Generac Power Systems XT-EFI Series User Manual

Section 5 Engine Diagnostic Tests
32 Diagnostic Repair Manual
Test 25 – Check Engine / Cylinder
Leak Down Test / Compression Test
General Theory
Most engine problems may be classified as one, or a
combination of the following:
• Will not start
• Starts hard
• Lack power
• Runs rough
• Vibration
• Overheating
• High oil consumption
General Theory
The Cylinder Leak Down Tester checks sealing
(compression) ability of engine by measuring air leakage
from combustion chamber. Compression loss can
present many different symptoms. This test detects the
section of the engine where the fault lies before
disassembling the engine. Figure 5-16 represents a
standard tester available on the market.
Figure 5-16. Cylinder Leakdown Tester
Procedure
1. Shut off the fuel supply.
2. Remove spark plug.
3. Gain access to flywheel.
4. Remove valve cover.
5. Rotate engine crankshaft until the piston reaches
top dead center (TDC). Both valves should be
closed.
6. Lock flywheel at top dead center.
7. Attach cylinder leak down tester adapter to spark
plug hole.
8. Connect an air source of at least 90 psi to the leak
down tester.
9. Adjust regulated pressure on gauge to 80 psi.
10. Read right hand gauge on tester for cylinder
pressure. 20 percent leakage is normally
acceptable. Use good judgment, and listen for air
escaping at carburetor, exhaust, and crankcase
breather. This determines where the fault lies.
Results
•
Air escapes at carburetor – check intake valve.
• Air escapes through exhaust – check exhaust
valve.
• Air escapes through breather – check piston rings.
• Air escapes from cylinder head – replace head
gasket.
Check Compression
To check engine compression, remove spark plug. Insert
an automotive type compression gauge into the spark
plug hole. Crank engine until there is no further in
pressure. The highest reading obtained is engine
compression pressure.
Minimum Allowable Compression Pressure Cold
Engine – 60 psi
If compression is poor, look the following causes:
• Loose cylinder head bolts
• Failed cylinder head gasket
• Burned valves or valve seats
• Insufficient valve clearance
• Warped cylinder head
• Warped valve stem
• Worn or broken piston ring(s)
• Worn or damaged cylinder bore
• Broken connecting rod
• Worn valve seats or valves
• Worn valve guides
NOTE: Refer to Engine Service Manual Part Number
0C1103A for further engine service information on the
410cc engine.
NOTE: Refer to Engine Service Manual Part Number
10000016870 for further engine service information on
the 426cc engine.
002419
0
0
0
A. Compressed air in
B. Air pressure regulator
C. Inlet gauge pressure set point
D. Outlet gauge pressure
E. To spark plug hole
F. Regulator adjustment knob
G. Outlet gaug
e
H.
Red range indicates unacceptable leakage
I. Needle indicates minimal air leakage
J. Green range indicates acceptable leakage
A
C
B
D
E
F
I
J
G
H

Generac Power Systems XT-EFI Series Specifications

General

Brand	Generac Power Systems
Model	XT-EFI Series
Category	Portable Generator
Language	English

Summary

Brushless Capacitor Excitation System

Troubleshooting Brushless AC Output

Guides users through diagnosing AC output problems using flowcharts and specific tests.

Problem 1: Zero or Residual Voltage Output

Outlines diagnostic steps for a generator that produces no or very low output voltage.

Direct Excitation (Brush Type) System

Troubleshooting Brush Type AC Output

Guides users through diagnosing AC output problems for brush type generators.

Problem 5: Zero or Residual Voltage Output

Outlines diagnostic steps for a generator that produces no or very low output voltage.

Problem 6: High or Low Voltage & Frequency

Provides troubleshooting steps for generators with incorrect voltage and frequency output.

Problem 7: Voltage/Frequency Droop Under Load

Guides diagnosis for voltage/frequency drops when electrical load is applied.

Problem 8: High Voltage at No-Load

Steps to diagnose generators that output excessively high voltage without load.

AC Diagnostic Tests for Generators

Test 1: Check No-Load Voltage and Frequency

Test 2: Check Main Circuit Breaker

Test 3: Check Receptacle Panel Continuity

Test 4: Fixed Excitation/Rotor Amp Draw Test

Test 5: Field Flash Alternator Procedure

Test 6: Check Generator Capacitor

Test 7: Test Brushless DPE Windings

Test 8: Test Brushless Stator Windings

Test 9: Test Brushed Stator Windings

Test 10: Check Load Voltage & Frequency

Test 11: Check Load Watts & Amperage

Test 12: Adjust Voltage Regulator Settings

Procedure to adjust the voltage regulator to achieve the correct output voltage.

EFI Engine Control Diagnostic Tests

EFI Fault Code Diagnostics

Engine Diagnostic Tests and Troubleshooting

Engine Diagnostic Flow Charts

Guides users through diagnosing engine issues using flowcharts and specific tests.

Problem 9: Recoil Cord Will Not Pull

Troubleshooting steps for a generator recoil cord that will not pull.

Problem 10: Engine Starts Hard and Runs Rough

Diagnostic steps for an engine that starts with difficulty and runs unevenly.

Problem 11: Engine Cranks But Will Not Start

Troubleshooting for engines that crank but fail to start, focusing on fuel and spark.

Problem 12: Engine Hunts or Has Erratic Idle

Steps to diagnose and resolve engines that exhibit unstable or fluctuating idle speeds.

Problem 13: Engine Will Not Crank

Diagnostic procedures for engines that fail to crank, checking battery, starter, and switch.

Problem 15: Engine Cranks But Will Not Start

Troubleshooting for engines that crank but fail to start, focusing on fuel, spark, and ignition.

Problem 17: Engine Starts Then Shuts Down

Troubleshooting for engines that start and then immediately shut off, checking oil level and pressure.

Problem 18: Battery Will Not Charge

Steps to diagnose why the generator's battery is not charging, checking charger and circuit.

Test 15: Check Battery and Cables

Test 20: Check Ignition Spark

Tests the engine's ignition system for proper spark generation using a spark tester.

Test 22: Check Carburetion

Test 25: Cylinder Leak Down/Compression Test

Test 36: Test Battery Charging Circuit