None of your descriptions are clear as to how you tested anything or bypassed something, but you might develop a different plan of attack if I explain how the system works. I am going to guess you jumped two terminals in the fuel pump relay's socket, then the fuel pump ran. That will verify the pump and its wiring are okay, but you could have observed that too by listening for the hum of the pump for one second when you turned on the ignition switch.
You did not say what the problem is, but most likely you have a crank/no-start condition. Way too many people get hung up on the fuel pump for some reason, and do not look any further. You have to check for spark too. Unlike GM fuel pumps that almost always start up, then fail by stopping while you are driving, leaving you sitting on the side of the road, Chrysler pumps almost always fail by failing to start up. When they do start up, they rarely stop running during the drive cycle. We have already established your pump is starting up, so we can rule it out as the cause of the no-start. In this case, about two percent of those no-starts are caused by loss of spark. About three percent are caused by loss of fuel pressure. Close to ninety five percent of no starts are caused by loss of spark and fuel pump, and loss of injector pulses.
When you turn the ignition switch on, the engine computer turns on the automatic shutdown, (ASD) relay for one second, then it turns it off. That relay sends current to the ignition coil(s), injectors, oxygen sensor heaters, alternator field, and the fuel pump or pump relay. Fuel pressure should hold for weeks, but if it bled down while sitting, that one second is usually enough time to get the pressure back up to where the engine will start.
The computer turns the ASD relay back on when it sees engine rotation, (cranking or running), and it knows that by the signal pulses it receives from the crankshaft position sensor and the camshaft position sensor. Those signals are used for spark and injector timing, and as mentioned, to know when to turn the ASD relay on. You asked about the computer turning the pump off if there is a pressure problem. You actually are not far off, but you are approaching this from the wrong direction. The injectors cannot spray fuel if the fuel is not under pressure. If your vehicle is hit in a crash, and the fuel supply line is ruptured, the pump would dump raw gas on the ground as long as the ignition switch was on. That would create a major fire hazard. Instead, there cannot be any pressure in a ruptured line. With no pressure, no fuel can spray from the injectors. That means the engine would stall. With the engine not rotating, there would be no signal pulses from the crankshaft position sensor or the camshaft position sensor. With those signals missing, the engine computer turns the ASD relay off, and that removes the voltage to the fuel pump. It stops pouring gas onto the ground.
The safety part of the system is extremely reliable. It is the two sensors that cause most of the trouble. Have you read the diagnostic fault codes? Chrysler made doing that 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. Here is a link to the code definitions, or you can list them in your reply, and I will interpret them for you:
https://www.2carpros.com/trouble_codes/obd2
There is a potential problem with setting fault codes for the cam and crank sensors. Often those codes will not set just from cranking the engine. They need more time to be recognized, as when the stalled engine is coasting to a stop. I have a Chrysler DRB3 scanner for all of my vehicles. That lists the sensors with a "no" or "present" to indicate whether the signals are showing up during cranking. It also lists the ASD relay is being commanded on or off. You can watch that information when the no-start is occurring to figure out the cause.
When you do not have a scanner, you can still check if the ASD relay is being turned on during cranking. Listening if the fuel pump resumed running is not an option because it cannot be heard over the starter's noise. Instead, check for twelve volts on one of the circuits it feeds. A test light works best for this. Digital voltmeters do not respond fast enough to show that initial one-second burst. Look for the wire that is the same color at both ignition coil packs and all of the injectors. That is commonly a dark green/orange wire. You can also use either smaller terminal on the back of the alternator if that is easier to access. You will see the test light tun on for one second when you turn on the ignition switch. What you are interested in is if it turns back on during cranking.
I also must mention that diagnostic fault codes never ever say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, it is actually the cause of that code about half of the time. First we have to rule out wiring and connector terminal problems, and mechanical problems associated with that circuit. In the case of the crankshaft position sensor, however, it has a high enough failure rate on every brand of vehicle that you're more likely to find a defective sensor than a wiring problem.
Be aware too that many cam and crank sensors in the 1990's had a critical air gap that was set with a thick paper spacer stuck on the end. You just push the sensor in as far as it will go, then tighten the mounting bolt. The spacer will slide off when the engine rotates, but it is done doing its job by then. Many aftermarket sensors have a thin plastic rib molded onto the end for this purpose. When you remove one of these, to reinstall it, you are supposed to cut the remaining part of that rib off, then use a new paper spacer.
Oct 9, 2017 at 8:15 PM
