truck has no spark except when you first turn key on it sparks or right when you let off from cranking it will give one spark. You can be cranking it and nothing and when you let off it kinda acts like it wants to start for a millisecond. Just hoping maybe someone knows a common problem before I start digging deep into this thing. Thanks for any info

 

You likely have a 'Duraspark' ignition. It provides voltage to the coil immediately when the key is turned to ON. When you turn the key to OFF, the voltage goes away, and the coil does what coils normally do when the 'points' open, or the duraspark takes away the ground from the coil, create a spark.
I bet your module is toasted. Look for a plastic 'grommet' where the wires come out of the box. When you go to replace it, find one that has the same color grommet. They are still available new, or you can search a boneyard.
The 'test' you have done so far indicates the coil is functional, along with the wiring connected to it. I do NOT know the test procedure for a duraspark module, just that if they quit you get no spark.
It IS possible the pickup in the distributor has failed, and is not signalling the module that it is TIME to fire. Quickest test is a replacement, but there should be other ways to check. The pickup coil in the distributor bowl can fail intermittently, and quit at certain temperatures if the windings open up due to thermal expansion, and they'll then get back in contact when the temperature drops. That is a pain. Taking the distributor apart to replace is a pain also. Hope for a bad module.
tom

 

Thanks Tom, I knew about the color grommet thing but that's about it. It does have power to the positive side of coil with key on so I tried to start by jumping solenoid while key was on but still no spark. I guess its going to be a guessing game. Let the games begin

 

i did not watch this video but


maybe it will help _________________---------https://youtu.be/wpxjEpksp9U?t=24 --- if not try to youtube it,,,they have video on just about everything

 

I pulled out the EVTM for the 85 model year, and there is a two page writeup on how to test the Duraspark system. I cannot possibly post that.
The last part I can paraphrase, if you get spark each time you turn the key ON-OFF, which indicates primary circuit is OK, and the problem is in the magnetic pickup or the ignition module. This is from the EVTM, step 6... so there is other stuff:

a. connect a VOM between the O/Y H and P/LB H leads on the harness side of the module 4-wire connector.
b. set meter on its lowest scale and crank the engine. Meter needle should oscillate slightly(approx 1/2 volt).
- if the meter needle does not oscillate check circuit through the magnetic pickup(inside the dist) for open, shorts, shorts to ground, and measure resistance. Resistance between O/Y H and P/LB H leads should be 400-1000 ohms; and between each lead and ground, resistance should be more than 70K ohms. Repair as necessary, PBT and repeat step 1.
- if meter does oscillate, problem is in the ignition module(R wire) or in the module itself, Perform step 7.
step 7
a - remove all meters and jumpers. plug all disconnected connections.,
b - turn the ignition to RUN and measure voltage to engine ground at
- battery pos terminal should be at least 12v
-the R lead of the module. use a straight pin to pierce the insulation of the lead on the module side of the connector, and connect voltmeter to pin.
c these two readings should be within 1 volt of each other.
- if readings are not w/i 1 volt, check circuit feeding power to R lead
- if readings are w/i 1 volt, the problem is probably in the module....
Disconnect the module and install a known good module in its place and repeat step 1. If it works, remove the new, replace the old and re-test, if it continues to fail, re-install the new, more or less. Step 1 is a check for spark when you rap the side of the distributor with a screwdriver, pickup inside dist lined up with armature tooth, and a plug connected to the coil output. I guess the 'rap' bonks the magnetic and sends a pulse to the module as if the dist was rotating. If you get a spark then, the primary is good, so skip to step 2. Not gonna type more...
tom

 

well just for craps and giggles I removed the module and went to my local O'reillys to see if they possibly test these and lo and behold they do. Even had an older gentleman who knew about these. We ran test 5 times and it passed every time so I am going to assume it is good and start removing distributor and go from there. I appreciate you guys help

 

Ok good feedback on the bench test. Does the distributor shaft have any side to side/wobble/play in it's bearing?

 

Did you do this test procedure:
a. connect a VOM between the O/Y H and P/LB H leads on the harness side of the module 4-wire connector.
b. set meter on its lowest scale and crank the engine. Meter needle should oscillate slightly(approx 1/2 volt).
- if the meter needle does not oscillate check circuit through the magnetic pickup(inside the dist) for open, shorts, shorts to ground, and measure resistance. Resistance between O/Y H and P/LB H leads should be 400-1000 ohms; and between each lead and ground, resistance should be more than 70K ohms. Repair as necessary, PBT and repeat step 1.

If you don't get a bit of response from the meter, the magnetic pickup may not be working. They have no moving parts, so a wire or coil failure are the major possibilities.
As the rotor passes the pickup, a signal is generated if it is working. The above test would check for that, and insure that replacing the distributor should get the job done.
tom

 

No Tom I haven't, I don't have a analog volt meter mine is digital so I didn't know if it would pick up that little of movement or not. Anyways picked up a pickup coil while in town so gonna try that and hope all is good. Will keep you updated good or bad.

 

Well I guess the O'Reilly's tester is a good tester. Put in the new pickup coil and wala she fired right up. Appreciate all the help guys.

 

Ok, more good feedback & to hear you got the fix put on that puppy. Thanks for closing out your thread.

 

To anyone driving a vehicle with the Duraspark ignition, here is how I feel about it:
Make sure you have a good working ignition. Then go to RockAuto (or any discount part store) and get the cheapest replacement module that you can find. Make sure the new module works. Then take that new, cheap, replacement module and put it in your glove box or trunk. This will be your spare. Because someday you will need it and a lot of part stores no longer keep these in stock.