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| Rough idle rapid misfire https://slantsix.org/forum/viewtopic.php?t=68748 |
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| Author: | Thebearded1 [ Mon Sep 07, 2026 3:49 pm ] |
| Post subject: | Rough idle rapid misfire |
So I installed a Mopar electronic ignition on my 225. 5 pin ignition control box, dual ballast resistor and coil with appropriate resistance. It is installed in my dirt track roadster and I have both mounted on the fire wall and the engine bay is enclosed with a hood and hoodsides. It runs fine until it doesn't haha. While drag racing after a few time runs it started idling rough in staging and when I made my pass it started misfiring rapidly like a machine gun. I got to the pits and used my multimeter and I noticed the 5 ohm side was .3 ohms higher and the 1.3 ohm side was .7 ohms. Is this difference minimal or would it cause problems. I let the car sit with the hood off and it ran fine after cooling down. I ran the rest of the event without the hood and had no more issues. Last weekend I drove to a friend's house 30 minute trip with the hood and hoodsides on in the sun on a 80 degree day and had no problems. However on the way home at night about 20 minutes into the drive home the idle started getting rough so I pulled in to a gas station and let it cool down some. I took off the hood side on the passenger side and sat it in the passenger seat and drove home with no issues till I got to my driveway and it shut off and wouldn't start back up at all. The next morning it fired right up quickly. Do you think the heat is causing issues to either the ballast resistor or box? I was thinking about mounting it inside of the cockpit to not have it in the engine bay. This ignition control box was a borg warner box I got from a friend, I also have an orange Mopar box from my dad that also works (started on my car) Could this just be an issue with the borg warner box? I was afraid to install the Mopar orange box in the current location if the heat was an issue. I didn't think to check my alternator when I was having the idle rapid misfire issue to see if it wasn't fully charging and that was causing the problem. It is charging fine when I have checked it now but it's not actively doing the problem. I figured though since it wouldn't restart that one night that the alternator was not the issue since it had no problem turning the started over. |
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| Author: | Dart270 [ Tue Sep 08, 2026 3:46 am ] |
| Post subject: | Re: Rough idle rapid misfire |
Could be the ingnition box. Many are low quality these days. See if your friend will let you borrow his for a while for a longer test. Is it possible you reversed the leads for the dist pickup? I did that once and it would run then be rough and die, something like what you describe. Lou |
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| Author: | Charrlie_S [ Tue Sep 08, 2026 4:42 am ] |
| Post subject: | Re: Rough idle rapid misfire |
A little off the wall info. I really don't know if/what effect it would have. But if you changed the pickup in the distributer, there is a difference in the pickup for a slant six, and a V-8. They look the same, and are physically interchangeable, but have a different electrical impedance. If I remember correctly, the leads are a different color, between them. I discovered this when I was sorting out parts I had in stock. |
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| Author: | mcnoople [ Tue Sep 08, 2026 5:37 am ] |
| Post subject: | Re: Rough idle rapid misfire |
Quote:
A little off the wall info. I really don't know if/what effect it would have. But if you changed the pickup in the distributer, there is a difference in the pickup for a slant six, and a V-8. They look the same, and are physically interchangeable, but have a different electrical impedance. If I remember correctly, the leads are a different color, between them. I discovered this when I was sorting out parts I had in stock.
Would that difference in impedance even matter? Don't the v8 and slant ignition boxes interchange?
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| Author: | Thebearded1 [ Sat Sep 12, 2026 6:07 am ] |
| Post subject: | Re: Rough idle rapid misfire |
Quote:
Could be the ingnition box. Many are low quality these days. See if your friend will let you borrow his for a while for a longer test.
I will leave the Mopar orange box in and do some drives this weekend and next week. I had a feeling heat shouldn't be too big of a problem here since these units were mounted under the hood originally. Also my friend who races with me has a slant six with Mopar electronic ignition in his model a hot rod with a hood and hood sides and doesn't have any issues with his box and resistor mounted on the firewall.Is it possible you reversed the leads for the dist pickup? I did that once and it would run then be rough and die, something like what you describe. Lou I rechecked the wires and they are correct going to the distributor. I know this isn't likely causing my problem but I have the plugs gapped at .035 from when I had the points ignition in. Should I open it up with the electronic ignition? I've seen posts of some people running .040-.045 with hei and petronix setups. |
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| Author: | Thebearded1 [ Sat Sep 12, 2026 6:09 am ] |
| Post subject: | Re: Rough idle rapid misfire |
Quote:
A little off the wall info. I really don't know if/what effect it would have. But if you changed the pickup in the distributer, there is a difference in the pickup for a slant six, and a V-8. They look the same, and are physically interchangeable, but have a different electrical impedance. If I remember correctly, the leads are a different color, between them. I discovered this when I was sorting out parts I had in stock.
I purchased the distributor new for a slant six so the pickup should be correct. My friend is using the same WAI distributor and has had no issues for several years so hopefully it's just the borg warner box giving me issues.
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| Author: | volaredon [ Sat Sep 12, 2026 7:24 am ] |
| Post subject: | Re: Rough idle rapid misfire |
Ok I see where you said you put in a 5 pin box. Did you run a 2 or 4 prong ballast? I remember something about being able to use a 4 pin ignition box in place of a 5 pin but not the other way around. At some point there was something about the aftermarket changing something within the boxes they made where the 5th pin became a "dummy" pin so that the box actually acts like a 4 pin. What exactly is the difference I don't really know. And how to tell if yours is the version with the "dummy pin" on position 5 that doesn't do anything vs the 5 pin version where pin #5 actually does something... Do you have another box that you can switch with just to test? And also back in the day there never was a "6 cylinder box" vs an "8 cylinder box" so I don't see where there would be any difference that would matter with the pickup between a 6 and an 8. The only thing I can think of there that definitely would matter would be the reluctor wheel having the right number of teeth. I have a pile of (I think they're either "Sorensen" or "niehoff" brand from back in the day) pick up coils "only" up in the attic-- without the plate they're meant to be mounted to-- that are marked "mopar 6&8 cyl". |
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| Author: | Thebearded1 [ Sat Sep 12, 2026 6:38 pm ] |
| Post subject: | Re: Rough idle rapid misfire |
Quote:
Ok I see where you said you put in a 5 pin box.
I have been using a 4 prong ballast and it was working fine most of the time. I now have the 4 pin Mopar orange box and it still works with the dual ballast resistor. Did you run a 2 or 4 prong ballast? I remember something about being able to use a 4 pin ignition box in place of a 5 pin but not the other way around. At some point there was something about the aftermarket changing something within the boxes they made where the 5th pin became a "dummy" pin so that the box actually acts like a 4 pin. What exactly is the difference I don't really know. And how to tell if yours is the version with the "dummy pin" on position 5 that doesn't do anything vs the 5 pin version where pin #5 actually does something... Do you have another box that you can switch with just to test? And also back in the day there never was a "6 cylinder box" vs an "8 cylinder box" so I don't see where there would be any difference that would matter with the pickup between a 6 and an 8. The only thing I can think of there that definitely would matter would be the reluctor wheel having the right number of teeth. I have a pile of (I think they're either "Sorensen" or "niehoff" brand from back in the day) pick up coils "only" up in the attic-- without the plate they're meant to be mounted to-- that are marked "mopar 6&8 cyl". I can't imagine much of a difference between a 6 cyl and 8 cyl box since they both have the same pins and I've never seen any special notation to distinguish them. The distributor is all new and for a slant six. Today's update: So far 3 short trips today and no issue. I will try driving it more tomorrow and take it to work Monday. I used some washers to move the ballast resistor and ignition box slightly off the firewall. I cleaned up the back of the ignition box mounting points as well as the firewall to make sure the box is grounded. I also have a ground wire to one of the mounting bolts too just for good measure. |
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| Author: | volaredon [ Sat Sep 12, 2026 7:37 pm ] |
| Post subject: | Re: Rough idle rapid misfire |
Yeah what I remember was that you could use. 4 pin box on any of them but you couldn't use a 5 pin on anything originally set up for a 4 pin |
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