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low voltage causing starting problems and rough idle? #1645387
07/11/14 06:00 PM
07/11/14 06:00 PM
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colorado
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68charger440strk Offline OP
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I have been chasing ignition gremlins for awhile and need some help. When I turn the key to the run position without starting it, the voltage to the coil + side seems to creep up over the course of 5 minutes from 7v to 11 or so. I did the 70s style electronic charging system conversion a few years back and I am running an MSD ignition with the ballast resistor bypassed. The car seems to have a hard time starting when the voltage is low but seems to start easier when the voltage is higher. My questions are:

What could cause the voltage creep when there is no ballast resister? What should the voltage be to the + side of the coil when there is no ballast resistor in the loop? I thought it should be around 12v.
Is there anything in the ignition switch or wiring behind the dash that would affect the voltage to the brown igition wire?
The car is a 68 Charger with 500" stroker.

Re: low voltage causing starting problems and rough idle? [Re: 68charger440strk] #1645388
07/11/14 07:03 PM
07/11/14 07:03 PM
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Lincoln Nebraska
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RapidRobert Offline
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With electrical issues especially strange ones like this start at the beginning (the battery), sub another one in & see how it performs. With nothing on you will have system voltage everywhere just like in a college dorm, all the toilets have equal water pressure till someone flushes one of em & the pressure drops which is why someone in the shower may scream from being scalded when a stool gets flushed in an antiquated system. When running you are going to have system voltage available except each connection will have a slight voltage drop (hopefully only several tenths per connection) & the device (coil/ecu) used will drop the voltage further from the amount of current (amps) it uses. If the batt is OK then unhook the coil & see what the voltage does then hook it back up & unhook the MSD & see what the voltage does. Holler back with any news.


live every 24 hour block of time like it's your last day on earth
Re: low voltage causing starting problems and rough idle? [Re: 68charger440strk] #1645389
07/11/14 07:23 PM
07/11/14 07:23 PM
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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What ohm coil you using with the MSD?

Re: low voltage causing starting problems and rough idle? [Re: RapidRobert] #1645390
07/12/14 06:40 PM
07/12/14 06:40 PM
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colorado
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68charger440strk Offline OP
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Quote:

With electrical issues especially strange ones like this start at the beginning (the battery), sub another one in & see how it performs. With nothing on you will have system voltage everywhere just like in a college dorm, all the toilets have equal water pressure till someone flushes one of em & the pressure drops which is why someone in the shower may scream from being scalded when a stool gets flushed in an antiquated system. When running you are going to have system voltage available except each connection will have a slight voltage drop (hopefully only several tenths per connection) & the device (coil/ecu) used will drop the voltage further from the amount of current (amps) it uses. If the batt is OK then unhook the coil & see what the voltage does then hook it back up & unhook the MSD & see what the voltage does. Holler back with any news.



The voltage at the feed to the positive side of the coil is 10v today(the gremlins are feeling generous today). That is the same when I disconnected it from the coil, and when the MSD dizzy is disconnected or connected also. I swapped the battery with no effect last week. The coil is an MSD blaster 3 which has .7 ohms primary resistance and 4.7 k ohms secondary resistance.
Is there something behind the dash that would keep the voltage down with the key on? Am I correct that I should have at least 12v to the coil since I have bypassed the ballast resistor?

Re: low voltage causing starting problems and rough idle? [Re: 68charger440strk] #1645391
07/12/14 06:50 PM
07/12/14 06:50 PM
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Cincinnati, Ohio
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I'd check the heavy red wire that goes through the bulkhead connector. It's worth checking or bypassing the connector in the bulk head connector instead of waiting for it to cor road and over heat.

I have solid wire red soldered in passing through my bulk head on my one car. Been that way since 1985 when "I fixed it" lol It's known to melt down.

Re: low voltage causing starting problems and rough idle? [Re: Challenger 1] #1645392
07/12/14 08:28 PM
07/12/14 08:28 PM
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68charger440strk Offline OP
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Quote:

I'd check the heavy red wire that goes through the bulkhead connector. It's worth checking or bypassing the connector in the bulk head connector instead of waiting for it to cor road and over heat.

I have solid wire red soldered in passing through my bulk head on my one car. Been that way since 1985 when "I fixed it" lol It's known to melt down.



I did that bulkhead bypass also for both the feed to and from the ammeter. I didn't connect the two wires to one side of the ammeter thus bypassing the ammeter altogether though. I am starting to wonder if the ammeter is where I am getting the inconsistrant voltage from.

Re: low voltage causing starting problems and rough idle? [Re: 68charger440strk] #1645393
07/13/14 03:52 AM
07/13/14 03:52 AM
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Norway
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General 68 Offline
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Yes you should see batteri voltage (or close, as there will be a slight drop) at the coil after bypassing the ballast resistor. If you have checked the bulkhead connector and other obvious connections maybe you are on to something abort the ampere meter. The increasing voltage over some time that you describe would be caused by loose connections. The studs behind the ampere meter can very well be loose and dirty. During the first minutes of current flow a bad connections creates heat and stuff expand and tightens the previous gap at the connections. This might not be your problem, but I have seen it happen with a othervice well working ampere meter. Lars

Re: low voltage causing starting problems and rough idle? [Re: General 68] #1645394
07/13/14 04:13 AM
07/13/14 04:13 AM
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Granite Bay CA
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May sound off topic a bit, but....
I have had Ballast resistors appear okay but make the car hard to start and run weaker than it should. I don't have the means to test the resistance these actually have but I would think that if they "resisted" too much current, the ignition system wouldn't function as well.

Re: low voltage causing starting problems and rough idle? [Re: Kern Dog] #1645395
07/13/14 10:23 PM
07/13/14 10:23 PM
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68charger440strk Offline OP
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Well I dropped the dashboard and checked the connections to the ammeter. They were still on there good and tight, but one side read roughly12v and the other side read between 7 and 10 kind of moving slowly up. Since the wires were new to and from the ammeter from when I did the bulkhead bypass, I knew the wire itself was not the problem. The only thing left was the ammeter itself. So I joined the two ammeter wires together eliminating it from the circuit, and finally the voltage is 12v to the coil. Now the car starts quickly and the rough idle is gone. The detonation problems I was having on acceleration are gone also. Its amazing what problems low voltage can cause!

Re: low voltage causing starting problems and rough idle? [Re: 68charger440strk] #1645396
07/13/14 11:26 PM
07/13/14 11:26 PM
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Lincoln Nebraska
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RapidRobert Offline
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Incredible I've never known an ammeter to act like that. We coulda been chasing that one for a long time


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Re: low voltage causing starting problems and rough idle? [Re: RapidRobert] #1645397
07/14/14 12:14 AM
07/14/14 12:14 AM
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Hi Robert. I believe this is a sympthom of an ampere meter about to burn if not taken care of. They are simple by design so I can not see many other things that can fry them. From the start the studs are fit tight through the U-shaped piece and held tight by the inner nuts. But after thousands of cyclings and temperature changes the fit and connection between the stud and nut and this U-piece get affected causing excessive heat.
Robert: When I am on here I would like to say that you are doing a great job and putting in a lot of work by helping so many on here! Thank you for your positive attitude and will to share your knowledge and experiance!
Lars

Re: low voltage causing starting problems and rough idle? [Re: General 68] #1645398
07/14/14 12:36 AM
07/14/14 12:36 AM
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Thank you Lars & online is the only place that I have a positive attitude


live every 24 hour block of time like it's your last day on earth
Re: low voltage causing starting problems and rough idle? [Re: 68charger440strk] #1645399
07/14/14 11:53 AM
07/14/14 11:53 AM
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I am coming on this a little late, but you say you are running MSD ignition? If so, then both wires on the coil come from the box, right? And if so, you don't get battery voltage there. In fact, as I recall, when running, it will be a high enough voltage that you don't want to measure it, and I believe the instructions imply or state that (+200 vdc). If your battery isn't up to full charge, MSD really doesn't want to work. Charge your batter fully, then see how it goes, but with MSD, I wouldn't be checking that coil voltage with anything. I did read that coil voltage with an "O" scope with an inductive pick up years ago and I seem to remember some +350 volts or something (running engine). But whatever it was, it was surprisingly high hence the huge spark at the plugs.

Re: low voltage causing starting problems and rough idle? [Re: SportF] #1645400
07/14/14 12:36 PM
07/14/14 12:36 PM
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colorado
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68charger440strk Offline OP
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Quote:

I am coming on this a little late, but you say you are running MSD ignition? If so, then both wires on the coil come from the box, right? And if so, you don't get battery voltage there. In fact, as I recall, when running, it will be a high enough voltage that you don't want to measure it, and I believe the instructions imply or state that (+200 vdc). If your battery isn't up to full charge, MSD really doesn't want to work. Charge your batter fully, then see how it goes, but with MSD, I wouldn't be checking that coil voltage with anything. I did read that coil voltage with an "O" scope with an inductive pick up years ago and I seem to remember some +350 volts or something (running engine). But whatever it was, it was surprisingly high hence the huge spark at the plugs.



Let me clarify... I am running an MSD HEI all in one dizzy without the separate ignition box hooked up. With that setup the dizzy does get the coil power directly.

Re: low voltage causing starting problems and rough idle? [Re: 68charger440strk] #1645401
07/14/14 01:08 PM
07/14/14 01:08 PM
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68charger440strk Offline OP
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One other thought on the ignition box... Aside from the fact that with my current setup my coil is fed directly from the ignition switch... even if I did have the separate ignition box hooked up, it gets a wire directly from the ignition switch that it uses in it's triggering process. With that ignition feed bouncing from 7v and maybe even lower on up to 11v the ignition box will be getting power it can not deal with.
Below is a quote from an MSD Tech on the MSD ignition site when talking about hooking up an MSD A6.
"the ballast resister is no longer needed because the MSD box works off of 12V's and the ballast resistor will lower that voltage and cause issues."
The part of interest is not the ballast resistor part, but the part where he says the lower voltage "WILL" cause issues. So even though the main power for the ignition box is coming from the battery, the triggering mechanism is still very dependent on clean power from the ignition.







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