Generac Power Systems 55, 75, 65 manual 32.– Testing Ignition System, 33.– Checking Engine Miss

Section 7

DIAGNOSTIC TESTS

4.Crank the engine rapidly. Engine must be cranking at 350 rpm or more. If spark jumps the tester gap, you may assume the ignition system is working properly. Repeat on remaining cylin- der spark plug.

5.To determine if an engine miss is ignition related, connect the spark tester in series with the high tension lead and the spark plug. Then, start the engine. If spark jumps the tester gap at regular Intervals, but the engine miss continues, the problem may be in the spark plug or fuel system. Repeat on remaining cylinder spark plug. Proceed to Test 33.

6.If spark jumps the tester gap intermittently, the problem may be in the Ignition Magneto. Proceed to Test 34.

Figure 7-32. – Testing Ignition System

Figure 7-33. – Checking Engine Miss

RESULTS:

1.If no spark or if engine miss is apparent, go to Test 34.

2.If ignition spark is good, go to Test 33.

CYLINDER BALANCE TEST:

If the engine is hard starting, runs rough, misses or lacks power, perform a cylinder balance test to deter- mine whether both cylinders are operating to their full potential.

Tools Required:

1. Two Ignition Testers (Generac P/N OC5969)

Attach an ignition tester between the spark plug lead and each spark plug (Figure 7-33).

Start and run engine running at top no load speed and note spark at ignition testers. If the spark is equal at both ignition testers, the problem is not ignition related. A spark miss will be readily apparent. Now note RPM of engine. Ground out one cylinder by con- tacting ignition tester and a good ground on engine (Figure 7-34). Note RPM loss. Then ground out the other spark plug and note the RPM loss. If the differ- ence between the two cylinders does not exceed 75 RPM, the amount of work the two cylinders are doing should be considered equal.

If the RPM loss is greater than 75 RPM this indicates that the grounded cylinder with the least RPM loss is the weakest of the two cylinders. Look to that cylinder for a problem.

Example:

Engine RPM - Both Cylinders = 2570 RPM

Engine RPM - No. 1 Cylinder Grounded = 2500 RPM Engine RPM - No. 2 Cylinder Grounded = 2300 RPM

Conclusion: No. 1 cylinder is weakest of the two cylinders.

Figure 7-34. – Cylinder Balance Test

The cylinder balance test will also detect a cylinder that is not functioning. When grounding out one cylin- der there will be no RPM loss. When the other cylin- der is grounded out the engine will stop.

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