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1973 Custom hatchback
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Discussion Starter · #1 · (Edited)
Having an issue with my 73.….I have not ben driving it much as I was working on it. but it seems to have always had this issue , in the back of my mind, but it seemed minor and sporadic. I fired her up and went for a ride and at WOT she would cut out, the tach( autometer) would freeze at various readings , like 4k. then she would come back to life, usually after, but not always, I let off the gas. SO it seems the HEI is loosing power, vice a fuel issue. My friend was with me and he said he got shocked getting out of the car...
I think I must have an intermittent ground in the + to the HEI circuit.
New HEI distributer, wires plugs etc. clean fuel and filter.
Yesterday I replaced the tach and + wire crimp on connections ( spade/ blade ) and added a Accel snap in connector ( PN 170072), thinking a vibration was loosening the + terminal at the Cap connection. Fired it up and connected my timing light. once warm the engine idled a bit rough, like it had a moderate cam , which it does not. and my eyes were burning some , although no smoke was visible from the exhaust. I attributed it to the PS header, which I painted with OER exhaust header paint and its burning off. DS I painted with rust oleum BBQ black and its fine. Now I think it was unburned fuel and the paint.....
Back to this issue. The timing light would fire correctly 4-5 times then skip...a beat. repeat. Next the idle smoothed out and went up to 1,000. I turned it down to 750 and base timing no vacuum was 10-12. about this time I realize that I have been adjusting the idle up and down frequently over the last few years.
I tried to check the timing at 4k and got around 34-36 initially. However when done I had 40 at idle. No idea whats up with that… borrowing my friends lite to check again tonight. Yes I checked 5 times and I'm on #1 plug wire. I shut her down and checked the cap rotor and weights , all good.
Then I started checking the + wire. For some reason it was routed towards the starter side vice the firewall.... eventually I found it doubled back and went in the firewall. all wires are wrapped in looms. I didn't find any problem yet with the wire, however in cleaning it the words "resistance wire do not cut" are visible. that explains why it was left so long.
I looked at my wiring diagram and :
The 6 and 8 cylinders came with different resistance wires, 1.35 ohms for the 8 and 1.80 ohms for the 6.
My car originally had a 6. now a 350.
Given my car was switched to HEI before I got it, does the resistance of the wire have any effect on the HEI?
IM thinking that the resistance wire was probably for condenser noise suppression?
SO I'm following the wire back to the ignition switch hopefully tonight. I intend to use my multimeter on ohms beep to see if the + wire is grounding as I move wires around. With key off yes .
I cant tell in my diagram: is there any of the ignition circuit up in the steering column or is it all in the plunger switch and the long flat connector under the column?

where is the ignition switch located?
Is the firewall plug and actual plug connection or just a sealed pass threw?
I order to access the plug from the inside does the fuse block need to be removed?
on the engine compartment of the plug the + wire is black with pink writing, and is resistance wire. Inside the firewall it should be a pink wire from the ignition keyed on switch.

Thanks for reading and for any replies.
 

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63 SS 350/700R4
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With the resistance wire you are only puting 9 volts to the HEI it needs the full 12 volts. Years ago I would get the GM HEI wire from a pick a part HEI car slide the old out of the engine firewall plug and slide the new in and put the harness back together. The getting shocked getting out of the car is part of a wiring ground problem somewhere?
 

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1973 Custom hatchback
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Discussion Starter · #3 ·
With the resistance wire you are only puting 9 volts to the HEI it needs the full 12 volts. Years ago I would get the GM HEI wire from a pick a part HEI car slide the old out of the engine firewall plug and slide the new in and put the harness back together. The getting shocked getting out of the car is part of a wiring ground problem somewhere?
Thanks man!
IDK about the shock thing, never happened before. but the car was running and I normally shut it off before I get out. could have ben static.

Ill check voltage at the wire with key on... that would be a PITA to get to the plug but well worth the effort to replace the wire. So there is specie HEI wire? seems like I could just use 12 ga wire as that's what used in the inside of the firewall for this circuit.
 

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63 SS 350/700R4
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You can wire it for 12 volts any way you want. My wiring skills are sort of good but not excellent. So when ever I can I try to stick with the way the General intended.
 

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Discussion Starter · #5 · (Edited)
Researching more: I will tap into the ignition circuit either in the firewall,, by removing the resistance wire from the 45 year old plug , which I doubt as its a PITA to even see, or in the dash tap into the pink wire 12 ga., run a 12 ga. wire to the HEI and add an inline fuse. Ten amps seems to be the recommendation for the HEI circuit. Otherwise there is no protection.
Anyone agree disagree with the fuse size?

What kind of connector is used at the firewall for the ign wire? any tricks n how to replace it? as that would e the cleanest way to do this job, despite what I said above.
 

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Mike - 74 Nova Baltimore, MD
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You definitely DO NOT want to connect the HEI distributor to a resistance wire.

When I installed my HEI, I ran a 10 gauge wire from the ING (ignition) spade on my fuse box directly to the BAT terminal on the HEI cap.
417679

If you go this route, be sure the ING spade at the fuse box is hot (12 volts) in both the "START" and "RUN" position when turning your ignition key... and NO voltage when the ignition key is in the "OFF" or "ACCESSORY" position.

If your engine issues continue after rewiring the HEI to full voltage (12+ volts), you may want to replace your HEI's ignition module. I like the NAPA TP45. Be sure to also install some heat/thermal compound to the bottom side of the module before installation... DO NOT use dielectric grease on the bottom side of the HEI module.
  • Note: If you have trouble finding heat compound, just use the same heat/thermal compound they put on the underside of a computer's CPU chip. Just apply a very thin coat... not much is needed.
 

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Discussion Starter · #7 ·
Thanks Mike!

The resistance wire has been providing voltage to the HEI since well, forever. Actually since the 2x PO swapped the 6 for a 305. then the PO put in the 350 that is there now. No one checked the wire until I did last night. I was looking for a ground. cleaned wire , read the lay line: resistance wire, do not cut.......light bulb went off..... but dimly as it only had 9v LOL.
I may try to remove the wire from the firewall connection and replace it there, and add a fuse, or do what you suggested

I understand about Keyed on / start and the problems starting that can occur. l check as yu describe

Your picture well 1,000 words. I do like the idea of taping into a fused circuit. Ill see how far I get over the next few days. I expect the outcome to be marvelous! 100 hp. increase, smooth idle, no more cutting out, 12.2 @ 112 MPH and maybe 5 more MPG....
 

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You can also use a 4 or 5 spade 30amp relay if you dont want to cut up the harness. 10 guage wire from battery to relay, 10g to hot on distributor, use the original resistor wire to "on" spade of relay. I used sell a lot of those for guys converting to HEI 20 years ago...( been a parts guy for almost 30 years..)
 

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1970 Nova SS 350 Brandon, MS
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The firewall connector is 3 pieces and plugged together. The engine side of the connecter is 2 plugs held to the interior side with one bolt. Remove the bolt and you can pull forward on the 2 plugs to disconnect them from the main block that is on the interior side.

the ignition switch is mounted on the column (top maybe?) between the dash mount and firewall. It has a rod actuating it via the key cylinder.
 

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Another thing to complement this is to Check Your Engine Grounds. Very Important that the engine is grounded to the frame.

I also used the Switched Fusebox Terminal.

Question: do you have headers? I fought mine for quite a while for burned spark plug wire boots until I learned that there are header plugs that pretty much help solve that issue.

I have a '73 as well, in Middle Tennessee. Pretty much stock. Maybe.
 

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The resistance wire has been providing voltage to the HEI since well, forever.
It might have but just like people having to add relays for headlights to make them brighter, the same problems could be occurring in your ignition system with voltage drop due to corrosion, age, whatever. If before through the resistance wire you had 9V on the end with let's say 14 volts off of the battery and alternator when running, poor connections could then be dropping the 14 volts down to 7 volts and then the HEI started not liking this voltage as well.

Jim
 

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Discussion Starter · #12 ·
Update:

Well this totally sucked. HEI wires and plugs are new. HEI is from Jegs, PN 555-4005.
Short version I went to the auto parts store and got 12 ga. auto wire. I got sexy yellow to match my plug wires. Soldered connection and heat shrunk at the engine compartment and crimped connection at fuse box, after checking for 12v at run and start position. Thanks rif raf. Fired right up. I set timing 10-12 deg. BTDC no vacuum idle 750. The miss was gone. I decided to run the car with and w/o vacuum and see which one I liked best.

I hooked vacuum up and it went to 30 deg. BTDC.....HMM rev to 4k and I get a scary 40 deg. total. Total advance is adjustable vacuum is not separately.

I went for a test run. slight bucking at part throttle and really not liking WOT above 4k( as before only not as bad). It would cut out briefly, almost like hitting a rev limiter. Got gas drove home. Volts meter reads just shy of 14 when running.

I removed vacuum hose and plugged ports, test drive. Same issues, only she started puking and dying and backfiring worse and worse and died. After a few minutes she fired up sputtered and died within a quarter mile. AAA only a 45 minute wait. Called friend because you can’t ride in the tow truck and I don't have uber app.

Got car home and tried to start, no spark. I tested and have 12v at the HEI + and the connection in the fuse box is tight.

I'm thinking The HEI was damaged somehow either due to the low voltage or maybe it was dropped etc.

I am looking into HEI troubleshooting, but I started by going to NAPA for lunch and picked up a NAPA TP-45, Thanks again RIF-RAF. I’d really like to figure out the issue vice replace parts, but this is the obvious fail. Maybe not the root cause but the module is not working. . when I got home I did not try to start the car, in hindsight, maybe I should have, just to see. I replaced the module ( yes on the heat paste) and she fired right up. No miss no skip. 35 deg @4k . I did not take a test drive as it was 530 on Friday and traffic near me sucks. Also no one was home to come get me if it failed again.

HEI failures. From the research I have been doing, it seems low voltage would not damage the module. Most failures seem to come from errant voltage feeding in from the tach wire, and or bad grounds.

I ran a few tests and no voltage at the tach wire, key off or on. that's good. No continuity to the engine block or to the battery( Tach wire disconnected from the HEI). I will run some more tests and push pull on the tach wire as I trace it and follow it home. . I also am concerned about the slight static? Shock my friend said he got last week and I got later. Both times the engine had just ben run. Both times it was after opening the door and standing on the ground. When he got shocked the engine may have ben running, we just went for a ride. I stopped to let him out in my driveway. When I got shocked I just shut the car off in my garage and got out. I had crocks on. So open door while sitting let go of door stand up grab top of door to shut it and get shocked. Doesn’t happen every time, seems to be a new thing, could be static.

I also am looking at the chassis/ body to engine ground and the engine to battery. I will clean and check both also look into replacing the engine to body ground strap.

Sunday I found a black gooey mess under the rear of the car. I have ben smelling an odor of old gar/ asphalt. I delayed dropping of the fuel tank so I could drive the car… when I got gas last week I filled it enough to find the leak. I t looks like the front seam was sealed with some black sealer and the gas dissolved it and made a nasty gooey sticky mess. I cleaned it up and slid a pan under the car. Then I walked over to my Harley and went for ride.
I'll have plenty of time to clean and check the grounds etc. while waiting on a new tank.
 

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Mike - 74 Nova Baltimore, MD
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Hope the new TP45 module fixed your HEI misfire issues.

I agree that you should connect the vacuum advance to a full-time vacuum source (manifold vacuum)…. but you may need to add a "Vacuum Advance Stop Plate" to your HEI.

Most Chevy small blocks like around 24-26 degrees BTDC of timing at idle, but that would create some difficult engine starting issue if you set your initial mechanical timing that high. So the best way to achieve the desired 24-26 degrees of advanced timing is to set your initial mechanical only timing anywhere between 12-16 degrees BTDC at idle (based on your cam) and provide the rest of advance with you distributor's vacuum advance canister when it is connected to a full time vacuum source.

The issue is that many adjustable vacuum advance canisters can provide 20 or more degrees of advance and require a vacuum advance stop plate to control/limit the amount of advance when the VA is connected to a full-time vacuum source.
Below is an image of the MSD 84281 vacuum advance stop plate that I installed on my HEI (red arrow). This type of stop plate is very easy to install on an HEI.
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Depending on where you set your initial mechanical advance, you would then limit your vacuum advance to around 10-14 degrees. If not, you could be seeing 32+ degrees of timing advance at idle with the vacuum advance connected to a full-time source.

The vacuum advance stop plate should also help if you are experiencing any "bucking" or "surging" (sometimes referred to as trailer hitching) while cruising.
 

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Discussion Starter · #14 ·
Thanks man. I'm concerned to the root cause of module failure as the HEI distributer is new both in age and use. I was thinking about the vacuum stop , that's exactly what I am looking for. I ordered new grounding strap for the chassis to engine and will clean/ tighten all ground connections before I run it again, as well as check and follow the tach input wire home. As always much appreciate your advice.
 

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Also have a good hard look at the wires from coil to the module and where they pass though the distributor for any damage. Come to think about it never come across or known of a bad capacitor in a HEI but it could be? as I have had issues with them in a points system????
 
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