| Subject: | Diagnostic Information on Poor Performance, Lack Of Power, Fuel System Not Returning Fuel Evenly |
| Models: | 2003-2005 Chevrolet Kodiak C6500-C8500 Series |
| 2003-2005 Chevrolet F-Model, T6500-T8500 Series |
| 2003-2005 GMC TopKick C6500-C8500 Series |
| 2003-2005 GMC F-Model, T6500-T8500 Series |
| 2003-2005 Isuzu FTR/FVR/FXR Commercial Models |
| 2005 Isuzu HTR/HVR/HXR Conventional Models |
| with Single or Dual Fuel Tanks and |
| 7.8L Diesel Engine (VIN 3 - RPO LG4) or 7.2L CAT Engine (VIN C - RPO LG5) |
This bulletin is being issued to inform Technicians that when diagnosing any of the above vehicles with poor performance, lack of power or fuel return concerns, first inspect the vent line at the fuel tank sending unit shown above for possible debris plugging
the line.
The horizontal orientation of the vent line may make the line more susceptible for debris/insects to enter. It has been found that insects have used the end of this vent line as a nesting location.
Clean out any debris from the vent tube/line and re-route the vent line down the channel of the fuel tank bracket as shown above. On most of the fuel tank configurations, there is enough line length to move it toward the bracket and push it down the opening
between the tank and the bracket. By locating the end of the vent line here, it is less likely for debris to enter or an insect using this line as a nesting location.
Models with a 94 liter (25 gallon) fuel tank and some of the other tanks (depending on location and cab configuration), may have shorter vent lines that won't reach the bracket area and may not be held securely. On these vehicles, remove
the current vent hose and obtain a compatible flexible hose (approximately 0.65 m (25.5 in) and reroute as described above.
If any of the conditions exist after relocating the vent line, refer to the diagnostic information available in SI to address the concern.
