I have a 1979 project F150 Ranger 4x4 manual 4 speed 400. I replaced everything, coil, ICM, battery, voltage regulator, distributor, cleaned the carb. and alternator. I'm think it maybe they key switch, it cranks and when you let off it fires, but won't start. Any of you guy can share your knowledge and help a guy out that wants his garage back, be much appreciated. It started before I replaced the alternator and then no start. It sat for 5 plus year. Thanks

 

Adjust your ignition switch down on the column.

 

So start at the alternator, you did something

 

Did you replace all of those items you listed before you realized it would not start? Or because it would not start?
An alternator can not keep an engine from starting normally. Even if you wired it incorrectly, which does happen, you usually can't effect the ignition sparking.
And if the starter is cranking, the battery is at least good enough for now. Of course, at some point the battery can be just weak enough to still crank but just barely, with little left over for other duties like sparking the plugs!
How is it cranking? Easily and fast, or labored and slow? When it starts to slow down make sure you re-charge the battery or you might be fighting the battery as well.

When did this start (no pun intended)? Did it happen while you were driving, or did it just not start after having sat all that time?

You could have one or two or three problems. Maybe even four, unfortunately.
Your new ICM (is it a Blue grommet model?) could be crap right out of the box. It happens all too frequently these days. Do you still have the old one around, just in case? Leave the new one in for now, but if you have to you can resort to the old one to compare.
Check very closely the wires running between the module and the distributor and everywhere in-between. Look for old cracked or otherwise deteriorated wires and/or connections.

Try this little experiment too. Start by disconnecting the little Brown wire from the right side of the starter relay/solenoid. Just to see if anything changes.
If no change, that's ok. Leave it off for now anyway. If it stops even trying to start when you let off the key, then you're on to something.

If you still have the little noise suppressor thingy connected to the positive side of the coil, disconnect it as well. They can short out internally and stop the ignition coil from building up enough charge to spark.

Have you checked for spark at all? If you have a timing light connect it and crank the starter again to see if you get a light. Do this on all 8 wires in fact. Look for good, consistent flashes.
If you don't have a light you can pull the coil wire off the top of the distributor cap and lay it there next to the tower. If you get a spark jumping, you know you have a spark at least.

While the Brown wire is still disconnected, measure voltage at the ignition coil's positive/"+" terminal. Should be between 6 and 12 volts depending on a few things. You might even see it start out at battery voltage and then slowly start to go down as the resistor wire gets hot.
If it's less than 6 volts however, you won't get a hot enough spark to light off the fuel.

If it's low voltage at that point, go to the back of the ignition switch and test the various wires. But especially the Red w/green wire that feeds the coil. It might actually be pink or light brown/tan at the switch, since that's the resistor wire.

Is this a Blue "grommet" (or wire strain relief) module? If so you should have a 2-wire connector with a Red (or Red w/blue) and a White wire. Correct?
With the key ON you should see 12v at one of the wires. It really does not matter (I've tried it both ways in fact) but it would normally be your White wire.
You might need a helper for this, but with the key in START you should see 12v at the Red w/blue wire.

If any of these things does not happen, let us know and we can dig deeper into it.

Good luck.

Paul

 

The truck did run prior, had old gas and the alternator wasn't charging. When we first got it running, there was a dead short from the starting relay. The previous owner had connected the brake controller to the relay which was a direct short to ground thru a bad fuse. I removed the short and removed all the wiring. After that it still started and ran, but struggled to start. I drained the bad gas, cleaned the carb, replaced the alternator. It then failed to start. I pulled the distributor to find some bad wires to the pick up coil, so replaced the distributor, timed the motor, tested the coil. Attempted to start with the same result, no start. I figured it must be the ICM, replaced that and at the same time replaced the voltage regulator. Tested continuity of the wiring from the ICM to the distributor, it was fine. Ohm'ed spark plugs wires which tested fine. Tested again the coil, no spark. Replaced the coil, tried to start again, same result. Measured the voltage on the starting relay had no voltage to the coil, replaced the starting coil last night, had 6 volts to the coil, tested once again the coil, it had good current to the distributor. Attempted to start the truck and it fired only after it would crank and the key was disengaging, which has put me down the path of a bad ignition switch. I'm going to put the timing light on the plug wires and see if it is sparking during cranking. But. It does appear that it is grounding out when it is cranking and when the key goes to the off position it will momentarily fire as the engine is still turning over and the short is lifted, but then kills itself as the ignition turned off. Thoughts?

 

Same as before. You may be on the right path with the ignition switch, but it sounds like you know your way around a volt-ohm meter so can check pretty quickly what's getting power and when.
Those same items (Brown wire at the starter relay and noise suppressors at coil) should still be disconnected as part of the testing though.

Paul

 

And I assume in all this you've recently re-checked down the throat of the carburetor to make sure you have gas?

Paul

 

Another thing you can check is the starter relay itself. It's not related to the overall engine not firing thing, but it could be contributing to the difficulty of tracking things down.

When the ignition switch fails to keep power to the coil during START, the Brown wire will send a secondary current to the coil to keep things rolling right along. You never know one or the other are failing until both stop working.
But on a Duraspark truck like yours, the Brown wire does not feed supplemental power to the module. No need for it normally since the module runs on the full 12v to begin with, and only the coil runs on the reduced voltage.

So yes, that makes it sound more and more like the ignition switch is not getting power the module and/or the coil during START.
Well worth checking out.

Paul

 

Thanks for the help, I'll keep trouble shooting this until I figure it out. And update accordingly.

The brown wire in the starting relay does have voltage. According to the one line diagrams and the sequence of operations (from what I'll read) say that this voltage is needed to help start, until the process is complete and then the ICM takes over providing the required power to the coil. Hope I can figure this out before I wear the starter out.
It does get fuel, the plugs are wet when I checked after I cranked it.

What do you think if I have the key switch on and jump it directly at the starting relay? I haven't tried that just to by pass the keyed ignition.
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Sounds to me like the stator goin' south....classic symptoms - The engine will crank over fine and run with the ignition switch held to START. As soon as the key is let go and in the RUN position, the engine croaks.

Test the stator: Disconnect the three prong male/female spade connection at the distributor. Check the connections for green fluffies and/or corrosion.
Ohm out the PURPLE and ORANGE wires going into the distributor at the connection. You want to see 400 - 1K ohms. Anything less or more, the stator is toast, don't care if it's a "new" distributor or not. The BLACK wire is a ground.

These offshore rebuilt things are more likely to be "prettied up" than done right.

 

Good call! Happens now and then and very easy to check.

Paul

 

I got it to start, but it would only fire on on releasing the key. I did install a new distributor, but I'll ohm it out and check the spark with the timing light. It appears to be a good solid runner with wanting to start...we will see as I run thru the the trouble shooting as you guys suggested. Thanks
.

 

I have but one Question for you..
When you replaced the battery, did you go ahead and replace the cable that goes to the starter?
I only ask based on personal experience when I rebuilt my motor, and overlooked the old cable which with a new battery chewed up my starter

lucky for me the starter came with a lifetime warranty
also one cannot stress checking and cleaning ground connections when doing engine work or when "Scooter" the electrical gremlin comes calling

 

All new cables. I leaned the hard way as well. Cheaper to replace in the garage than on the side of the road....

 

I'm hip....as stated before, ohm out the stator. With it being out of spec, when you release the key it doesn't stay but collapses the coil creating a spark.

Also the spec for reluctor to stator is 0.018"....as measured from one of the teeth to the magnet.


@ 1Ton: Thanks, man..(your post #10)