DodgeW200

I am reassembling my 1975 360 after a rebuild and can not get spark (Occasional, inconsistant arcing from primary when held very close to ground) I have replaced ECU, Distributor and Ballast resistor. Battery voltage is at 12 volts, ECU is grounded, dual ballast has resistance in range for respective sides. Coil primary and secondary resistance are within specs. I even tried replacing the battery to ensure sufficient voltage/amperage for good start.
My only indication something is amiss is that my voltage at the positive end of the coil is around 5.5 volts. It should be within a volt of battery voltage, correct? I do not detect a short with my ohm meter. This tells me it is a resistor problem, but it checks out fine? This is a relatively simple system and I mad at myself for not figuring it out.
Any suggestions?

Thanks for your time,

Ray

78D200

The ballast resistor is only allowing so much voltage to go to the coil, hence the word resistor in the name. Is it an after market coil that you have? Is it a known, good coil?

I use to have a ballast resistor on my AMC 360, I pulled it out and ran the wires to the coil and never had a problem. If anything, it ran great. I'm not sure what would happen if you did that in a Mopar though.

Are you sure that the rotor in the dizzy is spinning? Are the spark plug wires are set correctly?

DodgeW200

I was wondering what would happen if the resistor was removed too, but I assume it's there for a reason. It is an aftermarket coil, but the voltage is low to the positive wire feeding the coil, even when the coil is disconnected. It should be one volt less than battery voltage?

scotts74birds

Ok, I'm new to the mopar ignition setups, but I believe that the mopar coils are wound differently. Think of it as a step-up transformer. Most coils have an average output of 40kv. Most coils are 12v, but mopars are made to run on less voltage due to the ballast system they use. So I guess what I'm saying is that if you apply half the voltage to a 12v coil, then you will get half the voltage on the output side, say 20k or less. I'm not a mopar ignition expert, yet, but I do know electrical theory

DodgeW200

I understand the theory. I am not getting any consistant spark though. Could the ignition switch cause this if is not making a good connection? The way I read the schematic is that when the ignition is on, the ballast resistor limits voltage. When in the start position, the resistor is bypassed to create a larger spark until released. I am only getting 5.5 volts at the coil. My repair book states it should be one volt from battery voltage with ignition on or it's the ballast resistor. I have replaced it with no effect. Does anyone have experience with this in a similar situation?

theomahamoparguy

the mopar coil must be run with the reduced voltage.[except for lean burn equipped] the mopar electronic ign. must run a mopar coil {of original type to the vehicle year} the mopar coil only sees battery voltage when you are cranking the starter [for easier starting]. check voltage to the "hot side of the ballast. Should be 12.5 or more. 5.5 seems a little low at the coil but not too low not to work. do not run the mopar coil with 12+ volts {you could get by with 8-10 for a while} do not run a coil made to work on 12 volts with the mopar ign. control unit. [Little to no spark]
I think the mopar coil is a throwback from the 6 volt days, I guess since it worked, they just never bothered to change it, even when electronic ign. came around. Lean burn vehicles were the first mopars {i believe} to use a coil that ran on 12 volts, but the ign curve was controlled by computer. You could step up to a MSD ign added to the stock dizzy and then you would use a 12v coil. Mopar ign. box=stock coil @ ~6v with ign. in "run" position.
These are my opinions as far as my experience goes.

theomahamoparguy

might be the dist. itself??? {more testing}

DodgeW200

Thanks! I will look at the distributor again this coming weekend. I replaced it when I did the rebuild, but it could be defective. Other than continuity (which is good), how do you check the hall effect switch? Will continuity change across the hall effect switch as it is rotated? Enough to pick up on an analog meter (not digital)?
I don't think I am obtaining full voltage at hot side of ballast resitor either. ~ -3 volts from battery. This has to go through ignition switch on the column. I will check pre and post switch voltage there also. Thank you for the help.

DodgeW200

I removed the distributor from the block and with the ignition "on," I spun the shaft and had the most beautiful spark. As soon as I reinstalled the distributor and tested it while turning the engine over, I had weak inconsistant spark again. I tested the two coil circuits, "on" was at 6 Volts and "Start" was at 9.5 volts. Even with the starter turning over the engine, the "start" circuit fed at 9.5 volts to the coil. Is it possible that the correct voltage is there, but not enough amperage? I retested after applying jumper cables with no change. Could a weak starter that draws alot of power drain enough amperage to cause this problem?

theomahamoparguy

I think the dizzy might have a ground issue. Like it might be grounding when its not supposed to, hence the nice spark when its off the engine. Check the engine ground also [to the frame and the body]
Also check out the starter relay. those voltages are definitley low. Should be about 12+ volts when cranking and 8 + when running. More like 8.7 actually. I got the numbers wrong in my last post as far as the ohm readings. Only thing left would be the key switch. Hows the voltage to the "hot side of the ballast". Should be 12+ with key in run position. Mopar ignition modules have 43 degree of dwell when idling. Wow that is alot.

DodgeW200

Yes, they are all low, even before and at the ignition switch. The hot side to the ballast is also low. I am having difficulty finding were it steps down at. I will track it down this coming weekend. Thanks for helping me think it through.

67 GTX

have you checked the gap between the pickup and the reluctor?

DodgeW200

Will do this weekend. Thanks.

67 GTX

let us know how it goes

menomoniemopars

very interested in this as my car is doing the samething!...

DodgeW200

It turned out to be the air gap between the pick-up and the armature. It had a gap big enough to drive a Monaco in. Once I brought it within 0.008 of an inch, it worked better. However, when I rotated the distributor by hand slowly it was still reluctant to fire from all positions on the armature. I replaced the armature with a new one of better quality and the tabs were more consistantly machined, problem solved. My starter did turn over slowly and that turned out to be the primary wire leading to it. The wire looked new on the outside but the termianal ends were of cheap quality and slightly corroded from sitting. Once those problems were eliminated, my beast came alive. I do no have my exhaust system completed as of yet, so I let her rip with straight headers. When it was rumbling at idle, I was as giddy as a school girl going to a boy band concert. I have some various small end problems left to fix, vacuum leaks, a carb fuel fiting leak. I will start another post about my brake booster question. Thanks all for your help!!

67 GTX

great work

OutlawCuda

Good advice on the air gap check. Had that on the old 87 too.