Let's back up a minute because I'm probably not reading what you're typing.
Describe "fire over". Does that mean the engine cranks / turns over, or do you mean the spark plugs fire?
When you said, "It seems like your story is the other way, the battery is strong you get the van to fire up, but the battery is weaker and no fire.", After rereading it, I think you meant MY van will fire up, right? If I read that right, then yes, yours is doing the opposite.
So I don't send you on a wild goose chase, instead of "fire over" refer to having spark or no spark, or the engine cranks well or cranks slowly. I have some ideas of what might be happening, but I don't want us to be talking about two different symptoms.
Cranking with a weak battery is not the normal way the system should work, so, even though that might be an important clue, lets pursue this as a no-start with a charged battery, or with a charger on it. If you find no spark then, try to find one of the switched power wires to take a voltage reading. Look for the dark green / orange stripe wire on the coil pack or on the injectors, or, if you can get to it, on the back of the alternator.
You should find 12 volts there two times. First, it will be there for one second after turning the ignition switch to "run", then it will go back to 0 volts. During that one second, you should also hear the hum of the fuel pump in the tank. That is proof the Automatic Shutdown (ASD) relay is working, the Engine Computer has control of it, and the wiring to the coil, injectors, alternator field, oxygen sensor heaters, and fuel pump or pump relay are good.
Next, that voltage should come back when the engine is rotating, (cranking or running). In the rare chance that it does, we have to troubleshoot the individual inoperative circuit, spark or fuel. More commonly, the voltage will not come back during cranking. That would suggest a problem with the crankshaft position sensor. It's his pulses that tell the Engine Computer the engine is rotating and would he please turn on the ASD relay.
If you think it's a problem with the crankshaft position sensor don't replace it yet.
Saturday, March 20th, 2010 AT 8:47 PM