GM Caprice 1990-1993 Repair Guide

Diagnosis and Testing

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The symptoms of a defective component within the HEI system are exactly the same as those you would encounter in a conventional system. Some of these symptoms are:



Hard or no Starting
 
Rough Idle or Backfiring
 
Poor Fuel Economy
 
Engine misses under load or while accelerating.
 

If you suspect a problem in your 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 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.

Since the only change between electronic and conventional ignition systems is in the distributor component area, it is imperative to check the secondary ignition circuit first (plugs, wires, rotor and cap). If the secondary circuit checks out properly, then the engine condition is probably not the fault of the ignition system. To check the secondary ignition system, perform a simple spark test. Remove one of the plug wires and insert some sort of extension in the plug socket. An old spark plug with the ground electrode removed makes a good extension. Hold the wire and extension about 1 / 4 inch away from the block and crank the engine. If a normal bright blue spark occurs, then the problem is most likely not in the ignition system. Check for fuel system problems, or fouled spark plugs.


NOTE
It is also possible for there to be some type of internal engine damage (timing chain) and still have good spark.

If, however, there is no spark or a weak spark, then further ignition system testing will have to be done. Troubleshooting techniques fall into two categories, depending on the nature of the problem. The categories are (1) Engine cranks, but won't start or (2) Engine runs, but runs rough or cuts out. To begin with, let's consider the first case.

Engine Fails to Start

If the engine won't start, perform a spark test as described earlier. This will narrow the problem area down considerably. If no spark occurs, check for the presence of normal battery voltage at the battery (BAT) terminal on the ignition coil. The ignition switch must be in the ON position for this test. Either a voltmeter or a test light may be used for this test. Connect the test light wire to ground and the probe end to the BAT terminal at the coil. If the light comes on, you have voltage to the distributor. If the light fails to come on, this indicates an open circuit in the ignition primary wiring leading to the distributor. In this case, you will have to check wiring continuity back to the ignition switch. If there is battery voltage at the BAT terminal, but no spark at the plugs, then the problem lies within the distributor assembly. Go on to the distributor components test section.

Engine Runs, But Runs Rough or Cuts Out
  1. Make sure the plug wires are in good shape first. There should be no obvious cracks or breaks. You can check the plug wires with an ohmmeter, but do not pierce the wires with a probe. Check the chart for the correct plug wire resistance.
  2.  
  3. If the plug wires are good, remove the cap assembly and check for moisture, cracks, chips, or carbon tracks, or any other high voltage leaks or failures. Perform a "wiggle test" (feeling the wire for bad or broken connections) on all wires leading to and in the distributor. Replace any defective parts. Make sure the distributor rotates (checking timing chain and gears) when the engine is cranked. If everything is all right so far, go on to the distributor components test section following.
  4.  

DISTRIBUTOR COMPONENTS TESTING



See Figures 1, 2, 3, and 4

If the trouble has been narrowed down to the components within the distributor, the following tests can help pinpoint the defect. An ohmmeter with both high and low ranges should be used. These tests are made with the distributor wires disconnected and the cap removed from the distributor.


WARNING
The tachometer terminals must never be allowed to touch ground, otherwise damage to the module or coil is possible.

Ignition Coil
MOUNTED IN CAP

See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Testing Internally mounted ignition coil - 5.0L (VIN Y) Engine

  1. Connect an ohmmeter between the TACH and BAT terminals on the ignition coil. The primary coil resistance should be less than one ohm.
  2.  
  3. To check the coil secondary resistance, connect an ohmmeter between the high tension terminal and the BAT terminal. Note the reading. Connect the ohmmeter between the high tension terminal and the TACH terminal. Note the reading. The resistance in both cases should be 6,000-30,000 ohms. Be sure to test between the high tension terminal and both the BAT and TACH terminals.
  4.  
  5. Replace the coil only if the readings in Step 1 and Step 2 are infinite.
  6.  


NOTE
These resistance checks will not disclose shorted coil windings. This condition can only be detected with scope analysis or a suitably designed coil tester. If these instruments are unavailable, replace the coil with a known good coil as a final coil test.

EXTERNALLY MOUNTED

See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Testing externally mounted ignition coil - Except 5.0L (VIN Y) Engine

  1. Disconnect the coil wires and set the ohmmeter on the high scale.
  2.  
  3. Connect the ohmmeter as illustrated in test No. 1.
  4.  
  5. The ohmmeter should read near infinite or very high.
  6.  
  7. Next, set the ohmmeter to the low scale.
  8.  
  9. Connect the ohmmeter as illustrated in test No. 2.
  10.  
  11. The ohmmeter should read zero or very low.
  12.  
  13. Next, set the ohmmeter on the high scale again.
  14.  
  15. Connect the ohmmeter as illustrated in test No. 3.
  16.  
  17. The ohmmeter should NOT read infinite.
  18.  
  19. If the reading are not as specified, replace the coil.
  20.  

Pickup Coil

See Figures 3 and 4



Click image to see an enlarged view

Fig. Fig. 3: Testing the pick-up coil - with ignition coil mounted in cap



Click image to see an enlarged view

Fig. Fig. 4: Testing the pick-up coil - with ignition coil externally mounted

  1. Remove the distributor cap and rotor.
  2.  
  3. Disconnect the pick-up coil lead.
  4.  
  5. Set the ohmmeter on the high scale and connect it as illustrated in test No. 1.
  6.  
  7. The ohmmeter should read infinity at all times.
  8.  
  9. Next, set the ohmmeter on the low scale and connect it as illustrated in test No. 2.
  10.  
  11. The ohmmeter should read a steady value between 500-1500 ohms.
  12.  
  13. If the readings are not as specified, replace the pick-up coil.
  14.  
  15. If no defects have been found at this time, and you still have a problem, then the module will have to be checked. If you do not have access to a module tester, the only possible alternative is a substitution test.
  16.  

HEI System Maintenance

Except for periodic checks on the spark plug wires, and an occasional check of the distributor cap for cracks (see Steps 1 and 2 under Engine Runs, But Runs Rough or Cuts Out for details), no maintenance is required on the HEI system. No periodic lubrication is necessary; engine oil lubricates the lower bushing, and an oil-filled reservoir lubricates the upper bushing.

 
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