Replacing Fuel Injectors In Bmw's N52 Engine: Step-By-Step Guide

Replacing a fuel injector on a BMW N52 engine is a moderately challenging task that can be done at home with the right tools. The N52 engine is a naturally aspirated engine that uses standard fuel injectors that mount in the intake manifold runner and spray fuel on the back of the intake valves. The injectors can be replaced by removing the fuel rail, which is held in place by four bolts. The fuel rail is connected to the injectors by fuel lines, which need to be disconnected. The injectors are then pulled out of the cylinder head. New injectors can be installed, and the fuel lines and fuel rail reconnected. The injectors do not need to be coded to the DME, but the sealing O-rings should be replaced.

Remove the engine cover and cowl

To remove the engine cover and cowl, follow these steps:

First, grip the front of the engine cover and pull up to pop it off the front locating pins. Then, grab it by the right side and pull up to pop it off the last pin. For pre-2013 engines, there are also two vacuum lines on the passenger's side of the cover that need to be disconnected before you can remove the cover.

Next, remove the foam noise-reduction pad from underneath the plastic engine cover. Pull up on it to remove it from the engine.

Now, move to the engine cowl. Use a 10mm socket to rotate the fasteners at the back of the cowl a quarter turn. Then, remove the plastic rivets securing the cowl near the fenders.

Removing the forward cowl pieces exposes the strut brace. Remove the two plugs from the rear cowl's centre to reveal the strut brace's firewall mounting bolts. Then, pull the rubber strut covers off and remove the bolts with an E18 socket. You need to remove a plastic rivet to remove each strut cover.

After that, remove the cover that sits below the brace using a 10mm socket to remove its seven bolts.

At this point, you will have exposed the fuel injectors.

Disconnect the wiring from the cylinder head

Disconnecting the wiring from the cylinder head is a crucial step in replacing a fuel injector on a BMW N52 engine. Here is a detailed, step-by-step guide on how to perform this task:

• Locate the wiring harness: The injector wiring harness is attached to each injector with spring clips. These clips secure the harness to the injectors.
• Release the spring clips: To remove the wiring harness, you need to release these spring clips. You can do this by gently pulling or tugging on the harness. Be careful not to pull too aggressively, as you don't want to break the clips.
• Disconnect the wiring: Once the spring clips are released, you can now disconnect the wiring from the cylinder head. Gently pull the wiring harness away from the injectors.
• Inspect the connectors: Before proceeding, take a moment to inspect the connectors on both the wiring harness and the injectors. Ensure that they are not damaged.
• Clean the connectors (optional): If you notice any dirt or corrosion on the connectors, it is a good idea to clean them. You can use a contact cleaner or a mild solvent to gently clean the connectors.
• Releasing the wiring from the cylinder head: In some cases, the wiring harness may be held in place by a bracket or other components. If so, you will need to release it from the cylinder head. This may involve removing bolts or other fasteners.
• Disconnecting individual injectors: If you are only replacing a single injector, you will need to disconnect the wiring for that specific injector. Gently pry or release the connector for the injector you are replacing. Be careful not to damage the connector or the wiring.

It is important to work carefully when disconnecting the wiring from the cylinder head. Ensure that you do not damage any components or connectors. If you encounter any issues or are unsure about any steps, it is always best to consult a qualified mechanic or a BMW specialist.

Remove the fuel injectors

To remove the fuel injectors from your BMW N52 engine, follow these steps:

Step 1: Remove the fuel rail pressure testing cap

Place a rag under the port and use a small flathead screwdriver to press the Schrader valve and relieve fuel pressure. Ensure that the rag is wrapped around the screwdriver to minimise fuel spillage.

Step 2: Disconnect the fuel supply line

Working at the centre of the fuel rail, press the plastic collar towards the fuel line, then slide the fuel line off the rail. If the collar will not press in far enough, pull the fuel line towards the front of the vehicle, hold it there, and then press and hold the collar while sliding the fuel line off the rail. Place the disconnected fuel line on the valve cover, wrapped in a rag, to collect any excess fuel and keep dirt from entering the line.

Step 3: Disconnect the fuel injector harness

Use a large flathead screwdriver to gently pry up at each fuel injector. This will release the spring clips that hold the electrical harness to the fuel injectors. Be sure to lever straight up and keep the flathead next to the fuel injector connector you are releasing. Work your way down the injector electrical harness and disconnect each fuel injector.

Step 4: Remove the fuel rail fasteners

Remove the four 10mm fuel rail fasteners. Then, pull the fuel rail straight up and out of the cylinder head, being careful not to damage the fuel injectors. If the O-rings are stuck, lightly pry the fuel rail up using a flathead screwdriver. Pry between the edge of the valve intake manifold and the fuel rail.

Step 5: Remove the retaining clip

Remove the retaining clip by sliding it off the fuel rail using a flathead screwdriver. Then, pull the fuel injector straight out of the fuel rail. Be careful not to damage any of the fuel injectors when pulling the rail up and out of the cylinder head. If the injectors won't budge, use silicone spray to lubricate the injector holes to help them slide out.

Install the new fuel injectors

To install the new fuel injectors, you will need to follow these steps:

• Before installing the new injector, record the calibration numbers; you will need them later to perform a DME calibration for the new injectors. The top number on the injector is the energy calibration number and the lower number is the flow calibration number.
• After you record the number for the cylinder that the injector is being installed into, install a new decoupling element and remove the protective cap on the tip of the injector. The cap can be difficult to remove as it keeps the Viton seal compressed and the tip clean. Simply twist back and forth as you pull it off.
• You're now ready to install the injector by placing it back in the cylinder head. Don't worry about forcing it to bottom out; when you reinstall the retaining clip, the injector will bottom out on its own.
• Reinstall the fuel feed line onto the injector, tighten the flare nut on the injector and the flare nut on the fuel feed line.
• Reassemble the remaining items and check that there are no fuel leaks.
• If you do not have the ability to perform the calibration, you can safely drive your car to a shop or dealer to have the calibration carried out for you. Technically, it's not harmful to the engine, but we can say for sure that the engine will not perform optimally until the calibration is complete.

Reconnect the electricals and code the injectors

Now that you have installed the new injectors, it is time to reconnect the electricals and code the injectors.

First, reconnect the electrical connectors to the injectors. Be sure to lever straight up and be sure the flathead is next to the fuel injector connector you are releasing. Work your way down the injector electrical harness and reconnect each fuel injector.

Next, you will need to code the injectors. There are several ways to do this, depending on your budget and your access to tools. If you have a BMW scan tool, you can enter the injector numbers into the DME. If you do not have a BMW scan tool, you can drive the vehicle to a workshop that can program it for you. There may be a slight decrease in drivability until it is programmed, so do not drive it any further than you have to.

If you have a laptop, you can buy a USB to OBD2 cable and download ISTA. This will allow you to code the injectors.

If you have an Android phone, you can download a cracked version of the Protool app. This will allow you to code the injectors on your phone.

If you want to avoid the hassle of downloading software, you can buy a high-end scan tool like the Autel MX808 or the Foxwell NT510. These tools can go into the engine computer and recode the injectors.

Frequently asked questions