Cranks-only

Tiny
THOMAS RICHARD IVAN JR.
  • MEMBER
  • 1990 FORD RANGER
  • 2.3L
  • 4 CYL
  • 2WD
  • MANUAL
  • 144,000 MILES
Swapped alternator out bcuz the previous one I had put new brushes, but they burnt off. Now truck wont start, I dont hear the fuel pump, but the gauge works.
It cranks, but that's it, so I hot wired the fuel pump straight to fuse box and, still wont run.
What did I do wrong?
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Wednesday, September 7th, 2016 AT 8:52 PM

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Tiny
CARADIODOC
  • EXPERT
If the fuel pump doesn't run for one second after you turn on the ignition switch, you probably don't have spark either. Have you checked that? If you're missing spark, start by checking the fuses.

It is not possible to have an electrical problem inside the generator that burns the brushes. Look for a mechanical issue that resulted in a short to ground on the 12 volt feed brush. The voltage regulator is bolted to the back of the generator with four screws in a rectangular pattern. Close to the bottom of that rectangle you'll see two more screws that hold the brush assembly to the regulator. The one on the left is labelled "Ground here to test". It's the other screw, to the right, that must have 12 volts all the time. There might be a round, gray plastic cap on it. If the 12 volts is missing on that screw, look for a blown blue 15 amp fuse, but that only protects that circuit. It has nothing to do with the fuel pump or ignition system.

If the control-side brush, (the "Ground here, ... Brush") is shorted to ground, you'll have a constant three-amp drain on the battery which will kill it in a few hours or by overnight. That will not blow a fuse.

You must also have 12 volts all the time on the generator's output wire. That one is usually bolted to the back of the generator, but Ford had a few years and models where they used two fat wires in a plug-in connector. That design was a major disaster. That plug must never be unplugged because doing so degrades the integrity of the connections. That leads to resistance, which leads to heat build-up, which leads to resistance, which leads to heat build-up which leads to, ... When you replace that style generator, it comes with a new plug installed and you're supposed to splice and solder the wires. The engineers should have known you can't get 40 to 50 amps through each of those tiny connections, but it saved a little time on the assembly line so I guess it was worth it.

If that 12 volts is missing, there is either a blown very large fuse in the under-hood fuse box, or a burned-open fuse link wire. A fuse that size will be bolted in the fuse box, not plugged in. A fuse link wire was used on older vehicles. Test those by tugging on them. If they're good, they'll act like a piece of wire. If they're bad, they'll act like a rubber band.
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Wednesday, September 7th, 2016 AT 9:50 PM

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