The Chrysler Power Tech V8 was a big hit when introduced in 1999. It won a “10 Best” award from auto industry magazine Ward’s Automotive and served in the Grand Cherokee and Commander for ten years. It’s also found under the hoods of the Ram 1500 and Dodge Dakota pickups, as well as the Durango and Chrysler Aspen SUVs.
Here we’ll provide an overview of the fuel injection system used on this engine. This serves as a jumping-off point for those wanting to carry out maintenance work on the system in their Jeep or Chrysler.
The fuel injection system employed on the 4.7 liter PowerTech was somewhat novel for its time in that there is neither a fuel pressure regulator nor a return line.
Conventionally, in a fuel injection system the pump delivers a greater volume of gasoline than the engine can use, even at wide open throttle. The fuel is kept under pressure in the rail by a regulator – essentially a diaphragm valve – that opens when the rail is at pressure, allowing the excess to flow back to the tank.
This approach has two advantages: gas that gets warm under the hood goes back to the tank where it cools, and the pump only has to run at a constant speed. However, the downsides are the cost, complexity and weight of the return system.
In contrast, in a return less system the PCM varies pump speed to ensure an adequate fuel pressure in the rails. In the case of the 4.7 liter Jeep fuel injection system rail pressure is around 50 psi, comparatively low by modern standards.
There are three approaches to fuel injection: spray fuel into the inlet air at the throttle body, (which is analogous to carburetion,) inject it just upstream of the inlet valves, or directly into the cylinder. The 4.7 liter Jeep uses the second of these, an arrangement termed “multipoint fuel injection.”
In contrast with throttle body injection, multipoint allows precise control of the quantity of fuel going in to each cylinder. Unlike direct injection, the rail pressures are relatively low as there is no back pressure for the fuel spray to work against. This leads to a slightly unusual layout where the injectors are grouped in pairs so as to line up with the inlet valves.
Accessing the fuel injectors
As with all fuel injection systems, Jeep fuel injectors are buried beneath intake system. However, unlike some engine layouts, the fuel rail and injectors can be reached without removing the intake manifold.
Before starting work on any fuel injection system, always ensure it is depressurized. This can be done by pulling the fuel pump relay and then running the engine until it stalls. Alternatively, pressure can be released through the Schrader valve on the right side (as you face the engine) rail.
Removing the intake air duct and air box exposes the throttle body, intake manifold and fuel rails. The rails themselves are secured to the manifold with four bolts, two on each side. Before undoing these bolts the inlet fuel line should be disconnected. This done by first removing the securing metal clip, then using a special disconnect tool to separate the line from the rail.
With the fuel line disconnected all that remains is to unplug the electrical connectors on each injector. From here it is a straightforward job to lift out the rails to work on the injectors.