The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 47-55.1 Gas smell

dsraven · 02-16-2023, 10:33 AM

I have chased gas smells on lots ofvehicles over the years. a common one is the hose connections on the filler tubes, a sending unit gasket (not often the screws, but those too occasionally), a rusty spot on the back side of a frame mounted fuel line, a fuel pump leaking out the evnt hole due to a cracked diaphragm in the pump, fuel seaping out of the carb float bowl and out the throttle shafts due to a poor inlet valve needle and seat (after vehicle is just shut off, fuel leaks until pressure in the line is bled off), a leaking inline fuel filter housing, a fuel tank pin hole under the tank mounting straps, a leaking pinch weld on the tank where the upper and lower halves come together, and several other dumb ones. first looking for a damp spot, these usually are spots hat have collected some dust on the damp spot if the vehicle has been driven much. if you have access to dyed fuel it can help as the leak will show up as a coloured spot if the has dried up, which sometimes happens if the leak is near the top of the tank. check all along every line starting from the filler neck at the cap and then to the tank, top and bottom, sending unit and gasket or O ring seal, straps, pinch weld etc, then move along to the fuel delivery lines, filters, fuel pump-if not in tank, and up to the carb or injectors.remember to check the return lines and vent lines as well. on vent lines I like to use a long hose that goes up higher than the tank, diff, trans or whatever I am venting, and then makes a u turn and comes back down a little ( like an inch) before terminating. this keeps any water splash from dropping in. never lower than the top of the source or a siphon can get started. I use a diff vent on the end of the hose to keep debris out. a charcoal cannister is a great idea. I have had to use a slight pressure in the tank sometimes in order to force a leak to show up where it may not normally be visible. slight pressure, like a couple psi and be carefull when you release the pressure as it can bring fuel along with the air when the release is too fast. a full tank of fuel is sometimes a good idea to try after first trying it on less fuel in the tank but not finding anything. dont forget to check down the throat of the carb and around the throttle shafts.

02-16-2023, 10:33 AM	#10
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 7,839	Re: Gas smell I have chased gas smells on lots ofvehicles over the years. a common one is the hose connections on the filler tubes, a sending unit gasket (not often the screws, but those too occasionally), a rusty spot on the back side of a frame mounted fuel line, a fuel pump leaking out the evnt hole due to a cracked diaphragm in the pump, fuel seaping out of the carb float bowl and out the throttle shafts due to a poor inlet valve needle and seat (after vehicle is just shut off, fuel leaks until pressure in the line is bled off), a leaking inline fuel filter housing, a fuel tank pin hole under the tank mounting straps, a leaking pinch weld on the tank where the upper and lower halves come together, and several other dumb ones. first looking for a damp spot, these usually are spots hat have collected some dust on the damp spot if the vehicle has been driven much. if you have access to dyed fuel it can help as the leak will show up as a coloured spot if the has dried up, which sometimes happens if the leak is near the top of the tank. check all along every line starting from the filler neck at the cap and then to the tank, top and bottom, sending unit and gasket or O ring seal, straps, pinch weld etc, then move along to the fuel delivery lines, filters, fuel pump-if not in tank, and up to the carb or injectors.remember to check the return lines and vent lines as well. on vent lines I like to use a long hose that goes up higher than the tank, diff, trans or whatever I am venting, and then makes a u turn and comes back down a little ( like an inch) before terminating. this keeps any water splash from dropping in. never lower than the top of the source or a siphon can get started. I use a diff vent on the end of the hose to keep debris out. a charcoal cannister is a great idea. I have had to use a slight pressure in the tank sometimes in order to force a leak to show up where it may not normally be visible. slight pressure, like a couple psi and be carefull when you release the pressure as it can bring fuel along with the air when the release is too fast. a full tank of fuel is sometimes a good idea to try after first trying it on less fuel in the tank but not finding anything. dont forget to check down the throat of the carb and around the throttle shafts.