Car wiring question

I have this 1994 Ford Explorer that is driving me nuts! Whenever it is cold out there, it won’t start. If I leave the key on for a few minutes, it would start. This never happened after it has started during the day but only in the morning when it is parked overnight. Funny thing too is when this happens; the “service engine” light won’t come on. After I left the key on for sometime, the light comes on and it will start. I got no spark and no fuel that leads me to change the engine computer but the problem is still there. Please help!

Vehicle wiring advice

If your “check engine” light is not coming on during this problem, I agree with you in suspecting it is a computer problem but testing for spark and fuel is not enough. The computer will not work sometimes because there are problems in other parts of the electronic system. Begin this by accessing your ground supplies at the computer terminals. With your ignition key on, see if you get 0.250 volt or higher on any of the ground pins which will indicate a short.

Another factor to look at is your VREF signal pin at the computer terminal. With key on, you should get 5 volts. If not, one of the output solenoids or sensors is defective. You can test this by unplugging them one at a time until the VREF voltage becomes 5 volts. The last component that you unplug is the culprit.

NOTES

It is preferable if you use a wiring diagram to trace these computer pins but in case you don’t have it, ats can described the wire colors for you.

Disconnect battery negative terminal everytime you work any electrical component.

What ever you do when working under the dash panel, do not touch the yellow-taped wiring harness to avoid accidental deployment of the air bag which will activate even with the battery disconnected. Remember: you do this service at your own risk.

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