Guardian Quietpact 55 Repair Manual page 60

S S e e c c t t i i o o n n 7 7
D D I I A A G G N N O O S S T T I I C C T T E E S S T T S S
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.
Page 58
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.