Igniter Plug (2 Viewers)

[numby]

I went ahead and installed the new distributor. I bent up a bracket out of some scrap sheet metal to use the factory mounting location and hooked up the coil that initially showed a 2.9Ω resistance value across the primary circuit. Using a connector RagingMatt sent me and a weird black rubber seal I pulled of a junk yard Toyota I made up my new wiring. The heavy gauge red wire runs straight to the coil POS.

The truck started right up. I adjusted the timing and took it for a drive or two. Compared to the HEI which had a slightly different advance curve profile than most out there (10-12º initial, 14º vac, 17.5º mech at 3000rpm) the non-USA distributor had more noticeable acceleration at lower rpm levels but was a little less smooth at highway cruise of 55-60mph. I did not change plugs (just cleaned & regapped) or adjust the valves before the install. The HEI had been acting up for at least a month so it may not be a fair comparison. (NOTE:The smaller red wire from the coil/igniter plug goes nowhere and is for an HEI/whatever if I go a different route at some point.) After about 10 miles I popped the cap and inspected the points for burning or pitting. They were clean and shiny. As an afterthought I re-checked the coil primary resistance and got...

1.8Ω

What the??? How did that change from the 2.9Ω that I got on multiple occasions before running it? My multimeter gives consistent readings on everything else so far. It s a dirt cheap coil but c’mon. I let everything cool down and rechecked the coil. Still 1.8Ω.

So I installed a ballast resistor.

Immediately the truck was much harder to start either hot or cold. It ran exactly the same as before the resistor with only a slight occasional miss at idle with a stone cold engine that disappeared in a couple of minutes as the engine warmed up and the choke was reduced. Checking the points wire voltage I got 10.8V with the ignition on (not running).

So I hooked up a wire (yellow in pic) from the starter bypass to the coil POS which puts out about 10+V while cranking. This, so I’m told, is normal as the starter motor is hogging battery voltage during the starting process.

The vehicle started up much better - more like it has for years with the HEI. After warm up I can just turn the key and it will kick over without any goosing from the accelerator pedal. Ran another 10-12 miles at varying speeds and checked the points. As before, there was no evidence of pitting or discoloration. I’ll throw a spare set in the glove box so I don’t get stranded and put another 50 miles on the distributor and check them again.

Now I get to go through Mark's post above.

 

[Coolerman]

Good work, and thanks for updating the post!
I don't remember if you posted what VOM you have, but the cheap meters will not read low ohms well. Also, if your meter supports it, you need to zero out the meter lead resistance before trying a low ohms reading. My cheap meter is all over the place (.8 to 4.2 ohms) when trying to read a coil primary winding resistance. My Fluke 87, after the lead resistance is zeroed out, is rock steady at 3.2 ohms on the 1971 F engine coil I have.

 

[numby]

Good work, and thanks for updating the post!
I don't remember if you posted what VOM you have, but the cheap meters will not read low ohms well...

Oh, god, it's a real cheapie. Let's not disparage my bargain basement tool collection.

 

[numby]

I had to discontinue my diagnosis due to a relocation and loss of work space. I'll go by memory here...

This drawing might be closer to what you have in your truck.


The 12ga coil B+ wire starts at the key switch as BY (connected to IG), is spliced about 18" down to the Pink 1.2 ohm Yazaki resistor wire then near the firewall is spliced again to a 12ga BY going to the two pin connector. The small BY in the two pin connector is also spliced into the 12ga BY wire near the key switch, but BEFORE the Yazaki resistor wire. The small BY wire will always have full battery voltage.

Understood. That all checked out other than the test location I used for the Yazaki resistor wire was at the IGN/key switch so I never confirmed the length of said resistor wire.

So how does this circuit REALLY work, and how do you determine what voltages should be where with a resistor wire or a ballast resistor?

The Coil B+ Circuit
Note: We are going to use +12V for the battery voltage for simplicity when in reality it should be closer to 13.x volts. If you do this on your own truck, use the battery voltage you measure in all the calculations!

The actual coil circuit is a series circuit consisting of the battery, the resistor wire and the coil primary winding. Ignoring the battery resistance and the interconnecting wire resistance, you have the resistor wire at 1.2 ohms and the coil primary winding at say 4 ohms.
Ohms Law states that : I = E/R (Current (I) is equal to voltage(E) divided by the total circuit resistance (R). Since this is a series circuit, simply add up the known resistances. 1.2 + 4 = 5.4 ohms. Divide the battery voltage by the total resistance to get current measured in amps so I= 12/5.4 = 2.307 amps.

Now that we know the series circuit current, we can calculate the voltage dropped across each resistance in the circuit.
Lets start with the voltage drop across the Yazaki resistor wire.
To do this you rearrange Ohms law to be E=I X R. (voltage drop is equal to total current divided by resistance of the resistor wire) So E=2.307 X 1.2 meaning the voltage drop across the resistor wire is 2.768. Since voltage drops have to add up to the source voltage of 12V in a series circuit we simply subtract the 2.768 from the source of 12V to get 9.228 volts dropped across the coil.

Now to address why you seem to get a full +12V on the large BY wire. The first question is how did you measure this?
If you had the plug disconnected and measured the large BY wire to ground you will get the full battery voltage! Why? You have no other resistance in the circuit besides the meter (which is a very high resistance) and the 1.2 ohm resistor wire. The meter being high resistance will only allow milli-amps to flow. No current flow means, no voltage drop, so you will read almost the FULL battery voltage.

Okay, that makes sense. I did measure the voltage at the plug both with the ignition "on" and (as I remember) at the "start" position. Yes, I got 12V both ways.

Now if you plug the connector in so that the large BY wire supplies +12V to the coil B+, turn on the key, and measure from coil B+ to ground, you will read battery voltage minus the drop across the resistor wire because the coil and resistor wire will allow 2.307 amps to flow resulting in voltage drop. (Don't leave the key on for a long time!)

As I remember I did this at the points connector screw inside the distributor and got 12V (points closed). I'm not certain of that voltage at this point but I remember thinking "...Still the same...". Whether this before the installation of the ballast resistor or not I don't remember. I am running a non-electronic non US points dizzy with standard vacuum advance.

Now if you had it hooked up as above and measured the voltage AT THE COIL B+ terminal while CRANKING the truck AND you have a starter with the ballast bypass function AND it was hooked up correctly (see the black/white wire in the attached diagram labeled Z26A1) then you would once again read full battery voltage. WTF? Why? Well the purpose of the ballast bypass relay built into the starter is to provide the full +12V to the coil but only while cranking. Once the truck starts, the relay drops out and the coil is once again supplied power through the resistor wire or ballast resistor.

So in short you need to measure the voltage at the coil B+ WHILE THE TRUCK IS RUNNING in order to see the reduced voltage.

So I should also get the reduced voltage while cranking without the bypass or only while running? (The bypass wire only puts out 10ish V due to the starter motor draw down but it does "bypass" the ballast.) Would I also need to remove (temporarily, of course) the ballast to see what is actually getting through the coil from the Yazaki wire? I'd like to know whether or not I can, in the future, run another HEI or year-specific electronic distributor with the current wiring set-up or will I need to rewire. I guess that's my first concern - whether or not the resistor wire is doing its job despite not needing it for my current points distributor. How do I test the Yazaki wire specifically? How do I put a load on it?

I have no answer as to why the DUI seemed to run fine with the reduced voltage other than they don't seem to know their own products capabilities... or due to some creative re-wiring by the PO, it was always getting full battery voltage.

Therein lies the rub...

 

[Solace in Solitude]

HIJACK to expound on a couple of DUI-related things...

My 01/78 FJ40 harness also contains the 10ga PINK Yazaki resistor wire, spliced into
the 10ga BY.

When I installed my DUI, I left the Yazaki in place and simply quit using the 10ga BY wire

Instead, I used the 14ga(?) BY, as the trigger (86) for a new relay, with 30/51 to ground, 85 to battery+ and 87 to the power terminal in the DUI. This setup ensures full battery+ voltage to DUI.

With full battery voltage to DUI, 44 starts first time, every time, once the electric fuel pump is primed.

As soon as an apparent DUI-related issue arises (harder to start, throttle flutter, etc.), I pull the plugs, clean them and re-gap them at .050” and make sure the timing is still set at 12*BTDC.

In my case, the spark plug condition always suggests:

Carbon fouled

Black, dry soot on the electrodes and insulator tip indicates a carbon-fouled plug. This can be caused by a dirty air filter, excessive driving at low speeds, too rich of a fuel/air mixture or idling your vehicle for too long.

I spend a lot of time driving slowly on very rough roads... my air filter is pre-filtered, using one of my nylons, at the air intake ram (haven’t had to replace a dirty air filter in years, just keep the nylon clean).

So, my last step is to, tweak the idle mixture slightly... and the problems are gone again.

Hope this info helps someone down the line.


HIJACK OVER

 

[Coolerman]

If the starter bypass is NOT connected you will get the reduced voltage ALL THE TIME.

One other thing to be aware of that I did not mention in the above post: While cranking, the voltage available to the coil (due to the huge draw of the starter) will be around 10 volts for a good strong battery. This is normal. Therefore with the Yazaki resistor wire and NO bypass the voltage to the coil could be as low as 8 -9 volts! With the bypass installed it will be 10 volts.

Solace in Solitude: I had a kit designed that did this very thing. Sent it out to two separate MUD members for FREE with the only stipulation being they had to provide me with feed back about wire lengths (too long or too short) and any other issues they had installing it. Never heard back from either person, so I dropped the kit. It used a sealed, replaceable Hella 40 amp relay, had a built in sealed fuse holder, and pre-terminated battery connections...

 

[V8FJ4078]

@Coolerman
So I am finally working on my Jan 1978 main harness. I found this pink Yazaki resistor wire 1977 and was confused and I found this thread through searching.
I am running a 72 Chevy 350 with 87 Tuned Port Injection from a Firebird.
Everything I read says to hook everything up to 12+.
Anyone know if the resistor wire is needed?
I previously think I hooked the small black yellow to the coil on the Throttle body, but not sure if the power was sourced elsewhere.

What I found about TPI - FOR YOUR DISTRIBUTOR: The power wire used on the previous distributor
should work fine as long as there is no ignition resistor in the circuit. It must be a
power wire (14 ga. minimum) that is HOT (+12V) when the ignition switch is in
the START AND RUN positions.

I think I don't need the resistor wire and could run the 10gauge Black yellow direct to the coil from ignition. - correct?

Thanks!
Craig