Ford V10 RV Engine Codes P0171 P0174: Complete Diagnosis Guide

Short Answer

Since you've already checked vacuum lines and the MAF sensor on your 2004 Fleetwood Southwind V10, and both P0171 and P0174 codes are present with no drivability issues, common causes include failing fuel injectors or a weak fuel pump. With 68K miles, the injectors may be getting clogged or the fuel pump pressure may be dropping below specifications. Before replacing expensive parts, test fuel pressure first and consider a professional fuel injector cleaning service, which typically costs $150-200 versus $800+ for injector replacement.

Understanding the Problem

Your V10 engine is throwing lean codes on both banks, which means the oxygen sensors are detecting insufficient fuel relative to air. Since you've methodically checked for vacuum leaks using starting fluid and cleaned the MAF sensor, you've eliminated the most common air-side causes. The fact that your engine runs smoothly with normal acceleration and gas mileage actually points away from major vacuum leaks, which typically cause rough idle and poor performance.

On the 2004 Ford V10 in your Southwind, P0171 and P0174 appearing together often indicates a fuel delivery problem rather than an air leak. The fuel system components that commonly fail include the fuel pump (which can lose pressure gradually), fuel filter (if clogged), and fuel injectors (which can become restricted with deposits). The V10 is also known for developing hairline cracks in the intake manifold gaskets, but these usually cause more noticeable performance issues.

Another possibility specific to your coach is the fuel pump driver module, located in the engine bay. This module controls fuel pump operation and can cause intermittent lean conditions as it begins to fail. Ford issued several technical service bulletins about this component on V10 engines from this era.

What You'll Need

For diagnostic testing, you'll need a fuel pressure gauge with the correct fitting for the fuel rail test port (typically a 3/8" quick-connect). Most auto parts stores loan these tools for free. You'll also want a basic multimeter to test electrical connections and a fuel pressure regulator vacuum line.

WARNING: Have a fire extinguisher nearby when working with fuel system components, and ensure you're working in a well-ventilated area away from ignition sources. You'll also want safety glasses and nitrile gloves, as fuel can damage skin and eyes.

If you decide to clean the injectors yourself, you'll need a quality fuel system cleaner like Chevron Techron or Lucas Upper Cylinder Lubricant, though professional cleaning is more effective for stubborn deposits. For potential fuel filter replacement, you'll need a 5/8" and 3/4" flare nut wrench set to avoid damaging the fuel lines.

How to Fix It

SAFETY WARNING: Before working on fuel systems, disconnect the battery and relieve fuel system pressure by removing the fuel pump fuse and running the engine until it stalls, then crank for 5-10 seconds to ensure complete pressure relief.

Start by testing fuel pressure at the rail with the engine running. The V10 should maintain 30-45 PSI at idle (verify specific model specifications). If pressure is low, turn off the engine and check if pressure holds - it should drop no more than 5 PSI in 15-20 minutes. Rapid pressure loss indicates a leaking injector or fuel pressure regulator, while low running pressure points to pump or filter issues.

If fuel pressure tests normal, examine the fuel pump driver module, typically located in the engine bay. Look for corroded connections or heat damage to the module housing. These modules cost around $150-200 and are relatively easy to replace. Check for any loose or corroded ground connections in this area as well.

Try adding a high-quality fuel system cleaner to a full tank and drive for several hundred miles. Sometimes carbon deposits on injector tips cause intermittent lean conditions that don't affect overall performance. If codes return after this treatment, consider professional injector cleaning, which uses specialized equipment to remove deposits that over-the-counter cleaners cannot.

As a final step, check the intake manifold bolts for proper torque (verify specific torque specifications in your service manual as values vary by year and application). Over time, these can loosen slightly, causing small air leaks that don't trigger during your starting fluid test but still register with sensitive oxygen sensors. This is a free check that takes about 30 minutes and should be done in the proper sequence specified in your service manual.

Leave It to the Experts

If fuel pressure testing reveals pump failure, replacement typically costs $400-600 in parts plus 3-4 hours labor, as the fuel tank must be dropped. Most RV service centers charge $120-150 per hour for this work. Professional fuel injector cleaning services cost $150-200 and can resolve lean codes caused by deposits without the expense of injector replacement.

Consider professional diagnosis if you're uncomfortable working with fuel system components or lack the proper safety equipment. A good technician can perform smoke testing to find vacuum leaks your starting fluid test might have missed, and they have access to advanced scan tools that can monitor fuel trim data in real-time while driving.

For injector replacement, expect costs of $800-1200 for parts and labor if multiple injectors are failing. However, given your engine's smooth operation, this is less likely than fuel delivery or minor air leak issues. Many shops will provide a diagnostic fee credit toward repair costs, making professional diagnosis worthwhile if your initial tests don't reveal the problem.