Hi, Gang. A friend of mine has a '79 Riviera with the Olds 350 engine. Stock 4-barrel Quadrajet carb, mechanical fuel pump, and no computers of any kind (no ECM, no carb or distributor computer...nothing). The car is equipped with the charcoal cannister (one vac. controlled valve in and out that vents the carb fuel bowl, plus two other cannister connectors for gas tank vapors). The car runs great on the highway when the gas tank is full, and down through about two-thirds full. However, once the fuel gauge shows about two thirds full, the engine acts like it is running out of gas, when climbing a long hill at around 65 m.p.h. You can be climbing the hill at 65 m.p.h., and the engine will stumble if you step on the gas a little to maintain the 65 m.p.h. If you slow down to 55 m.p.h. and are easy on the gas pedal, the car will handle the hill. There seems to be no fuel delivery problem in around town driving at lower speeds, even when the tank is less than two-thirds full. Again, the car runs great on the highway and will zoom up any hills when the tank is over two-thirds full. The only stumbling or "starved for gas" problem exists when trying to maintain higher speeds while climbing a hill on highway, ONLY when the gas tank is less than two-thirds full. My friend is not on the computer, so I'm posting here to give him a hand. We will both appreciate any suggestions for I.D.ing the source of this problem you might have. Thanks. John
You might try removing the fuel cap when the engine stumbles. It is possible for the vacuum created by the fuel draw to starve the engine due to the suction against the fuel cap. It is also possible for the fuel pick-up in the tank to sit awkwardly in the tank, exposing the pick-up under certain maneuvers. One more thing to consider is the fact that the in-tank filter is clogged, and the fuel is being pulled through a leak in the system, rather than the filter. Just some ideas...
Hi, guys. Thanks for the ideas. I had also been thinking "fuel filter", either in the tank or at the carb.....however, why would the engine still perform fine when the gas tank was two-thirds or more full? Again, I do appreciate the help. John
Consider this... picture the fuel delivery line simply a pipe, attached to the sender plate. It typically has a joint in the pipe. If the fuel is trickling in through a leak in the joint, the fuel will deliver until the level drops below the joint. Then the pump will pull air through the leak, instead of liquid fuel.
