How to Troubleshot a 3.8L GM Buick Engine That Will Not Start

by Don Bowman
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Unlike earlier model vehicles, which incorporated a simple carburetor and distributor, the GM Buick 3.8-liter engine features a computer-controlled engine management system. If the system fails and the car won't start, you must follow a process of elimination to diagnose the problem. The job requires familiarity with modern engine systems as well as the right tools. Be sure to use appropriate safeguards to prevent electrical damage to critical components.

Step 1

Check all the fuses in the fuse relay box on the driver's side fenderwell. Replace any blown fuses and try starting the car.

Step 2

Plug the code scanner cable plug into the OBD (on board diagnostics) port under the dash on the left side of the steering column. Turn the ignition key to the run (on) position, but do not try to start the car.

Press the "Read" key on the scanner. Record the codes and cross-reference the codes with the code sheet that accompanies the scanner. The code sheet explains the object that has failed, when it failed and gives a brief summary of the expected cause of the failure. Repair the circuit indicated and attempt to start the car. Keep in mind that It is possible to have more than one problem.

Step 3

Determine whether the problem is fuel related or ignition related. Open the hood and locate the Schrader valve located on the fuel rail above the fuel injectors. Cycle the ignition key to the run position and off three times, allowing a four-second pause between cycles. Remove the plastic cap and briefly push the Schrader valve core with the small screwdriver. If fuel pressure is present, proceed to the ignition check. If fuel pressure is not evident, remove the air cleaner air duct from the throttle body using a screwdriver.

Step 4

Open the throttle plate with one hand by pushing on the linkage on the side of the throttle body. Spray a one-second shot of carburetor cleaner into the throttle body. Release the linkage and try to start the car. If the car starts for a few seconds until the carburetor cleaner is exhausted, a fuel pump problem is indicated.

Step 5

Look in the fuse relay box on the driver's fenderwell and find the fuel pump relay. If you flip the fuse box cover over, a description of the location of all fuses and relays is illustrated. Pull the relay out of the box.

The Buick has several identical relays,so look at the numbers on top of the relays and especially the way they are facing. The reason for this is so that they can be installed with the numbers facing the same way. Swap the two relays and try to start the car. If it still does not start, the fuel pump needs to be replaced.

Step 6

Pull a spark plug wire off the easiest spark plug to access. Insert the spare spark plug and lay the spark plug on the engine where it will get a good ground. Have a helper try to start the car while you watch the spark plug for a spark. If there is a spark, remove and check the spark plugs. If they are fouled or worn, replace them and retry. If there is no spark, check the ignition control module located under the coil packs on the passenger side front of the engine.

Step 7

Probe the electrical plug with 14 wires in the ignition control module. Looking at the plug, there are seven wires grouped together on one side of the plug and seven on the other side. Connect the black ground lead on the voltmeter to a good ground and turn the ignition to the run position. Probe the first two wires on the left side set of seven wires. Battery voltage should be present.

If no voltage is present, either the wires are broken or the ignition fuse is blown in the fuse relay box on the driver's side fenderwell. If power is present, probe the first wire on the right side group of seven wires. This is the computer 18X-pulse wire.

Have a helper attempt to start the car while you watch the voltmeter. If the voltage display shows no oscillations, the ignition control module is bad. If there are oscillations, the coils are bad.

Step 8

Check the intake manifold for vacuum leaks, given that the ignition and fuel system were both good. Look for any rubber hoses that are either disconnected or broken. A vacuum leak will cause a no start if the leak is large enough.

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