C 3500 Truck 2WD V6-262 4.3L (1990)
7)
Make sure vehicle is in CLOSED LOOP mode.
8)
Raise engine speed to 2600 RPM and maintain speed.
9)
Monitor BLOCK LEARN (BLM) values and CLOSED LOOP status at 2600 RPM - wait at least 30 seconds for BLM values to stabilize.
10)
If BLM value at 2600 RPM is less than 115, the timing chain sprockets are misaligned. Realign timing chain sprockets following REPAIR
PROCEDURE section of this bulletin (pages 5-6).
11)
If 2600 RPM BLM value is 115 or greater, let engine idle - automatic transmission equipped vehicles in DRIVE and manual transmission
equipped vehicles in NEUTRAL.
12)
Make sure system is still in CLOSED LOOP before continuing, if not, return to step # 7 and rerun testing sequence.
13)
Monitor BLM values and CLOSED LOOP status at IDLE - wait at least 30 seconds for BLM value to stabilize.
If system switches to OPEN LOOP too soon, rewarm oxygen sensor by shifting transmission to NEUTRAL or PARK and raise engine speed to
1500 RPM until system switches to CLOSED LOOP STATUS.
14)
If idle BLM value is less than 115, the timing chain sprockets are misaligned. Realign timing chain sprockets following REPAIR PROCEDURE
section of this bulletin (pages 5-6).
15)
If both BLM values are greater than 115, no repairs are required.
16)
Reconnect canister purge line to canister.
17)
Install Campaign Identification Label.
Figure 2
REPAIR PROCEDURE
NOTICE:
Perform repair procedure only if BLM values from diagnosis are less than 115 at 2500 RPM or idle.
a)
Remove spark plugs.
b)
Remove front timing chain cover - see section 6A3 in appropriate service manual.
NOTICE:
It is not necessary to replace front crankshaft seal.
c)
Thread a 7/16" x 20 x 1.00" bolt and torsional damper washer into crankshaft.
