Sep 142016
 

1990 GMC SierraMy 1990 Chevy sierra  truck has a 5.7l v-8 t.b.i engine, automatic transmission.                                 The engine runs decent cold but when it warms up, it runs poorly. My truck wants to stall when I come to a complete stop. It hesitates during acceleration. The engine has a very pronounced miss once it reaches normal operating temperature. The spark plugs read different on each side of engine, ranging from lean to rich on both sides. My truck engine ran very good until these symptoms presented themselves all at once. I recently replaced the distributor cap and rotor, spark plugs and spark plug wires. I am recently disabled because, in part, to my memory and cannot figure this out. Very frustrated.


RESPONSE

You stated you recently replaced “distributor cap and rotor, spark plugs and spark plug wires”. If the problem started after you worked on it, recheck your work first.

Assuming you replaced these parts after it started giving you trouble the first step would be to extract any existing diagnostic trouble codes from the On Board Computer. As luck would have it you do not need a scan tool for this. You can do it yourself.

Post any codes below in the comments for further information.

No Codes present. The most common cause would be the ignition control module breaking down.


If you suspect a problem in the ignition system, there are certain preliminary checks which you should carry out before you begin to check the electronic portions of the system. First, it is extremely important to make sure the vehicle battery is in a good state of charge. A defective or poorly charged battery will cause the various components of the ignition system to read incorrectly when they are being tested. Second, make sure all wiring connections are clean and tight, not only at the battery, but also at the distributor cap, ignition coil, and at the electronic control module.

  1. Check the cap for tiny holes and carbon tracks as follows.
    1. Remove the cap and place an ohmmeter lead on the cap terminal.
    2. Use the other lead to probe all the other terminals and the center carbon ball.
  2. If the readings are not infinite, the cap must be replaced.

Ignition Control Module Replacement

1.Remove the distributor cap and rotor as previously described.
2.Disconnect the harness connector and pickup coil spade connectors from the module. Be careful not to damage the wires when removing the connector.

Fig. 1: Be sure to coat the mating surfaces with silicone lubricant

ignition control module

 

3.Remove the two screws and module from the distributor housing.
4.Coat the bottom of the new module with dielectric silicone lubricant. This is usually supplied with the new module. Reverse the above procedure to install.

 

 

 

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