Hello, I have been going nuts over this. 73 1210 392, new distributor Holley, new coil 1.4 ohm, points gaped .017, base timming 5*. What happens is after about 15min of highway driving there is a loss of power and when that happens the tach starts to read irraticly. I have read all the posts that pertain to this problem and I cant seem to figure it out. Any help would be appreciated, thanks
ignition problem
- Thread starter eitmhl
- Start date
Michael Mayben
IHPA Tech Moderator - Retired & No Longer Online
You have an issue with the ignition feed to the coil with the ignition switch is in the "run" position. The oem resistor wire/circuit is heating excessively most likely because the wire is actually broken/burned through and once it gets really hot, it's resistive value is increasing.
All of the resistance wire is in the engine bay side of the harness/bulkhead connector, none of it should be inside the cab/under the dash.
Start at the bulkhead connector, remove it, and you will see evidence of heat damage/arcing/corrosion. Then unwrap the electrical tape from the harness and expose the resistor wire and you will find it doubled back on itself so that it can be hidden inside the harness. That is a major no-no in the use of that type item as it gets hot when in operation (thus the reason for the fiberglas overbraid).
If the resistor wire is beyond hope, then simply remove and discard completely, and run a new conventional wire to the positive coil terminal that is fed through a ballast resistor of 1.4>1.8ohms when hot. A ballast resistor and a "resistor wire" are exactly the same device/purpose, you must use one or the other with a breaker point distributor, along with a coil of a proper primary value (and your 1.4 ohm coil is just fine for that).
This is the resistor wire removed from a harness, it is spec'd to be exactly 72" in length, this one is good and shows no signs of ever being damaged, notice the actual resistance value at ambient temp, well within specification.
All of the resistance wire is in the engine bay side of the harness/bulkhead connector, none of it should be inside the cab/under the dash.
Start at the bulkhead connector, remove it, and you will see evidence of heat damage/arcing/corrosion. Then unwrap the electrical tape from the harness and expose the resistor wire and you will find it doubled back on itself so that it can be hidden inside the harness. That is a major no-no in the use of that type item as it gets hot when in operation (thus the reason for the fiberglas overbraid).
If the resistor wire is beyond hope, then simply remove and discard completely, and run a new conventional wire to the positive coil terminal that is fed through a ballast resistor of 1.4>1.8ohms when hot. A ballast resistor and a "resistor wire" are exactly the same device/purpose, you must use one or the other with a breaker point distributor, along with a coil of a proper primary value (and your 1.4 ohm coil is just fine for that).
This is the resistor wire removed from a harness, it is spec'd to be exactly 72" in length, this one is good and shows no signs of ever being damaged, notice the actual resistance value at ambient temp, well within specification.
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I should have mentioned, the first thing that I did was run a power wire directly from the battery with a 1.7 ohm resistor to the coil and it didnt change a thing.
I was thinking that the dist might not be grounded properly but .2 ohms from it to the batt seems good
I dont know if its related but my amp guage bounces irraticly also
I was thinking that the dist might not be grounded properly but .2 ohms from it to the batt seems good
I dont know if its related but my amp guage bounces irraticly also
Michael Mayben
IHPA Tech Moderator - Retired & No Longer Online
Typical breaker point resistance on any point-type system is 0.1>0.3ohms, we want as low as possible, that is why we clean new breaker points after they are installed.
An erratic ammeter indicates a bulkhead connector issue also, the longer the period of time a rotten contact point inside the male/female junction in the bulkhead connector is in operation, the hotter it gets until it either goes up in flames or the connectors (ampacity for a ten gauge wire run) themselves erode away.
So you are saying when you have the ignition primary side "hot-wired", the problem with tach bounce and poor running is still present?
Once the coil gets up to operating temp, test the primary and secondary resistance, it would have to show a significant change to affect ignition performance. Since you mentioned a coil with primary resistance of 1.4 ohms, I'd venture to say that the coil is a "yellow" accel aftermarket part? I have much experience with those in "failure" mode as they heat, I can demo that on my coil tester. While advertised with a primary resistance of 1.4 or so, their actual measurement at ambient is normally 1.6>1.8ohms. The one shown on the tester here works just great for thirty minutes, then turns to shit. Notice that it's lost it's insulating oil due to shoddy construction.
An erratic ammeter indicates a bulkhead connector issue also, the longer the period of time a rotten contact point inside the male/female junction in the bulkhead connector is in operation, the hotter it gets until it either goes up in flames or the connectors (ampacity for a ten gauge wire run) themselves erode away.
So you are saying when you have the ignition primary side "hot-wired", the problem with tach bounce and poor running is still present?
Once the coil gets up to operating temp, test the primary and secondary resistance, it would have to show a significant change to affect ignition performance. Since you mentioned a coil with primary resistance of 1.4 ohms, I'd venture to say that the coil is a "yellow" accel aftermarket part? I have much experience with those in "failure" mode as they heat, I can demo that on my coil tester. While advertised with a primary resistance of 1.4 or so, their actual measurement at ambient is normally 1.6>1.8ohms. The one shown on the tester here works just great for thirty minutes, then turns to shit. Notice that it's lost it's insulating oil due to shoddy construction.
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Yes it acts up (loss of power and tach jumping) with the coil "hot wired" . Yes it is a accel super stock crome one, 11.58 k ohm 1.7 ohm . So what your saying is that it is probable the coil taking a shiz once it gets hot? I guess that it could be, but it is like 2 months old with very little use. What kinda coil would you recomend replacing it with?
Michael Mayben
IHPA Tech Moderator - Retired & No Longer Online
Yes, the coil is taking a dump! The one in my pic lasted about five months in daily service before all the oil had drooled out, that is a quality issue, not the norm.
For a stock ignition, there is no need for any coil other than a $12 oem replacement in my world. For a true upgrade performance ignition, then we've addressed much of the "coil" topic in this thread:
http://www.forums.IHPartsAmerica.com/ignition-tech/644-ignition-system-performance-upgrades.html
Coils are either good or bad, in this day and age of shit-quality aftermarket parts, very early failure has become the norm, same for solenoids, relays, electronic modules, etc. Has nothing to do with the country of origin, has everything to do with the quality of the components and manufacturing costs.
Measure the resistance factors with the coil cold (and disconnected of course), then measure again when it goes into failure,...you will see the issue in the readings! That coil tester in the pic heats the coil for a five minute "burst", then it's output is tested again. I always test any coil by heating for thirty minutes to really abuse it. If it passes the thirty minute heat test, the coil is good for life! No coil gets installed in my shop without being fully tested and "burned in" nowadays.
If you have an ignition system capable of supporting an "e" core-type coil, those are the best you can do. But...the resistance factor of the "e" core design must match the type of ignition system used. In your case, that would 1.4>1.8 ohms and to do with the ballast resistor or primary feed. Msd has one, pertronix has one, mallory has one, etc.
Scoutboy74
Moderator
Yeah, 30 puts you smack in the middle of the 28-32 range.
Robert Kenney
Super Moderator
While 30* of dwell is where you would like to be, coil saturation at low speeds would be enough at 24*.
You need to measure stuff here to know what is going on..
1.7 ohm resistor and 1.4 ohm coil if that is all of the + coil power supply resistance and assuming 12v.
Points closed and ignition on the run position. Don't leave it there for more time than it takes you to take voltage readings.
Coil + term to ground voltage will be 5.4vdc
resistor voltage drop will be 6.6vdc. (across the two terminals)
the total of the two is system voltage or 12v. If you don't get close to that you have a wiring issue.
You need to measure stuff here to know what is going on..
1.7 ohm resistor and 1.4 ohm coil if that is all of the + coil power supply resistance and assuming 12v.
Points closed and ignition on the run position. Don't leave it there for more time than it takes you to take voltage readings.
Coil + term to ground voltage will be 5.4vdc
resistor voltage drop will be 6.6vdc. (across the two terminals)
the total of the two is system voltage or 12v. If you don't get close to that you have a wiring issue.
Michael Mayben
IHPA Tech Moderator - Retired & No Longer Online
Did you actually measure the primary and secondary resistance factors of the coil both when cold and when you suspect it's failing? If not, then we can only suspect the coil is/was the issue and haven't made any diagnostic progress.
With the oem resistance factors of the resistor wire (or workaround ballast resistor) and the primary resistance of the coil itself, and a correct dwell specification set (I always shoot for 30* on the sv engine which is right in the middle), the coil saturation/current draw through the system with the engine running should be in the 1.8>2.8amp range, that is absolutely perfect. Any less...not enough coil saturation above idle speed...any more....breaker point life is drastically reduced. These numbers are only for a v8 engine equipped with a breaker point distributor and all oem-spec components in the entire ignition system.
Nearly any el cheepo vom has a "10 amp" scale that can be used with the included test leads to measure primary current with the engine cranking and running. And inductive dvom can measure primary current by simply clamping the jaws around the coil negative wire that goes to the distributor/point set.
This pic shows a 196/I-4 engine running with a custom setup on the coil/distributor/breaker point showing how the actual coil saturation factor can be improved as compared to an oem setup which can greatly extend breaker point life resulting in increased dwell angle maintenance over the life of the breaker point set. The number displayed is in dc amps.
