HEI Conversion-Sudden Death

[67carry-all]

A little help from the HEI gurus, please. 292, swapped in a junkyard HEI from '79 Camaro years ago. Truck has run fine this way for years, but centrifugal advance was working poorly. This weekend, ot a new HEI from one of the local well-known auto parts stores installed. Installed fine, test drove a couple miles, also fine. Next day, hooked up an Autometer Tach (was not hooked up to the prior HEI dizzy), test drove, ignition died after 1/2 mile. There is still 12V to the Batt terminal, coil seems to test ok. Tach was reading accurately until the ignition died.

I vaguely remember a note in one of the HEI discussions where a tach could cause an issue, but can't remember in what way; the connection seems pretty straight forward. Just a bad new distributor? Any ideas on what happened?

[dmjlambert]

Not a guru but I am wondering is the tach now disconnected at the distributor, and will it run with the tach disconnected?

[67carry-all]

Well, you may not be a guru, but you're smarter than I am! I'd disconnected power to the tach with no joy. Tried starting it after disconnecting the tach lead from the HEI, started right up! Very happy about that, but still puzzled what caused the ignition to quit with the tach hooked up. Any further thoughts? It was really nice having the tach functional for those first two minutes!

[Stocker]

This is just a wild guess and may have no bearing on your problem. Did you run a new power wire to the HEI to replace the resister wire to the original points distributor? Just wondering if it might work OK without a tach, but not with one, if the resistor wire was still in place.

[geezer#99]

What did you use to hook the wire to the terminal?
Coulda been a short.

[dmjlambert]

One way to wire a kill switch, that is to prevent the engine from running, to short the tach signal from the distributor to ground. So your tach could have a problem, or the wire running to the tach shorted to ground.

['68OrangeSunshine]

I run a 292 with a GM HEI. I have an AutoSun tach. Never had a tach related problem that wasn't simple, like a broken wire under the dash. [A loopy ground wire got caught in the clutch pedal spring and was torn loose.]
I power the HEI Coil with a red 12 ga. wire from IGN Unfused in the fuse block.
Still running an external voltage regulator, too.

[67carry-all]

Good ideas about checking for shorts, I'll recheck the wiring routing tomorrow. I used a crimped connector to connect the tach sensor wire to the tach terminal on the HEI. As for 12V to the HEI, yes, doing that, but a little differently than most of the ways I've read. I have the original resistor wire going to a relay, triggering a full 12-14 volt feed with the key on.

Thanks for the kill-switch idea - been thinking of adding something like that.

[old51sedan]

Originally Posted by 67carry-all

A little help from the HEI gurus, please. 292, swapped in a junkyard HEI from '79 Camaro years ago. Truck has run fine this way for years, but centrifugal advance was working poorly. This weekend, ot a new HEI from one of the local well-known auto parts stores installed. Installed fine, test drove a couple miles, also fine. Next day, hooked up an Autometer Tach (was not hooked up to the prior HEI dizzy), test drove, ignition died after 1/2 mile. There is still 12V to the Batt terminal, coil seems to test ok. Tach was reading accurately until the ignition died.

I vaguely remember a note in one of the HEI discussions where a tach could cause an issue, but can't remember in what way; the connection seems pretty straight forward. Just a bad new distributor? Any ideas on what happened?

Is this tack strictly an 8 cyclinder tack or does it have a switch to set it to a 6 cylinder tack?

[geezer#99]

Originally Posted by 67carry-all

Good ideas about checking for shorts, I'll recheck the wiring routing tomorrow. I used a crimped connector to connect the tach sensor wire to the tach terminal on the HEI. As for 12V to the HEI, yes, doing that, but a little differently than most of the ways I've read. I have the original resistor wire going to a relay, triggering a full 12-14 volt feed with the key on.

Thanks for the kill-switch idea - been thinking of adding something like that.

Those crimped connectors are available in an insulated style too.

[67carry-all]

It's a configurable tach, set to 6 cyl. Can consider the insulated connector; the connection is pretty well isolated under the cap.

[67carry-all]

Truck is up and running this morning, did a 12 mile drive so far with no problem. Based on the comments so far, my working theory is that the tach signal wire must have shorted to ground yesterday. Still have to trace the wire to verify, but very glad the HEI internals aren't fried which was my initial fear. Thanks to you all for the great feedback and advice!

['68OrangeSunshine]

Originally Posted by 67carry-all

Good ideas about checking for shorts, I'll recheck the wiring routing tomorrow. I used a crimped connector to connect the tach sensor wire to the tach terminal on the HEI. As for 12V to the HEI, yes, doing that, but a little differently than most of the ways I've read. I have the original resistor wire going to a relay, triggering a full 12-14 volt feed with the key on.

Thanks for the kill-switch idea - been thinking of adding something like that.

The White/Purple/Orange resistor wire from the bulkhead connector on the firewall, is designed to increase resistance as it heats up in use. Going from full 12 VDC down to 7 VDC to not burn up the points. In an HEI system points are gone, and you need the full constant voltage at 12 VDC. If this lead is wired to trigger a relay, there is a possibility that the decreased voltage, [as resistance increases], may be insufficient to keep the 12 volt relay closed. This could cause an intermittant feed to the Coil.
Nice concept, but too complicated for an ignition circuit. They should be simple.

[dmjlambert]

Originally Posted by 67carry-all

As for 12V to the HEI, yes, doing that, but a little differently than most of the ways I've read. I have the original resistor wire going to a relay, triggering a full 12-14 volt feed with the key on.

At the firewall connector, you can squeeze the male terminal that feeds the resistor wire and push it out the back of the connector. Then insert a fresh Packard 56 male terminal with regular wire attached and power the HEI that way.







I recommend it, it's fewer components which means less to fail. Full thread here:
https://67-72chevytrucks.com/vboard/...d.php?t=708975

[hjewell2]

Originally Posted by dmjlambert

one way to wire a kill switch, that is to prevent the engine from running, to short the tach signal from the distributor to ground. So your tach could have a problem, or the wire running to the tach shorted to ground.

bingo!!!

[67carry-all]

First, I'd like to thank you all again for your input, help, and guidance - I'm very appreciative and grateful for the time and effort put in to helping me solve the HEI issue and go above and beyond in suggesting a better path toward trouble-free operation.

You've convinced me to ditch the relay set-up and simplify the 12V feed to the HEI. I'll get the Packard connector ordered and hopefully have it in time for a brief weekend project. Still need to track down where the tach wire was grounding out - that will be the second part of the weekend project. Once that's done, should be pretty easy to wire in a kill switch.

['68OrangeSunshine]

'67Carryall, what tach do you have?

[RustyPile]

Originally Posted by 67carry-all

...........<snip>..You've convinced me to ditch the relay set-up and simplify the 12V feed to the HEI. I'll get the Packard connector ordered and hopefully have it in time for a brief weekend project...<snip>...............

Why "order" the terminals.. The shipping will cost more than the terminals. Any parts store worth it's salt will have them in stock.. A package of 10 costs me $3.50 at my local parts store...

[67carry-all]

The tach is a 2 1/6" Autometer, 0-5,000 rpm; I don't recall the model number. It's been installed in the truck for literally years without being hooked up prior to this week, one of many little items that got put on the back burner along with the truck itself while life happened. My son's daily driver died, so the Suburban was pressed back into service. He loves the truck and gets positive comments about it virtually every day. The tach is certainly a non-necessity, but something I'd wanted to add a little interest to the non-gauge instrument panel.

"Any parts store worth it's salt ..." - yeah, about that. Nearest store is about 5 miles away, not sure how much further to find one worth it's salt (most recently, couple of guys at the store that should know better were stumped at my request for a new air cleaner stud). So, for something a little unusual such as a Packard terminal connector, it can be easier from a time and frustration standpoint to order from a reliable on-line vendor.

[67carry-all]

Well, guys, counterpoint from the guy I was ordering some electrical stuff from - his opinion is that the relay to power the HEI is the ideal way to go because it assures a constant 12+V. If I'm understanding him correctly, the power from the bulkhead goes through the ignition switch, as do other power demands such as heater fan and lights. When these are active, the demand is enough that it pulls down the power available to everything running through the ignition switch, and the HEI would therefore see a reduction in voltage. Thoughts?

Since we all like pics, here's one of the tach in question.

[Big Kev-O]

The lights do not go through the ignition switch, if they did you would not be able to turn them on without the key turned. Your ignition switch should be able to handle the load. Swapping out the resistance wire & using the Packard terminal is a clean & reliable way of connecting your HEI. Adding a relay has it's pros & cons. Yes it takes a small load off you ignition switch & provides a strong 12v power source but it also adds another potential point of failure. If you add a relay I recommend keeping a spare in your glove box.

Modern day Chinese made electronics are not exactly dependable. I have purchased 12v relays, ignition switches & headlight switches from auto part store that have failed. The first ignition switch I bought didn't last a month.

[RichardJ]

>>and the HEI would therefore see a reduction in voltage.<<

Only if the battery and charging system can't keep up and supply the needed current. The voltage regulator will regulate the 13-14 volts, as long as the total current demand does not exceed the total current available.
There's nothing wrong with using a relay. It's just overkill with a basic HEI that draws less than 2 Amps at idle. If you had a big MSD box and running your 292 at 6000 a relay would probably be a very good idea.


>>You've convinced me to ditch the relay set-up and simplify the 12V feed to the HEI<<
If you are using a basic Bosch type relay, powering it with the ballast resister wire is no problem. The relay coil draws about 150 milliamps. adding 1.8 Ohms to a relay coil with a DC resistance of 75 Ohms does nothing. Relay coil pull-in voltage is 6-8volts, so if that is all the battery you have, the starter won't crank the engine anyway.


>>for something a little unusual such as a Packard terminal<<

Actually, the terminal is not unusual, but inconsistency in the terminology is. NAPA calls them a GM 56 Series. Amazon sometimes list them simply as 56 Series Terminals. Some FLAPS sell Dorman Conduct-Tite Terminals , but most seem to be assortments with junk you don't want.

>>the power from the bulkhead goes through the ignition switch, as do other power demands such as heater fan and lights. When these are active, the demand is enough that it pulls down the power available to everything running through the ignition switch<<

Your guy is correct. The current in the 12 Gauge (12R) at the bulkhead connector splits and feeds the Ign SW, the horn relay, the light SW and part of the fuse box. The Ign SW splits what current is left from the 12R and sends it in the 12P wire to the bulkhead connector ballast resistor and also splits to the other part of the fuse box that is HOT with KEY-ON.
Using a new 12 gauge wire from the KEY-ON part of the fuse box is way overkill. The stock HEI only draws about 2 Amps and besides what is left after divvying up with everything else in the cab/truck, doesn't leave enough current to warrant another 12 gauge line.

GM never used a relay for the HEI and the original wire on the HEI vehicles connecting the bulkhead to the HEI Dist Bat terminal was 14 gauge.

[RichardJ]

I bought my GMC in '85. I was freshly divorced and it was my only insured vehicle and daily driver. Driving a lot of miles, the points change or cleaning and dwell adjusting was occurring way too frequently for my liking.
I installed a junkyard HEI. It started twice. I set the timing and put my tools away. It didn't start a 3rd time. I had wired it as above with a new wire and bulkhead connector.

The module was fried. I removed the by-pass (yellow) wire from the solenoid. I reinstalled the ballast resistor and connected it directly to the HEI.

It has been running with the ballast resistor powering the HEI since about 1989.
That original HEI was the coil-in-cap style. When I installed the AC, I switched to the '75 only external coil HEI for compressor clearance.

The truck will run 70-75 all day without a whimper and if i keep it at 65 it will get 15 MPG. It starts immediately and doesn't care that kind of **** I put in the back.

I have a 2018 RAM SLT 3500, but most days I drive the '67 GMC.

[Rustbuster]

You should check on YouTube for videos by Chris Craft. He has an excellent video on how to wire HEI distributor and tach.