Replacing Fuel Injectors: Diy Guide For Your 350 Tbi Engine

Changing the fuel injectors on a 350 TBI engine can be a complex task, but with the right tools and knowledge, it is certainly doable. The process typically involves disconnecting the battery, relieving the fuel system pressure, removing the air intake and fuel lines, and then carefully removing and replacing the injectors. It is important to ensure that the new injectors are properly lubricated and seated before reassembling the engine components. Additionally, there are several testing and inspection procedures that can be performed to ensure the injectors are functioning correctly, such as using a Kent-Moore Fuel Injector Tester.

Fuel Injector Installation

This guide will take you through the process of installing fuel injectors on a TBI 350 engine.

Step 1: Using a twisting motion, install a new injector filter on the injector.

Step 2: Lubricate the replacement small O-ring with automatic transmission fluid. Then, push the O-ring onto the nozzle end of the injector until it is seated against the injector fuel filter.

Step 3: Install the meter body back-up washer in the top counterbore of the fuel meter body injector cavity.

Step 4: Lubricate the replacement large O-ring with automatic transmission fluid. Then, install it over the meter body back-up washer in the injector cavity. Ensure the large O-ring is seated properly and is flush with the top of the fuel meter body casting surface.

Step 5: Install the injector into the injector cavity, aligning the raised lug on the injector with the notch in the fuel meter body cavity. Push down on the injector until it is fully seated in the cavity. At this point, the injector electrical terminals should be approximately parallel to the throttle shaft.

Step 6: Install the fuel meter cover.

Step 7: Connect the electrical connector, then install the air cleaner assembly.

Note: It is important to ensure that all components are properly seated and aligned during the installation process to avoid any fuel leaks or electrical issues.

Additionally, when working on fuel injectors, it is important to be cautious and avoid any potential hazards. Always wear the appropriate safety gear, such as gloves and eye protection, and be mindful of any flammable materials or open flames nearby.

Testing and Inspection

Another method is to test the injectors by connecting them to a 9-volt battery and pulsing the power on and off. If the injectors are functioning, you should hear them click open and close. This test can also be used to clean the injectors by spraying brake cleaner into the injector inlet while pulsing the battery. Ensure all excess cleaner is wiped off afterward.

Additionally, you can test for fuel pressure, as these TBI injectors are designed to operate between 11 and 13 psi, though they often run at around 10 psi. Increasing the fuel pressure can be an easy way to boost performance, as a 1-psi change can result in roughly a 4% increase in fuel flow.

You can also test for proper grounding, as the ECM grounds the injector to fire it. If there is no ground, the injector will not function.

Finally, you can perform a visual inspection of the injector spray pattern using a timing light to ensure it looks correct.

Fuel Pump Upgrade

Upgrading the fuel pump is one of the first steps in modifying a 350 TBI engine. The stock fuel pump will only support about 230 hp before the fuel pressure drops, so an upgrade is recommended if you're looking for more power.

A popular choice is the 1996 Vortec 155lph fuel pump, which can support up to 450 hp and plugs right into a factory TBI sending unit. This fuel pump is a direct bolt-in upgrade and will provide enough fuel for most modifications.

If you're looking for an even higher-performance fuel pump, you may need to consider an adjustable fuel pressure regulator. Companies like JET, Turbo City, and CFM Technologies offer adjustable pressure regulators that allow you to fine-tune the fuel pressure to your desired level. However, keep in mind that raising the fuel pressure will increase fuel delivery across the entire engine operating range, so you'll need to monitor the oxygen sensor and make adjustments as needed.

Additionally, it's important to measure the existing fuel pressure before making any upgrades. If your pump is already delivering 13 psi at the TBI, you may not need to invest in an adjustable regulator. Most stock pumps can't generate more than 14 or 15 psi, so there's a limited range for adjustments.

When choosing a fuel pump upgrade, it's also crucial to consider the quality of the pump. Avoid cheap options, as they may not provide reliable performance. Always opt for a reputable brand and purchase from a trusted source to ensure the pump's authenticity and quality.

In summary, upgrading the fuel pump in a 350 TBI engine is a common modification to support higher horsepower levels. The Vortec 155lph fuel pump is a popular choice for its compatibility and performance. For further adjustments, an adjustable fuel pressure regulator can be used, but it requires careful monitoring of the oxygen sensor and fuel delivery across the engine's operating range.

Exhaust Modifications

• Start with the exhaust system: It is crucial to ensure that the exhaust system can handle the increased airflow resulting from other performance modifications. A free-flowing exhaust system is essential, as the stock exhaust is typically restrictive. Address the Y-pipe and catalytic converter, as these components can impact back pressure and airflow.
• Upgrade the Y-pipe: The Y-pipe in the stock exhaust system is often restrictive, and GM intentionally designed it that way to increase back pressure. However, what you want is increased air velocity, not back pressure. Consider replacing the stock Y-pipe with a Flowmaster Y-collector, which can provide a dramatic improvement in airflow.
• Catalytic converter: While some people choose to remove the catalytic converter, it is important for emissions control and can help reduce the smell of exhaust fumes. Consider using a high-flow catalytic converter, such as the Thunderbolt 3 Catalytic Converter, which is available on eBay for around $50.
• Headers: Headers are not generally recommended for engines with less than 300 hp. If you decide to install headers, ensure they are compatible with your vehicle's emissions requirements and that you have the necessary number of catalytic converters.
• Muffler: When choosing a muffler, you can select one based on your preferred sound level. The FULL BOAR SS muffler from eBay is a cost-effective option that offers good performance and stainless steel construction.
• Exhaust pipe size: Refer to exhaust pipe sizing charts to choose the appropriate pipe diameter for your specific engine configuration and power goals. A larger pipe does not always mean better performance, so it is important to select the right size for your application.
• Dual exhaust systems: If you are considering a dual exhaust system, be aware that some muffler shops may be hesitant to install them due to legal and emissions concerns. Dual exhaust systems typically require two catalytic converters, and it is essential to check your local laws and regulations before making any modifications.

Injector Cleaning and Flow Matching

The first step in the process of changing fuel injectors is to ensure that the new injectors are clean and functioning correctly. This can be done by purchasing new injectors or by cleaning and testing old ones.

Fuel injectors can be purchased in bulk, either new or from junkyards, and are grouped together by part number. They are then tested for resistance and put through a cleaning process. This cleaning process involves multiple steps, including:

• Disassembling the injectors
• Ultrasonic cleaning: Using ultrasonic baths with special non-hazardous solutions to clean the injectors internally
• Back-flushing: Removing any internal debris
• Pressure and leak testing
• Spray/flow testing

After the cleaning process, the injectors are flow-matched. Flow matching involves testing the injectors to group together those that flow the same amount when fully open. This is done through static flow testing, which measures the amount of fuel that will flow through an injector when it is fully open, at a determined fuel pressure and over a specific period.

It is important to note that having a set of flow-matched injectors does not mean that they are balanced. For a truly balanced set of injectors, the following criteria must be met:

• The amount of fuel delivered by each injector must be exactly the same throughout the injector duty cycle range.
• Atomization and distribution of fuel should be an exact match across all injectors.
• Resistance and reluctance of the injector set must be the same.
• Fuel injector latency values, or the time it takes for an injector to fully open and close, should be identical.

While static flow testing is a common method for matching injectors, it does not provide information on the health of the injectors. For a more comprehensive understanding of injector health, dynamic flow testing is recommended. This type of testing evaluates the performance of the injectors under a range of pressures and rpm values, providing insights into the consistency of fuel delivery and injector latency.

Additionally, it is worth noting that some off-the-shelf injector cleaning solutions can cause blockage issues. It is generally recommended to avoid using these products unless they have been used consistently since the vehicle was new.

Frequently asked questions