Katerina Swanson
If you're experiencing issues with your 1979 Porsche 924's fuel injectors, it could be due to a variety of reasons. Fuel injectors deliver fuel into the air stream as it enters the combustion chamber, and if they're not working properly, it can cause the car to run poorly. One common problem with the 924 model is the hot-start problem, where the car won't start without excessive cranking when warm if it has been sitting for more than 15 minutes after shutdown. This is often caused by leaking injectors or fuel draining back into the tank. To prevent and fix such issues, Porsche recommends using Chevron fuel injector cleaner with Techron to keep the fuel injection system lubricated and clog-free.
1979 Porsche 924 Fuel Injector Backflush Characteristics
| Characteristics | Values |
|---|---|
| Fuel Injector Function | Deliver fuel into the air stream as it enters the combustion chamber |
| Injector Atomization | Atomize fuel under pressure |
| Fuel System Maintenance | Use Chevron fuel injector cleaner with Techron |
| Fuel Pump Behaviour | Can get hot before they die |
| Fuel System Enemy | Dirt and water |
| Fuel Tank Recommendation | Drain and flush with new clean fuel |
| Fuel Injector Tool | Screwdriver |
| Common Problem | "Hot-start problem" |
| Fuel System Component | K-Jetronic Warm Up Regulator |
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What You'll Learn
- Porsche recommends Chevron injector cleaner with Techron to prevent clogging
- The biggest enemy of the CIS system is dirt, followed by water
- The hot-start problem is caused by not maintaining high fuel pressure
- The K-Jetronic is capable of handling nearly double the output of the stock engine
- The basic function of the Control Pressure Regulator is to enrich the mixture during warm-up
Porsche recommends Chevron injector cleaner with Techron to prevent clogging
Techron Concentrate Plus is a complete fuel system cleaner that can help clean deposits from fuel injectors, carburetors, intake valves, and combustion chambers. It can also clean, restore and protect the entire fuel system, including sulfur-contaminated fuel gauge sensors. It is designed for gasoline carbureted or fuel-injected spark ignition engines.
The Chevron injector cleaner with Techron is safe for use in all gasoline engines and is formulated with high-quality ingredients. It is trusted by many major automakers worldwide and can be used for regular maintenance. It is recommended for use every season or right before an oil change.
Using Chevron injector cleaner with Techron will help keep the fuel injection components from clogging up and keep them lubricated. This covers everything from the fuel pump to the injectors.
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The biggest enemy of the CIS system is dirt, followed by water
The CIS system in a Porsche 924 is highly susceptible to dirt and water damage. Dirt can jam in the tight clearances of the fuel injection components, causing them to clog up. Water, on the other hand, can lead to rust, which will also jam these clearances.
To prevent this, Porsche recommends using Chevron fuel injector cleaner with Techron as a preventative maintenance measure. This should be done at least every 15,000 miles and will help keep the fuel injection system lubricated and clog-free.
Additionally, when restoring a car that has been sitting for a while, it is advisable to drain the fuel tank, flush it with new clean fuel, and then fill it with fresh fuel. This process ensures that any built-up dirt or water is removed, reducing the risk of damage to the CIS system.
Another common issue with the Porsche 924 is the "hot-start problem," where the car starts easily when cold but struggles to start when warm if it has been sitting for more than 15 minutes. This issue is typically caused by a failure to maintain high fuel pressure in the engine compartment due to leaking injectors or fuel draining back into the tank. To address this, ensure that the fuel accumulators and check valve in the fuel pump are functioning properly to prevent fuel from draining back into the tank.
Furthermore, the K-Jetronic system in the Porsche 924 has been known to be capable of handling nearly double the output of the stock engine without major modifications. This system is solid and reliable when properly maintained and will stay in tune, making it a notable advancement for its time. Additionally, load-sensitive enrichment can be added to the stock CIS system by replacing the stock Control Pressure Regulator with a vacuum-sensing unit, although this modification cannot be performed on a stock 924 unit without significant work.
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The hot-start problem is caused by not maintaining high fuel pressure
The 1979 Porsche 924 is a classic car, but like any machine, it can experience problems. One issue that owners may encounter is the "hot-start problem", where the car starts smoothly when the engine is cold but refuses to start without excessive cranking when warm. This issue is specifically caused by not maintaining high fuel pressure in the engine compartment.
There are several reasons why high fuel pressure may not be maintained, leading to the hot-start problem. One common cause is leaking fuel injectors. After engine shutdown, the injectors should close shut below a certain minimum pressure. However, if they leak, fuel can drain back into the tank, causing a loss of pressure. This issue can be resolved by replacing the injectors with new ones that seal properly.
Another potential cause of the hot-start problem is a malfunctioning fuel pressure regulator. This component plays a crucial role in maintaining consistent pressure in the fuel system. However, it can be affected by excessive heat, causing it to malfunction and resulting in fuel draining back into the tank. Replacing the fuel pressure regulator with a high-quality, heat-resistant part can rectify this issue.
Additionally, the fuel pump itself can contribute to the hot-start problem. The pump includes a check valve designed to maintain pressure in the fuel system. However, if this valve fails or leaks, it can result in a loss of pressure and fuel draining back into the tank. Replacing the fuel pump with a new one that includes a functional check valve can address this issue.
Beyond these specific issues, there are general maintenance measures that can help prevent the hot-start problem. Ensuring the cooling system is functioning effectively can reduce excessive heat buildup, which is a contributing factor to the problem. This includes maintaining the radiator, cooling fans, and thermostat in good working condition. Furthermore, installing proper heat shields and aftermarket insulation for fuel lines and electrical components can protect them from engine heat and reduce the likelihood of heat-related failures.
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The K-Jetronic is capable of handling nearly double the output of the stock engine
The K-Jetronic, also known as the Continuous Injection System (CIS), is a mechanical fuel injection system. It was first introduced in the Porsche 911 in 1974 and later in the 1976 Volvo 265 and the DMC DeLorean in 1981. The system is designed to continuously flow fuel from all injectors, while the fuel pump pressurises the fuel to approximately 5 bar (73.5 psi). The volume of air taken in by the engine determines the amount of fuel to be injected.
The K-Jetronic system is quite flexible and can be used on various engine configurations and displacements. It is known for its reliability, especially when compared to older carbureted cars. The system is capable of handling nearly double the output of the stock engine, as seen in the 924 Carrera GTS, a high-performance vehicle.
The K-Jetronic system has a few key components that contribute to its functionality. The fuel pump, for instance, must produce more than 6 BAR to maintain the system pressure of around 5 to 5.5 BAR. The accumulator is another critical component with two main functions: dampening pulsation in the fuel and maintaining pressure in the fuel lines when the engine is off, aiding in hot starting and vapour lock prevention.
The injectors themselves are simple spring-loaded check valves with nozzles. When the fuel system pressure reaches a certain level, the injectors start spraying fuel. However, a common issue with the 924 model is the "hot-start problem," where the car struggles to start when warm after sitting for more than 15 minutes. This is often caused by leaking injectors or fuel draining back into the tank, which can be prevented with the help of fuel accumulators and a check valve in the fuel pump.
To maintain the K-Jetronic system, it is essential to keep the fuel injection components clean and lubricated. Dirt and water are the biggest enemies of the CIS system, as they can cause clogging and rust, respectively. Regular use of fuel system cleaners, such as Chevron fuel injector cleaner with Techron, is recommended to prevent these issues.
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The basic function of the Control Pressure Regulator is to enrich the mixture during warm-up
The basic function of the Control Pressure Regulator, or Warm-Up Regulator (WUR), is to enrich the fuel mixture during the warm-up phase of the engine. This is particularly important in cars such as the 1979 Porsche 924, which are known to experience the "hot-start problem". This issue is characterised by the car starting easily when the engine is cold, but struggling to start when the engine is warm, if it has been sitting for more than 15 minutes after being turned off.
The WUR is an essential component in addressing this problem, as it plays a key role in maintaining high fuel pressure in the engine compartment. It achieves this by lowering the control pressure when the engine is cold, resulting in a richer mixture. Specifically, the WUR takes input from the fuel output line on top of the fuel distributor, which typically has a pressure of 5.0-5.6 bar. The WUR then drains some of this pressure to the fuel return line, reducing the pressure to the "control pressure" of 3.0-4.0 bar.
The WUR is temperature-dependent, with its functionality influenced by the engine block heat and the heater. When the car is warm (at a temperature of 84°C), the strip inside the WUR does not offer any significant counterforce. However, when the car is cold, the strip generates a significant counterforce, which relieves the pressure on the P-spot, thereby lowering the control pressure. This is further facilitated by the electric current (12V) that is constantly running when the engine is on, ensuring that the heater gradually raises the temperature of the strip, slowly reducing the enrichment.
The calibration of the WUR is crucial, as a poorly calibrated control pressure can negatively impact the engine's performance. To adjust the control pressure, one can carefully push the disc inside the WUR with a screwdriver and rubber hammer while the engine is running, increasing the pressure in small increments.
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Frequently asked questions
Fuel injectors deliver fuel into the air stream as it enters the combustion chamber. The injectors atomize the fuel under pressure.
If your car is running poorly, the injector should be checked.
Porsche recommends using Chevron fuel injector cleaner with Techron as a preventative maintenance measure. This will help keep the fuel injection components from clogging up and will keep them lubricated.
