'75 cranks but won't turn over. Help I'm going crazy!

[garberz]

.........Could the timing be so out of whack it won't fire? Ben

It will still have spark, no matter how far off the timing is. You’ve lost power somewhere. Get a schematic of a 75’ Duraspark system and power it up without the ignition switch. Hot wire it. Maybe you can narrow down where the issue is.

Mark

 

[SteveL]

Drop in a hei and be done with it.

 

[DirtDonk]

...So I checked the module and it is blue but so was the one on it I removed.
The plugs all match up but one has 2 wires (red, white) the other side of plug has 3 (Red, blueish, brown). The other plug has 4 wires that all seem to match.
Right or wrong module?

No. If it had a blue module before and worked, then a blue module is the correct one to replace it with. There is only one module of each color. You can't go wrong by replacing like with like here.
In most cases, the wrong module won't even attach to the connectors.

And not to worry about the power leads having a 3-wire plug on the chassis side and only a 2-wire plug on the module side. Or vice versa even. As long as the tabs and guides and contacts line up, and power gets to the correct sport, you're good to go.
It was just one of the running changes Ford made and, for seemingly no reason, didn't change the number of wires in the plug.

Last night we checked the power wires to module and it seems to register 12v with switch on but we didn't test cranking.

No real need to test cranking voltage at this point because ON voltage will still power up the module.
Keep the old module, and keep as an option swapping it back in if nothing else works, but for now keep the new module in place.

Thoughts on why the coil has no spark?

Well, let's test the coil.
For starters, with the key ON and power at the positive side of the coil, take a jumper wire and touch the negative side of the coil to a good ground. Each time you touch and release this ground wire (the trigger for the coil) you should get a good healthy spark from the coil.
If you don't, then let's dig deeper.

Paul

 

[75MIKE]

The green grommet module is unique to only the 1975. Blue after that. Just went though this. Someone or something changed in the ignition.

 

[DirtDonk]

I have looked all over for the radio noise suppressor and there is nothing else on the coil but the two wires plus the wire to the distributor.

Sounds like you don't have one then. The Red w/green wire would usually have a separate short wire connected to the suppressor and it would be visible right there bolted to the side of the coil mounting bracket.

There is a small cylinder next to voltage regulator on pass side firewall - is this it?

Yes, but a different one. Usually we have two of them and that's the one for charging system noise.
Apparently a PO removed the one from your coil at some point, or your truck was originally a radio delete model and Ford decided to leave one of them off.

Paul

 

[bmflinchum]

Well, let's test the coil.
For starters, with the key ON and power at the positive side of the coil, take a jumper wire and touch the negative side of the coil to a good ground. Each time you touch and release this ground wire (the trigger for the coil) you should get a good healthy spark from the coil.
If you don't, then let's dig deeper.

Have done this and have good healthy spark. When I've tried to test the main wire out of coil to dizzy is where I can't get it to spark...

 

[Muddy1966Bronco]

Problems like this are so hard when not there in person! A multimeter and wiring diagram are your best friends for stuff like this.

There’s a small possibility your plug wire could be defective. Do an ohm test to make sure it’s transferring power from the coil to distributor. I’ve had one disconnect from a terminal end through poor clamping and cause an issue before. It wasn’t noticeable until pulling back the boot.

 

[bmflinchum]

Problems like this are so hard when not there in person! A multimeter and wiring diagram are your best friends for stuff like this.

There’s a small possibility your plug wire could be defective. Do an ohm test to make sure it’s transferring power from the coil to distributor. I’ve had one disconnect from a terminal end through poor clamping and cause an issue before. It wasn’t noticeable until pulling back the boot.

We did test this the other night.....

You are right super difficult to do via internet but I'm thankful for you guys

Had a friend at work say an HEI would solve the problem.... is that true?

 

[Viperwolf1]

Don't believe the BS about the different modules not fitting different year connectors, they all interchange.

Wiring on the harness side is slightly different for 74, 75 and 76+. That means you can't plug a 76+ module into a 75 harness and expect it to work. You can swap 2 wires on the harness side and make it work though.

Look at both sides of the 4 pin plug. Are the purple and black wires matched when the connector is mated or are they swapped? Look at these diagrams.

Don't worry about the brown wire. You won't need it if you have a strong battery.

HEI is another headache waiting to happen. Fix what you got.

 

[bmflinchum]

Viper:

The purple and black ARE swapped. Do I need a new module? Can it be made to work? Would this be the major malfunction?

Thanks
Ben

 

[Viperwolf1]

Viper:



The purple and black ARE swapped. Do I need a new module? Can it be made to work? Would this be the major malfunction?



Thanks

Ben

The 75 modules are hard to find. You can make your harness work with the 76+ module, which is easier to get.

First you should verify a couple things. The black wire goes to a ground in the distributor. Can you test it with a meter to see if that's correct? You can test to any good ground.

You should also verify 400-800 ohms between the purple and orange wires.

If those are good you can swap the black and purple wires on the harness side.

 

[bmflinchum]

Ok... so I'm not sure if I'm testing the wires correctly. Testing for ground: test light from black wire to ground? Should light up? Ignition on?
To test the ohms from purple to orange: on firewall side or module side? from one to the other.... Wires are like a foreign language to me...
I have a meter but will need some more specific steps to check what you speak of..
I will try to upload photos

 

[Viperwolf1]

Take a picture of the meter so I can read the settings.

 

[bmflinchum]

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[bmflinchum]

She just wants to run!


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[Viperwolf1]

You will do the checks on the harness side. When you check for ground on the black wire leave the meter in the 200 ohm range it's in shown above.

When the meter reads 1---, like above, it means there is more resistance than the scale range. Ground should be less than 1.00 ohms. If you touch the meter leads together you'll see almost zero ohms.

Stick either lead in the harness side connector where the black wire is. The other lead goes to a known good ground like the base of the distributor. Make note of the reading.

To check the purple and orange wires stick the leads in to those pins at the harness side connector. You will need to change the scale to 2K, 2000 ohms. Make note of the reading.

 

[bmflinchum]

Black to known ground

Orange and purple

Key was in off.


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[bmflinchum]

With ignition switch in “on”


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[Viperwolf1]

Ok. On the orange and purple measurement the meter was on the 200K range but that reading should be equivalent to 600 ohms, which is good. The smaller range will provide better accuracy if the reading is within the range.

Try the black wire again. Maybe go to the negative side of the battery and wiggle the leads a little to see if you get a reading.

 

[Viperwolf1]

Leave ignition OFF.