2001 Ram 5.2l Manual trans.
Going 75mph truck shuts down and never started again. Motor will turn over but its not getting any spark, and no obd2 codes. Dodge Dealer diagnosis: replace PCM. Replaced PCM still nothing, motor turns over but no spark, and no diag codes. I have tested the crank pos sensor, cam pos sensor, all wires leading to all, and to the PCM. I've replaced the coil, distributor cap and button and still nothing. I have the positive voltage going to the coil but no neg voltage. Is there anything else I can check, any other sensors that could cause the PCM to not send out the negative signal to the coil?

I will try anything to get this thing back up.

 

Check your catalytic converter and make sure its not plugged I know that sounds dumb but that was the problem with mine.

 

Have you checked ALL the ground wires and the fuses and relays.

 

I have checked all the fuses relays and grounds using an ohmeter.

 

I believe the PCM won't send voltage down both the "positive" and "negative" wires. One of the wires is for voltage to go into the coil, the other is for voltage/a signal to be sent out. I could be wrong here, but from what I understand about electronics in general, thats what I gather.

Test the new coil. Sometimes a "new" coil can be bad out of the box. Use a multimeter and test the resistance between the two terminals, and then between one of the terminals and the ignition pole (where the wire to the distributor would plug on). What are the ohms for each of those two tests?

 

The specs in my service manual say the primary coil resistance should be about an ohm, while the secondary resistance (HV term to other connection, as jason stated) should be about 11-13kohm. One wire going to the coil (dark green/orange) should have constant 12 volts to it, and the other side (black/grey) is pulled down by the computer as required for spark (spark occurs when the "pull down" is removed and the field collapses in the coil). With a multimeter, at crank, you should see a pulsing by measuring between the black/grey wire and ground, or if it's pulsing too fast for the meter to respond, use the frequency setting, or alternately, an oscilliscope. If there is no pulsing present, it's either the wiring or the PCM, which you've already replaced...

 

Ive checked the new coil everthing test good. The coil has two wires connected to it. The first green wire is the positive voltage 12vdc from the asd relay, that is good. the other black and grey wire is directly connected to the PCM and that sends the drop down or negative voltage to the coil telling it when to send the spark to the distributor. I am not getting this drop down signal to my coil from the PCM.

 

I assume you've done a continuity check on the wire in question and checked the plug on the PCM end. And I know it would be too easy, but, have you checked the coil wire itself ?

And obviously if the PCM isn't sending the signal to the coil, the input for that operation is where the fault is. I think it that would be the cam sensor.

Just a thought, have you tried checking voltage from ASD while cranking the motor?

 

I have checked the coil wire and even replaced it just in case. The camshaft pos sensor is good and I have also swapped it just in case and it is still sending a fluctuation to the pcm, I have done continuity checks on the coil wires and pcm wires and all good.

 

If i'm not mistaken it's the crankshaft pos sensor that the computer uses for ignition timing....cam sensor is used for fuel sync (the "sequential" part of SMPI).