Fuel System - Cut-Off Specification Revision

91pontiac03

Bulletin Number: 91-6-31
Reference Number: 116508
Publish Date: 3/91


Subject: SERVICE MANUAL UPDATE/SECTION 6E3-C2 DRIVEABILITY/EMISSIONS-REVISED FUEL CUT-OFF SPECIFICATIONS

Models
Affected: 1990-91 6000, FIREBIRD, SUNBIRD AND GRAND PRIX MODELS WITH 3.1L, 3.4L


This bulletin revises the fuel cut-off specifications for the 1990-1991 6000, Firebird, Sunbird and Grand Prix models equipped with 3.1L (VIN T) and 3.4L (VIN X) engines.

1990-1991 Grand Prix models with 3.1L engines:

To prevent possible engine damage from over-speed, the Electronic Control Module (ECM) "cuts-off" fuel from the injectors when engine speed is above approximately 6200 rpm with the vehicle in any forward gear or reverse, and approximately 4000 rpm in park or neutral. To prevent tire damage, the ECM also has a fuel cut-off in excess of 100 mph (161 km/h) based on speed rating of the tires.

1991 Grand Prix models with 3.4L engines:

To prevent possible engine damage from over-speed, the Electronic Control Module (ECM) "cuts-off" fuel from the injectors when engine speed is above approximately 6500 rpm with the vehicle in any forward gear or reverse, and approximately 3000 rpm in park or neutral on vehicles equipped with automatic transmissions. On vehicles equipped with a manual transmission, the fuel is cut-off at approximately 7000 rpm. To prevent tire damage, the ECM also has a fuel cut-off in excess of 120 mph (193 km/h) based on speed rating of the tires.

1990-1991 6000, Firebird, Sunbird and Grand Prix models with 3.1L engines:


To prevent possible engine damage from over-speed the Electronic Control Module (ECM) "cuts-off" fuel from the injectors when engine speed is above approximately 6200 rpm. To prevent tire damage, the ECM also has a fuel cut-off in excess of 100 mph (161 km/h) based on speed rating of the tires.

When diagnosing any suspected fuel cut-off problems, carefully compare Tech 1 ("Scanner") engine rpm versus actual rpm. If the ECM is sensing rpm or vehicle speed in the fuel cut-off range due to Electro-Magnetic Interference (EMI) or other electrical "noise," thoroughly investigate harness routings and aftermarket equipment installations.