A few questions about pcm

[chris1070]

Ok i have a couple questions about what my truck does right after i reset the pcm by disconnecting the battery.,When i connect it back up and start the truck it dies sometimes. But after about 30 min of driving when the pcm sets it never does it. What causes this? Also normally when i rev my truck up it has a little backfiring...kind of a gurgling sound when i let off. But right after i reset the pcm and it is still learning it doesnt gurlge or backfire at all when i rev it up. But after a while when the pcm sets itself it starts doing it again. What causes this and can i make it not backfire all the time?

[PIDGAF]

Ok, here it goes, when you disconnect the battery you basically clear everything out of the PCM's adaptive memory. The PCM has a stored set of values like idle stratagy, Injector pulsewidth and timing characteristics. When you disconnect battery voltage you clear all of these "learned" values that the computer learns as you drive it. So basically when you reconnect the battery the PCM uses preset values programed into memory to determine all of the factors until it "relearns" all of this info by your driving characteristics. As far as the backfiring it could be alot of different things. What it sounds like to me though is that you have an exhaust leak and with that all of the unburned exhaust gasses have enough fuel left in it that when you let off of the throttle outside air gets sucked through the exhaust leak in the exhaust and if you have fuel, air and a hot exhaust pipe to ignite the mixturem, WHAM! instant backfire! Let me know if any of this info helps!

[Kevin_Rants]

[b]Here is a little article I copied on what the PCM monitors, etc.:[\b]

PCM operation

The PCM is a pre-programmed dual microprocessor ditital computer, which monitors various input signals from engine sensors, and then feeds its response to the engine control devices. The PCM operates in two modes: Open Loop and Closed Loop. Ignition timing and ignition coil dwell are adjusted in response to engine rpm, manifold absolute pressure, engine coolant temperature, throttle position, transmission gear, vehicle speed, and the brake switch. The PCM also controls the battery charge rate and the AC clutch, and provides speed control operation.

During open loop operation, the PCM receives input signals and responds according to preset PCM programming. Input from O2 sensors is ignored.
During closed loop operation, the PCM monitors O2 sensor signals and adjusts the injector puls based on the response from the O2 sensors. The PCM attempts to maintain the ideal 14.7:1 air/fuel ration by fine tuning fuel injection. This produces the best fuel economy and lowest emissions for a given engine load.
The fuel injection has these operating modes:

Ignition switch ON - open loop
Engine crank (start-up) - open loop
Engine warm-up - open loop
Idle - closed loop
Cruise - closed loop
Acceleration - open loop
Deceleration - open loop
Wide open throttle (WOT) - open loop
Ignition switch off
PCM Inputs PCM Outputs
Generator output
A/C request
A/C select
Auto shutdown (ASD) sensor
Intake manifold air temperature
Battery voltage
Brake switch
Engine coolant temperature
Crankshaft position
Ignition switch RUN position
Manifold Absolute Pressure (MAP)
Overdrive/Override switch
Oxygen sensors
Park/neutral switch
SCI receive (DRB scan tool connection)
Speed control resume switches
set, resume, on/off
Camshaft position
Throttle position (TPS)
Vehicle speed sensor
Sensor return
power ground
Signal ground
A/C clutch relay
Idle Air Controller (IAC) motor
Auto Shutdown (ASD) relay
Generator field
Malfunction indicator (check engine lamp)
EGR valve control solenoid
Fuel injectors
Fuel pump relay
Ignition coils
EVAP canister purge solenoid
SCI transmit (DRB scan tool connection)
Speed control vacuum solenoid
Speed control vent solenoid
Tachometer
The PCM also contains two 5 volt regulators
to power sensors.


There are several families of PCM's that were developed to meet EPA regulations. These various versions are not interchangeable.

1994 and 1995PCM's are OBD compliant.
1996 and 1997 PCM's meet OBD II specifications.
1998 and later PCM's meet OBD III specifications.

[Fluid]

If you are running the MOPAR high performance PCM you should be using 93 or better octane gas.

Lots of R/T owners don't run 92/93 with their MP PCMs and they report no pinging problems. A lot depends on the amount of internal engine deposits and on the "true" octane rating of the fuel....not all 92 octane is created equal. Some guys will mix 89 and 92 to save a little money. Personally I use 92 all the time, just like the instructions say to do.