Ordered the spark tester. Should be here Thursday will report back. I can handle that for sure. Thank you.

 

If you have spark, you will see a little orange light blink inside the tester. You will probably need help and get someone inside to crank it over while you watch it. Make sure everything is hooked back up, even the most experienced mechanics forget to hook things back up after doing some testing.

 

Well I didnt see anyone mention the actual ignition cylinder. I'm having similar issues and i'm fairly confident the key ignition is the issue. Sometimes when it starts it doesnt spring back to the run position and some electronics (like the radio, and the blinkers) dont function at all. I turn the key back slightly and everything resumes normal operation. Was like that for a year. Now, sometimes the truck wont start and just turns over but when I am turning the key to the off position, the engine will surge like it is starting for a split second. Leads me to think either the ignition cylinder or the ignition starter switch is bad.

 

He is going to get a spark tester and do some troubleshooting first I believe.

 

Hello all sorry for the delay. Finally got around to testing for spark using a plug light. Interesting results…

When turning the key and cranking the tester did NOT blink or light up. However, when I stopped cranking the light blinked as I returned the key back to the normal position.

That also corresponds to the sound of the crank. What I mean is, as I turn the key it doesn’t sound like it’s going to fire at all, but as I stop cranking it almost does give a slight rumble/sound like it wants to fire at the very end as I return the key back. If that makes sense…

 

Yes that dose and is the normal out put with no spark.

Now with out going through all the posts I would say
Bad ICM box
Bad dist pickup coil.
No power to the ICM
I have never seen a coil go Bad and needing to be replaced unless the plug wires were bad and spark burned through the coil tower..
Dave ----

 

So I went ahead and already replaced the ICM. Also tested an older one I had. Obviously that didn’t do the trick.

Should I go the pickup coil route? If so can someone tell me if it’s the module on fender or module on distributor? Also will probably need some guidance on the how to of this.

 

Post #18 mentioned the possibility of a bad ignition switch. Like a person wearing one high-heel shoe, I'm leaning that way, too. This theory is easy to test, so don't just rush out and replace the switch.

Wiring diagram here for an '85. Your '84 should be similar:

https://www.garysgaragemahal.com/sta...e-engines.html




Look at the power supply to the coil. It is the terminal labeled BATT.

With the key in the start position, the coil receives full battery power via the far right pole on the ignition switch.

When you release the key from start to run, power to the coil now travels through the center pole of the switch and through that resistance wire shown under the switch.

The basic logic: The coil is designed to run all day on 7 volts or so, not 12. Don’t quote me on the exact number, but it’s less than full battery power. That’s the purpose of the resistance wire, to drop the voltage to the design input. With the starter engaged, power bypasses this resistance wire for two reasons:

1) Battery voltage drops under the load of the starter. This is perfectly normal. Bypassing the resistance wire keeps the coil voltage from dropping too low.

2) A hotter spark is beneficial during start. It’s okay to briefly increase the input over the normal 7ish volts. With load of the starter pulling down available voltage, the coil gets around 10-11 volts momentarily.

I suspect your ignition switch is partially failed. The pole that bypasses the resistance wire is not working. Your coil is still getting power through the resistance wire, but now it’s really low (starter drawing down voltage) and the coil won’t fire.

When you release the key, the battery recovers and the voltage to the coil jumps just enough (7ish v) to show one spark on your tester as the crankshaft spins down.

To verify, rig up a test lead from the coil BATT terminal to the battery (+) terminal. Route the lead safely away from any moving parts. Make the connection at the battery easy to remove, as you may need to undo it to shut off the engine after this test.

Turn the key to start as normal. The coil will already be receiving full battery power via the test lead. If my theory is correct (is this even a question?), the engine should roar to life.

With the engine running and key still on, carefully disconnect the test jumper. The engine should continue to run. That means the coil is getting normal reduced voltage through the resistance wire and the center pole of the ignition switch.

Please note turning the key off may not stop the engine if the jumper is still installed. Don’t leave it installed for more than a minute or so, as the coil will overheat.

 

First do the "hot wire" test that Karl listed below as that will prove if power is getting to the IGN system to make it work if it is a bad switch.

The pick up coil is in the dist. and if you are going to replace it you will need to take apart the dist to R&R it.
I dont remember what year you are working with but some of the later years had the ICM (gray thing with a bunch of wires) in the side of the dist.
The early years had the ICM on the inner fender well and is a silver box.
If it dose not start / run with the hot wire then the IGN switch is not the issue.
Dave ----

 

If I’m reading this right, basically I need to run a wire from the positive battery post to the hot lead of the ignition coil? Like where the connector is?

 

Yep. This hot wire bypasses all factory wiring (and switch) between those points.

 

i should still connect the ignition coil connector right? Any specific gauge wire?

 

You will still need the other coil terminal connected. So, yeah, leave the connector on.

One way to do this is to install the coil connector on both terminals, as normal. Use a paper clip or similar to backprobe the BATT terminal. For the hot wire, connect an alligator clip to the paper clip.

Another method is to remove the coil connector. Attach the hot wire directly to the BATT mushroom post on the coil. For the other post, fabricate a short jumper from there to the connector you removed.

Either method would work.

The wire size isn’t critical. 14 or 16 gauge would be adequate.

 

Well? Any updates? By my estimate, you've had 16 hours to try the jumper test. No whining such as "I had to go to work" or "i'm scheduled to donate a kidney today" or other similar lame excuses. Or maybe you did the test already, but you're stuck on composing the perfect post to proclaim how wonderful I am. No problem, let me know, and I can help with that.

But the way I see it, your destiny is to run the jumper test for two very important reasons:

1) To prove I'm right (Seems kinda silly to even doubt, doesn't it?)

And to a lesser extent

2) Get your truck starting reliably again.

 

So I did the test, multiple times and checked my work to be sure…. And it did not work. There was no change. I tried it with and without the spark plug light and there was no change when it was connected. I double and triple checked the connections.

So.. there’s that.