ZD30 VP44 ICV Problems

Nissan Navara D22 ZD30 Black Smoke and Low on Power

The ZD30 have a VP-44 fuel system, which feature an electronically-controlled traditional-style rotary fuel pump. With the electronic control, there is finer tuning of engine timing throughout the rev range, and ultimately these pumps simply wear out. The main failure is the fact the engine can no longer reach full advance.

What ends up happening is the engine is therefore running retarded, and because it is retarded it is no longer making power efficiently. The driver then puts more throttle in and effectively you end up with a situation where the engine is now over-fueling. One check that can confirm is looking at the spill valve percentages. A new pump or a decently equipped setup is somewhere in the order of 50-70% in terms of spill valve percentage. At hot + idle, a dead pump will be anything less than around 20%, and generally you start to see symptoms at 28% and lower.

The way the timing works inside the pump is effectively governed by the internal pump pressure. It’s also worth noting that this internal pump pressure can be influenced by outside factors. The most common one is usually aerated fuel supply. If the fuel supply to the pump is aerated the pump cannot compress the fuel properly, which means it won’t get a decent internal pump pressure, and therefore can’t get internal pump pressure. It’s highly important that it’s without air and it’s also important the fuel flow to the pump is unrestricted. If you have a big vacuum on the pump-supply side, then obviously the pump isn’t getting the fuel. It’s losing internal pump pressure and therefore losing advance.

So first thing, always check the spill valve percentages (sometimes called ICV percentage). We always have a clear piece of fuel line with a T-piece to a vacuum gauge, and we just attach that on every car. It takes five seconds or five minutes to go for a quick run around the block to make sure there’s no air or vacuum in the fuel supply. This one quick step is the most vital to ensure a few thousand $$$$ is not lost in a miss diagnosis.

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