scan tool is attached to properly identify the correct cylinder by performing cylinder cutout (Scan tool name: "INJ. BALANCE").
This information replaces all information found in Section 3 under DTCs 91-98 Cylinder Balance Fault.
The following pages are being revised:
1994 Driveability, Emissions & Electrical Diagnosis C/K Truck: pages 3-119 and 3-120
G Truck and P3 Chassis: pages 3-113 and 3-114
1995 Driveability, Emissions & Electrical C/K Truck: pages 3-119, 3-120 and 3-121
G Truck: pages 3-113, 3-114 and 3-115
P3 Chassis: pages 3-113 and 3-115
DTC 91- 98 CYLINDER BALANCE FAULT
CIRCUIT DESCRIPTION
The PCM has the ability to increase and decrease the amount of fuel to each cylinder to provide smooth idle operation. If too great of a fuel adjustment is required, a DTCs will set. These DTCs indicate a possible mechanical or fuel delivery problem.
DTC 91 - 98 WILL SET WHEN
- Engine idling.
- Coolant at operating temperature.
- Cylinder fault constant.
- Fuel correction amount exceeds defined limits (internal to PCM) for 2 seconds.
Action Taken (PCM will default to):
- Rough idle.
- DTC will be stored as a current and history code, but, it will not turn on the MIL.
DTC 91 - 98 WILL CLEAR WHEN
Fault conditions no longer exist.
DTC CHART TEST DESCRIPTION
Number(s) below refer to the circled number(s) on the diagnostic chart.
- This step will determine if there is a specific cylinder at fault by using cylinder cutout (INJ. BALANCE). If a specific cylinder is not responding to cylinder cutout (RPM drop), this cylinder should be considered a suspect cylinder.
- This step will determine if a faulty dual mass flywheel is setting multiple cylinder balance DTCs.
DIAGNOSTIC AIDS
To properly identify suspect cylinders, a scan tool must be used. The scan tool "INJ. BALANCE" test will cutout the specific cylinder requested. The scan tool will cutout a specific cylinder for 60 second intervals (you can repeat cylinder cutout for the same cylinder as needed). Faulty injection nozzles will set cylinder balance DTCs and should always be checked first. A nozzle can be swapped from one cylinder to another as a quick check to identify a fault.