The Complete Guide to Solving Your 1979 Chevy 350 Fuel Pump Problems

Stuck with a stubborn 1979 Chevy 350 that won't start or keeps dying? Chances are, the fuel pump is the culprit. Replacing or troubleshooting the mechanical fuel pump on this legendary small-block engine is a common and manageable task for classic Chevy owners. This guide provides clear, step-by-step solutions to diagnose problems, select the right replacement, and install it correctly, ensuring your 350 V8 runs reliably for miles to come.

Understanding the 1979 Chevy 350 Fuel Pump

The 1979 Chevrolet 350 cubic inch (5.7L) V8 engine uses a mechanical fuel pump. Unlike modern electric pumps, this type is driven directly by the engine itself, specifically by an eccentric lobe on the camshaft. Located on the side of the engine block, typically near the front, the pump pulls fuel from the gas tank through a supply line and pushes it under pressure to the carburetor.

This design is simple and robust. Key components inside include a flexible diaphragm, inlet and outlet check valves, and a lever arm that rides on the camshaft eccentric. The pump generates low pressure, generally between 4 and 7 pounds per square inch (PSI), sufficient for the carbureted fuel systems used in 1979 vehicles.

Why 1979 Chevy 350 Fuel Pumps Fail

Mechanical fuel pumps are durable, but they don't last forever. Common failure points include:

  1. Diaphragm Failure: The most common issue. The rubber diaphragm can become brittle and crack over time due to age, exposure to ethanol-blended fuels, or extreme temperature cycles. A crack allows fuel to leak into the engine crankcase (diluting the oil) or leak externally, and prevents the pump from creating pressure.
  2. Leaking Seals/Gaskets: The gasket between the pump and the engine block can fail, or the seal around the actuating lever shaft can leak. This often results in visible external fuel leaks and a noticeable gasoline smell.
  3. Check Valve Failure: The one-way valves (check valves) inside the pump can wear out or become clogged with debris. If they don't seal properly, the pump loses its ability to draw fuel efficiently or maintain pressure, leading to vapor lock or fuel starvation under load.
  4. Stuck Actuating Lever or Broken Spring: Internal corrosion, lack of lubrication, or metal fatigue can cause the lever arm that rides on the camshaft eccentric to stick or a return spring to break. This prevents the pump from operating.
  5. Worn Actuating Lever: Over time, the tip of the lever arm that contacts the camshaft eccentric can wear down. Severe wear reduces the pump's stroke length, lowering the volume of fuel it can deliver.
  6. Clogged Inlet Screen (if equipped): Some pumps have a small filter screen at the inlet port. This can become clogged with rust or debris from the gas tank or fuel lines, restricting fuel flow.

Symptoms of a Failing or Failed Fuel Pump

Recognizing the signs of a bad fuel pump helps diagnose the problem quickly:

  1. Engine Cranks But Won't Start: The most obvious sign. The engine turns over normally but doesn't fire, indicating a lack of fuel reaching the carburetor.
  2. Engine Sputters, Stalls, or Loses Power (Especially Under Load): A weak pump might supply enough fuel at idle but cannot keep up when demand increases (accelerating, climbing hills, towing). The engine may surge, stumble, or stall completely.
  3. Difficult Hot Starting: A classic symptom of vapor lock or a failing pump. After the engine is hot and turned off, heat soak causes fuel in the lines and pump to vaporize. A weak pump cannot overcome this vapor and restart the engine easily. Extended cranking is required to cool things down and get liquid fuel flowing.
  4. Visible Fuel Leaks: Look for wetness around the pump body, particularly at the seams, gasket, or shaft lever entry point. Important: Gasoline leaks are a serious fire hazard. Address immediately!
  5. Gasoline Smell: A strong odor of gasoline in the engine compartment or inside the car (especially noticeable after parking) often points to a leaking pump or its connections.
  6. Fuel in Engine Oil: If the diaphragm ruptures, gasoline can leak into the engine crankcase through the pump's actuating lever opening. Check your dipstick. Oil that smells strongly of gasoline or is abnormally high is a major red flag. Driving with gas in the oil destroys engine bearings – do not run the engine if you suspect this!
  7. Decreased Fuel Economy: While less common as a primary indicator, a pump that leaks internally or bypasses fuel inefficiently might contribute to poor mileage.

How to Test Your 1979 Chevy 350 Fuel Pump (Simple Methods)

Before replacing the pump, perform these basic checks:

  1. Visual Inspection:
    • Look for obvious fuel leaks around the pump body and fuel lines.
    • Check the oil level and condition. Does it smell like gasoline? Look abnormally thin or high?
    • Inspect the rubber fuel hoses connecting the hard lines to the pump and carburetor for cracks, bulges, or softness.
  2. Pressure Test:
    • Attach a low-pressure fuel pressure gauge (0-15 PSI range) to the outlet line feeding the carburetor. You may need a T-fitting or can temporarily disconnect the line at the carb and connect the gauge directly.
    • With the ignition off, disconnect the coil wire to prevent starting. Have an assistant crank the engine.
    • Observe the gauge. A working pump should show steady pressure within the 4-7 PSI range while cranking. If pressure is zero or very low (< 2-3 PSI), or fluctuates wildly, the pump is likely faulty. Note: Specs vary slightly by model, but 5 PSI is common.
  3. Volume Test:
    • Safely disconnect the fuel line from the carburetor inlet. Route it into a clean container capable of holding at least a pint.
    • Have an assistant crank the engine for 15 seconds.
    • Measure the fuel volume in the container. A functional pump should deliver at least 1 pint (approx. 470ml) of fuel in 15 seconds during cranking. Less than this indicates insufficient volume, possibly due to a weak pump, blockage, or restriction upstream.

Choosing the Right Replacement Fuel Pump

Selecting a quality replacement pump is crucial for longevity and performance. Key considerations:

  1. OEM vs. Aftermarket:
    • AC Delco (GM Genuine): The original equipment manufacturer (OEM) supplier for GM. These pumps meet factory specifications and offer high reliability. Typically the most expensive but generally considered the premium choice for fit and durability. Look for part numbers like "P30009" or specific vehicle year/models.
    • Major Aftermarket Brands: Brands like Carter, Airtex, Delphi, Spectra Premium offer quality replacements, often at a lower price point than AC Delco. Ensure the box specifically lists compatibility with a 1979 Chevy with a 350ci (5.7L) carbureted engine (e.g., Impala, Caprice, Malibu, pickup trucks, etc.). Carter is often highly regarded in this segment.
    • Economy Brands: Very inexpensive pumps exist but are generally not recommended. Quality control and diaphragm material may be inferior, leading to premature failure or leaks.
  2. Ethanol Compatibility: Modern gasoline often contains ethanol (E10). Ensure the replacement pump explicitly states its diaphragm and seals are compatible with ethanol-blended fuels. Ethanol can degrade older rubber formulations quickly.
  3. Vapor Return Port: Some 1979 models, particularly those designed to meet specific emissions standards or in regions prone to vapor lock, might have used a pump with a "vapor return" port. This is an extra line fitting on the pump that returns excess fuel/vapor back to the tank to reduce vapor lock tendencies. Check your old pump carefully – if it has an extra fitting, you MUST replace it with a pump that also has this feature. Most replacement pumps offer "with return" and "without return" versions.
  4. Reviews Matter: Read reviews from other classic Chevy owners for specific brand experiences, especially regarding longevity under ethanol fuel use. Online forums and retail site reviews are valuable resources.
  5. Avoid Counterfeit Parts: Purchase from reputable auto parts stores (NAPA, O'Reilly, AutoZone, Advance Auto) or trusted online retailers (RockAuto, Summit Racing, JEGS) to avoid counterfeit or misrepresented parts.

Step-by-Step Guide to Replacing Your 1979 Chevy 350 Fuel Pump

Important Safety First: Gasoline is extremely flammable and explosive. Work outdoors or in a well-ventilated area away from sparks, flames, or heat sources. Have a fire extinguisher rated for gasoline fires nearby. Disconnect the battery negative terminal before starting.

Tools & Materials Needed:

  • New fuel pump (and matching gasket/seal)
  • New fuel pump pushrod (HIGHLY RECOMMENDED - see note below!)
  • Gasket scraper or old credit card
  • Screwdrivers (Flathead & Phillips)
  • Wrenches and/or sockets (typically SAE sizes like 5/16", 3/8", 7/16", 1/2")
  • Clean lint-free rags
  • Safety glasses and gloves
  • Small container for bolts
  • Penetrating oil (like PB Blaster) if bolts are rusty
  • Brake cleaner or carb cleaner for cleaning surfaces
  • Thread sealant (usually included with gasket or pump) or Aviation Form-a-Gasket sealant (optional, but preferred by many)
  • Small piece of vacuum line or rubber hose (to block lines temporarily)

The Critical Pushrod Note: DO NOT skip this! The mechanical pump is driven by a pushrod that sits in a bore between the pump mounting point and the camshaft eccentric. When you remove the old pump, this pushrod can easily fall down into the engine oil pan. Finding and retrieving it is a difficult task requiring oil pan removal. The safest practice is to replace the pushrod every time the pump is replaced. Buy one beforehand (it's inexpensive). Pushrods wear, and having a new one ensures proper pump stroke length. Using the old one risks premature wear and failure. New pumps often do not include the pushrod.

Procedure:

  1. Relieve Fuel System Pressure & Disconnect Lines:
    • Open the fuel filler cap to vent the tank.
    • Place clean rags under the pump area.
    • Carefully identify the fuel INLET line (coming from the tank) and the OUTLET line (going to the carburetor). If there is a VAPOR RETURN line, note which one it is.
    • Use pliers (protect fittings with cloth) to loosen the hose clamps securing the rubber hoses to the pump inlet and outlet nipples. Slide the clamps back on the hose.
    • Gently twist and pull each rubber hose off the pump nipples. If fuel drips, catch it with rags. Stuff a short piece of clean vacuum line/hose onto each metal pipe end to minimize drips and prevent debris entry. Plug the pump inlet nipple with a small bolt or golf tee if desired (less crucial).
  2. Remove the Mounting Bolts:
    • The pump is typically secured by two bolts threaded horizontally into the engine block. Some designs might use nuts on studs sticking out from the block.
    • Carefully spray penetrating oil on the bolt heads/nuts if they look rusty. Let it soak briefly.
    • Using the correct sized wrench or socket, loosen and remove both mounting bolts completely. Keep track of them.
  3. Remove the Old Pump:
    • Carefully pull the pump straight out and away from the engine block. There will be resistance from the pump lever pressing on the cam eccentric and from the pushrod.
    • Focus: As the pump comes free, note the small metal pushrod located directly behind it. Be prepared to catch it or carefully control its removal. It should be held in place by the pump lever.
    • Extract the pump and pushrod together. Place them on a rag.
    • Crucial Step: Immediately check the length and condition of the pushrod. Note how it seats inside the pump lever and its length compared to the new one. Discard the old pushrod.
  4. Clean the Mounting Surface:
    • Remove the old gasket and any sealant remnants from the pump mounting surface on the engine block. Use a gasket scraper carefully – avoid gouging the soft aluminum block surface. An old plastic credit card works well. Finish cleaning with brake cleaner on a rag.
    • Also, clean the mounting flange of the new pump if necessary.
  5. Lubricate and Install the NEW Pushrod:
    • Liberally coat the entire length of the NEW fuel pump pushrod with clean engine oil. This minimizes initial wear.
    • Carefully insert the pushrod back into its bore in the engine block. Make sure it slides all the way down and rests squarely against the cam eccentric lobe.
  6. Prepare the New Pump:
    • Identify the proper orientation (lever arm towards the block).
    • Most pumps come with a thin paper gasket or a thick composite gasket/shim. Some include a rubber seal. DO NOT use the old gasket.
    • Apply Sealant: Many mechanics prefer a thin coating of non-hardening sealer like Aviation Form-a-Gasket on BOTH sides of a paper gasket, or just on the pump flange if using a composite/rubber seal that specifies no sealer. If using paper, applying sealer only to the pump side can help prevent the gasket from sticking to the block permanently for future changes. Follow included instructions. Avoid excessive sealer blocking ports.
  7. Install the New Pump:
    • Hold the pump body so the lever arm is positioned correctly to engage the top of the new pushrod. The lever should point towards the block at approximately the same angle as when you removed the old pump.
    • Carefully insert the pump lever over the pushrod and align the mounting holes with the block.
    • Press the pump body firmly against the block mounting surface. You will need to push hard to compress the lever arm spring enough to align the bolt holes with the block threads/studs. This often requires significant force. Having an extra set of hands is helpful.
    • Once pressed firmly against the block, insert the mounting bolts finger-tight. Use a wrench/socket to gently tighten them evenly and gradually. Do NOT overtighten! Refer to a manual for exact specs (typically around 20-25 ft-lbs), but the general rule is snug enough to securely hold the pump without crushing the gasket. Tighten in a star pattern if multiple bolts.
  8. Reconnect Fuel Lines:
    • Remove the temporary plugs/caps from the metal fuel pipes. Slide the hose clamps back onto the rubber hoses.
    • Identify the inlet and outlet pipes on the new pump. Reconnect the tank supply hose to the INLET nipple and the carburetor feed hose to the OUTLET nipple. Make sure any VAPOR RETURN line goes to the correct port on the pump.
    • Slide the hose clamps back into position over the connection and tighten securely. Ensure hoses aren't kinked or touching hot exhaust manifolds.
  9. Check for Leaks & Start Engine:
    • Reconnect the battery negative terminal.
    • Before starting, cycle the key to ON and OFF a few times (assuming you have an electric choke). This allows the float bowl to fill without cranking. Observe the pump area carefully.
    • If no leaks are visible, start the engine. It might crank a few extra seconds as fuel fills the pump body and lines.
    • IMMEDIATELY check the pump mounting surface, fuel lines, and hose connections thoroughly for any signs of dripping fuel.
    • Shut the engine off immediately if any leaks are detected.
    • If no leaks, let the engine idle and warm up. Check again carefully for leaks.

Post-Installation Checks and Troubleshooting

  1. Run Engine Test: Drive the vehicle normally. Ensure previous symptoms (stalling, power loss, hard hot starts) are gone.
  2. Monitor Oil Level & Condition: For the next few oil checks, pay close attention. Ensure the oil level isn't rising abnormally and doesn't smell like gasoline. This verifies no diaphragm leak.
  3. Stuck Float Bowl: If the engine floods after sitting (raw gas smell), a small piece of debris from the new pump or line might have dislodged and stuck the carburetor needle valve open. Removing the carb top to clean the needle/seat might be necessary.
  4. Persistent Issues: If problems remain:
    • Recheck Fuel Supply: Confirm pump inlet line isn't kinked, blocked, or disconnected. Ensure the tank has fuel! Check the tank pickup tube for blockage. Consider replacing old rubber fuel hoses throughout the system.
    • Recheck Pump Operation: Repeat the pressure or volume test. If poor, suspect a defective new pump (rare but possible), incorrect installation (pushrod issue, gasket blocking ports), or a severe upstream restriction.
    • Consider Ignition Issues: Don't rule out ignition problems mimicking fuel starvation. Check spark plug wires, distributor cap, rotor, points/ignition module condition.

Maintaining Your New Fuel Pump

  1. Use Quality Fuel: Fresh, name-brand gasoline is best. Minimize the time fuel sits in the tank, as modern gas can deteriorate over months.
  2. Address Ethanol: Be aware of ethanol content. Use a stabilizer if the vehicle sits for extended periods to counteract ethanol's tendency to absorb water and degrade rubber.
  3. Replace Fuel Filters Regularly: A clogged inline filter or tank strainer puts excessive strain on the pump. Change filters according to your maintenance schedule or sooner if contamination is suspected.
  4. Inspect for Leaks Regularly: Make it a habit to quickly glance at the pump and lines during routine oil checks.
  5. Fix Engine Oil Leaks: Oil dripping onto the pump body can degrade the pump's rubber components over time.

Common Questions About the 1979 Chevy 350 Fuel Pump

  • Q: Can I upgrade to an electric fuel pump?
    • A: Yes, but it's not usually necessary for a stock engine. Electric pumps require wiring, safety switches (oil pressure/inertia), and often a pressure regulator, adding complexity. A correctly functioning mechanical pump is sufficient for most carbureted 350s. It's done for high-horsepower builds needing more flow/pressure than the mechanical pump can provide.
  • Q: How long should a mechanical fuel pump last?
    • A: Lifespan varies greatly. A quality replacement pump should generally last 7-15 years or more in normal use, assuming good maintenance and fuel quality. Ethanol fuel shortens lifespan.
  • Q: Why is my new pump noisy?
    • A: Mechanical pumps make audible clicks as they operate. A new pump may be slightly louder until it breaks in. However, excessive rattling or grinding could indicate incorrect installation, a damaged pushrod, or a defective pump.
  • Q: My pump is leaking from the lever shaft. Can it be rebuilt?
    • A: While rebuild kits exist, they are generally not economical or practical. Replacement of the entire pump is the standard and recommended solution.
  • Q: Where can I buy an AC Delco pump?
    • A: Major auto parts chains (NAPA often carries them), GM dealerships, and online retailers like RockAuto, Summit Racing, or JEGS.

Conclusion: Keeping Your Classic Chevy Rolling

Diagnosing and replacing a worn-out 1979 Chevy 350 fuel pump is a fundamental task for any owner of these iconic vehicles. By understanding how the mechanical pump works, recognizing its failure symptoms, testing methodically, and choosing the right quality replacement part, you can restore reliable fuel delivery. Remember the critical importance of replacing the pushrod during installation to prevent costly headaches later. With patience and the right tools, this repair is straightforward and ensures your small-block V8 continues to deliver dependable power and miles of driving enjoyment for years to come. A well-maintained fuel system keeps your classic Chevy starting easily, running smoothly, and preserving the legacy of one of history's greatest engines.

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