Guardian Technologies 4390, 4456 Test 56 Check Spark Plugs, Test 57- Check Engine Compression

SECTION 4.4

DIAGNOSTIC TESTS

PART 4

DC CONTROL

3.Attach the spark plug lead to the spark tester terminal.

4.Crank the engine while observing the spark tester. If spark jumps the tester gap, you may assume the engine ignition system is operating satisfactorily.

NOTE: The engine flywheel must rotate at 350 rpm (or higher) to obtain a good test of the solid state ignition system.

To determine if an engine miss is ignition related, connect the spark tester in series with the spark plug wire and the spark plug (Figure 21). Then, crank and start the engine. A spark miss will be readily apparent. If spark jumps the spark tester gap regularly but the engine miss continues, the problem is in the spark plug or in the fuel system.

NOTE: A sheared flywheel key may change ignition timing but sparking will still occur across the spark tester gap.

Figure 21. Checking Engine Miss

RESULTS:

1.If no spark or very weak spark occurs, go to Test 58.

2.If sparking occurs but engine still won't start, go to Test 56.

3.When checking for engine miss, if sparking occurs at regular intervals but engine miss continues, go to Test 16.

4.When checking for engine miss, if a spark miss is readily apparent, go to Test 59.

TEST 56 - CHECK SPARK PLUGS

DISCUSSION:

If the engine will not start and Test 55 indicated good ignition spark, perhaps the spark plug(s) are fouled or otherwise damaged. Engine miss may also be caused

by defective spark plug(s).

PROCEDURE:

1.Remove spark plugs and clean with a penknife or use a wire brush and solvent.

2.Replace any spark plug having burned electrodes or cracked porcelain.

3.Set gap on new or used spark plugs to 0.030 inch for single cylinder engines and 0.020 inch for v-twin engines.

RESULTS:

1.Clean, re-gap or replace spark plugs as necessary.

2.If spark plugs are good, go to Test 62.

Figure 22. Checking Spark Plug Gap

TEST 57- CHECK ENGINE COMPRESSION

DISCUSSION:

Lost or reduced engine compression can result in (a) failure of the engine to start, or (b) rough operation. One or more of the following will usually cause loss of compression:

❏Blown or leaking cylinder head gasket.

❏Improperly seated or sticking-valves.

❏Worn Piston rings or cylinder. (This will also result in high oil consumption).

NOTE: For the single cylinder engine, the minimum allowable compression pressure for a cold engine is 60 psi.

NOTE: It is extremely difficult to obtain an accurate compression reading without special equipment. For that reason, compression values are not published for the V-Twin engine. Testing has proven that an accurate compression indication can be obtained using the following method.

PROCEDURE:

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