Page 1
Instructions for
Compression Tester
Test Procedure
1. Start Engine and warm to normal
operating temperature.
2. Turn engine off
3. Remove and number spark plug wires
4. Loosen spark plugs one turn
5. Clean loose dirt and rust from and
around spark plug wells
6. Remove spark plugs and place on
clean flat surface in order removed
7. Remove air filter
8. Set carburetor throttle plate to wide
open using string.
CAUTION
Be careful not to damage linkage
or throttle body components.
CAUTION
Make sure to return
carburetor throttle plates to closed
position before starting engine.
9. Remove high tension lad from center
of distributor and connect to ground.
NOTE: To disable electronic ignition
systems, disconnect electronic ignition
module or remove primary battery
terminal from ignition coil.
NOTE: On GM HEI V-6 and V-8
disconnect primary lead from distrutor
cap.
Held Open Throttle
Plates
High Tension Lead
Ignition Disabling
Procedure
Primary Wire
GM HEI Ignition
Disabling Procedure
Carburetor
String
Jumper Wire
Page 2
NOTE: Engines with 14 mm long reach
plugs, use long reach adapter.
CAUTION
Do not use long reach adapter
on short reach holes
10. Hand tighten spark plug adapter
hose into a spark plug well
CAUTION
Do not use a wrench to
attach spark plug adapter hose.
11. Connect spark plug adapter hose to
gauge
NOTE: Hose adapter is attached to
gauge by pulling up on outer sleeve of
quick disconnect on gauge and allowing
sleeve to return when hose is inserted.
12. Crank engine until pressure reading
stops rising on gauge.
NOTE: Crank engine at least 4
compression strokes.
13. Record compression reading.
14. Press release valve on side of
gauge
NOTE. Repeat steps 12 through 14 on
the first cylinder
15. Remove gauge from hose.
16. Hand tighten spark plug adapter
hose into a spark plug well
17. Remove hose from spark plug well
18. Repeat steps 10 through 18 for the
rest of the remaining cylinders.
19. Refer to Test Results.
.
Installation of
Compression Gauge
Release Valve
Push Release Valve to
Relieve Pressure
Page 3
Test Results
Normal Cylinder:
Gauge needle should travel up-scale on each compression
stroke until a peak value is reached.
All cylinders should have a pressure within vehicle
manufacturers specifications.
Readings should not vary more than 10% from cylinder to
cylinder.
Needle fails to travel up gauge or remains at same value for
several strokes then climbs:
Check for a sticking valve.
Compression reading is alot higher than manufacturers
specifications
Check for carbon build-up in cylinder.
Reading on 2 adjacent cylinders is 20 pounds (or more)
lower than the other cylinders
Check for a defective head gasket.
Check for water (coolant) or oil in the 2 cylinders.
Reading are low or vary widely between cylinders
Pour teaspoon of SAE grade 30 oil into each cylinder and
retest
- If reading increases alot fault may be due to poorly
seated or worn pison rings.
- If reading remains about the same valves and associated
components are likely the problem.
Return to Original Configuration
1. Clean, regap and reinstall spark plugs or install new spark plugs.
2. Reconnect all spark plug wires
3. Remove string from carburetor throttle plates.
Make sure throttle plates return to closed position
4. Reconnect igintion system that was disconnected in step 9 of
test procedure.
CAUTION
Page 4
Compression Gauge Repair Parts
1
4
2
4
3
5
6
7
Number Part Number Description
1 31-255 Compression Gauge
1 400-1335 Replacement Bezel Only
2 180-772 Quick Disconnect Coupling & Valve Assy
3 32-109 Spark Plug Hose Assembly
4 180-775 (2 ea) Air Valve (High Pressure)
5 400-382 O-ring
6 400-381 (2 ea) O-ring
7 180-829 Deep Reach Adapter
CAUTION
Do not use automobile tire air valves as a replacement part.
©2003Actron Manufacturing Company. All rights reserved. 0002-002-1860
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