1992 Dodge Dakota wiring

Common do-it-yourselfer mistake is to find no spark, and troubleshoot that circuit without looking further. You MUST also check for fuel pressure or you will likely be looking in the wrong system.

Connect your test light or voltmeter to the coil terminal, then watch what it does when you turn on the ignition switch. You should see voltage there for up to two seconds, then it will go off. You might also be able to hear the fuel pump run for those two seconds. The voltage comes through the Automatic Shutdown (ASD) relay. It feeds the coil, fuel pump or pump relay, injectors, alternator field, and O2 sensor heater. After that initial two-second burst to get fuel pressure up for starting, the ASD relay won't turn on again until the engine computer sees engine rotation, cranking or running. So where you were measuring for voltage on the coil, it won't be there unless you're cranking the engine.

The most likely cause is a defective crankshaft position sensor in the distributor. With no pulses from it, the computer doesn't know the engine is turning, and wouldn't know when to fire the coil or an injector. More importantly, this is Chrysler's very effective and reliable way to prevent fires in a crash. In the event of a ruptured fuel line, raw fuel on the ground would be a fire hazard, but the engine can't run without fuel pressure. When the engine stalls, the computer turns the ASD relay off. Voltage to the fuel pump is removed so it stops pumping fuel.

Both the coil and fuel pump circuits are very trouble free. It's a little more likely to find corroded contacts on the ASD relay, but it's much more common to find a defective crank sensor.

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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.

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