Common Service Concerns and Solutions

During service procedures, there are two concerns related to the air induction system which the technician should be aware of. These are false or unmeasured air entry into the intake system and deposit buildup on the back side of intake valves.

False air is any air which enters the induction system unwanted and/or unmeasured. In addition to obvious leaks in the intake manifold, with an L type EFI system, false air can enter the induction system through the connecting pipe between the air flow meter and the throttle body as well as through leaks into the crankcase. Because this air is able to enter the intake manifold unmeasured, the result is an excessively lean air/fuel ratio. The end result of false air with L type EFI is rough idle, stumble, and/or flat spots.

With the D type EFI system, false air is typically measured by the EFI system because it results in an increase in manifold absolute pressure. The end result is an engine that idles excessively high but with a relatively normal air/fuel mixture.

There are several tests which can detect false air entry into the induction system. A good visual inspection of the intake air connector pipe and connection points as well as inspection of all vacuum hoses, engine oil filler cap, and dip stick seals are a must.

If this fails to identify a suspected leak, spraying carburetor cleaner around suspected leak areas while observing an infrared exhaust analyzer for carbon monoxide increase is another method to assist in leak detection.

Another method to locate suspected false air entry points is to pressurize the intake system with a regulated shop air supply (CAUTION: do not exceed 25 PSI). Spray a soapy water solution around all suspected leak areas. Simply listen and observe for bubbles to locate leak sources. This method requires sealing the air cleaner fresh air inlet and blocking the throttle valve open to pressurize the intake air connector pipe. The air pressure can be applied through any large manifold vacuum fitting.

Intake Valve Deposits


Perform Check V With Borescope

This condition manifests itself as hardened carbon deposits on the back side of the intake valves. It varies in degree depending on the engine, fuel quality, and customer driving habits.

Intake valve deposits present a dual problem. First, these deposits restrict the flow of air and fuel mixture into the cylinder, reducing volumetric efficiency and potentially affecting high rpm engine performance. Additionally, these carbon deposits act like sponges absorbing fuel vapor. This causes lean driveability problems, particularly during cold engine operation.

The best way to identify this condition is by symptom and then through visual inspection. A visual inspection can be performed using a borescope, SSI #00451-42889, to confirm the problem. The intake manifold can also be removed to confirm the existence and the degree of this condition.

The accompanying chart will help you to determine the appropriate action to take based upon visual inspection. Visual inspection can be performed without removal of the cylinder head or intake manifold by using a borescope, SSI 00451-42889. The engine can be manually rotated until the intake valve is fully open; then the borescope can be inserted through a spark plug hole for inspection.

Repairs can be affected by use of SST 00002216401, a walnut shell type Carbon Cleaner Kit, and 00002-217256, a Universal Plate & Gasket Kit. These tools will allow removal of deposits without removal of the cylinder head.

Summary In this chapter, you have learned that the air induction system filters, meters, and measures air flow into the engine. By using multiple port injection, the intake system can be designed with long tuned intake runners to improve the engine's volumetric efficiency.

Air flow into the engine is controlled by the driver by opening and closing the throttle valve. As air enters the engine, it is measured by one of three different types of air flow meters with L type injection or by a manifold absolute pressure sensor with D type injection.

To improve engine idle quality during cold engine operation, some engines use a mechanical air valve to control air flow past the closed throttle valve. There are two different types of air valves used, one heated by engine coolant, the other heated electrically.

Depending on engine application, there are several different types of throttle control and idle-up devices used. Throttle body mounted devices provide a deceleration dashpot function and/or throttle opener function. Remotely mounted idle-up devices are used on some engines to control additional air flow into the engine when load from the A/C compressor or power steering pump are placed on the engine.

In section 3, Fuel Deliver & Injection controls, you will learn about the fuel delivery system.


Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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