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Had my Starfire off the road for a few weeks after successful 1,000 mile run to LA & back. When I got it back from the brake shop it had developed a misfire.
I knew the cap & rotor were from March of this year, wires are fresh, as are the spark plugs. So a lot of the obvious candidates were long shots.
I pulled the cap & rotor and cleaned off the carbon just in case. But they weren't bad at all. But underneath the rotor, hey!
Turned out the little Green and White wires that move with the vacuum advance are wearing out. They were intermittently grounding out against the distributor floor. I slipped some shrink wrap over them as temporary fix.
Is there a good permanent fix? This happens to be a Taylor HEI of recent vintage, no quality problem, but I think I may lengthen and/or reroute the wires so there's more flex length and they may endure a longer time period.
The internal wires were a bit frayed, but still functional, so I did a light touch solder job on one.
I was thinking it might be smart to have a longer-length wire, maybe coiled, so that as the vacuum advance moves back and forth when the car is running, there would be more wire length to spread the bending load across.
This is the trigger mechanism which sits uner the rotor in a 75 & up HEI distributor. Those two little wires, white & green, move every time the vacuum advance gets a change in vacuum signal. They have to flex constantly so should be thick wire well insulation. By design they also tend to rub on the vacuum advance arm when they flex. In my case that lead to an intermittent short and erratic idle.
Wasn't comfortable with soldered 20 gauge wires moving inside a hot distributor. So I sprung for an HEI distributor Pole Piece Assembly. The wires in the latter day parts are a few gauges smaller than what GM did back in the 70's.
Here's a comparison of good vs less good parts. I suspect the left example is GM from the 70's, note the wire gauge thickness -- I'm pretty sure this was 14ga. wire - strong and flexible.
Thicker wires back in the day. Not sure, but I believe the left example is OEM GM from long ago. Notice the thinner wires on the right and cheapo connectors...sigh.
40 years on, manufacturers are using 20 gauge wire to do the work. Which lasts less long... At least I had the fore sight to create a rub strip out of a little zip tie so that the part of the wires which could touch the vacuum advance arm will have to wear through a zip tie and then through the wiring insulation before creating a problem again...
Hope this helps someone out there with a weird erratic idle on an otherwise-good ignition system.
I don't think the wires are 14 gage. If I recall they are 20 gage. The pick up coil will generate a voltage signal as low as 250 millivolts (.250 volts) during engine cranking and increase with engine RPM. It may not exceed 3-4 volts at max RPM. Such a low voltage would not work well with 14 gage. I think what's throwing you off is the thickness of the insulation. That wire is designed to flex. Again I can't remember exactly but I think copper was not used (the wire may be silver in color) and the insulation is thick to prevent abrasion. Since you have the defective pick up coil off can you strip a piece of the insulation off? I am curious about the insulation thickness, the wire gauge, and the conductor used. It may be a helpful learning experience for a lot of us. Perhaps Joe P. can enlighten us? At any rate I'm glad you found and repaired your issue. Good diagnosis!
Yeah thats a good find. I too wondered about the wire quality, type and number of strands. You said your new one already had broken wires, the OE GM ones were made to go 50k + w no issues.
Dynoking,
Sorry I went to take a picture for you, but garbage had gone out a day ago with the busted spares in it. Thanks for the diagnosis kudos. It was one of those moments when I went “Oh, maybe I have learned something over the past 40 years.”
I think you’re right, GM probably made smaller 16-20 gauge wires with purpose-built thicker insulation to work for a long time. Unfortunately latter day manufacturers care less about durability than GM did in the old days. They’re quite happy to use the smaller gauge, but are cheaping out on insulation thickness. My hunch is GM was aiming more for fewer returns & breakdowns as opposed to focus on quality products, but either way it wouldn’t bother me to find some thick insulation NOS parts along the way. 55 years later, I’ll take what I can get and modify as I can for durability.
If you want to dig deeper in, the green and white wires connect to a coil that sits in a cup. The wires run under a plastic coil retainer. It looks a lot like a teflon tape roll. You could solder thick wires in there with some care. The problem is getting a solder joint just the right thickness, then getting shrink wrap insulation to sit in side 2 channels on the underside of the coil retention ring. I opted for a replacement part and used a tiny zip tie to improve the wiring rub resistance on the vacuum advance arm.
I was toying around with trying to go GM one better with a coiled thick insulation wire, but decided against it. The environment inside the HEI is very hot and the wires move all the time. Getting them just the right length to not interfere with the mechanical works of the rotor, vacuum advance would have been a bet I didn’t want to make just now.
Ran the car today for 60 or 70 miles and it was just right. Timing was a couple of degrees too advance, but I can fix that in the morning. Nice to have a smooth idle and confidence.
Ill bet GM used rope type arrangement for their wiring. Because as you said prevent failures and returns.
ill also bet many after market suppliers will be less concerned about sourcing the best configuration in wire for a part like this ( although i hope some would)
You can go to an auto parts store and get a new pickup coil assembly for less than 30 bucks. I think they are the same for all 74-81 HEI. I have found this to be the case on MANY non running, or problematic older GM cars. The new ones are not as good, and may not last another 40 years, but will work fine for the reduced service most of these cars see. LX303 from rockauto.com.
September 15th, 2021, 01:20 PM
