1999 Jeep Cherokee engine stalls after about 20 miles

You might be looking at the ASD system backwards.

When you turn on the ignition switch, the Automatic Shutdown (ASD) relay turns on for one second, then turns off. That one second is enough time for the fuel pump to build fuel pressure in preparation for starting in case the pressure bled off over days or weeks of sitting.

The Engine Computer turns the ASD relay on again when it sees engine rotation, (cranking or running). It knows the engine is rotating by the pulses it receives from the crankshaft position sensor and camshaft position sensor.

When the ASD relay turns on, it sends current to the injectors, ignition coil(s), alternator field, oxygen sensor heaters, and fuel pump or pump relay. In the event of a crash that ruptures a fuel line, raw fuel would be pumped onto the ground creating a severe fire hazard. With the lack of fuel pressure, no fuel can spray from the injectors so the engine stalls. Pulses stop arriving from the camshaft and crankshaft position sensors, the computer knows the engine stopped, so it turns off the ASD relay. That turns off the fuel pump.

To get back to your question, the burned connector in the injector wiring harness will not cause the ASD relay to turn off, but if the injectors don't fire properly, the ASD relay is turned off by the Engine Computer in response to the engine stalling.

The easiest way to repair the burned connector is to find a good used one in the salvage yard and transfer the pins from the old connector body to the new one. The terminals must be cleaned up to remove traces of carbon which can conduct current and start the problem all over.

Caradiodoc

If you can reach the individual injectors, unplug one at a time while the engine is running. If the engine runs noticeably worse when you unplug one, that cylinder is working. Plug it back in and move on to the next one. When you unplug an injector and it has no effect on how the engine runs, that cylinder is not working. Check the feed wire in that connector for battery voltage on one wire. If it's there, plug it back in, and measure the voltage on the other wire by back-probing the wire where it goes into the connector. An old-fashioned pointer-type voltmeter works best for this because it will smooth out the pulsing voltages. If you use a digital voltmeter, expect to see the reading bouncing around. If you find exactly the same battery voltage on both wires, that injector has a break in the control wire going back to the Engine Computer. Look closely at the connector you replaced.

If every injector affects the engine, but it still runs rough, double-check the order of the pins in the repaired connector. If two are mixed up, those cylinders will still get fuel, but the injectors will spray the fuel at the wrong time. It could be spraying the fuel onto a closed intake valve.

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