1979 Riviera Fuel System Problem

[Jolly_John]

Hi, Gang. A friend of mine has a '79 Riviera with the Olds 350 engine. Stock 4-barrel 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<!-- google_ad_section_end -->

[Larry Schramm]

I would probably look at two things based on has the car been sitting for a while?

First I would put a fuel pressure gauge on the fuel line at the carb and check the fuel pressure. Work backwards to the tank. Firsta new fuel filter. Then I would probably pull the gas tank and look at the sock on the bottom of the tank unit. Sounds like there is some trash in the tank that is restricting the flow of fuel because of debris accumulation on the sock when the fuel level is low.

My thoughts because I have seen the restricted sock problem. you should be able to purchase a new sock if the sending unit is good.

[joe_padavano]

X2 on the restricted sock in the fuel tank. Either the tank has crud that is sucked up against the sock or the sock itself is dirty or deteriorated. It's time to drop the tank.

Another thing to check is the condition of all the non-metallic lines in the system. The rubber hoses can crack, allowing air into the suction side of the fuel pump.

[51dyno]

One thing to try drive it till it bogs down ,stop remove gas tank cap,if it runs good could be a collapsed rubber hose before the pump. Just a thought before dropping the tank. DK

[Jolly_John]

Thanks for another good idea, 51dyno. John