Thanks, I'll try it this afternoon. Rats, I hate the prospect of digging into the column again.
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| Author: | '74 Sport [ Thu Jul 23, 2009 6:18 am ] |
| Post subject: | Please explain the "start" circuit to me |
Aaron's slanted '74 Dart Sport finally had its first major issue in the past three-plus years he has been driving it. Since completing a total rebuild in March 2006, he has used it for his daily driver and has put about 30,000 miles on it. He called me after work about a week ago and said his car wouldn't start. We thought it might be flooded, but after letting it sit for a while, it still would not start, so I went to see if I could help him. We fiddled around for a while with this and that, not really doing much other than making sure no wires were disconnected or melted, vacuum lines were intact, carb was getting gas, jumper cables were boosting his system, and ignition wires were all on tight. No major diagnosing. Then it just simply started... He has driven it this past week without any other issues... until yesterday morning. Wouldn't start again. Cranks and cranks, just no go. So, we got out the multi-meter and ignition tester and went to work on it yesterday afternoon. Still won't start. Here's what we have determined so far: Installed ignition tester in-line on cylinder one... no spark Same on cylinder two Replaced coil with brand new one off the Duster project... nothing Replaced ECU with brand new one off the Duster project... nothing Installed ignition tester in-line on primary wire from coil... single spark Here's what I need explained... With the ignition tester connected to the coil's primary wire and grounded to the body, we get a single spark when the ignition key passes the "run" position, then there is no spark as it gets to the "start" position as the engine cranks. I understand the distributor is out of the loop in this scenario, so I would not expect the test light to "flicker" as it would if connected to a spark plug wire. Since there is no interruption of the circuit being introduced by the spinning rotor, why would the light not burn steady while the key is in the "start" position. I assumed there would be a constant supply of voltage as the engine tries to fire up, then once the engine starts and the key is released to the "run" position, the distributor takes over to "distribute" the voltage among the six plugs - hence the "flicker". What am I missing here? I will admit, since it was getting dark outside, we buttoned everything up before pulling the distributor cap and checking it and the rotor's condition. I can't tell you if the rotor was spinning or not. I just realized that there would be no spark at any of the plug wires if the nylon gear on the distributor shaft has broken off. That's the next thing we will look for is a spinning rotor. Any other comments or suggestions are welcomed, Jerry |
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| Author: | SlantSixDan [ Thu Jul 23, 2009 6:37 am ] |
| Post subject: | |
Sounds like a faulty ignition switch or a fault in its wiring. Try turning the key to "run", then going under the hood and operating the starter by carefully using a screwdriver to connect the small to the large starter terminal. |
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| Author: | '74 Sport [ Thu Jul 23, 2009 9:14 am ] |
| Post subject: | |
Thanks, I'll try it this afternoon. Rats, I hate the prospect of digging into the column again.
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| Author: | wjajr [ Thu Jul 23, 2009 12:37 pm ] |
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Check your porcelain resistor. I have had them give a little warning shot over the bow, and than fail a few days later. |
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| Author: | SlantSixDan [ Thu Jul 23, 2009 1:10 pm ] |
| Post subject: | |
A ballast resistor does not (cannot) prevent the engine from firing while cranking. When the ballast resistor dies, the engine fires but stalls as soon as the key is released from the "start" position (wherein the ballast is bypassed). |
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| Author: | '74 Sport [ Thu Jul 23, 2009 1:59 pm ] |
| Post subject: | |
Quote: A ballast resistor does not (cannot) prevent the engine from firing while cranking.
Quite true...On the other hand, in case someone might want to suggest it, the '74 has the infamous seatbelt interlock system. It does prevent the car from cranking prior to firing; however, during restoration we replaced the front seat with one from an earlier Duster lacking this feature. We completely removed the seatbelt sensor harness and have only twice had to press the reset button to enable the starter. Again, cranking is not the problem, it is not firing. Thanks for the input, however. |
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| Author: | '74 Sport [ Thu Jul 23, 2009 10:04 pm ] |
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Gentlemen, at this point, I am completely bumfuzzled. Aaron and I checked various wires for good connections, cleaned and re-seated the bulkhead connectors, checked vacuum lines, and it still would not fire. We disconnected the interlock switch, and still no go. We put the key in "run" position and cranked the engine by crossing the starter terminals (to by-pass the ignition switch, as suggested). We swapped out a new ECU and a new coil. Nothing made a difference. Then, we noticed that releasing the key from the "start" position to return to the "run" position would cause a slight backfire through the carb. That indicated there was that moment where a single spark occurred as voltage surged through the "run" circuit. Hmmmmm..... We changed the *&$%_@+~ ballast resistor and it popped right off. Purrs like a kitten. What the heck???? I can't count the number of times I have read and been told, "If the ballast resistor goes bad, the car will start, but will then stall and die when the key is released." That appears to be an old wife's tale. This car would not start at all, period, with a bad ballast resistor. We swapped the old coil and ECU back in, just to minimize the variables. It fired up on the first turn of the starter. In the morning, we will see... Thanks to all for your comments, Jerry |
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| Author: | 56 Dodge [ Fri Jul 24, 2009 3:35 am ] |
| Post subject: | |
I agree 74 sport I have had those !%**%% ballast resistors quite at a red light and one second you are idling next nothing! I always keep a couple of spares with me the six dollars is nice insurance for the next time that piece of pottery decides to try and ruin my afternoon! The motor will crank but you receive no spark it is always the start side of the four prong ballast resistor to go the one that ohms out around 1.8 ohms. good luck and remember always have a couple of spares. Jim |
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| Author: | Charrlie_S [ Fri Jul 24, 2009 4:04 am ] |
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Quote: We changed the *&$%_@+~ ballast resistor and it popped right off. Purrs like a kitten. What the heck???? I can't count the number of times I have read and been told, "If the ballast resistor goes bad, the car will start, but will then stall and die when the key is released." That appears to be an old wife's tale. This car would not start at all, period, with a bad ballast resistor. Jerry |
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| Author: | '74 Sport [ Fri Jul 24, 2009 5:36 am ] |
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It's a dual-ballast resistor. When Aaron pulled it off, there was black soot all over the firewall behind it. Something must have fried. This morning, the ol' girl popped right off - no cranking, no grinding - just a beautiful "vrrm purrrrr". So, what it sounds like is a single-ballast will allow the cranking, but not run. And the dual-ballast will not allow cranking if the "start" side is fried. I don't have a wiring diagram of an earlier model using the single-ballast. Can someone look into that theory and report? Again, thanks for all your help, Jerry |
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| Author: | SlantSixDan [ Fri Jul 24, 2009 6:59 am ] |
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Quote: Does your car have a dual or single ballast resistor? I would have to look at the wiring diagram, again, but I think if a dual resistor, then a bad resistor might cause a no start.
That makes perfect sense — please excuse my throwing you off the trail earlier. I tend to forget about the dual ballast resistor, half of which provides power to the module.
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| Author: | Aggressive Ted [ Fri Jul 24, 2009 7:33 am ] |
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74 Sport, I found a wiring diagram on MOPARTS.com and rewired my 74 Dart from the dual ballast to the single. It works so much better. Click on the red link below to see how it looks wired up. No more bad start mornings! You clip the wire going to pin 3 on the ECU. That should be the 5 ohm side and just run the bottom side which is about 1.2 ohms stock. I rewired mine with a MSD .85 ohm resistor so I get a full 10 volts to the coil at 600 rpm. All modern ECU's just use 4 pins. I just sent the schematic if needed. Tis another one of those items that should be a sticky. 
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| Author: | 6shotvanner [ Fri Jul 24, 2009 8:49 am ] |
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Hah!! knew it but kept my fingers quiet because I've been "throwed off the trail" in the past  I can remember at least half a dozen times over the years when the ballast died(dual)and was dead in the water till replaced,not so much as wimper when cranking.Glad you figured it out,carrying a spare in the glove box now right? 
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| Author: | '74 Sport [ Fri Jul 24, 2009 9:20 am ] |
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Quote: Hah!! knew it but kept my fingers quiet
Now you tell me...... gee, thanks!! Quote: ...carrying a spare in the glove box now right?
The silly part of all this is that Aaron had a spare in his glove box the whole time. Remember, the "diagnosis" of a bad resistor did not match the "symptom" of our problem with it not starting. Had it started and then died, I would have immediately gone to the resistor, as it has always been my understanding, however flawed, that a bad resistor would prevent running, not starting.Regardless, it was a lesson well learned (for many of us). And yes, a new resistor is on Aaron's shopping list for today. I wonder what it would take to fab up a solid state replacement for the ballast resistor? Thanks again, Jerry |
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| Author: | wjajr [ Fri Jul 24, 2009 1:34 pm ] |
| Post subject: | |
Glad to be of assistence! Had the same symptoms that you experienced with both my first Dart 38 years ago, and a new '76 Cordoba a few years later. |
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