Hot Coil !!!!!!

towpainter3

towpainter3

Member
:mad5: ok, this May be a dumb question but here goes. My 74 s2 with a 304 has a work around set up. The hot side of the coil is wired to the ign. On side of the alternator with an inline ballast resistor 1.8 ohm. And of course wired to the dist. On the other. My concern is that the coil and resistor get extremely hot during operation in fact really quick too. After a while, cruising in 4 low and tranny in low the motor will start to stutter . I can switch to a cold resistor and it willl clear up. Carb and distributor seem fine. And when I say warm you dont want to touch it . The coil is a cheap aftermarket.and it does call for the resistor. If anyone has any ideas please feel free to help a dumbass. Lol thanks brad
 
Simple brad, but many of ya have this same issue going on. Caused by the po virus and not knowing exactly what your setup is!

From your carb thread I gleaned you are running a breaker point distributor. No matter which distributor you have, delco, Holley, or prestolite, they all were originally wired with a "resistor wire" in the "run" circuit off the ignition switch. And all three systems used an oem coil with a primary resistance factor of 1.4>1.8ohms. That is important here!

Then, someone added a ballast resistor. Why?

If the original resistor wire is still in place, and then the ballast is stuck in there somehow, no tellin' what ya got going on..but that is why yore coil is takin' a dump as soon as it goes outta spec! Any coil would do that, it's not because of the oem mounting location, that idear is bogus!

If the existing coil has some statement printed on it that sez sumthin' like "internal resistor", then throw that sumbitch away, it's wrong for any application in the IH world!

Gitta coil with a primary resistance of 1.6>1.8 ohms, it'll say on the outside..."use with external resistor". Only...do not use a resistor if your oem resistor wire is still ok. Use one or the other reistive item, but not both!!!

The oem resistor wire is exactly 68">72" long and measures out at 1.8ohms nominal at 70*f.

A list of aftermarket coil part numbers is in one of the other threads here, posted a line item from my parts dbase with several typical numbers for greg r.

And there is a wide range of replacement "ballast resistors" on the market for many applications, including the chrysler dual circuit unit. You must check 'em with an ohmmeter at operating temp to determine the value. I keep 'em here in the shop in only 0.8ohm and 1.8 ohm values, the two commonly used in IH point/inductive ignitions (the 0.8 is used for the four bangers).
 
Michael, the resistor wire is like many others it has long since been burned up. The hot post on the coil is powered by the ignition wire on the small plug of the alternator only and is only hot when the switch is in the on position. I have verified that it has 10 to 12 volts. The ballast resistors that I have are of unknown origin. I know one came from a 90's model Jeep cherokee with a 4.0 6 cylinder and the other one was on the Scout when I got it. In other words I dont know wtf I've got.
Does the way it's wired sound right? And the coil does say it needs an external resistor. The coil is mounted horizontal on the rt inner fender so its out of the engine heat. Should I replace the coil and ballast resistor ? This shouldnt be confusing to me, but its freakin me out. Thanks brad
 
Stand back bubba!

Whatta botch job on the ignition system! Please...no offense! Let's make this right!! At least you are honest in describing the pile!

I do not endorse running the ignition system feed right off the alternator. That is a common drag race practice and is no where near appropriate for any other vehicle that runs for more than 15 seconds atta whack!

The ignition system (along with all electrical systems/loads) needs to pull from the battery. The battery provides a stable electrical current source, lets just think of it as a "accumulator" or "surge" device.

The alternator output changes constantly as the regulator "hunts" to try and send the proper charge to the battery so the battery is a happy camper without being undercooked/overcooked. For an ignition feed, ya don't want a supply of electrons that is constantly changing, without very precise lab equipment, you can't see that, typical consumer multimeters (especially analog) only "average" increase/decrease in current/voltage to feed the display, the actual readings are highly buffered. But the ignition system can see the very small/medium "adjustments" that alternator rpm and voltage regulator output provide.

If your oem electrical/ignition system switching is all munged up, then simply rewire with a separate starter switch and on/off switch for the ignition system.

You must know the ballast resistor value! No way around that! Measure it! I promise...you do not have a "matched" ignition system!

The designation on the coil is meant only when using that replacement coil on the original, intended ignition application. Which in your case means nothing!

Bottom line...measure the ballast resistor value and post. Measure the coil primary resistance and post it. Don't do anything else...and only measure the values with all wires disconnected! Don't buy anything else until we advise the next step!

This is called "diagnosis" and not "shotgun"!!!

By the way, don't be offended here, many of the folks on this forum have already received this standard lecture/beatdown from me in person!!!
 
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Aw hail brad...I jes' realized I've not really answered your question regarding "hot coil"! Sorry!

The reason for this is...the complete mismatch of ignition primary circuit component control values is allowing too high a current draw in the circuit. Works ok initially until the heat generated by the mismatched parts affects component performance. Then functionality begins to fade until the point at which it ceases!

All the "values" for the ignition system components are worked out at the engineering level and then production parts are "spec'd" according to the workout. Ya don't deviate from those specs unless ya compensate in other manners. The "performance" parts industry is terrible in that respect. They blow marketing smoke without fully explaining the "why" and "how" to do the big picture. Same for boneyardin' stuff!

Ya can't simply stuff a "high performance"coil onna motor that can't use a low resistance primary system without making other changes! I personally think msd is the worst in that respect, many times their instructions simply say "add a ballast resistor of value x" when they got no way of knowing what the original application is! Then when the part melts down and is "returned" under a warranty claim, they always chalk it up to "customer installation error" when in fact the only error is in their omission of proper documentation!
 
Ok,after sitting down last nite with the Scout manual and getting the sqint eye from lookin at wiring diagrams, I think I've somewhat figured it out. My 74 originally had an electronic ignition system that was removed by the former owner. Wire hackin bastard!!!!. From what I see I need to find the plug or wire that originally powered the coil to get my power from. After that I found a diagram that shows how to wire it for a full 12 volts at start only. I will check my resistor and coil and post the values before going any further though. This thing does have some engine compartment wiring issues that I shoud have lready taken care of but hey you know how it is lol.
 
Ok after an hour or so of cussin the wire hackin bastard that used to own this thing ,I think ive figured out the wire issues. Found the original wires that power the coil and the ones that go with the alternator including the field wire which was rolled up in the harness and got all back in place with good connectors and heat shrink. Now for the part about the ohm numbers on the coil and resistor.

Coil, 6.5 ohms wrong way f,ing wrong
resistor 3.5 ohms wrong way f,ing wrong

damn if your gonna throw parts at somethin at least use the right ones!!! God, I hate stupid people, but if they werent here ,who would we have to laugh at!!!
So now after I make a trip to the part store I might be able to make this thing run right.oh yeah im takin my meter with me to the local oil and neon light emporium. Nothing like a good game of stump the counter monkey. Lol
 
I feel yer pain, yessir I shorely do. I suffered from the scorchin' hot coil syndrome awhile back. It was a resistance mismatch, only not near as far off as yers. Fer me it would take 30 + minutes of hard driving before things started shutting down. You've come to the raht place. Professoree mayben'll git ya fixed up kwiker'n you can say chupacabra.
 
Speakin' of fat chicos de blanco...what tha hail is happenin' with the cambo and john electrical show??? Yawl too embarazzd to gimme a report??? I seen tha sky lite off real big towards tha south a few nites ago...I figgrd they was tryin' ta make the turn signals on one o' them s80 pos actually blink.

Obviously trev's still gotta kool koil or we'd hear him whinin' too.

So now tow has been infected by the po virus...that's a good thang, since once ya git over tha initial dose, you become immune ta stoopid and jes' fix shit as it happens! At least he ain't got tha krabs (but then how would I know??).

Ya know, if po's didn't fook over these rigs many of us wouldn't be able to afford ta play with 'em! They'd be just like early broncos...but then ya kin get anything new to build a Bronco, ya just gotta havea trust fund income or a sugarmomma to do so.
 
Oh boy !!!!! After an all day search at all the local oil stores, I found a coil and a resistor. Here are the numbers

bdw e30 coil 1.4 primary 9.65 sec.
Bdw ru4 resistor 1.9 to 2.0 meter fluxes between both

michael let me know if this is correct. I checked about 10 coils and a damn stack of resistors these are the best numbers I can get around here. I got this stuff at oreillys the were the only ones who carry name brand stuff around here.
 
One more question for ya what should the voltage be after the resistor. It should be lower than 12.5 volts shouldnt it?
 
The coil and resistor numbers ya posted are just fine!!!! Nice work!

The "running" battery voltage, the ballast resistor, together with the ignition coil primary resistance, and the distributor dwell factor, determine primary current "draw" through the system when the engine is running. That is the important factor. You are looking at a total primary current at say 650rpm of between 2.8amps and 3.8 amps. That is the "perfect" balance for a v8 inductive ignition system. That provides adequate coil saturation, and the current being conducted across the points will not reduce breaker point life. Those just "round numbers" and not definitive, but a "target during the engineering/design phase.

Don't sweat the "voltage", that is just a piece of the puzzle.

Nearly any dvom or analog vom will measure up to 10 amps dc intermittently. Simply put your dvom "in series" with the coil negative terminal and the wire going into the distributor and start it. The reading will be primary circuit "current draw"...so see how close you can come to the range I posted.
 
Ok here's some more numbers that May help someone else later.

Amp draw with engine runnin 3.1 amps
volts before resistor eng.runnin 12.8 volts
volts after resistor eng.runnin 9.52 volts
ohms with resistor hot no wires hooked up 3.4ohms
ohms with coil hot no wires hooked up 3.1ohms
secondary winding resistance hot 9.94 ohms

michael , engine runs great now if these numbers look bad let me know everything checked out good . Hopefully the breaking down bs will stop now. Hell, the only thing left is to is to give the rat on the wheel a shot in the ass lol
 
I see two items:

the primary circuit current draw with engine running is perfect! Absolutely right in the middle of where it should be!!! Indicates proper coil saturation and dwell!!!! That's perfect numbers for any v8, inductive ignition system running breaker points!!

However, yore "running" voltage (b+) at 12.8 indicates a considerable voltage drop between what the battery terminal voltage most likely is, and what you see.

After cranking the motor, let it idle/charge the battery with light off for say 15 minutes. Then check actual battery voltage across the posts. Then check voltage of the "run" feed before the ballast resistor, ya want those numbers to be as close as possible to the same. It's impossible to have 'em exactly the same in the real world due to the amount of resistance in the complete wire run/circuit.

But once the battery charge is replenished after the pulldown created during cranking, the voltage regulator should throttle back the charging rate onna 10si alternator to somewhere around 13.2>13.8 vdc or so, that is a nominal "range and every system will be slightly different and that is not critical.

What is critical is that battery voltage when the alternator is charging is greater than 12.8 though!

After doing all this, then repeat the test with the lights turned on and high beam engaged. Then compare the numbers for charging "quality".

Good work!!

So now you have a correctly functioning, breaker point system! In the future, ya might wanna convert to the pertronix trigger or the crane optical trigger. If so, then you have correct wiring and ignition coil functionality to do that, without having all the previous problems which would trickledown and screw with a distributor upgrade!!
 
amp draw with engine runnin 3.1 amps
volts before resistor eng.runnin 12.8 volts
volts after resistor eng.runnin 9.52 volts
ohms with resistor hot no wires hooked up 3.4ohms
ohms with coil hot no wires hooked up 3.1ohms
secondary winding resistance hot 9.94 ohms
Click to expand...
Hot damn! That was great.
I gotta say in 5 years, this is only the 2nd post I've seen with figures on reviv'in sumth'in that meant sumth'in!
Yore a helluva guud mentor Mike.
 
Ok, sorry for the delay on gettin this posted. Been busy doin, well you know.
After further investigation, battery voltage with alternator in what I call sleep mode is 13.2 volts , when the alternator wakes up it puts out 14.3 volts. With the system fully loaded, including 6 kc lites and 2 tractor lites it pulls down to 13.5 alternator seems good and battery checks out.. Drove the Scout to work bout 20 miles coil is warm but not hot and resistor is touchable . No misses or stuttering .
 
All good numbers!

Scratch the ignition system and charging system off the "to do" list and go on to the next 63 items!!!
 
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