If it runs on starting fluid, we know it has spark. That means the automatic shutdown (ASD) relay is turning on. That means the crankshaft position sensor and the camshaft position sensor in the distributor are working. The Engine Computer turns on the ASD relay and separate fuel pump relay, (when used), when it gets pulses from those two sensors, but there was a change made somewhere around the late '90s on some vehicles so the engine would still run if one sensor failed. I think it was the cam sensor. That one is used to synchronize the timing of the fuel injectors.
What I would recommend first is to find a mechanic with a Chrysler DRB3 scanner to view live sensor data, in particular, under "sensors", it will show those two sensors and "no" or "present". If the signal is missing from one sensor, the sensor itself is the most likely suspect. If the signal were to be missing from both, a wiring problem or Engine Computer problem would be more likely. (The engine wouldn't run on starting fluid either).
A different approach would be to measure the voltage supply to the injectors. The 12 volts comes right from the ASD relay which also supplies the ignition coil, (which is working), oxygen sensor heaters, alternator field, and fuel pump or pump relay. The ASD relay turns on for one second after turning on the ignition switch, then again when pulses are received from the cam and crank sensors. You should hear the fuel pump run for that one second.
The feed wire to the injectors can be measured on any injector. It's most likely dark green / orange, but you should see close to 12 volts on both wires for any injector. That voltage should be there for just one second after turning on the ignition switch, then again during engine rotation, (cranking or running). I'd be very surprised if it IS there for that first second and not during cranking because it's the same wire that feeds the ignition coil. I would expect you to find 0 volts at all the injectors. That would point to a corroded splice or broken wire. If you DO have 12 volts during cranking but the injectors aren't firing, suspect the cam or crank sensor first, Engine Computer last, and a broken ground wire for the computer.
The Engine Computer has four ground wires. Two are for sensor signals and two are for high-current devices, meaning the ignition coil and injectors. Check those ground wires for continuity before condemning the computer. If they are corroded where they bolt to the body, they might have just a few ohms of resistance but that's too much. After accounting for the resistance in the meter leads, the two high-current ground wires must have 0 ohms.
Thursday, September 29th, 2011 AT 7:51 AM
