No start - how to test coil wires?

[JohnJohn]

I am helping a fellow bronco brother install a Centech harness on his fiberglass Bronco. We got the new harness in and everything seems to be working fine except we cant get it to start.

He is using the Duraspark ignition. Before we replaced the harness it did run but had an intermittent no start issue before and we were hoping the new harness would fix the issue.

My Bronco is next to his but has been converted to EFI so I cant just compare them.

We tried the old coil then replaced it.
We tried the old ignition module and a new one with no change.
At first we did not use the Ballast Resistor but now have it wired up.

It is acting like we are getting a very week or no spark from the coil.

What voltage should I be seeing from the positive side of the coil wire?
What voltage should I be seeing from the negative side of the coil wire?
How can I test the coil to make sure it is good?

 

[Viperwolf1]

Disconnect the wires and measure the coil resistance. 1-2 ohms on primary side (small terminal to small terminal) and 7-8K ohms on the secondary side (pos terminal to big terminal).

You will see 12V, or close to it, on the positive side of the coil.

What year is the wiring harness and what color module is it? '74, '75 and '76 annd later all use different module wiring.

 

[JohnJohn]

Thanks Viper
The bronco is based on a 77. It has a new Centech harness. I will try to post a pic later of the Module.
The ignition module has two wire connectors. One has two wires, one white and one red. The other connector has 4 wires, a green wire on the 4 pin runs directly to the positive side of the coil.

 

[Viperwolf1]

Green wire goes to neg side of coil.

 

[JohnJohn]

Yup. The green is on the neg

 

[Viperwolf1]

Yup. The green is on the neg

Ok, that sounds better.

I was talking with oleguy74 (Mike) a while ago and he pointed out the fiberglass body. Something I missed in the original post. He suggested grounding the module body. The module should ground through the black wire to the distributor. However if there's a problem with that black wire the module won't have a ground. It might be worth the time to put a quick ground to it and see.

Another thing to test woud be the resistance of the stator in the distributor. It should be 400-800 ohms between the orange and purple wires (distributor unplugged).

 

[robbo1a]

First, I like to think john for helping me with my bronco. One more thing we might want to mention...
If I remember correctly, In the run position, it was showing 12 volts, and the volts dropped to 6 or 7 when cranking.
There was no spark at all while cranking, however the instant the key is released, a single spark happens, and in that instant, the engine seems like it might fire.
Thought that information might help.

 

[74fiberglass]

I don't know too much But i wired mine with a centech and i have glass innner fenders. Would not start till I ran a ground from the selonoid to metal

 

[Revelation]

.
There was no spark at all while cranking, however the instant the key is released, a single spark happens, and in that instant, the engine seems like it might fire.
Thought that information might help.

Mine does that, be sure the "RUN" and "START" wires are not crossed.

 

[JohnJohn]

I am going to use Vipers diagram and go over the wires tonight.

 

[NicksTrix]

sounds like it could not be getting power when in crank mode. varify ign switch wiring while you are playing with your grounds

 

[JohnJohn]

Doubke checked the diagram Viper privided and it looks correct. I also pulled the ignition and checked it. I noticed the coil is hot from a very short start test. Not sure why. It is a new coil.

I have an msd blaster coil and the one that came off but i dont remember if we tried it with the old coil.
what should the positive wire on the coil read for volts for start and run?
What should the i-post white wire read during start?

 

[Viperwolf1]

Positive side of coil should be 12V when not running, key on. When running or starting the resistance and current through the coil takes effect and you will see something less than that.

The I post will show battery voltage during cranking. Keep in mind that battery voltage will drop some during cranking.

 

[JohnJohn]

With the key on, not starting, i see 6v on the i term white wire. This is with a battery that has 12v tested.

 

[Viperwolf1]

With the key on, not starting, i see 6v on the i term white wire. This is with a battery that has 12v tested.

Disconnect the wires from the neg side of coil and try that again.

 

[JohnJohn]

Just did and got 12v on the i term.

 

[Viperwolf1]

How many wires on neg side? Module green wire only? Or is there a tach wire too? Figure out which one is grounding the coil.

 

[JohnJohn]

On the negative side is only 1 green wire. I tried to start it again and noticed if I wiggle the key it will bump over. When i wiggle the key when trying to start it almist starts then cuts out0 .I think my problem might be with ignition key area but am not sure. Maybe we could hit wire it to remove the ignition?

 

[Viperwolf1]

Here are some DSII testing procedures.

 

[JohnJohn]

I wanted to post an update.
After checking everything 30 times we still could not get it to fire so Rob picked her up and took her home on the trailer. When he got home he tried to start it one more time and wiggled the key while trying to start and it fired up.
It looks like the 35 year old key tumbler may be the issue or at least it looks like our problem is with the key area. He installed a new ignition a couple weeks ago and with the new harness the only old part now is the actual key tumbler.

Thanks for all the help and replies.