Tracking down leaks, swapping to electronic fuel injection, or restoring a rusted-out chassis on a classic squarebody pickup requires knowing where every single tube runs. A standard 73 87 Chevy truck fuel line diagram maps out the path of feed lines, return lines, vapor lines, and tank selector valves across both single and dual-tank layouts. Whether you're working on a carbureted C10 or planning an engine swap, tracing these hard lines and rubber hoses prevents costly mistakes and dangerous pressure leaks.
Factory fuel plumbing on these trucks uses a combination of 3/8-inch steel feed lines and 5/16-inch return or vapor lines running along the driver-side frame rail. On dual-tank models, a six-port selector valve bridges the left and right saddle tanks before routing fuel toward the engine bay. Knowing how these lines connect, where clips secure them, and how to replace degraded sections safely gets your classic pickup back on the road without guesswork.
Understanding Factory Fuel Line Layouts
General Motors built trucks from 1973 through 1987 with multiple configurations depending on whether the truck came with a single cab-mounted tank, single rear-frame tank, or optional dual saddle tanks. Carbureted models typically featured a mechanical fuel pump on the engine block, utilizing a simple feed line and a vapor return line to prevent vapor lock. Later fuel-injected models introduced electric in-tank pumps and higher operating pressures, requiring dedicated supply and return lines.
On standard single-tank trucks, steel lines run from the fuel sending unit on the tank forward along the inside of the driver-side frame rail. They weave past the transmission crossmember and terminate near the mechanical pump or inline filter. Dual-tank trucks introduce complexity via a frame-mounted selector valve located on the passenger side or driver side depending on the exact model year. Three hard lines cross the rear cab support bracket from each tank to feed this valve.
Line Sizes and Material Specifications
Factory specifications dictate specific outer diameters for each circuit to maintain correct fluid dynamics and pressure. Using incorrect hose dimensions leads to fuel starvation or excessive backpressure.
- Feed lines: 3/8-inch steel tubing for the main supply from the tank to the engine.
- Return and vapor lines: 5/16-inch steel tubing for excess fuel return or charcoal canister vapor routing.
- Rubber jumper sections: Short lengths of high-pressure or fuel-resistant hose used at connection points to absorb engine and chassis vibration.
Original factory lines were constructed of mild steel, which is prone to severe rust if you live in the rust belt or regions that salt winter roads. When replacing corroded sections, modern restorers frequently utilize stainless steel pre-bent lines or high-grade Summit Racing fuel line components for long-term durability. If you're converting to an LS engine swap, switching to PTFE-lined AN hoses handles modern ethanol-blended fuels much better than standard rubber lines.
Tracing Dual Tank Selector Valves
Troubleshooting fuel delivery issues on a dual-tank squarebody usually points directly to the fuel selector valve or its electrical wiring. The valve switches both the fuel feed and the fuel return simultaneously based on dash switch input.
The valve features six primary ports: two inlets and two returns for the dual tanks, plus one main supply feed and one main return line heading to the engine bay. If your truck draws fuel from one tank but pumps it into the other, or fails to switch tanks entirely, inspect the electrical spade connector on the valve solenoid and verify that your JEGS technical resources match your specific year's wiring schematic. A failing selector valve will often trap fuel or block flow entirely, mimicking a clogged fuel filter.
Step-by-Step Fuel Line Replacement
Replacing old, brittle, or leaking metal lines requires patience and methodical disassembly. Rushing the job can strip fittings or damage delicate sending unit tabs.
- Disconnect the negative battery cable to eliminate any spark hazard while working around flammable fuel vapors.
- Relieve system pressure if working on a factory fuel-injected truck (1987 models), or simply drain and drop the fuel tanks if you're replacing lines near the sending units.
- Unbolt the frame rail clips holding the original steel lines in place. Save original hardware if it's reusable, as exact reproduction clips keep restorations looking authentic.
- Unscrew flare fittings using line wrenches to avoid rounding off the soft brass or steel nuts.
- Route your new pre-bent hard lines or flexible hose kits along the inner frame rail, making sure to stay at least six inches away from exhaust components and moving driveshafts.
- Secure every two feet with insulated P-clamps to prevent chafing and vibration fatigue against the frame.
- Reconnect the lines to the sending units, selector valve, and fuel pump, using fresh fuel injection clamps on all rubber junctions.
- Prime the system, check for leaks under key-on engine-off conditions, and test drive.
Common Mistakes to Avoid
Avoiding shortcuts during fuel system maintenance saves you from dangerous roadside leaks or engine performance issues.
Don't run fuel lines directly against sharp frame edges or suspension mounting points without rubber grommets or bulkhead fittings. Friction from road vibration will wear through steel or rubber lines within thousands of miles. Never route fuel lines inside the passenger cabin unless you are using certified pass-through bulkheads and seamless hard tubing designed for safety.
Another frequent error is mixing up the 3/8-inch feed line with the 5/16-inch return line during reconnection. Forcing incorrect hoses onto barbed fittings creates immediate restriction and ruins fuel pressure regulation. Always double-check port sizes at the fuel pump and carburetor or throttle body before tightening clamps.
Frequently Asked Questions
Can I eliminate the dual tanks and convert to a single tank?
Yes, many owners remove the saddle tanks and install a single fuel tank between the rear frame rails out of a Blazer or Suburban. You'll need to plug or remove the selector valve, run a single continuous 3/8-inch feed line forward, and update your fuel gauge sending unit to match your dash gauge ohms resistance.
What size fuel line do I need for an LS engine swap?
Most standard LS swaps up to 450 horsepower run reliably on -6 AN (roughly 3/8-inch inner diameter) PTFE feed and return lines. If you're building a high-horsepower track engine, step up to a -8 AN feed line to ensure adequate volume under wide-open throttle.
Why does my truck smell like gasoline after parking?
A gasoline smell usually points to cracked vapor lines, a saturated charcoal vapor canister in the engine bay, or a leaking rubber hose connection near the rear cab support. Inspect the rubber transition hoses connecting the metal tank vents to the main hard line.
How do I stop fuel lines from vapor locking in hot weather?
Vapor lock happens when liquid fuel boils inside the metal lines due to close proximity to hot exhaust manifolds. Route your lines as far away from the exhaust as possible, wrap vulnerable sections in thermal insulating sleeves, and verify your mechanical fuel pump isn't getting heat-soaked.
