Fuel Pressure's Impact On Vp44 Cummins Performance

The VP44 injection pump is an electronic rotary pump that was fitted to the 24-valve ISB engine in Dodge's 1998.5-2002 5.9L Cummins. The VP44 is known for its unpredictable nature and tendency to fail unexpectedly. However, with proper maintenance and some aftermarket upgrades, it is possible to extend the lifespan of the VP44.

One of the most common issues with the VP44 is failure of the PSG (or EDC), the computer that controls the pump's fuelling. Excessive heat and heat cycling can cause the solder on the PSG's circuit board to fail, interrupting the electrical signal and leading to long cranking times when restarting a hot engine. Better soldering practices in recent years have improved the reliability of remanufactured VP44s.

Another issue, particularly in early VP44s, is rotor seizure in the distributor portion of the pump. This can be caused by an inferior de-burring process during manufacturing, which leaves a sharp edge on the rotor that can dig into the distributor and lead to seizure. This will stop the engine dead in its tracks.

The diaphragm, which supplies fuel to the distributor shaft, is also prone to failure in early VP44s due to the use of a material that couldn't handle high-pressure fuel spill pulses. This issue was addressed in later models with the addition of a solid steel backing behind the diaphragm.

A failing lift pump can also cause issues with the VP44 as it relies on adequate fuel supply pressure and volume to operate, lubricate and cool the pump. A lack of fuel supply can lead to hotter fuel being sent through the VP44, which does not react well to excessive heat. A minimum of 5 psi of fuel supply pressure is required to prevent damage to the VP44. Aftermarket electric lift pumps from manufacturers such as Fuelab, FASS and AirDog can provide the required pressure and volume to keep the VP44 happy.

To summarise, while the VP44 has its issues, many of these can be mitigated with proper maintenance and some aftermarket upgrades. Ensuring adequate fuel supply pressure and volume, and keeping the VP44 as cool as possible, are key to extending its lifespan.

Fuel pressure should be between 10 and 20 PSI

The fuel pressure for a VP44 Cummins engine should be between 10 and 20 PSI. This is the general consensus among CumminsForum.com users, who have experience with the VP44 engine.

Keeping the fuel pressure within this range is important for the health of the engine. Fuel pressure that is too low can cause damage to the VP44 injection pump, as the fuel is also used to cool and lubricate the pump's internal parts. A failing lift pump can starve the VP44 of fuel, causing it to overheat and fail.

The fuel pressure should be at least 5 PSI under load, and ideally between 12 and 15 PSI. This will ensure that the VP44 receives enough fuel for cooling and lubrication, preventing damage and overheating.

A fuel pressure of 10 PSI is generally considered the minimum safe level for a VP44 Cummins engine. However, some users have reported running their engines at lower fuel pressures without issue. It is recommended to keep the fuel pressure above 10 PSI to avoid the risk of damaging the VP44 injection pump.

Fuel pressure above 20 PSI is considered excessive and can be detrimental to the VP44. Excessive fuel pressure will increase the temperature of the fuel, reducing its cooling ability and putting additional stress on the lift pump. This can lead to overheating and potential failure of the VP44.

To maintain optimal fuel pressure, it is recommended to install an aftermarket electric lift pump from reputable brands such as Fuelab, FASS, or AirDog. These pumps can provide adequate fuel pressure and volume to the VP44, ensuring its longevity. Additionally, upgrading to larger diameter fuel lines, such as a 1/2" big line kit, can help reduce restrictions and improve fuel flow.

To diagnose fuel pressure issues, it is recommended to install a mechanical fuel pressure gauge. This will allow you to monitor fuel pressure at idle, driving, and wide-open throttle. A sudden drop in fuel pressure, especially below 10 PSI, can indicate a failing lift pump, plugged filter, or restrictive plumbing.

If you are unsure about how to diagnose or resolve fuel pressure issues, it is best to seek the help of a professional diesel mechanic or a specialist in VP44 Cummins engines. They will have the knowledge and tools to properly diagnose and address any fuel pressure-related problems.

A failing lift pump can cause VP44 failure

The VP44 is a Bosch electronic fuel delivery pump that needs at least 5-6 psi of pressure from the fuel transfer pump to function properly. If the pressure falls below 5 psi, there is a danger of the VP44 "overheating" as it uses fuel to cool and lubricate its internal parts.

A failing lift pump can cause low fuel pressure, which in turn can lead to VP44 failure. This is because the VP44 relies on fuel for cooling and lubrication. Insufficient fuel pressure can lead to a rupture in the diaphragm, allowing the timing piston to vibrate and damage the front cover until fuel bypasses, resulting in the check engine trouble code P0216.

Additionally, low fuel pressure can cause the pump fuel Bosch head rotor to seize in the head of the pump due to insufficient lubrication. This will result in the truck not starting and the need for a VP44 replacement.

To diagnose a failing lift pump, you can perform the following steps:

• Click the ignition key to the start function quickly and release it, leaving the key in the run position. The lift pump should run for 25 seconds.
• If the lift pump is not running, check for 12 volts going into the lift pump. If it doesn't have power, replace the fuse or relay.
• If the lift pump has power but is not running, replace the lift pump.
• If the lift pump is running, check the fuel pressure with a fuel pressure gauge. The pressure should be at least 5 psi at idle.
• If the fuel pressure is below 5 psi, replace the fuel filter and retest.
• If the fuel pressure is still below 5 psi after replacing the fuel filter, replace the lift pump.

It is important to note that revving the engine does not prove anything, as the VP44 requires a certain amount of fuel pressure under load. Therefore, it is recommended to test the fuel pressure while driving the truck under load to ensure that the pressure does not drop below 5 psi.

Rotor seizure is a common issue

The rotor seizure issue was caused by inadequate de-burring during the manufacturing process, which left sharp edges on the rotor slot. This issue was exacerbated by the high-pressure conditions within the VP44, which meant that mechanical tolerances had to be very small. As a result, the rotor was more likely to interfere with the distributor, leading to galling, binding, and eventual seizure.

To prevent rotor seizure, it is important to maintain adequate fuel supply pressure and volume to ensure proper lubrication and cooling of the VP44. A failing lift pump can lead to insufficient fuel pressure, which can, in turn, cause the VP44 to overheat and fail. It is recommended to maintain a fuel pressure of at least 5 psi and ideally between 12 and 15 psi to ensure the long-term reliability of the VP44.

Diaphragm failure is common in early VP44s

The diaphragm is a dome-shaped muscle that separates the thoracic and abdominal cavities and is the major muscle of respiration. Diaphragm failure is common in early VP44s, with the diaphragm being made from a material that was not up to the task of dealing with high-pressure fuel spill pulses. This resulted in the diaphragm cracking over time. The diaphragm's life is further shortened when it is exposed to lengthy periods with little or no fuel supply pressure from the lift pump. A hard cold start is the biggest indicator of diaphragm failure.

The diaphragm's function is to supply fuel to the bores of the distributor shaft. The diaphragm is located at the pump's distributor head inlet.

Heat is a major killer

The VP44 relies on an adequate fuel supply to operate, and a failing lift pump can cause disaster. The lift pump failure is common in the Cummins engine, and a lack of fuel supply leads to hotter fuel being sent through the VP44. The VP44 does not respond well to excessive heat, and the hottest it gets is actually 15 to 20 minutes after the engine has been turned off due to heat soak. Short trips and frequent hot restarts can cut the life expectancy of the VP44 in half.

The only way to ensure the VP44 stays as cool as possible is to feed it with good fuel supply pressure and volume. A fuel pressure of 5 psi is the minimum that should be maintained during idle, driving, and wide-open throttle to prevent lift pump failure from starving and killing the VP44. A fuel pressure gauge can be installed to monitor the health of the lift pump and quickly identify any issues.

Aftermarket electric pumps from Fuelab, FASS, and AirDog have proven capable of delivering adequate pressure to the VP44. A fuel pressure of 12 to 15 psi should be the goal to ensure the VP44 stays cool and receives sufficient lubrication.

Excessive cranking pressure can also lead to difficult starting problems. A simple test can be performed by pulling the fuel pump relay and attempting to start the engine, while observing the fuel pressure gauge during cranking.

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