Expert: Van - 12/20/2005

Question
HI HOPE YOU CAN HELP,,,HAVE REPLACED FUEL PUMP,, FILTER,, EGR VALVE,,MAP SENSOR,,OIL PRESURE SWITCH,WATER TEMP BOTH OF THEM,,IAC VALVE, CHANGED COMPUTERS OXYGEN SENSORS, WITH FUEL PRESURE GAUGE STILL ON WHEN IT DIES,, ITS HOLDS 12LBS I CAN WATCH THE INJECTORS JUST QUIT SPAYING GAS,, WILL NOT RESTART UNLESS I SPRAY A LITTLE EITHER TO IT,THEN RUNS FINE UNTIL IT DECIDES TO DO IT AGAIN,HAVE CHANGED INGNTION MODULE, WHAT ELSE KEEPS THE INJECTORS GOING,,GOING NUTS THANKS JEFF

Answer
Wow Jeff,
You have been checking all the correct stuff.
That fuel pressure is good.
Do you happen to have any Noid lights?
They connect to the injector wires, and could help you.
The ignition switch sends power to the injectors as long as it is in run or start.
So there should always be battery boltage there.
If voltage dissappears at the injectors, I would think ignition switch, loose fuse, or loose wire connection.

The pulsing of the noid lights at the injectors is from the ECM completing the ground circuit.
The injectors are just solenoid valves, and with the ignition switch supplying power, when the ECM grounds them, they open.
I believe they open about twice a second, and according to all the sensor signals to the ecm, it decides how many miliseconds the injectors stay open each time, thus how much fuel is allowed to spray.

One thing I didn't see replaced is the crank sensor. It is one of the sensors the ECM uses for injector pulse, and fuel pump control. However, even if the crank sensor goes out, the fuel pump will continue to recieve power, from the oil pressure switch, which is a backup system.

So get the noid lights, and watch them.
You may also need a test light, cause if the ecm quits grounding the injectors, the noid lights will also go out due to lack of ground, rather than lack of power, so it will be up to you to figure out if there is still power to the injectors, and go toward ignition or ecm control ground.

One other thought is a loose wire connection at the ecm ign wire. Like if you shut the switch off and then right back on, I don't know if it would pick up and continue to run, or if it would need to be cranked with the starter. That is just a thought to keep in mind. I haven't checked it, but am just thinking of some things that are read just during cranking, where it might forget if it looses power during operation.


It says dies while slowing down....I wonder if there is any stumble during higher speed operation that is just not noticed, and it catches itself.
Have you tried keeping it running on the starting fluid with a few small squirts as it is dying, to see if it will catch?
Van