89 Bronco no spark ignition

[mikefamig]

I set out for lunch in the Bronco today and it was kind enough to crap out in my driveway before I got down the road. The starter cranks but it does not start. A quick look under the hood told me that there is no spark to the spark plugs.

After some research and learning the components of the the TFI system and I found that there is no power to the ignition coil with the key in the run position. The little info I could find on the net leads me to think that the power to the coil pretty much comes straight from the ignition key switch but I suspect that it may go from the switch to the ICM and then to the coil.

Question - does the coil get power from a wire from the ICM? Can a bad ICM cause no power to the coil?

Thanks in advance, Mike.

 

[Motech]

Question - does the coil get power from a wire from the ICM? Can a bad ICM cause no power to the coil?

No. The coil gets power from the EEC Power Relay as shown here:




Here is a more simplified look:




You can see the TFI and coil both share the same power input.

 

[Motech]

First make sure you have power in and out of the coil. Both + and - sides should light up your test light with key on, engine off (KOEO)
If no power at coil +, check EEC Power Relay.
If it's good on +, but bad on -, you have a bad coil.

If both good, hook your test light clip to battery positive, probe coil negative and crank it.
Test light should flash well.
If not, grab a hold of your TFI connector and twist it a little while cranking. If it fires up, replace the TFI module (ICM) and ignition coil. (ALWAYS replace ignition coil with ICM. Bad coil can still fire, but will cook ICM)
If it does flash, but still no spark, replace your coil. You'll probably need a new coil wire too as it's likely to be corroded at the coil tower.

 

[Motech]

One more thing...

Check spark with SPOUT disconnected. If it's better, it's a weak pickup coil inside distributor (PIP sensor)

 

[mikefamig]

First make sure you have power in and out of the coil. Both + and - sides should light up your test light with key on, engine off (KOEO)
If no power at coil +, check EEC Power Relay.
If it's good on +, but bad on -, you have a bad coil.

If both good, hook your test light clip to battery positive, probe coil negative and crank it.
Test light should flash well.
If not, grab a hold of your TFI connector and twist it a little while cranking. If it fires up, replace the TFI module (ICM) and ignition coil. (ALWAYS replace ignition coil with ICM. Bad coil can still fire, but will cook ICM)
If it does flash, but still no spark, replace your coil. You'll probably need a new coil wire too as it's likely to be corroded at the coil tower.

Thanks man, just what I needed. I have already learned that there is no voltage at the primary/positive side of the coil and none at the dist side either. I'll look to the eec relay and trace the supply wire back to the key switch if necessary next.

Can you give me a clue where to find the eec relay?

 

[mikefamig]

Also is there anything else that would go dead if the eec relay was bad? What else would I expect to not work if the relay was dead?

 

[mikefamig]

Thanks man, just what I needed. I have already learned that there is no voltage at the primary/positive side of the coil and none at the dist side either. I'll look to the eec relay and trace the supply wire back to the key switch if necessary next.

Can you give me a clue where to find the eec relay?

Never mind, I found the relay

 

[mikefamig]

Now I am in search of that fusible link that I see in the wiring diagram

 

[mikefamig]

Eureka I found the fusible link. It wasn't so hard to find, it was the burnt one.

The problem now is the fact that the fusible link goes into a large plastic connector which will be hard to remove it from. I'm also wondering why it went over-current and burned.

The car has been sputtering at times on the road since I got it as if the link has been damaged for a long time and maybe it was damaged from an old short that has been since repaired, I can hope.

 

[mikefamig]

and does anyone know what gauge that fusible link is?

 

[mikefamig]

and so I was able to save a stub end of the original fusible link that I will be able to put a butt end connector on. I jumped a wire in place of the FL and the car started right up.

All that is left to do is to determine the correct size link to put there. I'm thinking about 18 gauge?

 

[mikefamig]

and thank you very much Motech, you made short work of the trouble-shooting for me. Here's to those who share!

 

[L\Bronco]

and does anyone know what gauge that fusible link is?

Congrats on the solve!
In the wiring diagram it appears to be a 20 ga fusible link.
The rule for fuse links is 2 gauge sizes smaller than the wire its protecting.
Cheers

 

[mikefamig]

Congrats on the solve!
In the wiring diagram it appears to be a 20 ga fusible link.
The rule for fuse links is 2 gauge sizes smaller than the wire its protecting.
Cheers

Thanks for the compliment and the tip! It is really satisfying work which is why I've been doing my own for over 50 years. I first picked up wrench to work on my mini bike when I was 11 years old and I've been wrenching on one thing or another ever since. I love trouble-shooting, or I should say it's a love/hate relationship.

I saw the "20" in the diagram but wasn't sure if it meant the wire gauge. I ran down to the local Ford dealer and the parts counter confirmed that is is a 20 gauge link but they didn't have any. I ran over to the NAPA nearby and they will have some for me later today.

Interestingly the 20 gauge link at NAPA is gray and the blue one is 18 gauge. The original ford one is blue. Makes wonder if there is a standard color code here?

 

[L\Bronco]

Thanks for the compliment and the tip! It is really satisfying work which is why I've been doing my own for over 50 years. I first picked up wrench to work on my mini bike when I was 11 years old and I've been wrenching on one thing or another ever since. I love trouble-shooting, or I should say it's a love/hate relationship.

I saw the "20" in the diagram but wasn't sure if it meant the wire gauge. I ran down to the local Ford dealer and the parts counter confirmed that is is a 20 gauge link but they didn't have any. I ran over to the NAPA nearby and they will have some for me later today.

Interestingly the 20 gauge link at NAPA is gray and the blue one is 18 gauge. The original ford one is blue. Makes wonder if there is a standard color code here?

Mine was an old Briggs and Stratton 3HP when I was 10, dads words were, "if you can make it run, you can have it." (I was in the middle of a go-cart build at the time).
However, as soon as I got it cleaned up and running, it promptly went back on the bale stuker, (farm life...sigh.)
I'd say its unlikely there is a color code. (At least none that I'm aware of.)
The factory ones might have some designation, but, it seems to vary year to year. I've seen them in yellow gray, black, green, and blue, all the same size. the only standard is the size I referenced and Ford marks the gauge size on the plastic lug that covers the splice where the link is attached, (looks a bit like a tag.) The aftermarket ones have it printed on the wire. (Too small for me to read anymore!)
Not too sure what China does...
Cheers

 

[Motech]

and thank you very much Motech, you made short work of the trouble-shooting for me. Here's to those who share!

You are welcome. I'm glad my input was useful.

You know, I wanted to mention that fuse link, includ it in the troubleshooting steps, but I did not want to muddy things up too much. The fact that you traced it back with that diagram and found your culprit is impressive. Congratulations!

 

[Motech]

Also is there anything else that would go dead if the eec relay was bad?

That EEC Power Relay powers up just about every item in the EFI system, including injectors, PCM, and all your output solenoids like EGR and air injection. It's massive.

For future reference, the easiest clue would be no key on engine off check engine light. Also no clicking when you turn the key on, and no fuel pump prime.

 

[Motech]

I'm also wondering why it went over-current and burned.

That is a very valid and excellent point to ponder.

Even though that power relay powers up so many other things, the ignition primary is isolated from the rest by that fusible link, so all you have to focus on to find the source of what cooked it is that white and blue wire.

Inspect around the ignition coil. The primary wires there tend to get frayed and could easily touch against metal somewhere. The frame of the coil and the radio suppressor are the most susceptible areas.

 

[mikefamig]

You are welcome. I'm glad my input was useful.

You know, I wanted to mention that fuse link, includ it in the troubleshooting steps, but I did not want to muddy things up too much. The fact that you traced it back with that diagram and found your culprit is impressive. Congratulations!

I'm no stranger to wiring diagrams and electrical circuits. In the 70s I worked in a Shell gas station garage where we specialized in auto electrical and carbs. I also hobbied in transistor radio repair and home security and automation systems. I learned a lot about low voltage DC circuits while installing an Elk security/automation system here in my home back in 2011.

 

[mikefamig]

Mine was an old Briggs and Stratton 3HP when I was 10, dads words were, "if you can make it run, you can have it." (I was in the middle of a go-cart build at the time).
However, as soon as I got it cleaned up and running, it promptly went back on the bale stuker, (farm life...sigh.)
I'd say its unlikely there is a color code. (At least none that I'm aware of.)
The factory ones might have some designation, but, it seems to vary year to year. I've seen them in yellow gray, black, green, and blue, all the same size. the only standard is the size I referenced and Ford marks the gauge size on the plastic lug that covers the splice where the link is attached, (looks a bit like a tag.) The aftermarket ones have it printed on the wire. (Too small for me to read anymore!)
Not too sure what China does...
Cheers

That is a very valid and excellent point to ponder.

Even though that power relay powers up so many other things, the ignition primary is isolated from the rest by that fusible link, so all you have to focus on to find the source of what cooked it is that white and blue wire.

Inspect around the ignition coil. The primary wires there tend to get frayed and could easily touch against metal somewhere. The frame of the coil and the radio suppressor are the most susceptible areas.

I just took it out on the road for just a few miles and all is well. I felt around after the ride and the wires are nice and cool. I'll snoop around some more tomorrow. Time to go put my feet up now.