Engine turns over but wont start

The tcm and pcm are the very last things you look at. First of all, you need to get power to the fuse box for the accessories. I would check all the fusible links by the battery for one that is open. If there is, you need to find out why it burned up as it does not blow without a good reason. It may be wiring, or a failed component.

If you are not sure, let a shop do this for you that is expierenced at these types of repairs. It will cost you but is better than throwing parts at it that do not repair anything.

Roy

There should be a group of them. Look around the fuse box. There may be 6 or 7 of them together.

Roy

You have to check for voltage while cranking the engine. Voltage will appear at the coil, injectors, alternator field, and oxygen sensor heaters for only one second after turning the ignition switch to "run", then the voltage will go to 0 volts. You might hear the hum of the fuel pump for that one second. The voltage will come back during engine rotation, (cranking or running). It comes through the automatic shutdown (ASD) relay. The Engine Computer, (PCM), turns the ASD relay on when it receives pulses from the camshaft position sensor and the crankshaft position sensor. Somewhere around the early to mid 2000s they changed the strategy so the engine could still run when one of those sensors failed but before that signals were needed from both sensors for the ASD relay to turn on.

To test the entire ASD switched circuit, connect a test light to the positive ignition coil wire, the 12 volt feed wire to any injector, or either small wire on the back of the alternator. The 12 volt feed wire is often dark green / orange. Whatever the color, it will be the same on all injectors and the coil. Watch for the test light to light up for one second when you turn on the ignition switch. A digital voltmeter might not respond fast enough for you to see it. If you see that one-second pulse, the ASD relay and wiring are okay and the computer has control of it. No need to check fuses.

What's important is if that voltage comes back during cranking. In the rare event it does, you have to determine if you're missing spark or fuel pressure. Usually it will be the fuel pump that fails to start up. Banging on the bottom of the tank often gets them going. Unlike GM fuel pumps that suddenly leave you sitting on the side of the highway, Chrysler pumps almost never quit while they're running. They typically intermittently fail to start up after being turned off.

There have been times no diagnostic fault code is set related to the cam and crank sensors. In that case it is helpful to have the Chrysler DRB3 scanner connected or an aftermarket scanner that can display live sensor data and has a "no-start" troubleshooting menu. It will display those two sensors with "no" or "present" to indicate if signals are being received from the sensors. Even if it does finally set a code related to a sensor, that never means "replace the sensor". While it's true the sensor is usually the cause of the problem, the code really means that's the circuit that needs further diagnosis. There could be a wiring problem such as a corroded connector pin or cut wire.

One of the strategies the Engine Computer uses to know when to set a fault code is if it's getting a signal from one sensor, it had better be getting a signal from the other one. They have their ground return wire and 5 volt, 8 volt, or 10 volt feed wire in common. If either of those wires are open circuit, (cut, or corroded at the splice), neither sensor will produce a signal. The computer will not know the engine is rotating so it won't set a fault code related to the two missing signals.

I think you've unknowingly identified the problem. Measure the voltages on all three wires on the back of the alternator while the engine is running. You'll find full battery voltage on the large output wire bolted to the back. One small wire must also have full battery voltage. The other one will have less but not 0 volts. 4 - 11 volts is typical. I suspect you're going to find 0 volts on both small wires. Since you're jumping battery voltage to the coil / injectors and the engine runs, the alternator is on that same circuit, ... It should be working too. If you find 0 volts on the small wires, there has to be a break at the splice for all the wires in that circuit.

If you do find battery voltage on one small alternator wire, and the same voltage on the other one, that would suggest the Engine Computer isn't turning on the voltage regulator built into it, and that's why the alternator isn't recharging the battery. That would point to some other cause.

Of course there could be two totally separate problems but that isn't real common. It IS common for the brushes to wear in the alternator and cause intermittent charging. Those brushes can be replaced easily, often without even removing the alternator from the engine. That problem should be addressed last though because it won't be related to the no-start problem.

I just replaced the brush assembly on my alternator. Nine bucks for the part and an hour to remove it from the engine and replace the part. If you would have let us know I could have told you how to test it with an ohm meter and replace the brushes if that was the problem. "Darn the bad luck".

For the no-start, check the voltage to the ignition coil or injectors. See if you have 12 volts there for one second after turning on the ignition switch, then again during cranking.

Boy I hear you about all the unnecessary, unreliable computers. I just got done typing another novel related to my disgust with the car designers, but I do have to admit, the Engine Computer in my daily driver '88 Grand Caravan has been extremely reliable and the tail pipe is real clean compared to my carbureted cars.

First of all, which engine do you have? I only have '00 and '02 service manuals but the circuitry should be the same. Naturally they don't label the fuses the same way in the manuals as they do on your fuse box cover. I drew up a diagram of the fuse box layout. Tell me which fuse, by the letter, that is missing the voltage, then I should be able to find it in the manual and see where it comes from.

Double-check that missing voltage for the first second after turning on the ignition switch. I added the letters to the ASD relay in my drawing. Sounds like you found battery voltage on "A" and "B" all the time. That is normal. Terminal "D" should have voltage for one second after turning on the ignition switch, then go back to 0 volts. Measure that with the relay in place. If it's hard to access the relay terminal, fuses "S" and "T" will have it or you can back-probe any dark green / light green wire at any injector or ignition coil. If that voltage doesn't appear for one second, there is something wrong with the Engine Computer or there's a break in the dark blue / yellow wire going to pin 3 in connector C3 on the computer. If you back-probe terminal "C" of the ASD relay while it's installed, you will find battery voltage there. Grounding that terminal will make the relay click on.

If you do find voltage on fuses "S" and "T" for one second, that proves all of that circuitry and relay are okay and the computer has control of it. If the voltage doesn't come back during cranking, suspect the camshaft position sensor and crankshaft position sensor. On older cars both of them had to be working for the computer to turn on the ASD relay. On newer models the engine will run when one fails. Your engine might run on just one sensor when you jump 12 volts to fuses "S" and "T", but the computer might not be turning the ASD relay on to supply that voltage due to a missing sensor signal.

Without hooking up my tv test equipment, and in the absence of a diagnostic fault code, there's no easy way to tell if one of those signals is missing except with the scanner. It will display "no" or "present" for each one during cranking or running.

ALL RIGHT! One in a row! Gonna make some notes to myself that two sensors are needed to turn on the ASD relay but it can run on just the crank sensor. For my reference, do you recall if you had 12 volts coming from the ASD relay for that first one second? I think you would.

The alternator problem was totally unrelated. Very uncommon to have two problems at the same time. Darn the bad luck, but happy you can buzz off, ... Ahh, ... I mean SAIL off into the sunset.