One more thing to be aware of; by blindly replacing the engine computer, (power train control module / PCM), a whole bunch of new variables have been introduced into the problem. As you drive, the computer watches the readings from the oxygen sensor(s) and modifies fuel metering accordingly. These repeated modifications are called short term fuel trims and long term fuel trims. Every time you drive the truck, the computer starts from these memorized values.
Once the computer was unplugged, the fuel trim values were lost. Also, the computer has memorized various sensor values and knows what to expect under a multitude of conditions. For example, at a given highway speed, if it sees low voltage from the throttle position sensor, it knows you're coasting, and it had better see a high manifold vacuum reading at the same time. There are dozens of such sensor readings and operating criteria that the computer tries to reconcile to verify proper sensor operation and engine performance. That stored information was also lost when the computer was unplugged.
You might not notice any change in performance with the new computer, but you should be aware that if it doesn't seem to run right, don't panic. Just drive the truck normally until the computer has a chance to learn the operating characteristics of the engine and sensors. This could happen in just a few minutes of driving.
Throughout the early 1990s, Chrysler had WAY much less computer trouble than any other manufacturer. I have six from 1988 through 1995, and have never replaced a computer. GM is another story. More problems are solved with new computers in their cars and trucks than any other brand of car. With Chrysler computers, there are so many safeguards built in to protect against shorted sensors and actuators, the computer should be the last thing suspected to be defective.
Sunday, November 29th, 2009 AT 10:39 PM