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No voltage to coil

Tiny
TECTRON
  • MEMBER
  • 1980 JEEP CJ7
  • 5.0L
  • V8
  • 4WD
  • MANUAL
  • 100,000 MILES
With key on there is no voltage to coil.
Wednesday, September 26th, 2018 AT 8:12 AM

17 Replies

Tiny
TECTRON
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  • 9 POSTS
Here are some starter pitures, few mods were done to this (just got this Jeep), intake, carburetor and headers on a a stock 304 as far as I know at this point. It has been sitting almost seven years, last emissions test was in 2012 and it passed in Arizona.
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Wednesday, September 26th, 2018 AT 9:36 AM
Tiny
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Update: Did some cleaning on connections, I have voltage to coil now when turning key to on position, but, here are some findings:

Coil across to small terminals = 1.6, Battery side of Coil to Coil wire input = 13.2k

Ballast resistor: = 15 ohms even when switching leads around.

Key on position findings:

Ballast resistor = battery voltage on both sides of resistor.

Coil = battery voltage on both small terminals.

So I am thinking things are not right here, ballast resistor should be cutting down the voltage? And coil should not read battery voltage on both sides of coil with the key in the on position?
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Wednesday, September 26th, 2018 AT 11:29 AM
Tiny
CJ MEDEVAC
  • MECHANIC
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Wiring may be an issue here.

Do you still have Motorcraft ignition? (Module)

Mr. Distributor is plugged off where it should have vacuum advance hooked up.

Never run since you got it?

Will it crank (turn over), I assume it will not start (bust off!).

Someone did some over wiring if there is 12 volts on both sides of the resistor.

See if you can straighten things out!

I have a diagram for a 1979, it is probably about the same for an 1980.

I am going to send several diagrams. Keep in mind I had to color all of the wires in "Microsoft paint" from two pages scanned from a manual. I did this years ago. Colored markers used in a manual with lines close together just never did cut it when following wires!

Solid colors are correct. White wires show up black. Along the wires somewhere it is written the color.

Note: Wires with stripes or color tracers are colored with the correct "main" color. The diagram did not denote what the color of the stripe was. I made "dashes" on these wires just to let you know it does have a tracer stripe-color unknown. You will see this. You will get used to it.

In these diagrams, the 304 is shown top left. However, it shares the rest of the wiring with the 258 six cylinder (Like I have).

I "rob" parts of the diagrams to explain things, you will see this with my ignition diagram.

I had the office store blow up my two pieces, I mated them (they overlap) and had the whole deal laminated. About $25.00, it was well worth it in tracing things out.

I can help you 100% with a CJ - any stock type problem, until we get you running and tuned up. CJs are where I soar the best!

Let me know what needs to be tackled or any questions you have along the way. I am not perfect, so you may run up on an imperfection or hard to see something in my diagrams.

The Medic
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Wednesday, September 26th, 2018 AT 4:59 PM
Tiny
CJ MEDEVAC
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Pictures were a no show, I try again!
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Wednesday, September 26th, 2018 AT 5:03 PM
Tiny
CJ MEDEVAC
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? Whoa! That was weird, It would not take my pictures that I have posted many times in the past.

The Medic
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Wednesday, September 26th, 2018 AT 5:07 PM
Tiny
TECTRON
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  • 9 POSTS
"Do you still have Motorcraft ignition?" (Module) - It has WELL'S on it, big square and aluminum.

"Mr. Distributor is plugged off where it should have vacuum advance hooked up." - I will fix that.

"Never run since you got it?"" - No Has not run but was before it was parked till I got it, Rats have done damage to wires mostly spark plug wires (replaced those already).

"Will it crank (turn over), I assume it will not start (bust off!). "- Yes it cranks over and gauges come on in dash.

"Someone did some over wiring if there is 12 Volts on both sides of the resistor." - That is my thinking also.

"See if you can straighten things out!" - I will do my best, when it comes to ignition issues I lack experience.
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Thursday, September 27th, 2018 AT 5:13 AM
Tiny
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I do have the Haynes Manual shown in your picture, covers my year - 1980.
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Thursday, September 27th, 2018 AT 5:21 AM
Tiny
CJ MEDEVAC
  • MECHANIC
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Ignition module is probably a Motorcraft look alike (which is just fine!)

You will see it in the diagrams.

Are you able to follow my diagrams? Have you started tracing them down?

I have many pictures and diagrams that I made to help CJs.

The Medic
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Thursday, September 27th, 2018 AT 3:45 PM
Tiny
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I decided to take a chance on one thing, the coil, so I bought a new one along with a new battery, was tired of jumping it of the truck. So after replacing those I gave it another try and manage to get a pop out of the carburetor. So two things after that, one the ignition key was off. So I am still looking at someone wiring mess I think. I tried to get it to fire with the key on - no luck, tried again with the key off - could not get it to fire again. I put a spark tester light in line on a spark plug and it seems to be firing, it lights up, so I am getting spark to the plugs now which I will call progress. :) But firing with the key off, I am scratching my head on that one. The left half of that schematic is blurred, cannot read the characters.
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Thursday, September 27th, 2018 AT 4:03 PM
Tiny
CJ MEDEVAC
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Sitting so long, did you pull the tank off and clean it?

The Medic
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Thursday, September 27th, 2018 AT 4:49 PM
Tiny
TECTRON
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Pulling tank today, also wires going to the electric fuel pump are chewed, so fixing that today also. Plus I see the fill neck hose to the tank is cracked, so replacing that. I think I have the the stuff for all that, went to town yesterday (closest one is an hour from me) and picked it up, also saw that the distributor cap does not lock in place, no tab that goes into dist, it is like it is missing, so might just make another trip for cap, and just because. I will get a pick up coil for it too. And :) the supply hose among others is leaking, so I need to go through and check all the sizes on the vacuum lines, basically all the rubber tubing on the thing. The vacuum advance hose coming from the carburetor can go to any intake fitting correct? There is an available port on the carburetor.
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Friday, September 28th, 2018 AT 6:47 AM
Tiny
CJ MEDEVAC
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Ported vacuum will go to the distributor, I will find you a picture for the port you need to use. (Give me a little time!)

Electric fuel pumps are over-rated in my opinion.

I would much rather have a mechanical one, less hassle, they seem to live longer, they will not over pressure the carburetor, they cut off when the engine does! Added bonus $24.00 with a lifetime warranty at Advance Auto Parts!

Failures from the past that I am always prepared for now are: I keep a spare fuel pump, a coil, and an ignition module in my console. Now that I do this, I have not needed them yet, however two CJ7s I ran across not running were made happy. One needed a fuel pump and the other the module, I fixed them right up!

The Medic
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Friday, September 28th, 2018 AT 5:03 PM
Tiny
TECTRON
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Everything is still in place for the manual fuel pump, so that is an option as long as it can supply the needed fuel to that Edelbrock 4 barrel.
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Friday, September 28th, 2018 AT 7:14 PM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
I do not know where you are working on your baby.

If it is in a garage, it may be a good idea to push it outside and have a big wet towel handy, and for a second line of defense, at least a five pound fire extinguisher!

Not knowing what may happen while you are attempting a start, be safe!

When you get ready, dump two teaspoons of gas down your carburetor's throat and try to start it. What does it do?

I also made a screenshot off of YouTube, not sure if this is your carburetor or not. Picture below.

Has the distributor been taken out since it run last?

Keep us posted on what you have done or are doing!

The Medic
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Saturday, September 29th, 2018 AT 6:55 PM
Tiny
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Right now I am thinking it might be at the dist, the cap does not seem to want to find a lock in spot, like the cap does not have a tab on it. So I think I am going to get a new cap and then check the timing. The distributor has not been removed since I have had it. I did take the cap off to visually inspect the innards but that was all. At first glance that carburetor does look like what is on this one, I will double check. I still have not traced the wires out. I have got spark to the plugs with the key off.
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Sunday, September 30th, 2018 AT 7:30 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
Here is the diagram 304 and in the Jeep.

The only other source of power to the coil is from the "I" terminal on the solenoid. This would be full battery voltage. It is only powered up when the solenoid is activated. When the Jeep is running the "I" wire is technically dead, however it will show whatever volts are being fed to the coil off of the resistance wire or ballast resistor.

"I" is basically a temporary "jump start" for the coil.

The Medic
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Sunday, September 30th, 2018 AT 8:41 AM

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