Katerina Swanson
The P7100 pump is a complex piece of engineering that controls the maximum fuel output of a diesel engine. The fuel plate can be adjusted to increase horsepower, with sliding the stock plate forward being one method. However, this can cause EGT problems. Another method is to remove the fuel plate completely, which will also increase horsepower. Adjusting the star wheel can increase rack travel, and the popular Mack rack plug increases rack travel from 19mm to 21mm, adding 70cc of fuel to the mix. The P7100 pump is used in 94-98 models and is known for its robustness, performance and reliability.
| Characteristics | Values |
|---|---|
| Location of fuel plate | Inside the 8mm Allen head plug on top of the AFC housing |
| Function of fuel plate | Controls the maximum fuel output of the P7100 |
| Adjustment of fuel plate | Slide forward or backward, loosen screws and adjust the governor arm |
| Tools required | Hand impact tool, light hammer, T15 TORX bit, center punch, sharp chisel |
| Precautions | Ensure Governor Arm does not go under the fuel plate, adjust Starwheel and Smoke Screw inside AFC housing |
| Additional power options | Larger injectors, custom fuel pin, larger turbos, governor spring kit, Mack rack plug |
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What You'll Learn
Adjusting the governor lever
Firstly, it is crucial to understand the role of the governor lever. The governor lever is part of the governor assembly, which controls the fuel rate of the pump. Specifically, the governor lever interacts with the cam plate or fuel plate, dictating the amount of fuel delivered to the engine.
When adjusting the governor lever, the goal is to ensure it makes proper contact with the cam plate or fuel plate. Here are the steps to achieve this:
- Remove the AFC Housing: This step is necessary to access the internal components. The AFC Housing has a break-off screw that needs to be removed using a hand impact tool with a 6-inch long 1/4" extension and a T15 TORX bit.
- Adjust the Governor Lever: With the AFC Housing removed, locate the governor lever. Adjust the lever so that it just touches the cam plate or fuel plate. This adjustment ensures the lever does not hinder the movement of the governor arm and allows for proper fuel delivery.
- Fine-Tune the Governor Lever Height: In some cases, you may need to fine-tune the height of the governor lever to ensure it strikes the cam plate or fuel plate at the correct position. Loosen the locknut with a 10mm socket and make small adjustments to the screw, then tighten the locknut again.
- Check the Adjustment: To verify the adjustment, move the throttle lever until the governor lever just touches the cam plate. Look through the opening behind the cam plate to see where the lever is striking. The lever should hit the cam plate flush at the very bottom edge or slightly above, but not too far down, to prevent loss of bottom-end power.
- Reassemble and Test: Once the adjustment is set, reassemble the AFC Housing and any other components that were removed. Test the engine to ensure the desired results have been achieved.
It is important to note that adjusting the governor lever is just one aspect of modifying the fuel plate. Other steps, such as sliding the fuel plate forward or purchasing a cut plate, adjusting the star wheel, and fine-tuning smoke levels, are also part of the overall process of improving engine performance in a diesel pusher with a P7100 pump.
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Removing the AFC housing
To remove the AFC housing, you will need to remove the front passenger side AFC housing break-off screw. This screw is a factory break-off screw with a rounded head and no screwdriver, Allen head, or TORX slot. You can use a hand impact tool with a 6-inch long 1/4" extension and a T15 TORX bit to remove this screw. Start by setting the hand impact tool in the removal position (counter-clockwise) and use light hammer taps on the impact tool to loosen the screw. Tap progressively harder until the screw loosens. This method will form a TORX shape into the screw, allowing it to be reinstalled later with the T15 TORX bit.
In some cases, the hole in the top of the screw may be too large for the T15 bit, so you may need to use a T20 TORX bit instead. There is usually a lock washer and a flat washer under each of these screws. If you do not have access to the right tools, you can use a sharp chisel to remove the break-off screw. First, make a notch in the outside diameter of the head, and then apply a tangential force with light blows to the chisel counterclockwise to remove the screw.
Once the screw is removed, you can lift the AFC housing and set it aside. With the AFC housing removed, you will be able to see and access the fuel plate. It is important to note that sliding the stock plate will increase HP, but this is not recommended as it can result in EGT problems. Additionally, pump experts advise against completely removing the plate as it can cause expensive damage to the pump.
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Modifying the fuel plate
Firstly, it is important to understand the function of the fuel plate. The fuel plate controls the maximum fuel output of the P7100, and adjustments can be made to increase horsepower and torque. The stock fuel plate is typically conservative, and modifications can unlock greater performance.
To begin modifying the fuel plate, first remove the AFC housing. This will expose the fuel plate, which can then be adjusted. You can either slide the fuel plate forward to increase horsepower, or purchase a custom-cut fuel plate for more precise adjustments. Sliding the stock plate forward will increase horsepower, but it may also result in EGT problems, so proceed with caution.
When adjusting the fuel plate, be mindful of the Governor Arm. This arm rides up and down the plate and dictates how much fuel is delivered. Ensure that the arm does not go under the fuel plate, as this will require further adjustments. The basic rule of thumb is that moving the fuel plate towards the front of the engine allows the Governor Arm to travel further forward, adding more fuel. Conversely, moving the fuel plate towards the firewall reduces the travel of the Governor Arm, reducing fuel delivery.
Fine-tuning can be achieved by loosening the fuel plate screws and sliding the plate towards or away from the fueling arm. Moving the plate towards the radiator (full forward) will increase fueling, while moving it away from the radiator will reduce fueling.
After adjusting the fuel plate, the next step is to adjust the Governor Lever so that it contacts the fuel plate correctly. This adjustment varies depending on the design of the cam plate being used. For cam plates with a taper at the bottom, adjust the lever so that it hits at the tip of the bottom nose of the plate.
The Starwheel, located inside the AFC housing, can then be adjusted to fine-tune the settings. Turning the Starwheel towards the engine lessens the preload, while turning it away from the engine increases it. Adjust the Starwheel until you achieve a slight "puff" of black smoke under initial throttle, as any more smoke indicates wasted fuel.
Finally, test your adjustments by reinstalling the AFC housing and taking the vehicle for a test drive. Repeat the adjustments as needed until the desired results are achieved.
It is important to note that some engines respond to pump adjustments better than others. Additionally, always exercise caution when making modifications, as incorrect adjustments can lead to reduced performance or potential damage.
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Cranking the star wheel
To access the star wheel, you need to remove the AFC housing. This involves removing the front passenger side AFC housing break-off screw, which may require the use of a hand impact tool with a 6-inch long 1/4" extension and a T15 TORX bit. Once the AFC housing is removed, you will be able to see the fuel plate and the star wheel.
When cranking the star wheel, you have to consider the direction in which you turn it. Adjusting the star wheel towards the motor or engine increases the preload, resulting in more fuel being delivered to the engine. On the other hand, adjusting it backwards or away from the engine lessens the preload and reduces the amount of fuel. It is important to make these adjustments in small increments, as it may take repeated attempts to get the desired results.
The goal is to adjust the star wheel to achieve optimal engine performance without wasting fuel. You should aim for a slight "puff" of black smoke under initial throttle. Adjusting the star wheel too far forward can lead to excessive smoke, increased EGTs, and possibly decreased power. Therefore, it is crucial to find the right balance by making fine adjustments to the star wheel.
Additionally, keep in mind that the star wheel works in conjunction with other components, such as the AFC housing and the fuel plate. Adjustments to these components may also be necessary to achieve the desired engine performance. Always refer to reliable sources and seek professional guidance if you are unsure about any steps in the process.
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Adjusting the smoke screw
To access the smoke screw, start by removing the AFC housing. This step requires the use of a hand impact tool with a 6-inch long 1/4" extension and a T15 TORX bit to remove the factory break-off screw. In some cases, you may need to use a T20 TORX bit if the hole in the screw is too large for the T15. Additionally, you can use a sharp chisel to create a notch in the screw head and apply light blows counterclockwise to remove it.
Once the AFC housing is removed, you will have a clear view of the fuel plate. The smoke screw is located in the back of the AFC housing, and it plays a crucial role in adjusting the fuel delivery and smoke production. Adjusting the smoke screw can be done by turning it either clockwise (CW) or counterclockwise (CCW). Turning the smoke screw CW, or farther, will increase the preload fuel and smoke. On the other hand, turning it CCW will reduce smoke and fuel delivery.
It is important to note that the adjustments made to the smoke screw should be fine-tuned to achieve the desired results. You should aim for a slight "puff" of black smoke under initial throttle. Excessive smoke indicates wasted fuel, and it may be necessary to adjust the AFC housing and the Starwheel to fine-tune the settings. Additionally, the Mack rack plug can be installed to increase rack travel and fuel delivery, resulting in potential power gains.
By carefully adjusting the smoke screw and making any necessary adjustments to the AFC housing and Starwheel, you can optimise the performance of your diesel pusher with a P7100 pump, ensuring efficient fuel usage and managing smoke production.
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Frequently asked questions
First, remove the AFC housing. Then, either slide the fuel plate forward or purchase a cut one.
Adjust the lever so that it hits the tip of the bottom nose on the plate. It is okay to be slightly below that, but too far down will cause a loss in bottom-end power.
The star wheel changes the quickness of the fueling response to boost. Adjust it forward to lessen the preload and backward to increase it.
The AFC (air fuel control) is in charge of controlling the pump's fuel rate at low boost. It is located at the back of the P7100.
One way is to install a "Mack rack plug", which increases rack travel and adds fuel to the mix, resulting in additional horsepower. Another way is to disable the wastegate on the turbo, which can increase boost production by 10-15 psi.
