sdseva

i said that out loud... to myself...

Angry Johnny

OK then so we've eliminated a lot of things with that. It's down to the PCM or CPS. If the PCM does not see the CPS signal it doesn't know the engine is running. So that would be next. The only way I know to really check a CPS is with an oscilloscope so unless you have one of them I think I would just get a new sensor or borrow one off another truck.

sdseva

Thank you!! Ill pull mine off..

sdseva

CPS from my truck changed nothing for my dads.. so to recap. Battery is good, alt is good, cps is good, and i tried setting his up with the same external VR that mine is running. Alt charges to 17v when green is touched to ground. does all of that equal a bad pcm?

Angry Johnny

Either the PCM or the wiring to it of either the green alternator wire or the CPS wiring. The CPS should have battery voltage at one wire, 8 volts at the signal wire (which comes from the PCM) and a ground. Disconnect the sensor and check on the harness side, key on.

sdseva

I butt spliced the cps to the harness.. can is still check with it connected? i can prob the butt...splice i got 5.5 for the grey/black. .5 at the white and nothing at the blue/black.???

Angry Johnny

I think you've found your problem. I need to look at a schematic for what wire is what, but go ahead and cut the splices off and then check the voltages again to make sure you are getting a true reading. The wire that has no voltage should be a ground so ohm that one to a good ground, key off, it should be less than 0.2 ohms.

Angry Johnny

There is a connector by the thermostat housing, round, three wires, that goes to the CPS, You could disconnect there.

j_martin

CPS supply voltage should be 8v. Blue/black should be "nothing", as it's signal ground. The other should toggle between 0.5 and 5v as the gap passes it.

That said, I think you said you installed an external regulator with no resolution of the problem. That bypasses the CPS, and the PCM completely. There must be something basic wrong with either the alternator or it's wiring.

12 v is supplied to one field terminal. Something (regulator or PCM) switches the other field terminal to ground. Current flows in the field coil, creating a magnetic field.

Belt rotates the field (wound on the armature) inside a stator. Current flows. Normally at idle there is plenty at the large power post to charge the battery, ie 14v at 30 or so amps.

You can verify that 12V is present on one field terminal. Wire the other to ground with a jumper. Run the engine, and verify that 14V or so . It depends on the charge state of the battery, could be as low as 12v and as high as 15v, higher with a bad battery. It will be real high if the fusible link or main power wire is bad.

The only thing left is the regulator circuitry, which is where you've been chasing your tail. Odds are it's OK.

hope it helps

sdseva

tan wire. 9v, blue/black nothing, grey/black 5v.

Angry Johnny

OK, now we are getting somewhere. the blue/black should be your ground, go ahead and ohm that wire to a good ground, engine block and/or battery. Key off. If it's less than 0.2 ohms you need to go back down to the CPS and cut your splices and measure voltage and ohms there or at the least ohm those wires from the upper connector to the sensor but that doesn't always tell the whole story, even one strand of wire may check good but can't carry a load.

sdseva

i had already cut the splice work.. blue/black shows .4 ohms to battery ground

Angry Johnny

That seems a little high, it should really be 0 or very nearly 0. Try adding an additional wire from there at the splice to the battery ground.

Angry Johnny

Also,, no one asked, is this truck an auto or a stick?

sdseva

auto