Accelerating from stoplight van made pop noise

BBCABBIE9

MEMBER
1999 DODGE VAN
5.9L
V8
RWD
AUTOMATIC
84,000 MILES

When accelerating from stoplight van made pop noise (didn't sound like backfire), then began to stumble and quit running. Seemed like it wanted to start but couldn't. Engine turns over, distributor is turning, don't smell fuel. I am physically unable to get under vehicle, or into much of the engine compartment /doghouse. Unable to pull plug wire to check spark. Van is a handicap conversion w/wheelchair lift and some of the wiring has been changed. Any suggestions You could make would be greatly appreciated.

3 Replies

CARADIODOC

MECHANIC
33,916 POSTS

The first thing you need to do is read and record any 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 numbers show up in the odometer display.

The most common causes of what you described are the crankshaft position sensor and the camshaft position sensor. Quite often the engine coasts to a stop before the computer has time to detect the missing signal. It knows there won't be a signal from either sensor when the engine isn't rotating, so it will not set a code after the engine has stalled. For that reason, you can't assume those sensors are good just because there's no fault code related to them.

When you turn on the ignition switch, you might hear the hum of the fuel pump, but only for one second, then it will turn off. The pump gets it's voltage through the automatic shutdown (ASD) relay, which also powers the ignition coil and injectors. If the signal is missing from either sensor, the Engine Computer will not turn the ASD relay on again during engine rotation, in this case that means during cranking. If there is a diagnostic fault code, we'll need that number to know where to start. If there is no code, we need to know if the ASD relay is turning on. This is best done with a test light. Most digital voltmeters don't respond fast enough. Back-probe through a connector next to a wire for any injector, the ignition coil, or either smaller terminal on the back of the alternator. The wires at the injectors and coil will all be the same color, usually dark green / orange. Have a helper turn the ignition switch on while you watch the test light. It should light up for one second, then turn off. The important detail is does it light up again during engine cranking? If it doesn't, those two sensors are suspect. That will cause loss of spark AND loss of injector pulses and fuel pump. If you do get 12 volts, then you have the much less common failure in a single system, either loss of just spark or just fuel pump.