DIAGNOSIS AND TESTING - CYLINDER COMBUSTION PRESSURE LEAKAGE
The combustion pressure leakage test provides an accurate means for determining engine condition.
Combustion pressure leakage testing will detect:
- Exhaust and intake valve leaks (improper seating).
- Leaks between adjacent cylinders or into water jacket.
- Any causes for combustion/compression pressure loss.
All gauge pressure indications should be equal, with no more than 25% leakage.
FOR EXAMPLE: At 552 kPa (80 psi) input pressure, a minimum of 414 kPa (60 psi) should be maintained in the cylinder.
Refer to CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART.
| CONDITION | POSSIBLE CAUSE | CORRECTION |
| AIR ESCAPES THROUGH THROTTLE BODY | Intake valve bent, burnt, or not seated properly | Inspect valve and valve seat. Reface or replace, as necessary. Inspect valve springs. Replace as necessary. |
| AIR ESCAPES THROUGH TAILPIPE | Exhaust valve bent, burnt, or not seated properly | Inspect valve and valve seat. Reface or replace, as necessary. Inspect valve springs. Replace as necessary. |
| AIR ESCAPES THROUGH RADIATOR | Head gasket leaking or cracked cylinder head or block | Remove cylinder head and inspect. Replace defective
part |
| MORE THAN 50% LEAKAGE FROM ADJACENT CYLINDERS | Head gasket leaking or crack in cylinder
head or block between adjacent cylinders | Remove cylinder head and inspect. Replace gasket, head, or block as necessary |
| MORE THAN 25% LEAKAGE AND AIR ESCAPES THROUGH OIL FILLER CAP OPENING ONLY | Stuck or broken piston rings; cracked piston;
worn rings and/or cylinder wall | Inspect for broken rings or piston. Measure ring gap and cylinder diameter, taper and out-of-round. Replace defective
part as necessary |