2000 Dodge Ram

Hi jimm72. Welcome to the forum. I've read of a few instances where aftermarket replacement coils weren't holding up. Other people had the same repeat failures until they used a coil from the dealer. You might check for an original part in a salvage yard.

Have you determined what was wrong with your new coil? If it was arcing or had burn marks on the side, I would chalk it up to something to do with manufacturing techniques. If resistance measurements showed one side had an open circuit, that could possibly be the result of it vibrating from not being bolted tightly to the engine.

Caradiodoc

Ahhh. When you have no spark, you're only half done. You must also check to see if the fuel pump is running while cranking the engine. Chrysler pumps can be kind of hard to hear so there are other ways to tell if the systems are turning on. You can pop the cover off the automatic shutdown (ASD) relay and watch the contact while a helper cranks the engine, or, if you have a test light or inexpensive digital voltmeter, there are a number of places you can measure. The easiest will probably be the dark green wire with orange stripe in the plug for the coil. The same wire feeds the injectors, fuel pump or pump relay, and alternator field. You can measure on either of the small terminals on the back of the alternator, but they can be a little hard to reach.

You should find 0 volts on all of those points until the ignition switch is turned on, then you'll see 12 volts for just one second, then it will go back to 0 volts. That proves the ASD relay is turning on and the Engine Computer has control of it. The important thing is the 12 volts must come back during engine rotation, (cranking or running). If it does not, besides the missing spark, you won't have fuel pressure and the injectors won't be firing either.

If you do find 12 volts to the coil during engine cranking, then you are right to be in the coil circuit, but it is much more common to have a failure of the camshaft position sensor or crankshaft position sensor. It's the pulses from those that tell the computer to turn on the ASD relay. Since they are inputs that are observed by the Engine Computer, it will set a diagnostic fault code and turn on the Check Engine light if the signal is missing from one of those sensors. The place to start is by reading any stored codes. You may be able to rent a code reader from some of the auto parts stores.

Caradiodoc

Yup. Although possible, a coil usually will fail completely and not be intermittent. Since it started now, the sensors are a real good possibility. Unfortunately you're going to have to recheck the ASD relay operation when the engine doesn't start. If the Check Engine light was on, the diagnostic code stored in the computer's memory may point to which one failed.

Caradiodoc

My dart board is broken. :) That's what fault codes are for. Replacing parts without knowing with reasonable certainty they're defective is a bad way to troubleshoot a circuit. Every part you replace adds a new variable and potential additional problem to the story. The air gap for the crankshaft position sensor is critical. If it is just slightly too large, it can cause stalling after the engine warms up even though the sensor itself is ok. If a new paper spacer isn't used when reinstalling an old sensor, the gap could be too small and the sensor will be broken by the spinning flex plate.

The camshaft position sensor has a much higher failure rate on the four cylinder engines in '95 and newer cars. The crankshaft position sensor fails more often on V-6 minivan engines. My best guess is there's a 50 / 50 failure rate between the two sensors on truck engines. Once you know the fault code, some people just replace the related sensor, and most of the time that will solve an intermittent problem, but there could also be a break in one of the wires. With that fault code, if the new part doesn't solve the problem, at least you know you're in the right circuit so you don't go blindly jumping around to other parts and circuits.

Caradiodoc

Nope. The fuel pump isn't the problem. It will only run for the first second after turning on the ignition switch. After that, it will not turn on again if the ASD relay isn't turning on during cranking. If the pump was defective, you would still have spark.

Caradiodoc

Rats. A code would sure be helpful. If the battery was recently disconnected or run dead, that will erase any codes that were stored in the Engine Computer. You'll have to wait for them to set again. You should get one when the engine doesn't start. When a code of that severity is memorized, it will cause the Check Engine light to turn on.

If you don't get a code, you'll have to go back and double-check the operation of the ASD relay, and check for the presence of 12 volts during cranking at the coil, injectors, or alternator. If voltage is missing to all of those things but the relay is turning on, then there has to be a break in the wire feeding the 12 volts to the relay. When no code is set, a no-start problem has to be caused by an output circuit that isn't monitored by the computer. That means the coil, fuel pump or pump relay, or common feed wire to all of the injectors.

Caradiodoc

Nope. !2 volts at the coil during cranking means the sensors are working. Double-check for spark. If it is missing, your coil could be bad again, or the computer is not firing it. At that point you would have to just try a new coil or you would need a scope to check for a triggering pulse on the other coil primary wire.

Caradiodoc