1999 BMW 328i Air Injection System Line Replacement Cost

Air injection systems send clean air into the exhaust system to encourage the complete burning of fuel in exhaust gases. To accomplish this task, rubber, synthetic, or metallic lines are used to transport air from the air filter box or throttle body inlet to the air injection pump, then from the air injection pump into the exhaust or intake manifold, depending on the state of the control valve.

The lines between the exhaust manifold and air injection pump are typically metallic, and this prevents them from damage due to excessive heat. However, the other lines for the system are likely to be rubber, plastic or synthetic, as these lines are only subjected to minor heat and light pressures.

Leaks in the air injection system lines are likely to cause no issues unless they occur between the check valve and the exhaust manifold, or the bypass valve and the intake manifold. In these two situations, the vehicle would likely run slightly rough, and may hesitate on acceleration. If the check engine light does come on, the codes will likely be for the catalytic converter, oxygen sensor, air to fuel ratio, or air injection system. A small leak is not likely to be detected. If the leak becomes large, you may notice the engine attempting to stall at idle, or any time the throttle is not applied.

Since this error can result in the ECM operating in a closed loop with the oxygen sensors, the air to fuel ratio for the engine may become excessively rich or excessively lean. At the very best, this will result in additional fuel consumption, but lean conditions are hazardous to engine components due to excessive heat. This should be addressed right away to prevent adverse effects and collateral damage to the catalytic converter, exhaust manifold, and engine cylinder head valves.

The air injection system is typically trouble free, however, when issues do arise from these systems it seems to occur between the 80,000 and 120,000 mile mark. This is no guarantee, and most vehicles will never have an issue with this system due to its lack of complexity and design to operate near high heat.

Checking a line for leakage or damage is a simple task, Removing and flexing rubberized lines will allow the technician to observe the material for cracks, deterioration and brittleness. Metallic and plastic lines can be examined for failure as well, and signs of exhaust leaks at the manifold may indicate the seal or line has failed.

Replacing lines is straight-forward and simple, but there may be some issues gaining access or working in the tight spaces these components are mounted in. These lines may disconnect by pressure, clamps, clips, or threaded connections, but they will all need to be disconnected from both ends before installing the new line. It should be mentioned that some lines will need to be disassembled to allow transfer of inline components from the old line to the new.

Since the air injection system uses rubber press-fit hoses and other components subject to deterioration, any time the system is serviced it is advised to perform a complete inspection of the secondary air system. This includes inspecting for exhaust leaks where the air injection system connects to the exhaust manifold or exhaust pipe.

Portions of this system become extremely hot to the touch as they are directly connected the the exhaust system. Any time this system is service, ensure that the engine has had adequate time to cool. Laser thermometers are advised to locate high temperature areas prior to servicing the system.

Air injection lines are easily replaced by anyone. Gaining access to the lines moving from the air injection pump to the exhaust manifold may be tricky, and removing the line from the manifold may be even worse. If a controlled heat source and penetrating fluid are available, even replacing this line will be simple. Always wear personal protective equipment when working with heat.