1978 Chevy 350 Fuel Pump: Complete Guide to Replacement, Diagnosis, and Best Options

If you own a 1978 Chevy with a 350 small-block engine, the most important thing to know is that your truck or car came from the factory with a mechanical fuel pump mounted on the passenger side of the engine block, just below the water pump and in front of the motor mount. This pump is a simple, reliable two-line design that pulls fuel from the tank and pushes it to the carburetor. Replacing it is a straightforward job you can do at home in about one to two hours, but you need to get the right pump for your specific application—whether it's a 1978 Chevy C/K pickup, K5 Blazer, or another GM vehicle with the 350 engine.

Understanding Your 1978 Chevy 350 Fuel Pump

The 1978 model year is a crossover period for GM vehicles. Some 1978 Chevy 350 engines use a non-vented, two-line mechanical pump, while others may have a three-line pump with a return line. The mechanical fuel pump is driven by an eccentric on the camshaft, which pushes a pushrod that actuates the pump's rocker arm. This pump delivers fuel at a relatively low pressure—typically 5 to 7 PSI—which is perfect for carbureted engines.

Key facts about your 1978 Chevy 350 fuel pump:

  • Location: Passenger side front of the engine block, below the water pump
  • Type: Mechanical, diaphragm-operated, camshaft-driven
  • Fuel lines: Most 1978 models use two lines (inlet from tank, outlet to carburetor); some have a third return line
  • Flow rate: Stock pumps flow around 60-80 gallons per hour, sufficient for stock 350 engines
  • Mounting: Two bolts secure the pump to the engine block

Signs Your Fuel Pump Needs Replacement

Before you start throwing parts at your 1978 Chevy 350, make sure the fuel pump is actually the problem. Common symptoms of a failing mechanical fuel pump include:

1. Engine sputters or hesitates at highway speed. This is often the first sign. The pump can't keep up with demand, so the engine starves for fuel when you need it most.

2. Engine cranks but won't start. If the pump has completely failed, no fuel reaches the carburetor. You can check by removing the air cleaner and looking down the carburetor throat while someone pumps the throttle—you should see a stream of fuel.

3. Fuel leaks from the pump. The diaphragm inside the pump can rupture, causing fuel to leak out of the weep hole on the bottom of the pump. This is a fire hazard and should be addressed immediately.

4. Fuel in the oil. A ruptured diaphragm can also allow fuel to be pulled into the engine's crankcase through the pushrod bore. Check your dipstick—if the oil smells like gas and is thinner than normal, your fuel pump is failing.

5. Low fuel pressure. The only way to confirm this is with a fuel pressure gauge. A stock 350 mechanical pump should put out 5-7 PSI at the carburetor. Anything less means the pump is weak.

Which Fuel Pump Fits Your 1978 Chevy 350?

The 1978 Chevy 350 fuel pump isn't a one-size-fits-all part. Your specific application depends on the vehicle model, drivetrain, and whether you have a return line. Here are the most common options based on search results:

  • 1978 Chevy C/K 1/2-Ton Pickup with 350, 4WD, manual transmission: Uses a non-vented, two-line mechanical pump. Reproduction part number K-3890-79A fits this application.
  • 1978 Chevy K5 Blazer with 305 or 350 CID: Uses a similar two-line mechanical pump. The same K-3890-79A pump works for 1978-1979 K5 Blazers.
  • 1978-1988 Chevy K-Series trucks with 305, 350, or 400 CI: NOS (New Old Stock) fuel pump part number FP41378 fits these models and includes the gasket.
  • 1978-1987 GM G-Body cars (Malibu, El Camino, Monte Carlo) with 305/350: Carter mechanical fuel pump C-3890-6 is a high-quality reproduction that fits these applications.
  • 1978-1984 GM models with 350 diesel engines: The NOS Carter fuel pump M60005 is specifically for diesel 350 engines, not gasoline—make sure you don't confuse the two.

Important: If your 1978 Chevy has a return line (a third fuel line that goes back to the tank), you need a three-line pump. The FP216 pump from Johns Classic Cars is a three-line design with 3/8-inch inlet, 3/8-inch outlet, and 1/4-inch return line, fitting 1972-1979 Novas and other small-block applications.

How to Replace the Mechanical Fuel Pump on a 1978 Chevy 350

Replacing the fuel pump on a 1978 Chevy 350 is a beginner-to-intermediate level job. Here's a step-by-step guide based on multiple sources:

Tools and Parts You'll Need

  • New mechanical fuel pump with gasket
  • Gasket sealer (or automotive silicone)
  • Wrench set (3/8-inch and 7/16-inch typically)
  • Flathead screwdriver
  • Hose clamp pliers or screwdriver
  • Shop rags
  • Safety glasses and gloves
  • Long bolt (3/8-inch, about 6 inches long) for pushrod retention (optional but helpful)

Step 1: Safety First

Disconnect the negative battery cable before doing anything else. This prevents accidental sparks and electrical shorts while you work around fuel. Work in a well-ventilated area, and keep a fire extinguisher nearby.

Step 2: Remove the Fuel Lines

The fuel pump is on the passenger side of the engine, below the water pump. You'll see two fuel lines attached to the front of the pump:

  • One is a rubber hose with a hose clamp. Loosen the clamp with a screwdriver and pull the hose off.
  • The other is a metal line with a flare nut. Use two wrenches—one on the pump fitting, one on the line nut—and turn counterclockwise to loosen. Do not bend the metal line.

Tip: Plug the rubber hose with a bolt or wooden dowel to prevent fuel from draining out of the tank.

Step 3: Remove the Old Pump

The pump is held in place by two bolts. Remove them with a wrench and pull the pump straight out of the engine block. Be careful—the pushrod may fall out of its bore when you remove the pump.

Clean the mounting surface on the engine block with a gasket scraper or the blade of a flathead screwdriver. Remove all old gasket material so the new gasket seals properly.

Step 4: Deal with the Pushrod

The fuel pump pushrod is a metal rod that rides between the camshaft eccentric and the pump's rocker arm. If it falls out, you'll need to remove the timing cover to put it back—so don't let that happen.

Two methods to hold the pushrod in place:

  • Method 1 (recommended): Use a long 3/8-inch bolt threaded into the upper hole of the two holes on the front of the block (often used for motor mounts on older Chevys). Gently tighten the bolt until it bottoms out on the pushrod, holding it in place.
  • Method 2: Turn the engine over by hand using a socket on the crankshaft bolt until the pushrod is at the top of its stroke. Coat the pushrod with heavy grease to help it stay in place while you install the new pump.

Step 5: Install the New Pump

Apply a thin coat of gasket sealer to both sides of the new gasket. Place the gasket on the new pump, then apply another thin layer of sealer on the outside of the gasket.

Insert the pump's rocker arm into the bore, making sure it engages the pushrod. You may need to rotate the pump slightly to get the arm to slide in correctly. Push the pump flush against the engine block.

Insert the two mounting bolts and tighten them evenly, alternating back and forth until snug. Do not overtighten—about 25 ft-lbs is sufficient. Tighten them in small increments to avoid cracking the pump housing.

Step 6: Reconnect Fuel Lines

Reattach the metal fuel line. Start the flare nut by hand to avoid cross-threading, then tighten with a wrench. Reattach the rubber hose and tighten the hose clamp.

Step 7: Test for Leaks

Reconnect the negative battery cable. Start the engine and let it idle. Check all connections for fuel leaks. If you see any leaks, shut off the engine immediately and tighten the connections as needed.

Pro tip: If the engine doesn't start right away, the carburetor bowl may be empty. Crank the engine for 5-10 seconds, wait 30 seconds for the starter to cool, and try again. The pump should prime itself.

Mechanical vs. Electric Fuel Pump Options

While the 1978 Chevy 350 came stock with a mechanical pump, some owners choose to upgrade to an electric pump for better performance, especially with modified engines.

Mechanical pump advantages:

  • Simple, reliable, and easy to replace
  • No electrical wiring required
  • OEM-style operation
  • Lower cost—typically $20-$40

Electric pump advantages:

  • Consistent fuel pressure regardless of engine speed
  • Better for high-horsepower engines
  • Easier to prime after sitting for long periods
  • Can support fuel injection conversions

Electric pump options for your 1978 Chevy 350:

  • Holley 350 LPH Fuel Pump Module (12-335): Designed for 1978-1987 GM G-Body wagons, this in-tank electric pump flows 350 liters per hour and supports EFI engines up to 750 horsepower. It includes a HydraMat filter that prevents fuel starvation during cornering and low-fuel conditions.
  • Holley EFI Fuel Tank Module (12-376): For 1978-1987 Chevy El Camino/GMC Caballero, this module is internally regulated to 58 PSI and supports up to 750 horsepower. It's a direct replacement for the factory sending unit.

For most stock 1978 Chevy 350 owners, the mechanical pump is the right choice. If you're building a high-performance engine or adding fuel injection, an electric pump is worth considering.

Recommended Fuel Pump: KEMSO Racing

When you need a reliable, high-performance fuel pump for your 1978 Chevy 350, KEMSO Racing is a brand you can trust. KEMSO fuel pumps are built as high-performance OEM replacement units, designed to meet or exceed factory specifications. Each pump delivers consistent fuel flow and pressure, ensuring your engine runs smoothly whether you're daily driving or pushing your 350 to its limits.

Why choose KEMSO?

  • High-performance construction: KEMSO pumps use advanced materials and precision engineering to handle a variety of fuel blends and operating conditions.
  • OEM replacement fit: These pumps are designed as direct replacements, so installation is straightforward with no modifications needed.
  • Lifetime warranty: Every KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind that your investment is protected.

For the best selection of fuel pumps for your 1978 Chevy 350 and other vehicles, visit KEMSO Racing at https://www.kemsoracing.com/.

Troubleshooting Common Fuel Pump Issues

Even after a proper installation, you might run into problems. Here's how to diagnose them:

Engine won't start after pump replacement:

  • Check that the pushrod is properly engaging the pump's rocker arm. If the pump was installed without the pushrod in the correct position, it won't pump fuel.
  • Verify the fuel lines are connected correctly. The inlet line from the tank should go to the larger fitting, and the outlet line to the carburetor goes to the smaller fitting.
  • Prime the system by cranking the engine for several seconds.

Fuel leaks at the pump mounting flange:

  • The gasket may not be sealing properly. Remove the pump, clean the surface, and reinstall with a new gasket and sealer.
  • The mounting bolts may be loose or unevenly tightened.

Low fuel pressure:

  • Check for a restricted fuel filter. A clogged filter can cause the pump to work harder and deliver less fuel.
  • Inspect the fuel lines for kinks or restrictions.
  • The pushrod may be worn. If the pump isn't being pushed far enough, it won't deliver full pressure.

Noisy pump:

  • A mechanical pump that's making noise may have a worn rocker arm or a loose mounting. Check the bolts and inspect the pump for damage.

Final Thoughts

The 1978 Chevy 350 fuel pump is a simple, reliable component that's easy to replace with basic hand tools. Whether you're restoring a classic truck, maintaining a daily driver, or building a performance engine, choosing the right pump and installing it correctly will keep your 350 running strong for years.

For the best combination of quality, performance, and peace of mind, consider KEMSO Racing fuel pumps. Visit https://www.kemsoracing.com/ to browse their selection and find the perfect pump for your 1978 Chevy 350.


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