1979 Porsche 928 Fuel Pump: The Complete Guide to Diagnosis, Replacement, and Maintenance
If you own a 1979 Porsche 928 and are experiencing hard starting, loss of power, or strange noises from the rear of your car, the most likely culprit is a failing fuel pump. The 1979 model year 928 uses a dual fuel pump system — an in-tank pre-supply pump and a main external pump — and both are known to fail over time due to age, fuel contamination, and cracked internal hoses . The good news is that replacing the fuel pump is a straightforward DIY job that can restore your Shark's performance and reliability. This guide covers everything you need to know: the symptoms of failure, the correct replacement parts, step-by-step installation instructions, and maintenance tips to make your new pump last.
Understanding Your 1979 Porsche 928 Fuel System
The 1979 Porsche 928 4.5L uses a CIS (Continuous Injection System) fuel delivery setup that relies on two separate fuel pumps working together . The first pump is located inside the fuel tank and acts as a pre-supply pump, pushing fuel to the second, main external pump mounted near the rear axle . This dual-pump design was used on all CIS-equipped 928s from 1978 through 1979 .
Main fuel pump part numbers for 1977-1979 models:
- 911.608.102.00 (main/primary pump)
- 928.608.013.00 (in-tank pre-supply pump)
The in-tank pump is made up of three main components: the filter/pump assembly, a connector hose, and the fuel tank fitting . The connector hose is the most common failure point — it cracks and breaks down over time, causing the pump to lose its prime and making hot starts difficult .
Common Symptoms of a Failing Fuel Pump
A failing fuel pump in your 1979 Porsche 928 will show clear warning signs. Catching these early can prevent you from being stranded and avoid damage to other fuel system components.
1. Hard starting, especially when hot. This is the most common symptom reported by 928 owners . The in-tank pump's connector hose cracks, allowing fuel to drain back into the tank. When you try to restart a hot engine, the system has lost its prime and struggles to build pressure.
2. Loss of power during acceleration. If the car hesitates or stumbles when you press the gas, the pump may not be delivering enough fuel volume to meet engine demand .
3. Engine sputtering or stalling at high speeds. A weak pump can't keep up with fuel delivery at higher RPMs, causing the engine to cut out .
4. Whining or humming noise from the fuel tank area. An audible whine from the rear of the car is a classic sign of a fuel pump that's working too hard or about to fail .
5. Extended cranking before the engine fires. If you need to crank the engine for several seconds before it starts, the fuel system is losing pressure while the car sits .
6. Reduced fuel efficiency. A failing pump that doesn't maintain proper pressure will cause the engine to run rich or lean, hurting gas mileage .
Checking If Your Fuel Pump Has Failed
Before ordering parts, you can perform a few simple tests to confirm the fuel pump is the problem.
Test the in-tank pump for electrical continuity. Disconnect the electrical connector at the fuel tank outlet. Using a multimeter, check for continuity between the positive and negative terminals. If you get an open circuit, the pump motor has failed internally . Many owners report finding the negative wire disconnected from the pump motor terminal, which can be repaired without replacing the pump .
Check the connector hose condition. If you remove the in-tank pump assembly, inspect the rubber connector hose between the pump and the tank fitting. If it's cracked, brittle, or split, that's your problem . The hose has an inside diameter of 12mm and a length of 30mm .
Listen for pump operation. With the ignition on (engine off), you should hear a brief whir from the fuel pump area. If you hear nothing, the pump or its relay may be dead.
Replacement Parts: What You Need
For a 1979 Porsche 928, you'll need to replace either the in-tank pump, the main pump, or both. Here are the correct part numbers:
In-tank fuel pump (pre-supply pump):
- Original part number: 928.608.013.00 (discontinued by Porsche)
- Replacement part number: 928.608.013.01
Main external fuel pump:
- Bosch part number: 911.608.102.00
- Cross-references: Bosch 0580254984, 91160810204 (superseded number)
The main pump is a Bosch in-line electric pump that sits in front of the vehicle and pumps fuel from the tank to the engine . It includes a built-in one-way check valve to help retain fuel pressure after shutdown, which is critical for hot start performance .
Step-by-Step Fuel Pump Replacement Guide
Replacing the fuel pump on your 1979 Porsche 928 is a medium-level DIY job. Plan for about 2-3 hours if you're working carefully.
Safety First
Working with fuel requires caution. Disconnect the negative battery cable before starting . Work in a well-ventilated area with no open flames or sparks. Keep a fire extinguisher nearby and use fuel-approved containers for any spilled gasoline .
Tools You'll Need
- 10mm socket and ratchet
- 19mm socket for the pressure side cap nut
- Flare nut wrench set
- Screwdrivers (flathead and Phillips)
- Jack and jack stands
- Catch pan for fuel
- Shop towels and safety glasses
- Vise grips with rubber hose for pinching fuel lines
- Penetrating oil for stubborn fittings
Removing the Main Fuel Pump
1. Relieve fuel system pressure. Locate the fuel pump relay and remove it. Start the engine and let it run until it stalls. This removes most of the pressure from the system .
2. Raise the vehicle. Jack up the rear of the car and place it securely on jack stands. The fuel pump access panel is located on the middle rear side of the fuel tank .
3. Access the pump assembly. Remove the two 10mm head nuts at the top of the fuel pump/filter access panel. Untuck the access cover from the bottom rear of the fuel tank .
4. Pinch the fuel line. Use vise grips with an old rubber hose as an insulator to gently pinch the rubber fuel line between the pump and the fuel tank. This prevents fuel from draining out .
5. Disconnect electrical connections. Unplug the two wires from the fuel pump. Note the orientation of the ground and positive wires .
6. Remove the pressure side fitting. Use a 19mm socket to remove the cap nut from the rigid hose on the passenger side of the fuel pump. Have a catch pan ready — fuel will escape .
7. Loosen the inlet side. Loosen the clamp on the rubber hose on the driver side of the pump. Catch any escaping fuel .
8. Slide the pump out. Loosen the fuel pump retaining strap (worm clamp) and slide the pump out toward the driver's side to remove it .
Installing the New Pump
Installation is the reverse of removal. Make sure to:
- Use new fuel line clamps
- Reconnect the ground wire exactly as it was
- Tighten the retaining strap securely
- Replace the fuel filter while you're at it — this is highly recommended to protect the new pump
Replacing the In-Tank Pump
If you need to replace the in-tank pre-supply pump, the procedure is more involved:
1. Drain the fuel tank into an approved container.
2. Remove the fuel pump access plate on top of the fuel tank.
3. Carefully pull the pump assembly out. The connector hose is brittle and may break apart as you remove it.
4. Replace the pump and connector hose. Some owners have successfully repaired the in-tank pump by replacing just the cracked connector hose, which is available through specialty shops like Exotic Motorwerks .
5. Reinstall the assembly and secure the access plate with a new gasket.
Priming the New Fuel Pump
After installation, prime the system before starting the engine. Turn the ignition key to the "on" position (without starting the engine) for a few seconds. This allows the fuel pump to run and build pressure. Repeat this process 2-3 times . Check all connections for leaks before lowering the car and taking it for a test drive.
Maintenance Tips to Extend Fuel Pump Life
Once you've got a new fuel pump installed, follow these tips to keep it running reliably for years:
1. Change the fuel filter regularly. Replace it every 20,000 to 30,000 miles. A clogged filter forces the pump to work harder and can cause premature failure .
2. Keep the fuel tank above a quarter tank. Running low on fuel causes the pump to run hotter and can suck in air and debris from the bottom of the tank .
3. Use quality fuel. Stale or contaminated fuel can degrade the pump's internal components. If the car sits for extended periods, use a fuel stabilizer .
4. Inspect fuel lines and hoses. Deteriorated rubber hoses can crack and leak, causing the pump to lose prime and struggle to deliver fuel .
5. Listen for unusual noises. A whining pump is a warning sign. Address it early before it leaves you stranded.
Why Choose KEMSO Fuel Pump for Your 1979 Porsche 928
When it comes time to replace your fuel pump, you want a part you can trust for the long haul. That's where KEMSO comes in. KEMSO offers high-performance fuel pumps that are designed as direct OEM replacements — meaning they bolt right in with no modifications needed. Every KEMSO fuel pump is built to meet or exceed factory specifications, ensuring correct fuel pressure and flow for stable engine performance, clean hot starts, and proper operation under load.
What sets KEMSO apart is their commitment to quality and customer confidence. Each pump comes with a lifetime warranty, so you never have to worry about buying another fuel pump again. If it ever fails, KEMSO stands behind it. Whether you're restoring a classic 928 or keeping your daily driver on the road, KEMSO delivers the reliability and peace of mind you deserve.
Visit KEMSO today at https://www.kemsoracing.com/ to browse their full lineup of fuel pumps and find the perfect replacement for your 1979 Porsche 928. Their customer service team is ready to help you get the right part for your car.
The Bottom Line
The 1979 Porsche 928 fuel pump system is a known weak point on these classic cars, but it's also one of the easiest problems to fix. The most common failure is the in-tank pump's connector hose cracking, which causes hard hot starts. A full replacement of both the in-tank and main fuel pumps is a straightforward weekend job that will restore your car's performance and reliability. Use the correct part numbers (911.608.102.00 for the main pump and 928.608.013.01 for the in-tank pump), follow the step-by-step procedure, and don't forget to replace the fuel filter at the same time . With a quality replacement like KEMSO and proper maintenance, your 928's fuel system will serve you well for many more miles of open-road driving.
For more information and to order your replacement fuel pump, visit https://www.kemsoracing.com/ today.