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Old 09-11-2017, 04:59 PM   #1
zachste
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HEI issues?

So driving yesterday was fine for about 10 minutes, came to a stop light slowing down, and truck shuts off like I turned the key off. Try to crank it back over and just cranks and cranks (sounds normal though). 1 minute later on the phone with the wife to come pick my boy up (he was riding with me), and I turn it over and it fires up.
Finish my trek a mile to Home Depot, return some lumber. Fires right and runs great when I'm leaving. Stop at the grocery store and fires right up leaving there as well as the rest of the way home.
Took it out again later that night to run a couple errands and ran like normal.
Did some poking around, no loose grounds, or hoses, or plug wires or anything. I am going to re-check the wiring and connectors on the distributor tonight, and maybe another look at the grounds.
After doing some searching I'm thinking maybe an HEI issue? ICM?

350/350 (thumpr cam, edelbrock carb, 2k stall converter and shift kit)
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Old 09-11-2017, 05:02 PM   #2
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Re: HEI issues?

Module.
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Old 09-11-2017, 05:38 PM   #3
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Re: HEI issues?

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Originally Posted by '68OrangeSunshine View Post
Module.
X2. I've chased an intermittent module for weeks before.

Make sure you use the heat transfer paste under it when you replace it.
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Old 09-11-2017, 05:55 PM   #4
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Re: HEI issues?

Yep x3 on the module, been there...
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Old 09-11-2017, 06:15 PM   #5
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Re: HEI issues?

Also check the main power feed at the buss bar on your horn relay. Whether it be located under the dash or on the radiator support drivers side backside of the headlight.
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Old 09-11-2017, 07:04 PM   #6
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Re: HEI issues?

may be the pole piece has a broken wire gm. hei system were known for this. take the module out the two wires on the pole piece check with ohm meter move wire back and forth check to see if you loose resistance. if it does you need a new one
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Old 09-11-2017, 09:36 PM   #7
zachste
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Re: HEI issues?

Quote:
Originally Posted by '68OrangeSunshine View Post
Module.
Quote:
Originally Posted by truckster View Post
X2. I've chased an intermittent module for weeks before.

Make sure you use the heat transfer paste under it when you replace it.
Quote:
Originally Posted by 7tee View Post
Yep x3 on the module, been there...
Thanks guys. Any brand or kit recommended over others?

Quote:
Originally Posted by toolboxchev View Post
Also check the main power feed at the buss bar on your horn relay. Whether it be located under the dash or on the radiator support drivers side backside of the headlight.
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Originally Posted by anew4961 View Post
may be the pole piece has a broken wire gm. hei system were known for this. take the module out the two wires on the pole piece check with ohm meter move wire back and forth check to see if you loose resistance. if it does you need a new one
Thanks for the tips guys check these out as well.
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Old 09-11-2017, 09:38 PM   #8
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Re: HEI issues?

Someone has posted a complete troubleshooting flow chart around here somewhere. Don't just throw parts at it without actually diagnosing the problem. #1 problem I have seen with the HEI is the rotor has burned through. This doesn't cause an intermittent stalling scenario, your truck will just run badly. #2 is the module. That troubleshooting flow chart shows how to check that. In all my time, I've seen only one pickup fail.
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Old 09-11-2017, 09:56 PM   #9
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Re: HEI issues?

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Someone has posted a complete troubleshooting flow chart around here somewhere. Don't just throw parts at it without actually diagnosing the problem. #1 problem I have seen with the HEI is the rotor has burned through. This doesn't cause an intermittent stalling scenario, your truck will just run badly. #2 is the module. That troubleshooting flow chart shows how to check that. In all my time, I've seen only one pickup fail.
Oh nice, I'll do some searching and try to find the flow chart.
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Old 09-11-2017, 10:47 PM   #10
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Re: HEI issues?

Do you have a dedicated 12v supply to your hei?
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Old 09-11-2017, 11:22 PM   #11
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Re: HEI issues?

The starter is cranking the engine over, so it's getting 12 V to the ignition switch. If that circuit gets its 12 V by way of the horn relay as a junction block, wouldn't make any difference. The ignition switch needs to connect that 12 V to the Ignition circuit as well as starter solenoid.

The HEI modules are incredibly reliable. I'd check to see if you are getting the 12 V from that 50 year old ignition switch to the batt terminal on the HEI.

Unlike pertronix modules which have a reputation for intermittent problems, any HEI failure that I have ever heard of, including one of my own, when they die, they die.
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Old 09-11-2017, 11:35 PM   #12
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Re: HEI issues?

If the resistance wire from the ignition switch to the distributor is still being used then he won't have 12v. Likely nearer 7v which causes undue heat in the module.
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Old 09-12-2017, 08:34 AM   #13
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Re: HEI issues?

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Originally Posted by geezer#99 View Post
Do you have a dedicated 12v supply to your hei?
Not sure, I'll have to do some testing/digging, as I didn't build the truck.
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The starter is cranking the engine over, so it's getting 12 V to the ignition switch. If that circuit gets its 12 V by way of the horn relay as a junction block, wouldn't make any difference. The ignition switch needs to connect that 12 V to the Ignition circuit as well as starter solenoid.

The HEI modules are incredibly reliable. I'd check to see if you are getting the 12 V from that 50 year old ignition switch to the batt terminal on the HEI.

Unlike pertronix modules which have a reputation for intermittent problems, any HEI failure that I have ever heard of, including one of my own, when they die, they die.
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If the resistance wire from the ignition switch to the distributor is still being used then he won't have 12v. Likely nearer 7v which causes undue heat in the module.
Sounds like it's time to grab a multimeter and start testing some stuff.
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Old 09-12-2017, 08:06 PM   #14
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Re: HEI issues?

Think I may have found the culprit? Blue wire was very loose. Pushed back up in a bit and tried starting and it wouldn't start. Came right out when I gave it a light pull.
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Last edited by zachste; 09-12-2017 at 09:03 PM.
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Old 09-12-2017, 09:33 PM   #15
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Re: HEI issues?

Or is that just a tach wire?
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Old 09-12-2017, 10:32 PM   #16
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Re: HEI issues?

Tach wire is the one in the back [in this orientation]. The terminal we see in the ''front'' is/should be [BATT +] 12 VDC hot Ign "ON" wire from 12 volt source. I would crimp a new connector on the end to minimize intermittent contact.
In fact, if it was my truck I'd replace the blue line with a fresh 12 ga wire in red, add a Packard [locking] connector and run the feed end of the red line from IGN UNFUSED in the fuse block on the cab firewall.
You can get sets of ''Batt'' and ''Tach'' connectors, each with a color coded 12'' wire lead, for pretty cheap from Jegs or Summit. Red for BATT, Black or Brown for TACH. They slot right into the HEI cap and have extra tabs to prevent mis-connecting in the wrong slot. Jeg's p/n: 555-10552, $11.53.
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Old 09-12-2017, 10:46 PM   #17
zachste
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Re: HEI issues?

Quote:
Originally Posted by '68OrangeSunshine View Post
Tach wire is the one in the back [in this orientation]. The terminal we see in the ''front'' is/should be [BATT +] 12 VDC hot Ign "ON" wire from 12 volt source. I would crimp a new connector on the end to minimize intermittent contact.
In fact, if it was my truck I'd replace the blue line with a fresh 12 ga wire in red, add a Packard [locking] connector and run the feed end of the red line from IGN UNFUSED in the fuse block on the cab firewall.
You can get sets of Red ''Batt'' and Grey ''Tach'' connectors, each with a color coded 5'' lead, for prett cheap from Jegs or Summit. They slot right into the HEI cap and have extra tabs to prevent mis-connecting.
You're saying the blue is the power wire? I thought it was power wire in back, tach in the front. After pulling it out from the connector, tried putting it back in and crimping. It actually fired right up, like a dummy I tried the multi meter while running and it died as soon as I grounded it. Started back up, but tried to rev it a tiny bit and it cut out and died. Started back up though. I seem to be causing more problems for myself here. Wiring tends to be out of my wheel house. Unless it's just a bad connection on the batt side.
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Old 09-12-2017, 11:40 PM   #18
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Re: HEI issues?

You want a fat and sassy wire to the power on the HEI coil. You can also buy that pigtail mentioned at Autozone or O'Reilly's. Also, as has been mentioned, look for an IGN Unfused connector. When cranking, the ignition switch sends power to the starter only, in this year truck. In it's original configuration, your truck had a (yellow) wire coming from the the "R" terminal on the solenoid that fed the coil power during cranking. That blue wire has enough resistance to give you grief, as has been noted. It's entirely possible that that blue wire is fed power through the factory resistance wire. I've seen that. The vehicle runs much better when the ignition gets enough 'trons.
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Old 09-13-2017, 08:44 AM   #19
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Re: HEI issues?

There should be "male" connectors for the female end to plug into the fuse block correct?
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Old 09-13-2017, 11:29 AM   #20
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Re: HEI issues?

Quote:
Originally Posted by '68OrangeSunshine View Post
Tach wire is the one in the back [in this orientation]. The terminal we see in the ''front'' is/should be [BATT +] 12 VDC hot Ign "ON" wire from 12 volt source. I would crimp a new connector on the end to minimize intermittent contact.
In fact, if it was my truck I'd replace the blue line with a fresh 12 ga wire in red, add a Packard [locking] connector and run the feed end of the red line from IGN UNFUSED in the fuse block on the cab firewall.
You can get sets of ''Batt'' and ''Tach'' connectors, each with a color coded 12'' wire lead, for pretty cheap from Jegs or Summit. Red for BATT, Black or Brown for TACH. They slot right into the HEI cap and have extra tabs to prevent mis-connecting in the wrong slot. Jeg's p/n: 555-10552, $11.53.
So I looked on the coil cover, and confirmed, the blue wire is the Tach and the black wire is the Batt. I think I'm going to heed the advice to run a new 12 gauge wire from the fuse block to the HEI. I'm also safe to assume the module is burned up due to undue heat from not receiving enough volts correct?
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Old 09-13-2017, 12:13 PM   #21
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Re: HEI issues?

With an HEI... always carry a spare module and some heat sink grease. Do not use dielectric grease on the back of the module.

Gary
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Old 09-13-2017, 12:23 PM   #22
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Re: HEI issues?

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Originally Posted by GASoline71 View Post
With an HEI... always carry a spare module and some heat sink grease. Do not use dielectric grease on the back of the module.

Gary
That's been on my to-do list for years. One of these days I might get around to it before I get bit....
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Old 09-13-2017, 01:00 PM   #23
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Re: HEI issues?

>> I'm also safe to assume the module is burned up due to undue heat from not receiving enough volts correct? <<

No and hell no.

So much BS it's hard to figure out where to start.

Most HEI Caps have markings on the top that identify wire connections.



Now I want to show the silliness of running a new wire in to the fuse box. The electrical drawing below has all wiring removed except charging circuit, starting circuit and ignition circuit. Use your browser to enlarge or "Copy" and "Paste" to WIN PAINT or something similar.

Follow the 12R from the Battery junction block down and over to the firewall bulkhead connector. These connectors on drawn on these drawings so that the two mating connectors are mirrored left-to-right. Vertically the wiring matches, but horizontally are flipped.
Now follow the Red 12R from the inside connector, up to the ignition switch. With the key ON, the Ign switch connects the 12R directly to the Pink 12P.

THE PINK 12P RETURNS DIRECTLY TO THE BULKHEAD CONNECTOR.

Connecting a new ignition wire to the fuse box is connecting to a side leg that branches off the 12P wire. This is a less direct source for the ignition supply voltage and makes no sense.

THE PINK 12P RETURNS DIRECTLY TO THE BULKHEAD CONNECTOR. This 12P is a copper wire. On the engine side of the bulkhead connector the 12P connects to a 20W/OR/PPL wire. This is the Resistance Wire.

As a side note; the 12 PPL coming from the Ign switch and goes to the starter solenoid is the starter wire and is Hot only when the key is in the "Start" position.,

The resistance wire is Nichrome (shiny silver). It has a White insulation covered by a W/OR/PPL braided cloth. At 50 years old it usually looks like a dirty yellow. The Resistance wire measures a terrifying 1.6 Ohms. The engine will run just fine if it is still in place. I'll have more on that later.

The drawing shows the 20W/OR/PPL meeting two yellow wires near the starter solenoid. That crimped junction is farther away from the solenoid than indicated. The ones I've looked at are usually up behind the pass side head or intake manifold. On inline six engines, it's along the side of the valve cover.
The Yellow wire to the solenoid is usually eliminated and I agree with that.

This post is long enough. I'll start another to try an debunk the unrealistic fear of the dreaded, devil, the resistor wire.
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Old 09-13-2017, 01:07 PM   #24
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Re: HEI issues?

Quote:
Originally Posted by GASoline71 View Post
With an HEI... always carry a spare module and some heat sink grease. Do not use dielectric grease on the back of the module.

Gary
Just for clarification's sake, we are talking about the ICM correct? Like this https://www.summitracing.com/parts/sum-850100/overview/
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Old 09-13-2017, 01:20 PM   #25
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Re: HEI issues?

If you need more help check this: http://www.crankshaftcoalition.com/w...EI_distributor

From the bottom of the page additional informative links:

Resources

Spark plug cross-reference
Exploded view of an HEI distributor
Ported vs. manifold vacuum
GM HEI rebuild, install info
GM HEI distributor notes, etc.
Description of an HEI rebuild

Return to: Distributor shaft end play adjustment, above

HEI vacuum advance specs
GM points-type vacuum advance can specs and info (Lars)

Return to: Vacuum advance, above.

Crankshaft Coalition wiki articles:

Firing orders of various engines.
Several articles on valve adjustment
Carb vacuum port ID
How to install a distributor
Determining top dead center
How to find the number one cylinder in an engine
How to make a timing tape
Timing tabs and damper TDC lines SBC
Estimating timing chain wear
How to make a timing tape

Here is another accurate source of info: http://www.hotrodhotline.com/md/html/ignition.php

Last edited by toolboxchev; 09-13-2017 at 01:32 PM.
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