Katerina Swanson
Pulling a CIS fuel injector is a complex process that requires careful attention to detail. It is important to first check for vacuum leaks and fuel pressure at the fuel distributor inlet. The next steps involve pulling the injectors, removing the intake boot, and hotwiring the fuel pump relay. With the key turned on, use a magnet to raise the metering plate and observe the spray pattern. If this does not provide any insights, specialised tools such as CIS fuel pressure gauges and a Bentley manual can be used for further diagnosis. Additionally, it is recommended to test the flow rate of the injectors and ensure that they are functioning optimally. This process can be challenging, and seeking assistance from a local VW specialist or consulting a trusted forum for detailed guidance is always a good idea.
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What You'll Learn
Check for vacuum leaks and fuel pressure
Checking for vacuum leaks and fuel pressure is crucial to ensure your engine runs optimally and to prevent fire outbreaks from external injector leaks and vacuum leaks. Here is a step-by-step guide on how to check for vacuum leaks and fuel pressure:
Step 1: Check for Vacuum Leaks
Vacuum leaks can cause problems in regulating the mixture and may result in an uneven idle. To check for vacuum leaks, spray some carb cleaner or starting fluid around the hoses and injectors of the fuel injection system. If the engine idle increases, it indicates a probable vacuum leak that needs to be addressed. Make sure to have a fire extinguisher nearby, as there is a risk of igniting the carburetor cleaner if there is arcing in the spark plug wires.
Step 2: Inspect Injector Seals and Intake Manifolds
The injector seals and plastic inserts at the base of the intake manifolds can also be sources of vacuum leaks. Carefully examine these components and replace them if there is any evidence of leaks.
Step 3: Check Fuel Pressure
Install an EFI gauge kit and start your car engine, allowing it to idle. Observe the fuel pressure closely for 20-45 minutes. The pressure should ideally be between 35-50 psi. A rapid drop in fuel pressure, such as 2 psi per second, indicates a potential issue.
Step 4: Measure Fuel Pressure
Use a syringe or a similar tool to measure the fuel's pressure accurately. This will help you determine the level of fuel entering the container during the testing process.
Step 5: Test Voltage and Spray Rate
Use a multimeter to test the voltage on your injector sockets. Most cars' injectors have two pins, and readings between 3.70 and 3.89 are acceptable. Remove your fuel fuse and examine PIN 87 and 30, which are the main fuel lines. Send a current to your injector and inspect the spraying rate of each injector individually.
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Remove the boot over the air flow sensor
To remove the boot over the air flow sensor, you will need to use a pen-style magnet to pull up on the sensor plate via the hex bolt head in the centre. As you pull, you want to feel uniform resistance. If you do not feel uniform resistance, clean the sensor plate and its hinge. Then, undo the fuel lines and remove the fuel distributor.
The first step in this process is to locate the sensor plate. This is found underneath the boot, which is the plastic cover over the air flow sensor. Once located, place the pen-style magnet on the hex bolt head in the centre of the sensor plate.
Next, begin to pull up on the sensor plate with the magnet. As you do this, pay attention to the resistance you feel. The resistance should feel uniform and similar to wading in molasses. If the resistance is not consistent, the sensor plate and its hinge may need to be cleaned. Use a suitable cleaning agent and a microfibre cloth to gently clean the sensor plate and hinge.
After cleaning, if necessary, proceed to undo the fuel lines connected to the fuel distributor. Once the fuel lines are disconnected, carefully remove the fuel distributor from the vehicle. With the fuel distributor removed, you can now access and remove the boot over the air flow sensor.
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Pull injectors and take the intake boot off
To pull the injectors and take the intake boot off, you will need to relieve the fuel system pressure. Look for the Schrader valve on the fuel rail along the top of the engine. Wrap a shop rag around the valve and use a small screwdriver to depress the inside stem as you catch the squirt of fuel with the rag.
Next, carefully lift the fuel rail as you pull the injectors from the intake manifold. Place clean shop rags on top of the intake injector openings to prevent contamination or small objects from falling inside the manifold. Detach the injector you want to replace from the fuel rail. Depending on your particular model, the injector might be attached with a screw or pressed fit into the fuel rail. Use a wrench or ratchet and socket if necessary.
Now, to take the intake boot off, there should be clamps that secure the intake boot to the air cleaner housing and throttle body. Loosen and remove them, keeping track of the nuts and bolts with a container. Take off the breather tubes as well. It's only after you've removed both breather hose sets and mounting clamps that you can safely remove the boot. Some models have electrical modules attached to the air intake boot. Remove them too. Disconnect the boot with a screwdriver by twisting the tool and loosening the seal.
Finally, check all your hoses and clamps to see if they're put in place and nothing is missing. Afterwards, start your engine and keep an ear out for any vacuum leaks or hissing sounds. If problems persist, consult your mechanic.
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Hotwire the fuel pump relay
To hotwire the fuel pump relay, you will need to access the fuel pump relay in the underhood power distribution center. You can then jumper terminal #5 (yellow wire) to terminal #6 (orange-black wire). This will bypass the relay and send direct power to the fuel pump when the ignition key is turned on.
You can also jump it at the relay terminals, but you must be absolutely sure which one is for the fuel pump. Typically, 30 is the fused ignition power, so this will be the terminal you will use for power. 86 and 85 are usually for the electromagnet inside the relay, and 87 or 87a (if applicable) are the leads to the fuel pump. If you have a multimeter, you can measure for resistance to the ground on 87 or 87a to determine if this goes to the fuel pump.
Another method is to power all the way to the inertia switch and the sending unit in both tanks, which will read on the instrument panel. When you turn the key, the pumps should prime. If not, you may need to direct wire from the battery to the fuel pumps to check if the pumps are bad or if it is a wiring issue.
To rewire your fuel pump, you will need to first get to your fuel pump's wiring and find the 12v supply wire from the ECU to the fuel pump. Once found, cut that wire so that you have half of the wiring running to the fuel pump, and the other half to the factory ECU. The relay should be a four-prong relay with at least 14-gauge wiring. Wire pin 85 of the relay to the 12v supply wire from the stock ECU that you just cut. This 12v wire will now energize the relay to turn on. Now, instead of the stock ECU energizing the fuel pump, it will energize this relay. Run a dedicated wire from your battery to pin 30 on the relay. Then, run a wire from pin 87 to your factory wire that you cut that runs to the fuel pump.
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Test the flow at each injector
Testing the flow at each fuel injector is a crucial step in ensuring the optimal performance of your engine. Here's a detailed guide on how to approach this process:
External Cleaning and Inspection:
Begin by cleaning the exterior of the injectors with a specialised detergent designed for this purpose. This step ensures that any dirt or grease accumulated on the injectors is removed, providing a clear surface for inspection. Once cleaned, carefully inspect the injectors for any visible damage.
Resistance, Shorts, and Current Draw Testing:
Proceed to test the injectors' coils for resistance, shorts, and current draw. This step involves testing the resistance across the terminals of the injector connector, usually measured in Ohms. While the coil may pass this test, it's important to understand that it could still malfunction when the engine is under stress, such as during highway driving. Therefore, it's crucial to simulate a load to check the coil windings and identify any potential issues.
Ultrasonic Cleaning:
After the initial testing, place the injectors into an ultrasonic cleaning tank. This process involves electronically cycling the injectors on and off while they are ultrasonically cleaned with special detergents. This step ensures the removal of any remaining contaminants.
Static Flow Test:
The static flow test is conducted to assess the flow rate of each injector. The injectors are held fully open (static) for 15 seconds at a specific fuel pressure of 43.5 psi or 3 BAR. During this test, measure the volume of fuel (in cc/min) that flows through each injector at this standard pressure. For optimal engine performance, the flow rate among the injectors should be within 5% of each other.
Dynamic (Pulsed) Flow Test:
The dynamic flow test replicates real-world driving conditions, including idling, acceleration, deceleration, low speed, and high speed. During this test, the injectors are energised and run for 30 seconds at different duty cycles, with varying pulse widths. The pulse widths are typically measured at 3 ms, 6 ms, and 12 ms. This test evaluates how well the injectors perform under dynamic conditions, ensuring they can handle the varying demands of different driving scenarios.
Recording Results and Necessary Repairs:
After completing the flow tests, record the results on a data evaluation sheet. If any injector fails the leak down or flow tests, mark them as defective or not serviceable. At this stage, you may need to consider rebuilding or replacing components. It is important to consult a professional technician if you are unsure about the results or the necessary repairs.
Remember to handle the fuel injectors with care and ensure they are securely packaged during transportation to avoid any potential damage.
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Frequently asked questions
First, check for vacuum leaks and check the fuel pressure at the fuel distributor inlet. Then, pull the injectors, take the intake boot off of the fuel distributor metering plate, and hotwire the fuel pump relay. Turn the key on and raise the metering plate with a magnet. Observe the spray pattern.
If you don't see a spray pattern, get the CIS fuel pressure gauges and the Bentley. Pull the fuel pump and bypass the accumulator and test the injectors at the same time.
Pull them out of the intake, stick each one in a container, then turn the ignition on. Use a magnet to pull up on the metering plate. The injector flow should rise and fall with the up/down movement of the plate.
Opening a fuel distributor is not trivial. There are lots of springs and valves inside. Once you open it, you will find a spring on top and below each valve for each injector. They are difficult to put back together and might take a few tries.
