Starter Relay to Ignition Coil Jump

[CincoBravo]

I have insufficient voltage to the positive terminal of my ignition coil during cranking. I have replaced the starter relay and I believe the problem lies between the relay and the coil. I know there is a lot more testing that needs to be done to track down the real problem, but in the meantime I was thinking of trying a short term solution. Here's my question:

Can I safely hook up a wire to the "I" terminal on the starter relay and run it directly to the positive terminal on my ignition coil? Assuming there is sufficient voltage at the I terminal, I'm thinking this "work around" will supply sufficient voltage to the coil to allow the engine to fire. (It already runs fine IF I can get it to start.)

If it is safe to do this to get the engine started, is it then safe to leave this wire hooked up while the engine is running?

Obviously I don't want to fry something or burn the thing to the ground.

Please advise. Thanks!

 

[gr8scott]

If it is safe to do this to get the engine started, is it then safe to leave this wire hooked up while the engine is running?

Yes and yes, in fact that is the way the factory wired it.

 

[Lawndart]

Year? Points?
Turning the key to "start" - activates the starter solenoid which sends 12V to the starter and the coil.
Relaxing the key to "run" - deactivates the starter solenoid. Now the ignition coil receives a reduced running voltage via the resistive wire from the ignition switch to the coil. This reduced voltage isn't as hard on the points.

In a pinch/testing - you can leave the jumper from the relay to the coil to get down the road. I would not recommend this for a lengthly time.

Here is a '73 schematic for your question.

 

[CincoBravo]

'77. Duraspark II.

 

[Lawndart]

Errr, never mind. There be a happy box in there...

 

[Broncobowsher]

Just meter the "I" post to the positive on the coil. Should be less than an ohm of resistance.

Also measure the voltage on the "I" post while cranking and compare to the battery while cranking. The low voltage might just be a bad battery or a bad starter solenoid (even new ones can be bad)

 

[Broncobowsher]

What's a happy box?

 

[Lawndart]

edit - I looked at the 77 schematic and the ign to coil, solenoid to coil, ign to coil is virtually the same in either case. In either case, the voltage is reduced at the coil during "run" mode.

 

[DirtDonk]

What's a happy box?

Probably the "sarcastic" box description. Meaning it's more wires, more hassle, harder to test, and can give some people problems.
Just more fun to say than the "little black box" thingy.

Just my guess anyway.

Paul

 

[Lawndart]

Sure, some fun. However we have been using the term "happy box" in aviation for years.
Get this thing to communicate with this other thing, change the data sentence, change voltage levels, blah, blah - via an inline "happy box". There may be a way of testing the spark module, but I don't know how to do it.
Any-a-way, the coil power does change from "start" to "run" mode. That sparky-happy-box does not effect that portion of the magic.
In the end, Ford did not have full 12V at the coil during run mode.

Once, I was test riding a motorcycle and lost my Bronco key during the ride. I am generally outstanding at finding lost things, but this time it was for naught.
Too many gawkers on a Sat morning at the moto dealership. I popped a jumper from the solenoid to the coil, used a screwdriver at the solenoid for the starter and off I went with the Bronco.
Down the road, I pulled over in a secluded area. A couple more jumpers and I had it running with stop lights and proper line to the coil.

 

[gr8scott]

He's talking about the brown wire that bypasses the resistor in start mode. That can and should be left in permanently. Duraspark II uses a resistor.


Sent from my SM-G900V using Tapatalk

 

[CincoBravo]

I took some readings today. Here are the results:

In the Start position the positive side of the coil reads 9.5V. In On, it was about 7.9v without the engine running. Also without the engine running, the battery read about 12.4v. While the engine was running the battery was 13.9-14.2v and the positive side of the coil was around 12.2v.

Also, after taking these readings and jiggling all the wires around (i.e. no real changes), the truck started perfectly all day (yesterday I was getting no spark at all). So, I'm stumped.

However, the truck is intermittently dying at low engine speed. In a couple of cases it died while I was slowing to a stop. I found later than when it did this I could prevent it from dying by applying more throttle, but as soon as I let off the throttle it would die. It always started right back up though. Then, after keeping it alive long enough to get back up to speed, it would idle fine at the next stop with only my foot on the brake. Does this make any sense to anyone? (Also, when I'm on the highway and go to wide open throttle, it runs great. Doesn't stumble at all.)

Do I maybe have a bad coil that sometimes works and sometimes doesn't?

I'm using a relatively stock 302 with C4 trans, and a 500 CFM Summit 4 barrel carb.

 

[DirtDonk]

What were the original readings that made you think you had insufficient voltage to the coil? And it was only during cranking?
Current readings seem reasonable for the circumstances, if not just a bit high. But they're consistent.

And whenever you have no spark, you need to verify voltage to not only the coil's positive terminal (through the Red w/green resistor wire) but also to the ICM through it's 2-wire connector (also Red w/green perhaps) via the ICM's Red wire.
The White wire should see voltage during START only.

What is the idle speed set to? Maybe it's just a little bit too low and that's why the engine was dying under decel. If it's running strong under heavy acceleration, then the spark is fairly healthy.

What is the initial ignition timing?

Are all the original smog devices and vacuum lines still present, or has it been cleared of many?

Have you checked for vacuum leaks while all this is going on? Might have multiple issues and vacuum leaks often creep up on you unnoticed while hunting down electrical gremlins.

Was the engine dying while still cold, or only when fully warmed up

Paul