I have a 1987 F-150 with a 4.9L Inline 6 Cyl.

The truck ran fine about 1 year ago, when I parked it.
Tried to start it last week, but no spark.
Here is what I know.

I get 12 VDC to the coil when I turn on ignition.
The coil and coil wire are good.
The rotar turns when cranking engine.
No spark comes out of the coil.

I have one of those haynes manuals, its about as helpfull as the roll I have hanging near the toliet when it comes to schematics.

I am assuming the electronic ignition module controls when the discharge or what ever it may be called goes through the coil. So even though the 12 volts is there it dosnt get discharged. I also assume this electronic ignition works like the condenser and points since it elimanates them. But I'm not sure how it works.

My question is how can I troubleshoot the electronic ignition module. (I have another one that I tried but not sure if it is any good)I suspect this is where the problem lies. But i would like to be sure before i go and buy a new one. (electrical parts dont rteturn to well) Also if anybody knows where I could get a "real" schematic for the ignition would be a help too.

Thanks

 

Here is what's roughly going on with the duraspark system.



Measure the voltage from the negative of the coil to ground on the engine. You should see the voltage switch on and off when you crank the engine. This is what the module is doing. It's grounding and then not grounding the negative of the coil. This is what makes the coil fire, just like points.

 

I recently had trouble with a spark that appeared and disappeared at random on my 1981 300 six with Dura-spark ignition. We checked and replaced the ignition switch, module, distributor, and coil but still had the trouble. I then started checking if any of the components were grounding out and found one of the wires to the pick-up in the distributor had an intermittent ground some where in the wiring harness. I re-wired from the module to the distributor to replace that path through the wiring harness and so far it works fine. Good luck!

 

The above schematic is for the DuraSpark II ingition system. You may have a TFI system. The two systems are similar but if you have a TFI, please be aware that your wiring will be different. Most auto parts stores will test the ingition modules.

Good Luck, let us know what happens.

 

You are exactly right. Good catch. I don't know what I was thinking.

His truck is probably fuel injected. He would have the module mounted on the side of the distributor. The on-off voltage check on the negative of the coil still should be valid though.

 

Thanks for the info. My engine is fuel injected and I think I dont have the dura spark Ignition.I think I have the TFI ignition system, that was mentioned in a reply. As my coil only has 2 wires going in instead of 3 like the drawing you sent me. Did a little more on it this weekend. Still no go. I tried another ignition control module and that did nothing. I still get +12 VDC sitting on both of the wires that go into the coil when I turn the key on.

When I crank it over each of the 12 volts on the wires dip down. I assume its being grounded off/on and my DVM is slowly reacting.

Couple more questions.
1. Do you have a schematic of the TFI Electronic ignition module ?
2. Is there something in the distributor that interacts with the Ignition module that might control the grounding/ ungrounding ?
3. Or is the module a self contained unit using some sort of RC time constant to ground/unground ?
4.Or is the ignition feed input from another source like a computor when to gound/unground the voltage to the coil ?

Thanks again !

 

It would be interesting to run a code test to see if the computer sees something wrong with the distributor. You may get a code 14 in the memory codes.

I would also check the wiring from the TFI module on the side of the dist to the wiring harness. I have heard of some problems with the shielded cable grounding out the wires on the inside of the shield.