Stranger Things Have Happened
The PCM strategy
in these vehicles
is to raise the
transmission line
pressure when it sees
a problem in the
knock sensor signal.
uses these signals to control fuel flow
through the fuel solenoid and fuel
solenoid driver.
This problem has been known to
happen with a new fuel solenoid driv-
er right out of the box. Just because
Figure 5
it’s new doesn’t mean it’s good. There
may not be any noticeable drivability
issues with the way the engine oper-
ates.
As you can see in figure 5, the
fuel injector pump assembly, sensors
and module are in an area that can
become quite hot. So the solenoid
driver module is available through the
aftermarket with a pigtail harness to
relocate it to the firewall.
Problem 3: This time the condi-
tion occurs on GM trucks with a 4.3L
V6, 5.0L, 5.7L or 7.4L V8 gas engine
and a 4L80E or 4L60E transmis-
sion. The transmission exhibits high
line pressure, causing harsh upshifts,
coastdown shifts and engagements.
When monitored on a scan tool,
the PCM is commanding line pressure
high. There are no transmission codes.
Check for a knock sensor (KS) code
43, P0325, P0326, P0327, P0330,
Figure 6
P0332, P0335 or P0336 being present,
pending or in history. sensor signal. ohms) than the single sensor (3900
A knock sensor is a piezoelectric In some engines the knock sen- ohms) systems and can’t be used in
device which the PCM uses to detect sor is located close to the starter and place of one another.
abnormal engine vibrations (spark the wire loom runs near the exhaust Problem 4: This one occurs on all
knock). The vibration causes the knock manifold. It isn’t uncommon to find the 1996-up GM vehicles. The TCC surges
sensor to produce a very low AC signal, wires melted (figure 6). This problem in and out at cruise, or there’s no lockup
sent from the sensor to the KS module may occur soon after someone works at all. The problem may be intermittent
in the PCM. The PCM uses this signal on the vehicle and accidently relocates and more noticeable on rough roads.
to retard ignition timing until the knock the wiring when replacing the starter. When monitored on a scan tool, the
stops. Some vehicles with a 4.3L V6 PCM will be commanding lockup on
The PCM strategy in these vehicles engine will have two knock sensors and off or there won’t be any command
is to raise the transmission line pressure (figure 7). The knock sensors on dual for lockup at all. Again, no transmis-
when it sees a problem in the knock systems have higher resistance (8200 sion codes are stored.
28 GEARS January/February 2010
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