Hi guys, Ive got an issue that is testing me and it has finally won. Im going to ask for help. The car is a 73 montecarlo, no means a classic or collector. Its the first car my parents bought when married and my first car as well The problem is that I can not get the voltage at the positive side of the coil under 12 volts. I have always thought the voltage should be around 9 at the positive side of the coil. Things I have tried, new alternator, same. disconnecting yellow, starter wire, from coil. ignition switch, same battery, same I think it may be a grounding issue. I think it started after I put in an oil pan gasket, which I unhooked the motor mounts. Any one have any good ideas on what to try or where the grounds are for the points ignition. Does the valve cover ground do anything? Car is in poor shape physically but it runs great, all orginal. Looking for any help, thanks, mike PS. looking for 1970 L78 parts as well.......
there should be a ballast resistor between the 12 volt source and the coil..... but there is also a 'start' wire from the starter to the coil that provides 12 volts during cranking I am guessing when you did the oil pan, you removed the starter, and re-wired it incorrectly during installation
:error: OE 1970 would have a resistor wire, not a ballast resistor, which drops the coil voltage in the "run" position. It's also possible that your starter solenoid, even if connected properly, may be bad and is not opening the circuit to the "R" terminal in the run position. This would put 12v to the coil in the "run" position also. :TU:
But he said he removed the yellow wire from the starter to the coil and still had 12 v. Its not a groung issue either. The resistance wire should be 1.35 to 1.50 ohms resistance end to end did you replace that wire at some point. You said the problem started when..... Is this when you noticed there was a problem or did you check it before the pan replacement? o No: I would look at the pink and black wire really good, I think the problem is there!
Since you are not looking for perfection here, just go to any auto parts and ask for a coil resistor for a 70 or 71 Mopar. Run 12VDC into it, a wire out of it to the coil and you're set. Grounding is not the issue. It is always available and costs a dollar and a half last time I checked. Good luck.
Ok, update. I forgot to add that I have added an exturnal resistor, thinking it was the cheap and easy fix, but that only got the voltage to 12 volts. The voltage increases with engine speed, aka alternator, but even while the alternator is unhooked, the voltage still increases. Car runs with 10.83 volts with no alternator. Thats with 2 resistors, 1 line, one exturnal. If I unplug the black wire from the coil, car dies. If I disconect yellow nothing happens. Yellow wire does aid in starting though. Car is 100% orginal, minus 1 mopar ballast resistor. What is the theory with the starter? Where is the black and pink wire theory? My wires are black and yellow. Should the coil only have 9 volts? Im thinking it should...... Problem is after the car runs awhile, or when rpms increase the car dies like you shut of the key. Slip the trans in neutral and it fires right back up. Many people have told me its just bad points but ive tried them all. Have 1 set of delco's that I paid way to much for to try but I want the voltage at 9. Thanks for the replies.
If you've got a decent sized ballast resistor (or resistor wire) feeding the coil, and the coil voltage is still too high, that means the primary side of the coil isn't conducting enough current -- due to some extra impedance somewhere. Imagine if your coil was open-circuit: since no current flows, there is no voltage drop across the ballast resistor, so it would measure the full 12V. Measure the DC resistance of the coil's primary; is it within spec? How about the wire from distributor to coil -- is the wire good and clean with solid connections? Next in line is the points; if they're new, you'd think they're good, but stranger things have happened. Next is the ground connections -- from points to distributor, from distributor to block, and from block to battery. Finally, it's worth noting that some multi-meters do a lousy job of making a DC measurement of signals with strong AC on them -- which is exactly what your ignition primary circuit looks like, since the points are opening and closing very fast. It might be worth trying a different meter.
Blackgold, where do I look for the ground spots. Is it the distributor clamp? I have tried new distributors, new coils, points, I have replaced each and every part on the ignition primary and secondary side with no avail. Each part is added signally and then tested. I do not fully trust my guage, but on a 58 chevy it measured 9 volts at the coil. Again Im looking for anything, the car is just puzzling. It started with brand new points from carquest burning instintly. Then I put the resistor in, and the points last awhile, but the car dies when at speed or high rpm. I also noticed once I hit a bump, large bump, and the car fried the points and died and wouldnt start again. Thanks for the replies. Any ideas where to look next? Clamp? valve cover ground?
I'm no Chevy expert, but I assume the points get their ground connection through the distributor body and clamp. And I assume there should be a thick copper braid between engine block and firewall, and a thick negative battery cable to the block. I'm puzzled by the points burning up. They do have a condenser, right? Dwell adjusted correctly?
The first few years of use with my Ramrod, we burned out points every 5000 miles. Right before it totally quit, it would only run WOT and I thought it was a fuel problem. Same exact thing happened with a friend's new 70 Camaro (350 4 speed). Points begin to deteriorate the minute you hit the key when they're new. On the GM's they would run OK between 28 and 32 degrees dwell, but we always set them by the seat of the pants. (Turn it in until it misfires, back it off 1/2 turn.) Amazing how accurate that was when checked with a dwell meter later.
Yeah, it has a condensor. I dont really know what is going on. I know its missing the valve cover ground. I can check the clamp, it was lose for a bit while I changed distrubitors. It was tight last time I checked. I dont know what to think, I mean I have tried my whole bag of tricks.
I'm definately no expert in these matters, but couldn't you add additional resistance (i.e. another resistor) to get the voltage down? If one resistor dropped it to twelve, what would two do? They'd have to be hooked up in series, of course. It seems like a band aid approach to your repair, but, if it works, at the very least it gives you another bit of information. Nick
Added, another resistor in the same line and it made no difference in the voltage. Also added a wire from the distrubutor hold down bolt to the alternator top ground. Through all of this I figured that the voltage cannot be the problem. I then took the carb off and checked the float. It was low. So I raised the float and the car has not died on me yet........ It does has a top end miss, But with 220,000 miles it has the right to miss a little up top. I figure it is a worn cam, or weak valve springs, or intake ports on the heads so carboned up. Anyway, I have no idea why this point ignition runs on 12 volts. Maybe Im checking in the wrong place. I have always tested on the positive side of the coil. On other cars the voltage has been 9 volts. What Im guessing is that somehow the alternator is charging through the ignition. I really dont know..... Thanks for the help mike
Are you checking the voltage with the engine running or with the engine off? The 9-10 volt number is for an engine running. With the points open and the engine off you will have nearly 12 volts, no matter how many resistors you put in the line.
