#21  
Old 05-22-2020, 01:06 AM
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68lemans462 68lemans462 is offline
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Originally Posted by Sun Tuned View Post
I’m a little late here to the party.



As Schurkey has Sluder to above, at minimum I would replace the coil, and unless it’s pretty new might as well go ahead and put a new cap with it.



Lately, I’ve noticed if a module fails, you can almost guarantee it was one of three things that caused it.

1. A coil on its way out.

2. Welding on the car/exhaust

3.lack of heat sink compound



Even though a coil may still seem to function properly if it takes the module out, I’ve found in the last 5 years ,you can play patch the parts, or just fix the issue at hand. That I have found is a coil That ain’t far from leaving the building with Elvis. Several times we’ve replaced the module only to find out the coil will take out another one in short order.



Had a Monte Carlo up the street that wiped 4 modules in nearly 6 months. Just for the hell of it I checked out everything and decided to feed it 2 more for good measure. One day we decided to scope it,and thought hmmm.... replaced the cap and coil haven’t had an issue in a year and a half.



FWIW.
Lately, I’ve noticed if a module fails, you can almost guarantee it was one of three things that caused it.

1. A coil on its way out.

2. Welding on the car/exhaust

3.lack of heat sink

*******
Exhaust is all new no signs of leaks.

Checked my receipts and the cap/rotor/rotor bushing are new MSD as of 1/2018 at the same time I installed the failed JUNK MSD 8347 digital hei. I bought the coil new from Napa before that and it might have a thousand miles on it but likely ALSO CHINESE JUNK. Seldom used in past 5 years maybe 500 miles.. Not replaced at the same time.

What is the recommended coil (part number /mfg?) it's time for a new coil undoubtedly.

I plan to order a new OEM wiring harness (all I have are ugly) /capacitor/COIL and put in a used 990 module. Go from there, keep it simple.

I did yank the distributor several times over the winter to adjust total mechanical advance and dial in my advance limiter to attain 12dgs at idle and 30 at 3200rpm. I suspect I disrupted something during this time..........Who knows?

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Last edited by 68lemans462; 05-22-2020 at 01:23 AM.
  #22  
Old 05-22-2020, 09:35 AM
Sun Tuned Sun Tuned is offline
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In all honesty there’s about 10 things that need to be tended to when putting these things back together.
I’ll try and go over them here in a bit. First let me say that it’s no new news that most parts do not come from here anymore. So that said we have to make due with what we have to work with.

Starting with these cap harnesses. I’ve got 8 delco replacements left from about 20 years ago and bar none those were the best you could get. Alas they don’t sell them anymore. Napa was the go to when I needed something other than Delco. They’ve changed them up a bit also. And all of them have jumped in price from the 14.00 they used to be to close to 36-37.00 now. The ones they ship these off shore distributors with are ALL a total hot pile of...

The modules in these things are and have always been pretty tough. If things are normal or close to it it really takes a lot to kill one. There are however a few things that will wreck one in a hurry and I believe the ic chip they put in most these days isn’t very robust compared to the older ones. At least I think the newer ones are more susceptible to voltage spikes and such than they used to be.

With a good thermal compound under the module, that’s as good as that gets, let’s move on out and work our way up. I’ll adress a few things along the way as we go. I may have to check in and out a few times today as I’m needing to get going here. The harnesses used to be virtually bombproof. Especially the terminals. They were built from Delco and even the better quality ones from Napa, very well. Specifically the spade slide terminals. They retained their springiness very well. The current ones you have to watch a lot these days. Not sure what metal they’re made of but I think they’re plated brass and the originals were much thicker, probably allowing for the springiness they had. If they don’t hold tight to the coil blade connections they will build her due to the extra resistance from being loose. This is not goid and the first path of problems to look for. That connection has to be tight and stay that way.

  #23  
Old 05-22-2020, 09:59 AM
Sun Tuned Sun Tuned is offline
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This will be one of my last posts on this issue and it will be long, and since I’m on my phone doing it it has had a habit of “losing” long posts. I really don’t want to type all this just to lose it.

Doesn’t really matter whether the harness is the replaceable condenser style or the latest last chip style. The originals had a replaceable condenser, then they went to a fixed round condenser like the first ones except it was hard wired into the connector body. The last ones are a hardwired chip or wafer style. The condenser was a rfi radio interference capacitor or filter. But this harness is actually the heart and soul of the whole operation. Have a glitch here and nothing will work correctly on up the food chain.

Really there in my opinion wasn’t an advantage to either of the three different harness styles, although the early replaceable capacitor style was nice cause if the condenser got out of spec you just connected another replacement. Kinda handy. You will if using one of these need to pay attention to the split brass female receptacle part of the condenser plug. It can get loose, and crusty. Simply wire brush it out and you can fit a pair of smaller needle nose pliers in to recriminations and shrink the brass receptacle so it fits snugly back again and you should be goid for another 20 years.

About the only thing in the harness you had to look out after was the plastic clips that locked to the cap. They would get brittle and if you got in a hey or even if you weren’t they might break. Didn’t matter much on the originals as they fit so tight you couldn’t blow em off, but this new stuff I’ve actually seen come disconnected on their own.

If you have an original with broken clips I’ve taken the cheap replacements and pulled the harness clip plug off the elcheapo and replaced the factory broken one for those that want to keep the original harness.

There is a very specific order the three wires go in on these and with enough removals of the plug over the years even the goid factory stuff might need some terminal attention sooner or later. This offshore junk gives you about 3 disconnects before the spade blades become squashed and need service.

I suggest removal of each terminal one at a time. There is a lock tab on the back of the terminal that releases it from the plastic connector body. When you get the terminal out we need to look at the flat spring ramp on the inside of the female terminal. You’ll need to wire wheel or clean this and note that the flat ramp should be resprung or basically restored up tight so it creates a pinching connection on the male spade portion of its matching connection. This is best accomplished by using a tool much like an ice pick or at the least a very small pocket screwdriver or a pic. Spring the ramp back up and reconnect the three terminals in the plastic connector and lets move on to something else.

  #24  
Old 05-22-2020, 10:39 AM
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MMMMmmmmm. Automotive Oscilloscopes!

Thousands of years ago, they were a huge rolling cabinet,
Yep, I have a Sun roll around machine with the Oscilloscope.

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  #25  
Old 05-22-2020, 10:55 AM
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Had one too but gave it away...too much space for infrequent use...but like a lot of tools ,invaluable when you need it. Nowadays, I just use my bench scope.

George

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  #26  
Old 05-22-2020, 10:59 AM
Chief of the 60's Chief of the 60's is offline
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Interesting to see that some people still make use of a scope. Its been decades since I got to use the words "cathode ray tube".

  #27  
Old 05-22-2020, 12:56 PM
Sun Tuned Sun Tuned is offline
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Let’s look at the cap assy now.
Or rather let’s build one up with new parts.
Except for a brief year and a half deal GM did with the coils, and excluding the ACCEL Super coils, all of the HEI coils should have 3 wires exiting out of the coil epoxy. Either a red/yellow, Or a red/white and then the third wire a black ground. Like I said the accel super coil and the 75 Gm coil will only have two. There won’t be the third ground wire. They changed that deal up to the three wire and then that’s what Gm had until the end of the 135 mm cap “large” hei.

That being said ALL of the coils will require yet a 4th connection. This will be the coil frame ground , in the form of a formed metal strap or the ring terminal and wire type . Either will work but as far as my preference I like and prefer the ring terminal wire type. But in all instances these need to be present regardless of the design of the ground itself.

I like the ring terminal type better as I feel it’s a more positive connection. The ring on it has about 8 teeth that dig into the frame of the coil. I think this works better than the metal strap type that sandwiches or squeezes in between the coil frame and the cap. I just like it better.

The rotor brush will be of two types the O.E. design will run about 12-14,000 ohms resistance. The aftermarket powdered copper ones will read near dead zero. I prefer these over the O.E. ones. They certainly allow the coil to run much cooler. I haven’t had any issues with am radios and ignition static running these no resistance brushes.

Put the brush in the cap, install the little round rubber insulator washer. I always cost it with dielectric grease to seal the deal off. And place coil on top and lower down. Put in the screws that holddiwn the coil and be sure you have a ring terminal ground wire coming out of the coil epoxy on one side, and the external ground wire on the opposite side (if your using the wire type ring terminal ground strap).

Now here’s a spot where you can get in a pinch. Sometimes coils get changed. A lot of times the replacement coil frame thickness is thicker or thinner than the original being replaced. Problem is you have to watch the holdown screws, because if they’re too short the coil may pull out, but the real deal killer is if they’re too long and they pierce the cap into the open area, you will have one-hell of a fire show, and a miss you’ll be looking for.

Tuck the color coil wires down into their pockets and secure the ground terminal also if using the wire type ground, the strap type will have already been in place if using that. Flip cap over and look at terminals and straighten a little if needed. Put the coil cover in and button it up. Be sure if using different coil cover holdown screws that they also don’t go through inside of cap.

If you have access to a working scope to play with be sure you see 4-6 coil oscillations on the trace . 6 is better. That one we looked at only had 2,not nearly enough.

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  #28  
Old 05-22-2020, 02:12 PM
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Chief: modern scopes have a color LCD display and are digital so one can store waveforms and such, copy them to a thumbdrive, look at them on a computer, send them to your fone for instant view.

Great stuff this modern equipment.

George

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  #29  
Old 05-22-2020, 02:19 PM
Chief of the 60's Chief of the 60's is offline
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Originally Posted by george kujanski View Post
Chief: modern scopes have a color LCD display and are digital so one can store waveforms and such, copy them to a thumbdrive, look at them on a computer, send them to your fone for instant view.

Great stuff this modern equipment.

George
I guess I'm just stuck in a time warp. Hell, I don't even have text messaging.

Thanks George

  #30  
Old 05-22-2020, 03:20 PM
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Originally Posted by george kujanski View Post
Had one too but gave it away...too much space for infrequent use...but like a lot of tools ,invaluable when you need it. Nowadays, I just use my bench scope.

George
I keep it around as a nostalgia piece as that's the theme I'll accomplish in the shop if I ever get around to finishing it. I do use it once in a while.

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  #31  
Old 05-22-2020, 03:22 PM
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Originally Posted by Chief of the 60's View Post
I guess I'm just stuck in a time warp. Hell, I don't even have text messaging.

Thanks George
You aren't the only one so don't feel bad. I actually prefer the dummy down version of stuff. It's one of the reasons we all daily drive classic cars and sold all the new stuff.

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  #32  
Old 05-26-2020, 05:27 PM
70GS455 70GS455 is offline
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Quote:
Originally Posted by george kujanski View Post
Do you know if the HEI coil specs are suitable for being driven from the MSD Capacitive Discharge?

George
Yes, and will actually work better as a transformer (for a CD ignition) than as an inductive storage for HEI

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  #33  
Old 04-11-2021, 04:26 AM
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Originally Posted by Schurkey View Post

Seems clear to me the guy meant using the "stock" HEI distributor housing, and the "stock" HEI mag-pickup (with or without the "stock" HEI module; I've done it both ways.) The MSD then fires the "stock" HEI ignition coil.

.
How do you wire it if you are using the stock 4-pin hei module? I was hoping that I could trigger it off the module because i do not want to remove it. Does the 4 pin module need power to it or just the trigger wire from the 6al? Thanks, I've been trying to find this answer everywhere.


Last edited by CodeMang; 04-11-2021 at 04:31 AM.
  #34  
Old 04-11-2021, 02:27 PM
Schurkey Schurkey is offline
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Originally Posted by CodeMang View Post
How do you wire it if you are using the stock 4-pin hei module? I was hoping that I could trigger it off the module because i do not want to remove it. Does the 4 pin module need power to it or just the trigger wire from the 6al? Thanks, I've been trying to find this answer everywhere.
You COULD trigger the MSD using the 4-pin module.

Don't do that. There's no point to it, you're adding a bunch of circuitry into the system that doesn't need to be there.

Leave the module in place but electrically disconnected, for when the MSD dies. BYPASS the module using the harness supplied with the MSD spark-box. Trigger the MSD directly from the pickup coil.

When the MSD fails, you remove the distributor cap, remove the MSD harness, plug the pickup coil back into the module, and drive away using the HEI ignition instead of the MSD spark-box.

The instructions are supplied with the MSD box, and they used to be downloadable from the MSD web site. Probably still are.

The 5- 7- and 8-pin modules are kept in the system when adding an MSD spark-box, because of their electronic timing features--either electronic retard, or computer-controlled timing. The spark-box takes the timing signal from the module, but works it's voodoo on it to trigger the coil. Since the 4-pin module doesn't do any deliberate spark timing adjustment, there's no reason to keep it in the system.

  #35  
Old 04-11-2021, 02:33 PM
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Originally Posted by 68lemans462 View Post
I have a GM stock HEI with an MSD rev limiter module (the one that replaces the stock module). This thing failed me tonight (had to tow car home) and I have also had problems in the past with GM and aftermarket HEI modules.

One of the guys I know from the dragstrip said to get a MSD 6AL and run it with the HEI with the stock coil. What are thoughts on this setup? I also read the older non-digital version is preferred vs the newer version. Is this true?

I'm not doing this for nor expecting any change in performance and pretty much going for better reliability. Is it worth the $ or should I go back to a stock GM module with a couple extras in the glove box and no rev limiter? I really like having a rev limiter especially when I make the bad decision to put the radials on the rear. The tach gets pegged QUICK!
I have always setup an MSD 6a or 6al (for the 4-speed guys) using an HEI in any modified street engine. The MSD coil works, i just vent the cover. Just make sure to use the required conductor for an MSD. Have had a few stock ones melt prematurely.
Anytime an electrical device fails, it was either hooked up wrong, or was just defective. Doesn't mean the setup won't work together.

  #36  
Old 04-11-2021, 03:01 PM
CodeMang CodeMang is offline
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Originally Posted by Schurkey View Post
You COULD trigger the MSD using the 4-pin module.

Don't do that. There's no point to it, you're adding a bunch of circuitry into the system that doesn't need to be there.
I appreciate your opinion but I would still like to keep the 4 pin module hookt up. If you don't know how, that's fine. Just say that and I'll ask someone else.

  #37  
Old 04-11-2021, 07:49 PM
Schurkey Schurkey is offline
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I appreciate your opinion but I would still like to keep the 4 pin module hookt up. If you don't know how, that's fine. Just say that and I'll ask someone else.
It's right in the MSD instruction sheet. Wire it up as if it were a 5- or 7-pin module.
Page 14 of this .pdf
https://documents.holley.com/6425.pdf

"GM IGNITIONS Wiring an HEI 5 or 7-pin Module (Amplifier Trigger)."
The MSD-supplied "red jumper" and "white jumper" would be helpful but not essential. Easy enough to make your own.

Use the white wire on the MSD to trigger it--not the mag pickup (violet and green) wires.

But...doing it this way is CRAZY. There is NO NEED and NO BENEFIT to keeping the 4-pin HEI module in the system. Leaving a four-pin module mounted to the distributor housing, ready for use is one thing. Using it to trigger the MSD spark-box is another.

There's a reason that MSD takes the 4-pin HEI module out of the circuit, even though it would wire in the same way as the 5- or 7-pin unit.


Last edited by Schurkey; 04-11-2021 at 08:34 PM.
  #38  
Old 04-11-2021, 10:01 PM
CodeMang CodeMang is offline
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Originally Posted by Schurkey View Post

But...doing it this way is CRAZY. There is NO NEED and NO BENEFIT to keeping

It provides a benefit for me in the fact that wiring this way will allow me swap between the two without even needing tools. Literally just unplug the 6al and replug the dizzy. So simple, my wife can do it.

  #39  
Old 04-12-2021, 07:34 PM
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Half-Inch Stud Half-Inch Stud is offline
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Very hard to beat the HEI because of the built-in variable Dwell. Unique.

Capacitve Discharge needs a different Primary-wind count coil than Magnetic discharge.

  #40  
Old 04-13-2021, 05:55 PM
Schurkey Schurkey is offline
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Originally Posted by Half-Inch Stud View Post
Capacitve Discharge needs a different Primary-wind count coil than Magnetic discharge.
I think "needs" is a stronger word than necessary. I don't doubt the ignition coil could be optimized for CD vs. inductive operation, but there's zillions of people using OEM and aftermarket "HEI" or points-style round canister ignition coils that are triggered by CD boxes; and MSD sells their line of ignition coils that are advertised for use with their line of CD boxes but also for use with HEI, or other inductive ignitions.

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