Table of Contents
Advertisement
CS
ENGINE 3.5L (Continued)
CONDITION
OIL CONSUMPTION OR SPARK
PLUGS FOULED
DIAGNOSIS AND TESTING - CYLINDER
COMPRESSION PRESSURE TEST
The results of a cylinder compression pressure test
can be utilized to diagnose several engine malfunc-
tions.
Ensure the battery is completely charged and the
engine starter motor is in good operating condition.
Otherwise the indicated compression pressures may
not be valid for diagnosis purposes.
(1) Check engine oil level and add oil if necessary.
(2) Drive the vehicle until engine reaches normal
operating temperature. Select a route free from traf-
fic and other forms of congestion, observe all traffic
laws, and accelerate through the gears several times
briskly.
(3) Remove all spark plugs from engine. As spark
plugs are being removed, check electrodes for abnor-
mal firing indicators fouled, hot, oily, etc. Record cyl-
inder number of spark plug for future reference.
(4) Remove the Auto Shutdown (ASD) relay from
the PDC.
(5) Be sure throttle blade is fully open during the
compression check.
(6) Insert compression gauge adaptor Special Tool
8116 or the equivalent, into the #1 spark plug hole in
cylinder head. Connect the 0–500 psi (Blue) pressure
transducer (Special Tool CH7059) with cable adap-
tors to the DRBIII . For Special Tool identification,
(Refer to 9 - ENGINE - SPECIAL TOOLS).
(7) Crank engine until maximum pressure is
reached on gauge. Record this pressure as #1 cylin-
der pressure.
(8) Repeat the previous step for all remaining cyl-
inders.
(9) Compression should not be less than 689 kPa
(100 psi) and not vary more than 25 percent from cyl-
inder to cylinder.
POSSIBLE CAUSES
1. PCV system malfunction.
2. Worn, scuffed or broken rings.
3. Carbon in oil ring slots.
4. Rings fitted too tightly in grooves.
5. Worn valve guide(s).
6. Valve stem seal(s) worn or
damaged.
(10) If one or more cylinders have abnormally low
compression pressures, repeat the compression test.
(11) If the same cylinder or cylinders repeat an
abnormally low reading on the second compression
test, it could indicate the existence of a problem in
the cylinder in question. The recommended com-
pression pressures are to be used only as a
guide to diagnosing engine problems. An engine
should not be disassembled to determine the
cause of low compression unless some malfunc-
tion is present.
DIAGNOSIS AND TESTING - CYLINDER
COMBUSTION PRESSURE LEAKAGE TEST
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 seat-
ing).
• Leaks between adjacent cylinders or into water
jacket.
• Any causes for combustion/compression pressure
loss.
WARNING: DO NOT REMOVE THE PRESSURE CAP
WITH THE SYSTEM HOT AND UNDER PRESSURE
BECAUSE SERIOUS BURNS FROM COOLANT CAN
OCCUR.
Check the coolant level and fill as required. DO
NOT install the pressure cap.
Start and operate the engine until it attains nor-
mal operating temperature, then turn the engine
OFF.
Clean spark plug recesses with compressed air.
Remove the spark plugs.
Remove the oil filler cap.
Remove the air cleaner.
ENGINE 9 - 9
CORRECTION
1. Check system and repair as
necessary. (Refer to Appropriate
Diagnostic Manual)
2. Hone cylinder bores. Install new
rings.
3. Clean pistons and install new
rings.
4. Remove rings and check
grooves. If groove is not proper
width, replace piston.
5. Replace cylinder head(s).
6. Replace seal(s).
Advertisement
Table of Contents
