Cranks over but will not start

Have you read the diagnostic fault codes? What is the fuel pressure? If you have a scanner, look at the camshaft position sensor and the crankshaft position sensor to see if their signals are listed as "No" or "Present". Other common suspects are a jumped timing belt and bad gas.

Try firing the injectors with the scanner. If that does not work, check for twelve volts feeding them during cranking.

Chrysler made reading the diagnostic fault codes yourself much easier than any other manufacturer. Cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine, leave it in "run", then watch the code numbers show up in the odometer display.

Code 12 means the battery was recently disconnected. That can be ignored. Code 55 just means it's done displaying fault codes. Those two-digit codes were used up through 1995 models. '96 and newer use three-digit codes in the odometer.

In the absence of fault codes, you need a scanner to view live data and see what is showing up for signals from the camshaft position sensor and the crankshaft position sensor.

First, to address the fuel issue, pressure is not monitored in any way, and has absolutely nothing to do with turning the pump on or off. For it to stay running with the engine off would create a major fire hazard if a fuel line got ruptured in a crash. The Engine Computer turns on the automatic shutdown, (ASD) relay for one second when the ignition switch is turned on. Some models use an additional fuel pump relay that is turned on at the same time by the same circuit. If there is no separate fuel pump relay, the pump is powered through the ASD relay. The ASD relay sends current to the ignition coils, injectors, alternator field, and oxygen sensor heaters. Any of those can be used to take the voltage readings to monitor the operation of the relay.

The fuel supply system is capable of maintaining pressure for weeks, but the ASD relay runs for one second when you turn on the ignition switch to insure pressure is up for starting in case it bled down while sitting. After that, the computer turns the relay on again during engine rotation, and it knows that by the signal pulses it receives from the crankshaft position sensor and the camshaft position sensor. Some engines only have one of those sensors. If a fuel line is broken in a crash, pressure drops to 0psi. With no pressure, no fuel flows through the injectors, so the engine stalls. With a stalled engine, there will be no signal pulses from the sensors. With no signal pulses, the computer turns the ASD rely off, and that stops the fuel pump from dumping raw fuel onto the ground. Bad news for the Hollywood special effects people!

If you have spark, but the engine won't run on starting fluid, the next suspect is a jumped timing belt. The starting fluid might be igniting, but it won't do any good if the pistons aren't near top dead center when that occurs.

The spark occurs when the air / fuel mixture has been compressed and the molecules are close together. That enables the flame front to jump from one molecule to the next to burn all the fuel. If the spark occurs when the piston is not near top dead center, it is real difficult for all of the fuel to burn, and what does burn and expand can't push the piston to develop any power because it is already too far away from top dead center. We know we need fuel and air, but we forget that compression and proper timing of the events are just as important.

The 3.0L engine is not an interference engine, but Chrysler did start using one of that design in '95. If the timing belt jumps on those, open valves will be hit and bent by the pistons. To prevent that expensive damage, the Engine Computer can detect when the belt has jumped only one tooth. The driver may not notice the reduction in power, but a diagnostic fault code, "Cam and crank sync" will be set, and the Check Engine light will turn on. If the belt jumps two teeth, the computer will shut the engine down to protect the valves. At three teeth off, or if the belt breaks, the valves will be bent.

There is one engine that was available in the '97 Caravan that is an interference engine. If the safeguards were built into the Engine Computer for that application, it isn't hard to imagine that would be incorporated into the computers for the other engines to reduce design costs. To add to the misery, my reference lists your engine as an interference engine, which I can't argue with, but the same reference lists the 3.0L for a '90 Dynasty and an '88 Grand Caravan as interference engines too, which I know for a fact they are not.

Regardless, the timing belt should be checked to see if it has jumped. Due to the design of the oil pump's housing, the belt can not jump on the crankshaft sprocket unless over a dozen teeth are stripped off. That would stop the camshafts from turning. For the belt to jump only a few teeth, it has to do that on one or both camshaft sprockets. The belt has to be loose for that to happen, and that too isn't likely. The pulley that sets the tension on the belt is spring-loaded, but once its job is done, the pulley is bolted tight to hold it in place. If the belt did jump, you're going to find that tensioner pulley or the water pump are wobbling around allowing the timing belt to be loose.

The next question is how does the Engine Computer stop the engine from running when the timing belt has jumped? I've always gone by the diagnostic fault codes, then diagnosed the cause of the timing belt issues. I never checked to see if spark or injector pulses were missing. Knowing that wouldn't have helped the diagnosis, and might have confused it.

Another thing to consider is bad gas. Had that happen twice in two days to a former coworker. After a day and a half of frustration, he threw a sample onto the floor, then threw a lit match on it. The "fuel" put the match out! Both cars had just been filled at the same station.

Nope. The front O2 sensor readings only get added to the fuel metering calculations once the coolant reaches a certain temperature. The only way for an oxygen sensor to cause a crank / no-start is if its heater circuit becomes shorted to ground. That will cause the fuse to blow that feeds the ASD relay, and that would result in no spark or injector pulses. Most commonly that short is due to the wiring harness falling down onto hot exhaust parts, not a sensor that's shorted internally.

I never did that job on a '96 or newer model, but I have done it twice on my '88 Grand Caravan. That design is much easier to work on. The job took about four hours the second time. The first time I found the key slot in the crankshaft to be broken away. It took an extra few hours to modify an over-sized key to fit snugly.

One important detail to be aware of is the belt tensioner pulley is spring-loaded, but the pivot can cause it to stick and not put enough tension on the belt. That can lead to the water pump slipping and the engine overheating on a hot day. Once the belt is tight, rotate the engine two full revolutions by hand, in the normal direction. That puts the slack on the back side where the tensioner is. Loosen the lock bolt for the tensioner, then use a small pry bar on the tensioner to insure it is putting plenty of tension on the belt. Tighten the bolt while holding that pressure on the pulley.