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Edit: Cleaning and setting the points did the trick, along with a new distributor cap, plugs and plug wires. Just got the car started for the first time in about 14 years!
Can someone tell me what the lead in the attached image is for in the distributor? I cannot find any information for it in the chassis manual.
I'm trying to diagnose no spark to the plugs so I'm checking everything.
Coil seems to test fine (ohms) on primary and secondary windings. Coil is getting 12v power from the starter. The small guage lead that goes from the coil into the distributor points is getting 12v.
Distributor rotor is turning when the engine is turned over.
I've replaced the distributor cap because it looked corroded. I've also replaced the plug wires and large lead from coil to distributor cap.
Last edited by ProfVanNostrand; January 1st, 2023 at 02:48 PM.
The wire that the red arrow is pointing to is a ground lead. Make sure you have a correctly gapped set of points and a good condenser. As the points open and close, it is supplying the ground side of the circuit.
X2, it grounds the breaker plate, the plate the points and condenser mount on. Do you have spark out of the coil into the center of the cap? Coil wire check out ok?
X2, it grounds the breaker plate, the plate the points and condenser mount on. Do you have spark out of the coil into the center of the cap? Coil wire check out ok?
Good luck and please post the solution.
I get spark out of the coil doing a "bench" test. Which coil wire are you referring to? If it's the one that goes to the points, I get 12.5v when the key is on.
The secondary high voltage out of the coil to the center of the distributor cap. If you get spark out of the coil but not out of the wire the wire is bad. If you get spark into the distributor but not out to a plug then its in the cap or rotor. Did you check for spark at multiple plug wires?
To expand on the original question, the points open and close the circuit from the primary winding of the coil to ground. The points bolt to the point plate. That plate rotates on greased bearings in response to the vacuum advance can. Since greased bearings are not a reliable ground path, GM added that wire to ensure a low resistance electrical path from the point plate to ground. Note that one end of the wire is spot welded to the underside of the point plate. The terminal being pointed to in your photo is the other end of the wire that is grounded to the distributor housing through that screw (the primary function of that screw is to retain the vacuum advance can, but it threads into the distributor housing). The distributor housing is grounded to the block through the clamp and clamp bolt. For max spark voltage, all of these connections need to be clean and shiny. Here's a shot of the underside of the point plate showing the wire spot-welded in place.
The secondary high voltage out of the coil to the center of the distributor cap. If you get spark out of the coil but not out of the wire the wire is bad. If you get spark into the distributor but not out to a plug then its in the cap or rotor. Did you check for spark at multiple plug wires?
I got new plug wires and it came with a new wire that goes from coil to distributor. I get spark out of that high voltage lead when I test it using direct wire from the battery (what I would consider a bench test). I'm using a new distributor cap because the old one was corroded and I thought that was the issue.
To expand on the original question, the points open and close the circuit from the primary winding of the coil to ground. The points bolt to the point plate. That plate rotates on greased bearings in response to the vacuum advance can. Since greased bearings are not a reliable ground path, GM added that wire to ensure a low resistance electrical path from the point plate to ground. Note that one end of the wire is spot welded to the underside of the point plate. The terminal being pointed to in your photo is the other end of the wire that is grounded to the distributor housing through that screw (the primary function of that screw is to retain the vacuum advance can, but it threads into the distributor housing). The distributor housing is grounded to the block through the clamp and clamp bolt. For max spark voltage, all of these connections need to be clean and shiny. Here's a shot of the underside of the point plate showing the wire spot-welded in place.
Nice explanation. As you can see from my picture it's pretty dirty in there. I'm wondering if a bad ground is part of my problem.
I got new plug wires and it came with a new wire that goes from coil to distributor. I get spark out of that high voltage lead when I test it using direct wire from the battery (what I would consider a bench test). I'm using a new distributor cap because the old one was corroded and I thought that was the issue.
Need more info about the direct wire, I'm assuming the 12v to the coil positive terminal. How are you firing the coil?
Need more info about the direct wire, I'm assuming the 12v to the coil positive terminal. How are you firing the coil?
^^^THIS. You can test functionality of the coil by hot wiring 12V to the "+" terminal and intermittently grounding the "-" terminal (which is what the points do). If that works, the coil is good. Now try it with the distributor. Again, you just need the points to open and close, you don't need the cap in place at this time. If there's a spark from the coil wire to ground, that's all working. If not, figure out why the circuit from the coil "-" terminal to the points to ground isn't functioning. Use a voltmeter at the "-" terminal of the coil. With the points open you will see battery voltage when the points are open and 0 when they are closed.
Need more info about the direct wire, I'm assuming the 12v to the coil positive terminal. How are you firing the coil?
Originally Posted by joe_padavano
^^^THIS. You can test functionality of the coil by hot wiring 12V to the "+" terminal and intermittently grounding the "-" terminal (which is what the points do). If that works, the coil is good. Now try it with the distributor. Again, you just need the points to open and close, you don't need the cap in place at this time. If there's a spark from the coil wire to ground, that's all working. If not, figure out why the circuit from the coil "-" terminal to the points to ground isn't functioning. Use a voltmeter at the "-" terminal of the coil. With the points open you will see battery voltage when the points are open and 0 when they are closed.
This hotwiring method is what I used to test the coil. I have not tried it while connected to the distributor. I will try this next. I have also cleaned the points since my last attempt so maybe that will help also. I also bought a new coil, points, and condenser today to have over the holiday weekend as a last resort.
I've experienced bad/fouled plugs exhibiting the same no-spark condition.
Everything bench tested yet still no spark using an inline spark tester down at the plugs. How they got fouled is another story.
New plugs varooommm fired right up.
Don't forget to examine the negative wire where it threads up through the distributor.
Over time and with age it will fatigue from normal vac advance/breaker plate movement.
The wire becomes intermittent and then will eventually completely fail as an open circuit.
I'd pull that distributor and give it a good overhaul/cleaning/relube. Much easier to work on it on the bench.
Remember to keep the new points (contact set) clean.
No grease or dirt from a dirty feeler gauge is allowed.
Grease dirt oil will drastically reduce contact set life.
Verify your engine has a good clean ground from the battery negative and other grounds mentioned.
I've experienced bad/fouled plugs exhibiting the same no-spark condition.
Everything bench tested yet still no spark using an inline spark tester down at the plugs. How they got fouled is another story.
New plugs varooommm fired right up.
Don't forget to examine the negative wire where it threads up through the distributor.
Over time and with age it will fatigue from normal vac advance/breaker plate movement.
The wire becomes intermittent and then will eventually completely fail as an open circuit.
I'd pull that distributor and give it a good overhaul/cleaning/relube. Much easier to work on it on the bench.
Remember to keep the new points (contact set) clean.
No grease or dirt from a dirty feeler gauge is allowed.
Grease dirt oil will drastically reduce contact set life.
Verify your engine has a good clean ground from the battery negative and other grounds mentioned.
I have new plugs in it currently and I've been testing with both the old and new just to be sure.
I'm trying to avoid pulling the whole distributor out because it looks/sounds like it's hard to get it back in the exact location it was in prior to pulling. Not saying I won't get to that point, but I'm trying everything I can with it in place.
X2, it grounds the breaker plate, the plate the points and condenser mount on. Do you have spark out of the coil into the center of the cap? Coil wire check out ok?
Good luck and please post the solution.
See my edit in the original post for the solution. Edit: Cleaning and setting the points did the trick, along with a new distributor cap, plugs and plug wires. Just got the car started for the first time in about 14 years!
For those curious here are my coil voltages with details of key position and points open or closed.
Those numbers all look good - well, there's still some resistance in the ground side, but workable. This would be a good addition to a troubleshooting sticky.
Do it Mr Moderator! Agreed on good visual troubleshooting.
Professor, did you verify the neg battery to engine block connection? There should be a 10gauga wire coming off the battery terminal of said neg wire which attaches to the radiator core support. If not there get the correct replacement neg cable. There should be a braded ground strap from the rear of one of the heads to the firewall. Install one if its missing.
Also, loosen the dist just enough so it moves and rotate it back n forth to induce a clean ground contact between the dist & block, (Take a timing reading beforehand to get back to square one).
Do it Mr Moderator! Agreed on good visual troubleshooting.
Professor, did you verify the neg battery to engine block connection? There should be a 10gauga wire coming off the battery terminal of said neg wire which attaches to the radiator core support. If not there get the correct replacement neg cable. There should be a braded ground strap from the rear of one of the heads to the firewall. Install one if its missing.
Also, loosen the dist just enough so it moves and rotate it back n forth to induce a clean ground contact between the dist & block, (Take a timing reading beforehand to get back to square one).
I haven't removed the negative battery cable to engine block but I see where it connect behind the power steering pump.
Is the wire in the image below the other one you are referring to? It's probably a 10g.
It's disconnected currently along with several other chewed/cracked wires and loose vacuum lines. A raccoon was living under the hood and so have several cats over the years.
The ground wire from (-) battery terminal to chassis (at the radiator support) is not hooked up to the (-) battery terminal cable in your picture. It appears to be just dangling (or, at least not hooked up - can't see its end in your picture). Sorry for the poor image (below) of the 1969 diagram, but it's going to be same location for 1970 & 1971 (which are better images). Each image was taken from each respective year of the PIM. It's important that ground wire is attached to the (-) battery terminal to supply a good ground to chassis.
Did you find the ground strap from the back of the engine block to the firewall?
1969 (-) Battery Terminal Cable to Chassis 1970 (-) Battery Terminal Cable to Chassis 1971 (-) Battery Terminal Cable to Chassis
The ground wire from (-) battery terminal to chassis (at the radiator support) is not hooked up to the (-) battery terminal cable in your picture. It appears to be just dangling (or, at least not hooked up - can't see its end in your picture). Sorry for the poor image (below) of the 1969 diagram, but it's going to be same location for 1970 & 1971 (which are better images). Each image was taken from each respective year of the PIM. It's important that ground wire is attached to the (-) battery terminal to supply a good ground to chassis.
Did you find the ground strap from the back of the engine block to the firewall?
1969 (-) Battery Terminal Cable to Chassis 1970 (-) Battery Terminal Cable to Chassis 1971 (-) Battery Terminal Cable to Chassis
The grounding strap is there and connected but I can't tell how clean the connection is. Seems like a real pain to try to get lose and reattach.
The grounding strap is there and connected but I can't tell how clean the connection is. Seems like a real pain to try to get lose and reattach.
I'll offer up what others are going to tell you and which you already know. The "ground" side of your electrical system is the most "important" aspect to your "entire" electrical system. A 53 year old ground strap (which looks in modestly good condition) is critical. Try your best to clean both ends of that block-to-firewall ground strap (including the previous ground wire which is not connected in my previous image/diagrams).
I'll mention this as it relates to the importance of the ground side of a car's electrical system. Electrons flow from the (-) battery terminal to every single point on the vehicle and these electrons return to the (+) battery terminal. Any impedance to electron flow will increase resistance.
I'll offer up what others are going to tell you and which you already know. The "ground" side of your electrical system is the most "important" aspect to your "entire" electrical system. A 53 year old ground strap (which looks in modestly good condition) is critical. Try your best to clean both ends of that block-to-firewall ground strap (including the previous ground wire which is not connected in my previous image/diagrams).
Adding to Norm's post, this is a picture of the block to firewall strap. They are not that expensive, just replace it with new, and as Norm pointed out pretty critical to your electrical system,
I'll offer up what others are going to tell you and which you already know. The "ground" side of your electrical system is the most "important" aspect to your "entire" electrical system. A 53 year old ground strap (which looks in modestly good condition) is critical. Try your best to clean both ends of that block-to-firewall ground strap (including the previous ground wire which is not connected in my previous image/diagrams).
It was a challenge but I got the ground strap off, cleaned all connections, and put it back on. The ground strap itself was still in good shape (no breaks or fraying).
It was a challenge but I got the ground strap off, cleaned all connections, and put it back on. The ground strap itself was still in good shape (no breaks or fraying).
December 31st, 2022, 09:59 AM
