Quote:
Quote:
Is there a reason the newer units are prone to failing
Cheap ѕhіt from China.
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| What's the 5th wire in a 5 pin ICM do? https://slantsix.org/forum/viewtopic.php?t=61214 |
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| Author: | silverhead [ Fri Jun 02, 2017 6:33 pm ] |
| Post subject: | What's the 5th wire in a 5 pin ICM do? |
My '74 D100 has the 5 wire variety ICM. I'm wanting to buy a modern replacement to keep as a spare (Yes, I've read the Chevy HEI conversion, but I want to keep my pickup stock.) I also read that you can use a 4 pin ICM as plug and play. I'm just curious what the 5th pin does? My Haynes manual mentioned something about an RPM limiting feature to prevent damage to the engine. Is this is what's going on, or what's the purpose of the 5th pin? Also, of any of the generic aftermarket brands, is there an ICM that is known to be more reliable than the others? Prices I'm seeing vary from 12 dollars to 85 dollars, so I'd just like to get one that is known to work well. I'm just rounding up spares of the ignition relay, ICM, voltage regulator, ceramic resistors, etc.. to have on hand. Thanks! |
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| Author: | DusterIdiot [ Fri Jun 02, 2017 7:03 pm ] |
| Post subject: | Yes... |
Quote: I also read that you can use a 4 pin ICM as plug and play.
This is correct.On the 5 pin system, I was told a long time back the 5th pin is a reduced voltage power supply, but that doesn't make a lot of sense... especially since one of the pins already receives full voltage from the ignition circuit before the ballast resistor... Tracing the wiring: Power from the ignition circuit is fed to both resistors in the dual ballast resistor... the dual ballast resistor has different resistances depending on the set of prongs used.... One set feeds the coil and the negative side of the coil is hooked to the ECU. The 5th pin goes from the other prong on the ballast resistor and directly to the 5th pin. I'm not sure about about rev limiting, I ran the modded engine in my Feather Duster up to 6000 rpm on the stock ECU without a problem, but went to an Orange Box I had on hand since I was going to race it eventually. |
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| Author: | kesteb [ Fri Jun 02, 2017 10:25 pm ] |
| Post subject: | |
Ignition retard for startup? The only problem that I have seen, is that some of the 4 pin boxes don't have a hole for the fifth pin. . |
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| Author: | SlantSixDan [ Fri Jun 02, 2017 10:36 pm ] |
| Post subject: | |
The fifth pin is not for rev limiting or timing retard/advance. The 5-pin module uses the "extra half" of the 4-pin ballast resistor, which provides 5-ohm resistance. The 4-pin module has the 5-ohm resistor built in, that's all. You can drop a 4-pin module right in place of a 5-pin module without making any other changes, but not the other way around. As for good modules: tough to find these days. Best bet is probably a NOS American-made module from Old Car Parts Northwest. |
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| Author: | silverhead [ Sat Jun 03, 2017 6:05 am ] |
| Post subject: | |
That makes sense that as time progressed forward the need for the dual ballast resistor was eliminated. The presumably OEM unit I have in there is working and the epoxy on the rear side is translucent. I see oldskool tube capacitors in there. Is there a reason the newer units are prone to failing in the older vehicles, such as over/under voltage from the charging system? Is there a need for someone to be building bullet proof ones using the old ones as donor units? I'd be interested to figure how how they work and what causes them to fail if anyone else has already done this sort of research. If the new ones are all known to be junk, I feel like there's need to have one on the market that isn't? The visible 'guts' I'm seeing in the epoxy don't look complicated to me. If the answer is simply more robust diodes, capacitors, and transistors I feel like it could spawn a whole new winter hobby. |
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| Author: | SlantSixDan [ Sat Jun 03, 2017 8:39 am ] |
| Post subject: | |
Quote: The presumably OEM unit I have in there is working and the epoxy on the rear side is translucent.
Great, keep driving!Quote: Is there a reason the newer units are prone to failing
Cheap ѕhіt from China.Quote: Is there a need for someone to be building bullet proof ones using the old ones as donor units?
No. Plenty of NOS American-made modules are still around, those who want to upgrade can go to HEI, and those who want to stealth-upgrade can hide an HEI module inside a Mopar ignition box.
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| Author: | silverhead [ Sat Jun 03, 2017 10:06 pm ] |
| Post subject: | |
After figuring out the required purchase items for the HEI convsersion and reading about the 4 pin Chevy ICM is it possible to gut a Chrysler ICM box and solder the factory pin leads to the Chevy HEI unit and use the factory wiring harness? With the required additional changes being - purchasing a proper ignition coil that can handle straight 12+ volts (no ballast resistor required) - bypassing the ballast resistor with a jumper wire in the factory wiring so the circuit sends full system voltage to the positive side of the ignition coil Or am I dreaming? |
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| Author: | Reed [ Sat Jun 03, 2017 10:26 pm ] |
| Post subject: | |
Quote: Quote: Is there a reason the newer units are prone to failing
Cheap ѕhіt from China.
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| Author: | SlantSixDan [ Sun Jun 04, 2017 1:33 pm ] |
| Post subject: | |
Quote: those who want to stealth-upgrade can hide an HEI module inside a Mopar ignition box.
Quote: is it possible to gut a Chrysler ICM box and solder the factory pin leads to the Chevy HEI unit and use the factory wiring harness? Or am I dreaming?
Well...um...those who want to stealth-upgrade can hide an HEI module inside a Mopar ignition box.  But unless you mount that emptied-and-refilled Mopar ignition box close to the distributor, like on the RH inner fender panel, your long wires between the distributor and the HEI module are going to cause crosstalk and resultant driveability problems. |
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| Author: | silverhead [ Sun Jun 04, 2017 3:13 pm ] |
| Post subject: | |
That's good to know. I won't bother for the time being then. I was hoping the factory wiring might actually work out after looking at how they both are utilized. |
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