The results of a cylinder compression pressure test can be utilized to diagnose several engine malfunctions.
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 traffic 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 abnormal
firing indicators such as fouled, hot, oily, etc. Record cylinder number of spark plug for future reference.
4. Remove the Auto Shutdown (ASD) relay from the Power Distribution Center (PDC).
5. 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
adaptors to the DRBIII®. For Special Tool identification, see
Engine - Special Tools
.
6. Crank engine until maximum pressure is reached on gauge. Record this pressure as #1 cylinder pressure.
7. Repeat the previous step for all remaining cylinders.
8. Compression should not be less than 689 kPa (100 psi) and not vary more than 25 percent from cylinder
to cylinder.
9. If one or more cylinders have abnormally low compression pressures, repeat the compression test.
10. 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 compression
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 malfunction is present.
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 seating).
Leaks between adjacent cylinders or into water jacket.
Any causes for combustion/compression pressure loss.
Check the coolant level and fill as required. DO NOT install the pressure cap.
Start and operate the engine until it attains normal operating temperature, then turn the engine OFF.
Clean spark plug recesses with compressed air.
WARNING:
DO NOT REMOVE THE PRESSURE CAP WITH THE SYSTEM HOT AND
UNDER PRESSURE BECAUSE SERIOUS BURNS FROM COOLANT CAN
OCCUR.
2010 Jeep Wrangler Sport
2010 ENGINE 3.8L - Service Information - Wrangler
viernes, 1 de octubre de 2021 05:18:29 p. m.
Page 8
© 2011 Mitchell Repair Information Company, LLC.
