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Old 10-26-2012, 03:42 PM
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SBC ignition problem

So I just got done rewiring a 76 corvette, and everything has gone smoothly until I went to start it. Now mind you; the car ran fine when I parked it at the beginning of summer and the only reason it was being rewired is because I had rewired it before when I was still learning and had a lot of poor craftsmanship. I used a generic painless universal harness. When I turn the key the engine cranks just fine, but i don't appear to have any spark. I checked the voltage on the +coil wire and it reads 12 V. I have the ground on the HEI going to the choke's ground on the carburetor (though I did also try a different ground when I was troubleshooting). From what I can see, everything is working the way it should but I can't see a spark either with the plug or with a socket shoved in the wire boot. So far I have swapped out the ignition module, cap, and coil but nothing has got it to fire. I've now become more certain that it must be my wiring, but I have no idea where to look next. An HEI only has 3 wires going to it correct? (tach, coil, ground?) I even checked the +coil wire's voltage as I turned the key to "start" to see if the voltage was cutting out of something, but no dice. Someone please help!



Hammer S

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Old 10-26-2012, 05:01 PM
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run a temp jumper from the pos post on the battery to the + terminal on the HEI...... try and crank it up, if it starts and runs you've got a wiring problem from the switch......

YOU WILL HAVE TO PULL THE JUMPER to kill the motor if it starts!
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Old 10-27-2012, 12:20 AM
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Quote:
Originally Posted by Hammerstein View Post
So I just got done rewiring a 76 corvette, and everything has gone smoothly until I went to start it. Now mind you; the car ran fine when I parked it at the beginning of summer and the only reason it was being rewired is because I had rewired it before when I was still learning and had a lot of poor craftsmanship. I used a generic painless universal harness. When I turn the key the engine cranks just fine, but i don't appear to have any spark. I checked the voltage on the +coil wire and it reads 12 V. I have the ground on the HEI going to the choke's ground on the carburetor (though I did also try a different ground when I was troubleshooting). From what I can see, everything is working the way it should but I can't see a spark either with the plug or with a socket shoved in the wire boot. So far I have swapped out the ignition module, cap, and coil but nothing has got it to fire. I've now become more certain that it must be my wiring, but I have no idea where to look next. An HEI only has 3 wires going to it correct? (tach, coil, ground?) I even checked the +coil wire's voltage as I turned the key to "start" to see if the voltage was cutting out of something, but no dice. Someone please help!



Hammer S
what was wierd is i learned something about the HEI and older coil in cap had a blue clamp running off a brown wire one of the three wires running to the cap.. It was a green wire, and i really dont know what this wire does. but i made sure that this wire was hooked up after changing distributors. its a blue clamp piece that joins the green and brown wire together by exposed wire, but this is based off my old chevy pick up around the same year.
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Old 10-27-2012, 06:21 AM
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You might want to check the magnetic pick-up. I had the same problem with a 78 SBC, but it wasn't HEI. It was running great when I shut it off. Then it wouldn't start. No spark.

Chris
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Old 10-28-2012, 08:42 PM
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Quote:
Originally Posted by chevy302builder18 View Post
what was wierd is i learned something about the HEI and older coil in cap had a blue clamp running off a brown wire one of the three wires running to the cap.. It was a green wire, and i really dont know what this wire does. but i made sure that this wire was hooked up after changing distributors. its a blue clamp piece that joins the green and brown wire together by exposed wire, but this is based off my old chevy pick up around the same year.
do you mean that one of the wires going the the HEI had a blue little clamp thingy, that has one go in and two come out? Because I found that on my old harness.
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Old 10-29-2012, 03:59 AM
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The little blue clamp thingy....... commonly called a "T" tap, it's used to splice one wire to another...... and to my knowledge not an OEM item on the dizzy.
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Old 10-29-2012, 10:31 AM
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Quote:
Originally Posted by Hammerstein View Post
So I just got done rewiring a 76 corvette, and everything has gone smoothly until I went to start it. Now mind you; the car ran fine when I parked it at the beginning of summer and the only reason it was being rewired is because I had rewired it before when I was still learning and had a lot of poor craftsmanship. I used a generic painless universal harness. When I turn the key the engine cranks just fine, but i don't appear to have any spark. I checked the voltage on the +coil wire and it reads 12 V. I have the ground on the HEI going to the choke's ground on the carburetor (though I did also try a different ground when I was troubleshooting). From what I can see, everything is working the way it should but I can't see a spark either with the plug or with a socket shoved in the wire boot. So far I have swapped out the ignition module, cap, and coil but nothing has got it to fire. I've now become more certain that it must be my wiring, but I have no idea where to look next. An HEI only has 3 wires going to it correct? (tach, coil, ground?) I even checked the +coil wire's voltage as I turned the key to "start" to see if the voltage was cutting out of something, but no dice. Someone please help!



Hammer S
I'm not following you on the choke ground wire. The choke heater is grounded through the choke housing to the carb body, intake, cylinder head, etc. on through to the battery, no ground wire needed. The only wire required at the choke itself is a 12 v current carrying wire.

The ground on the distributor is connected to the coil on one end and the body of the distributor on the other. The rest of the ground pathway is through the dist. body through the clamp and bolt into the engine block, etc. on to the battery eventually.

As for the power supply wire having a splice in it (if that's the case), I would caution you against using the coil power wire to run anything else. The HEI needs full battery current to work at its best.

Be sure there is a male terminal in the center position in the coil cover that mates w/the female 3-wire connecter/pigtail that's attached to the distributor. That's the ground for the coil. The way the ground is made, it can be accidentally left off. It will be either a wire or solid metal conductor running to one of the coil holddown screws. If it's left off, the coil will not be grounded.

Last edited by cobalt327; 10-29-2012 at 10:44 AM.
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Old 10-29-2012, 02:23 PM
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Originally Posted by cobalt327 View Post
I'm not following you on the choke ground wire. The choke heater is grounded through the choke housing to the carb body, intake, cylinder head, etc. on through to the battery, no ground wire needed. The only wire required at the choke itself is a 12 v current carrying wire.

The ground on the distributor is connected to the coil on one end and the body of the distributor on the other. The rest of the ground pathway is through the dist. body through the clamp and bolt into the engine block, etc. on to the battery eventually.

As for the power supply wire having a splice in it (if that's the case), I would caution you against using the coil power wire to run anything else. The HEI needs full battery current to work at its best.

Be sure there is a male terminal in the center position in the coil cover that mates w/the female 3-wire connecter/pigtail that's attached to the distributor. That's the ground for the coil. The way the ground is made, it can be accidentally left off. It will be either a wire or solid metal conductor running to one of the coil holddown screws. If it's left off, the coil will not be grounded.
When I said its grounded on the choke's ground, I was referring to a Summit aftermarket carb that has a 3-4 inch wire coming from the choke housing to another screw on the carb (grounding it to the manifold, cylinder heads, ect) I ran a wire from the center pin on the HEI (the ground) and ran it to that same screw to ground the coil, but its not appearing to be working. I then grounded it to the terminal on the alternator to be sure my ground was good, but had no luck. Everything says its a bad ground, but I can't figure out how it could be bad.
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Old 10-29-2012, 09:24 PM
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Quote:
Originally Posted by Hammerstein View Post
When I said its grounded on the choke's ground, I was referring to a Summit aftermarket carb that has a 3-4 inch wire coming from the choke housing to another screw on the carb (grounding it to the manifold, cylinder heads, ect) I ran a wire from the center pin on the HEI (the ground) and ran it to that same screw to ground the coil, but its not appearing to be working. I then grounded it to the terminal on the alternator to be sure my ground was good, but had no luck. Everything says its a bad ground, but I can't figure out how it could be bad.
OK, I understand.

Try connecting the 3-wire female pigtail coming from the distributor to the male connectors under the coil cover instead of running the ground separately. Be sure there are all three male connectors, and that they're also connected to the BATT and TACH positions of the coil cover.

If you have a tach attached to the TACH terminal, try removing the tach.
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Old 10-30-2012, 03:59 AM
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I'd run a temp jumper from the neg post on the battery to the neg terminal on the dizzy and see if it starts.

If it doesn't, I'd leave that one in place and run a seperate jumper from the pos post on the battery to the pos terminal on the dizzy and see if it starts. (You'll have to pull the jumper to kill it)

if it doesn't run "hot-wired" then you have an internal dizzy problem. When you did all that swapping out did you put the carbon coil transfer pin, It's that pin that connects the coil to the cap normally has a spring and a rubber washer and needs some di-electric grease on it.
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Old 10-30-2012, 07:28 AM
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You replaced the rotor, right? Don't laugh too hard- I once pissed around for a half an hour w/a no start condition ('68 Le Mans w/the Sprint engine) until I discovered the rotor in my shirt pocket and not under the cap!
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Old 10-30-2012, 12:09 PM
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Originally Posted by EOD Guy View Post
I'd run a temp jumper from the neg post on the battery to the neg terminal on the dizzy and see if it starts.

If it doesn't, I'd leave that one in place and run a seperate jumper from the pos post on the battery to the pos terminal on the dizzy and see if it starts. (You'll have to pull the jumper to kill it)

if it doesn't run "hot-wired" then you have an internal dizzy problem. When you did all that swapping out did you put the carbon coil transfer pin, It's that pin that connects the coil to the cap normally has a spring and a rubber washer and needs some di-electric grease on it.
Yea I got the transfer pin in there. I'll try running a jumper ground to the batt and sees what happens. And Cobalt: I used a universal harness, so I have no actual 3-pin connector to plug into the distributor. Just 3 separate wires (coil, tach and my separate ground. feel me?
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Old 10-30-2012, 05:56 PM
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Quote:
Originally Posted by Hammerstein View Post
And Cobalt: I used a universal harness, so I have no actual 3-pin connector to plug into the distributor. Just 3 separate wires (coil, tach and my separate ground. feel me?
If you are using a GM hei, there is a three wire pigtail or harness coming from the distributor that goes to the coil (red arrow below). It has the ground for the coil. Did you remove the ground wire from the hei pigtail/harness to be able to use your own ground wire?


Last edited by cobalt327; 10-30-2012 at 06:04 PM.
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Old 10-31-2012, 03:51 PM
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Originally Posted by cobalt327 View Post
If you are using a GM hei, there is a three wire pigtail or harness coming from the distributor that goes to the coil (red arrow below). It has the ground for the coil. Did you remove the ground wire from the hei pigtail/harness to be able to use your own ground wire?

I didn't remove it. But, so then here is my question: If that pigtail you showed is where you are supposed to plug the distributor into the harness, then what of the pins that are on the cap itself? There is the pigtail you showed, but there is also pins for the same thing on the coil/cap itself. I never used the pigtail before (just had the coil+ wire, ground, and tach hooked up to the cap) and it always ran fine.
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Old 10-31-2012, 06:31 PM
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Quote:
Originally Posted by Hammerstein View Post
I didn't remove it. But, so then here is my question: If that pigtail you showed is where you are supposed to plug the distributor into the harness, then what of the pins that are on the cap itself? There is the pigtail you showed, but there is also pins for the same thing on the coil/cap itself. I never used the pigtail before (just had the coil+ wire, ground, and tach hooked up to the cap) and it always ran fine.
The pigtail (white arrow below) plugs in to the coil/coil cover behind (as in closer to the coil) the main power feed and the tach terminal (blue arrow).

There's no need for a separate ground wire unless the distributor clamp and bolt that hold the distributor down on the intake manifold were insulated from the distributor body by paint or whatever.

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