Engine Performance - Poor Idle Quality: Overview
03.1-04DATE
7/95
Sedan Range
MODEL
1995 MY
4.0L NA
VIN
See engine no. below
Poor Idle Quality - Normally Aspirated AJ16 Engine - Valve Timing Modification
ISSUE:
To improve idle quality, revised camshafts with reduced valve timing overlap were introduced on the normally aspirated engines as running change 95/13. The original camshafts, with a maximum opening position of 110 degrees have been superseded by camshafts with a maximum opening position of 114 degrees. This change is accomplished by machining the camshaft slot in a different position. The valve timing overlap is reduced from 22 degrees on the 110 camshafts to 14 degrees on the 114 camshafts.
The maximum opening position of the 114 intake camshaft is 114 degrees after top dead center (ATDC) while the maximum opening position of the exhaust camshaft is 114 degrees before top dead center (BTDC).
Normally aspirated engines with the 110 camshafts, that exhibit poor idle quality, can be modified to achieve the same reduction in valve timing overlap as with the 114 camshafts.
NOTE:
Refer to Illustration 5, to identify engines with 110 camshafts that have already been modified.
The 114 camshafts were introduced for a period, withdrawn, and then reintroduced as a permanent change.
The table lists the change points by engine number as shown.
ACTION:
In case of a customer complaint of poor idle quality on a vehicle equipped with the 110 camshafts only, first check for punch marks on the timing cover near the camshaft position sensor, Illustration 5, to determine if the timing modification has already been performed. If not, reset the camshaft timing and spark plug gap as described below.
In addition, on engines with numbers below 9J103935, modify the bolts retaining the upper chain damper to the upper damper saddle as described at the appropriate point in the procedure.
PARTS INFORMATION:
DESCRIPTION PART NUMBER QTY
Cylinder head bolt (if needed) JZB 100053 2
Loctite 545 (if needed) 54531 -
Camshaft cover seal NBC 2525AA 1
Sprocket coupling tab washer C 33917 4
Spark plug boss seal NBC 2579AA 6
On-plug coil gasket DAC 11510 6
WARRANTY INFORMATION:
NOTE:
Record engine number in the comments section of the claim.