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Emission Control Maintenance Bruce Bonebrake does an emission test on a 1998 Jeep, then performs emission system service including plugs, wires, distributor rotor, MAP sensor, fuel injectors, O-rings and air filter. From "Weekend Mechanic" episode WKM-413

A vehicle emissions test not only reveals if the system is working properly and reducing harmful pollutants, but it can also detect engine problems. These can be as simple as worn spark plugs or as major as a fuel leak which could lead to an engine fire.

In this Weekend Mechanic project, host Bruce Bonebrake tests a 1998 Jeep, repairs a lean air/fuel condition and corrects an ignition misfire.

The basic steps, as demonstrated in episode 413 of Weekend Mechanic, are summarized below.

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Bruce uses an exhaust probe and an engine analysis system to display emissions results on a laptop computer.

Emissions Control Basics

Figures released by the Environmental Protection Agency on cars that had failed their emissions test suggest that around 25 percent of the cars needed spark plug adjustment — either cleaning, gapping or replacement. About 20 percent required a new, clean air filter. A third of the cars studied had incorrect timing settings and up to 75 percent had incorrect idle speeds. Aside from these afflictions, faulty catalytic converters are another common problem leading to undesirable emissions.

Project Overview

For this project, Bruce Bonebrake examines common emission problems on a 1998 Jeep Wrangler. To do the vehicle emissions test on our jeep, Bruce uses an exhaust probe and an engine analysis system which will display the results on a laptop computer.

After a tailpipe emissions test, he finds the engine is running lean and that there is a fuel leak in the #2 cylinder injector. The computer also shows an ignition misfire. Bruce replaces the spark plugs and spark plug wires and distributor rotor to correct the engine misfire. He services the fuel injection system, replacing the injector and O-rings on the rest of the injectors. He also cleans the throttle body of deposits, and installs a new MAP (Manifold Absolute Pressure) sensor, oxygen sensors (which measure the oxygen content of the exhaust) and air filter. Finally, Bruce retests the exhaust emissions, does a gas cap emissions test and takes the Jeep for a test drive.

Important: Included here is a basic summary of the steps in this automotive procedure as shown in the episode. These steps are general guidelines that are applicable to most vehicles. With any particular vehicle, there may be procedures, specifications, settings, tolerances, components, etc. that are specific to that vehicle. There are also variations according to the type and brand of repair-kit or replacement parts you select. Always consult your vehicle's service manual when undertaking significant automotive repairs, and read and follow the manufacturer's directions and precautions that come with your kit or replacement parts.

Tools and Materials

In addition to standard auto-mechanic's tools (wrenches, ratchets, extenders, screwdrivers, nut-drivers, torque wrench, etc.), some of the tools required for this project include:

fuel injector line disconnect tool
replacement spark plugs and plug wires
replacement air filter
replacement fuel injectors
replacement MAP sensor
fire extinguisher

Safety Alert: When working on the fuel system, it's an important to have good ventilation in the work area. It's also critical to have a fire extinguisher handy.

Safety Alert: As a standard safety precaution, always disconnect the vehicle's negative battery cable before you begin work on any electrical or mechanical components.

Safety Alert: Always wear eye protection and follow proper safety precautions when working with power tools or pneumatic tools. Also wear eye protection any time you are working underneath a vehicle.

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