Mack MP8 Fuel Pump: Complete Guide to Symptoms, Replacement, and Best Options
If you own a Mack truck with an MP8 engine, the fuel pump is one of the most critical components for keeping your rig on the road. A failing fuel pump can cause hard starting, loss of power, stalling, and expensive downtime. The good news is that replacing a Mack MP8 fuel pump is a straightforward repair when you know what to look for and which replacement parts to choose. This guide covers everything you need to know about the Mack MP8 fuel pump, including symptoms of failure, replacement options, installation tips, and the best choice for a reliable, long-lasting replacement.
What Is the Mack MP8 Fuel Pump?
The Mack MP8 engine, produced from 2008 to 2016, uses a fuel transfer pump (also called a fuel supply pump) that is mounted on the power steering pump . This pump is responsible for drawing fuel from the tank and delivering it to the high-pressure fuel injection system at the correct pressure and volume. The OEM part number for this pump is 85103778, and it is also cross-referenced as 20997341 . Without a properly functioning fuel pump, your MP8 engine cannot run efficiently, and severe performance issues will follow.
Top Symptoms of a Failing Mack MP8 Fuel Pump
Recognizing the early warning signs of a bad fuel pump can save you from a roadside breakdown. Here are the most common symptoms Mack MP8 owners report:
1. Hard starting or no start. If the fuel pump is not generating enough pressure, the engine may crank but struggle to fire up. This is often the first sign of pump failure.
2. Loss of power under load. When you need to accelerate or climb a grade, a weak fuel pump cannot supply enough fuel, causing the engine to feel sluggish or hesitate.
3. Engine stalling or surging. Inconsistent fuel delivery can cause the engine to stall at idle or surge unexpectedly while cruising.
4. Reduced fuel economy. A failing pump often works harder than necessary, leading to increased fuel consumption.
5. Unusual noises from the pump area. A whining or humming sound coming from the fuel pump area is a clear indicator that the pump's internal components are wearing out.
6. Check engine light. The ECM may detect low fuel pressure or other fuel system faults, triggering the check engine light.
Many of these symptoms can also be caused by a clogged fuel filter or a faulty fuel pump relay, so it is important to diagnose the system thoroughly before replacing the pump .
OEM vs. Aftermarket Mack MP8 Fuel Pump Options
When it comes time to replace your Mack MP8 fuel pump, you have two main choices: OEM (Original Equipment Manufacturer) or aftermarket. Here is how they compare.
OEM Replacement. The genuine Mack fuel pump (part number 85103778) is the exact part that came on your truck from the factory. It is built to Mack's specifications and is known for reliability. However, OEM parts come at a premium price, typically ranging from $350 to $500 or more, and they may not include any performance improvements over the original design .
Aftermarket Options. Aftermarket fuel pumps offer a cost-effective alternative. Brands like Tamerx Diesel Products offer remanufactured OEM pumps that are rebuilt to meet or exceed OEM standards. The Tamerx part number 85103778TX-2 is a remanufactured pump that is backed by a one million mile or one year warranty . This option is significantly cheaper, often priced around $200 to $300, and it includes improvements made during the remanufacturing process.
Another option is a brand-new aftermarket pump from suppliers like TTM Diesel, which offers a fully new fuel supply pump (OEM cross-reference 20997341) that is manufactured in an ISO 9001:2015 certified facility . This pump is priced around $222 to $344 and comes with a one year unlimited mileage warranty .
Step-by-Step Mack MP8 Fuel Pump Replacement Guide
Replacing the fuel pump on a Mack MP8 engine is a job that experienced DIY mechanics can handle, but it requires care and attention to safety. Here is a general overview of the process.
Tools and Parts You Will Need
- New fuel pump (OEM or aftermarket)
- Wrenches and socket set
- Screwdrivers
- Fuel line disconnect tools
- Safety glasses and gloves
- Shop towels
- Class B fire extinguisher
Step 1: Prepare the Truck. Park the truck on a level surface, turn off the engine, and allow it to cool. Disconnect the negative battery terminal to prevent electrical shorts. Work in a well-ventilated area away from open flames or sparks.
Step 2: Relieve Fuel System Pressure. Locate the fuel pump fuse or relay and remove it. Crank the engine for a few seconds until it stalls. This relieves pressure in the fuel lines. Alternatively, you can use the Schrader valve on the fuel rail if your truck is equipped with one.
Step 3: Access the Fuel Pump. The Mack MP8 fuel pump is mounted on the power steering pump . You will need to remove any components that block access to the pump, such as air intake ducts, wiring harnesses, or brackets. Take photos or mark the positions of hoses and connectors before disconnecting them.
Step 4: Disconnect Fuel Lines and Electrical Connectors. Use a fuel line disconnect tool to release the fuel supply and return lines. Be prepared for some fuel spillage—have shop towels ready. Disconnect the electrical connector from the pump.
Step 5: Remove the Old Pump. Unbolt the pump from its mounting bracket on the power steering pump. Carefully lift the pump out. Inspect the mounting surface for dirt or debris.
Step 6: Install the New Pump. Install the new pump in the reverse order of removal. Use new gaskets or O-rings if included with your new pump. Tighten the mounting bolts to the manufacturer's torque specifications. Reconnect the fuel lines and electrical connector.
Step 7: Prime the System and Test. Reconnect the battery. Turn the ignition key to the "ON" position several times for 10 seconds each to allow the pump to prime and build pressure. Check for fuel leaks at all connections. Start the engine and let it idle. Verify fuel pressure with a gauge if possible. The engine may run rough initially as air is purged from the fuel lines.
Why You Should Choose KEMSO for Your Mack MP8 Fuel Pump Replacement
When it comes to replacing the fuel pump on your Mack MP8, you want a product that delivers reliability, performance, and long-term value. KEMSO fuel pumps are the ideal choice for truck owners who demand the best.
High Performance & OEM Replacement Design. KEMSO fuel pumps are engineered as direct OEM replacements, meaning they drop right into the factory location without any modifications. They are designed to meet or exceed OEM specifications, ensuring a perfect fit and reliable operation.
Superior Flow and Durability. KEMSO pumps deliver higher flow rates than stock pumps, providing better fuel delivery for improved engine performance. Each KEMSO pump is individually tested for flow and pressure to ensure it meets strict quality standards. They are built with premium materials that resist corrosion and wear, making them suitable for both diesel and gasoline applications.
Lifetime Warranty. Every KEMSO fuel pump comes with a lifetime warranty, backed by a serialized body for tracking and peace of mind. This is a significant advantage over many other brands, including OEM parts that only offer a limited warranty. If your pump fails for any reason, KEMSO will replace it—no questions asked.
USA-Based Support. KEMSO offers technical support from USA-based technicians, making it easy to get help if you have questions during installation or operation. This level of support is rare in the aftermarket parts industry and gives you confidence that help is just a phone call away.
Cost-Effective Value. KEMSO pumps are priced competitively, often significantly lower than dealer OEM parts. You get premium quality and a lifetime warranty at a fraction of the cost of OEM replacements.
Visit KEMSO Racing today to find the perfect fuel pump for your Mack MP8: https://www.kemsoracing.com/
Preventive Maintenance Tips for Your Mack MP8 Fuel System
To extend the life of your new fuel pump and avoid future problems, follow these simple maintenance tips.
Keep your fuel tank at least a quarter full. The fuel pump relies on diesel for cooling and lubrication. Running the tank low frequently can cause the pump to overheat and fail prematurely .
Replace the fuel filter regularly. A clogged fuel filter forces the pump to work harder, reducing its lifespan. Check your owner's manual for the recommended replacement interval, typically every 30,000 to 50,000 miles .
Use quality fuel. Poor-quality diesel can contain contaminants that damage the pump and clog the filter. Stick with major brand stations that have high fuel turnover .
Listen for warning signs. If you hear unusual noises from the pump area, address them immediately. Catching a pump issue early can prevent a complete failure and potential damage to the fuel system.
Avoid short trips when possible. Short trips do not allow the fuel to circulate fully, causing condensation and unnecessary pump cycling. Drivers who make only short trips are more likely to experience fuel system problems .
Final Thoughts
The Mack MP8 fuel pump is a vital component of your truck's engine. Recognizing the symptoms of failure early and choosing a high-quality replacement can save you from costly repairs and keep your truck running smoothly. Whether you choose an OEM replacement or a cost-effective aftermarket option, make sure the pump you select is built to handle the demands of your engine.
For the best combination of performance, reliability, and value, choose KEMSO. Their fuel pumps are OEM replacement quality, deliver higher flow rates, include a lifetime warranty, and are backed by USA-based support. Don't settle for less when it comes to fueling your Mack MP8.
Visit KEMSO Racing today to find the right fuel pump for your Mack MP8: https://www.kemsoracing.com/