1977 F150 HiBoy 4x4 400cid, C-6 tranny

While driving, engine shut down as if I switched off key. Replaced coil, stator pickup, and replaced vacuum advance while I was there. Checked modulator for fire, unplugged 4 prong harness, switched on key and had fire on 2 prongs. Still will not start. Before you ask, I did pull distributor and noted position of rotor cap. Replaced in same position. Still will not start.

 

Can you describe what you mean when you say you have "fire" on the terminals running to the ignition module? Are you measuring a voltage? What was that voltage? What are the colors of the wires leading to these terminals?

 

More than likely had your ignition module crap out. Take it to one of the parts stores and have them test it.

 

I'd take the fender mounted duraspark (Ignition Module) down to the parts store and get it checked. I had one of these do something similar, it'd start dropping cylinders and eventually shut down entirely. Took me about two or three times before I figured out what it was.

Try to get a Motorcraft module if you can.

 

Pick up coil in the distributor. My 460 would do the same thing, Its like you cut the key off. Replaced it good to go. Just another place to look

 

Had Module checked and it is good, Replaced coil, Pickup coil is the magnetic mechanism in distributor with wiring harness correct? If so, it has been replaced.

fmc I tested the terminals with a test light. one wire is green and the other is black and green. Module tested good at parts store.

Still will not start.

Been down in my back and have not fooled with it. That's why the delay getting back to you.

 

Thanks for the clarification. With the key in RUN and the module disconnected, the GREEN wire is the only wire in the 4-terminal plug that should light up (you're seeing a "false" 12 volts through the coil primary winding). The BLACK with GREEN stripe wire is ground coming from the distributor; it should be hard-tied to zero volts.

You can't have power at a ground signal unless that ground has been physically disconnected and shorted to a power source. Are you still seeing power at the BLACK with GREEN stripe wire with the key in RUN and the module disconnected? If so, there's something going on with the wiring in between the module and the pickup. It has nothing to do with the ignition components themselves. This is why I don't recommend folks replace parts until I understand where their measurements are coming from.

 

Thanks guys for your help. fmc I will trace down that bad ground. Thanks man.

 

Good day fmc, Just to make sure we're on the same page, when I checked for fire the other day I checked the male terminals on the modulator side. I left the 2 prong plugged up, and got fire on the green and green and black. I did trace the green and black over to distributor and it looked good.

Let me ask you this, The radio noise filter wire. One end is attached to the hot side of the coil clip, and the other end is grounded to the coil bracket. I have fire on the coil side of the filter wire and no fire on the ground side.

 

Got it, thanks for the clarification. That makes a lot more sense. What you see on the module side of that 4-connector pigtail with the module powered doesn't mean much; what you're seeing doesn't sound alarming.

The radio filter sounds like it is hooked up properly. The test light results you're describing sound correct, too. With the key in RUN and the engine OFF, power should be applied to the positive terminal of the coil, and the module grounds out the negative terminal of the coil.

While you've got the 4-connector pigtail apart, check the resistance between the ORANGE and PURPLE wires on the truck side of the connector. You should see between 400 and 700 ohms. If you do, you know the new pickup module is good, and the wiring to it is fine.

Other things to check are to make sure power is applied to all the appropriate locations. With the key in RUN, you should have 6-to-7 volts at the coil positive terminal (I suspect you will based on your previous results). With the key in START, the coil positive terminal should have whatever the battery voltage is while the engine is cranking (careful there, especially if the engine decides it wants to start. Maybe think about disconnecting the starter for that test).

On the truck side of the 2-terminal connector going to the module, the RED wire coming from the truck should have battery voltage with the key in START, and the WHITE wire coming from the truck should have battery voltage with the key in RUN. If you have a later-model module, then these colors most likely get flipped on the module side of the connector, but that's normal.

If all that checks out fine, then maybe it's worth swapping out for a spare module. Sometimes they can exhibit an intermittent or temperature-related failure and test fine at the parts store, but fail once put to service. On another note, I also had a similar situation where all the parts checked out fine, but the 4-terminal pigtail coming from the truck was corroded enough that the signals weren't actually making a connection with the module.

 

Ok I'll try those. Thanks for your help. Will let you know how it turns out.

 

Swapped out module and fired right up. Thanks for your help.

 

Awesome, glad to hear you got it worked out.

 

Keep a spare one under the seat for the next time.