Systematic Check; Check Ignition; Check Ignition (Engine Running); Check Ignition (Fouled Plug Or Other Causes) - Generac Power Systems GTV-990 Manual

SECTION 1: GENERAL INFORMATION

SYSTEMATIC CHECK:

If the engine will not start and the cause of malfunction is
not readily apparent, perform a systematic check in the following
order:
1. Ignition
2. Fuel
3. Compression
This check-up, performed in a systematic manner, can usu-
ally be done in a matter of minutes. It is the quickest and surest
method of determining the cause of failure. The basic checkup
procedure is the same for all engine models, while any varia-
tion, by model, will be shown under the subject heading.

CHECK IGNITION:

If spark does not occur look for:
• Shorted ignition/kill wire
• Two closed diodes in ground wire harness
• Incorrect armature air gap
• Armature failure

CHECK IGNITION (ENGINE RUNNING):

If engine runs but misses during operation, a quick check to
determine if ignition is or is not at fault can be made by
installing a spark tester (Generac P/N OC5969) between the
spark plug lead and each spark plug, Figure 1-6. A spark miss
will be readily apparent when the engine is running. If spark
is good but engine misses, check for a fouled spark plug.
SPARK
PLUG
LEAD
TESTER
Figure 1-6. Running Check

CHECK IGNITION (FOULED PLUG OR OTHER CAUSES):

To check for a fouled spark plug or a non-functioning cylin-
der, attach the spark tester (Generac P/N OC5969) between the
spark plug lead and each spark plug. Start and run engine at
top no load speed. Now ground one spark plug, Figure 1-7. The
engine should continue to run on the other cylinder. Repeat this
test with the other cylinder. If the engine will not continue to
run when making this test, the cylinder that is NOT grounded
is not functioning and/or the spark plug is fouled. Install a new
spark plug before proceeding. If miss continues, problem may
be carburetion or compression. See Check Carburetion, Check
Compression. Also see Cylinder Balance Test.

CYLINDER BALANCE TEST:

If the engine is hard starting, runs rough, misses or lacks
power, perform a cylinder balance test to determine 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 1-6.
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 contacting ignition tester and a good ground on
SPARK PLUG
engine, Figure1-8. Note RPM loss. Then ground out the other
spark plug and note the RPM loss. If the difference between
the two cylinders does not exceed 75 RPM, the amount of work
the two cylinders are doing should be considered equal.
1-4
Figure 1-7. Checking For Fouled Plugs