1970 chevelle 454 burning thru points

Is 6.5 volts at the coil the proper voltage? This seems rather high to me. I remember that the old 6 volt cars dropped the voltage to 2 or 3 volts through a resistance in the primary circuit, usually a ballast resistor. I don’t know if the voltage to the coil was increased when manufacturers went to 12 volt systems. If you can find the specifications on the resistance wire, you may want to check is resistance with an ohmmeter to see if it is within specifications. Another thought might be to temporarily connect an old ballast resistor in series with the resistance wire and see what happens.

The condenser is another suspect. If the replacements have been sitting on the shelf for a long time, it’s possible that they could have broken down internally. One rough check on a condenser is to use an ohmmeter. Discharge the condensor and then put the probes across the condenser. It should start at a low resistance and then as it charges up, the resistance should become very high. Discharge the condenser with a screwdriver after this test before you pick it up.

Going back to Tester’s question, find out what the compression ratio is. Higher density in the fuel mix caused by very high compression changes the discharge breakdown voltage through the spark plug gap and is generally compensated for by increasing spark plug gap and using a high intensity discharge ignition system.

I too would beinclined to start with an oscilloscope and see what the discharge looks like. It should be a large sharp spike with a sweeping oscillating trailing trace. I can’t think of the correct terms right now 'cause I’m suffering with a headcold.

Just some thoughts.

I would suspect the coil drawing too much current. From my general knowledge of point ignition systems, I seem to remember that the closed point voltage across the coil should by about 9 volts. If the voltage across your coil is 6 volts the coil is drawing too much current so the ballast resistor is dropping the voltage excessively. Also the current may go even higher when the starter is engaged and the coil is switched to direct battery voltage (~9 volts DC). If you can get the specs on the coil current draw, you could measure it directly. If you can get a known good coil, try using it and see how the points last.

Hope that helps. Let us know what solves this problem.

This problem is bizzarre. The proper dropdown voltage is 6.5 volts and you are right the voltage will go up in the starter phase of the firing. As far as current draw and potential spike conditions the starter was replaced and the blower motor on the heating system was check for possible grounding effect. The only part that has not been replaced is the coil which maybe is bad but highly unlikely. i would like to keep the ignition original but may have to go hei which may be a gm hei if i can get it to fit (the car has cowl induction on it. This is such a simple circuit what could we be missing.

I know you’re probably trying to keep it original…but this is a GREAT candidate to MODERNIZE. Electric Ignition is well worth it. Put it in…get it set…forget about it until you sell the car.

If you do get your hands on an O-scope, post back with what the pulses look like. My gut tells me that will tell you what’s wrong. Besides, I’m highly curious as to what the trace looks like.

First step is properly checking the voltage at the ignition coil.
Probing both sides of the coil with the VOM is not the way this is done; neg probe to engine ground and pos. probe to the + side of the coil.
You should have 12 volts when cranking the engine and 6 volts when running. (approx.)

If the voltage comes out correctly then you need to consider a condenser change. Since you have material transfer to the stationary side this points to a weak condenser; as in bad construction or improper for the application.

Specifically, what happens when the points ‘burn up’? Lets say you are driving down the road and the problem manifests itself. What does the engine do – stumble, die, lose power? Are the points blued from overheating?

We get so many (what is the proper technical term…uuuummmh…crapola) substandard metal alloys from China, that that may be your problem. Make sure the points are made in any other country than China.

Did you install a high intensity coil as part of your rebuild, hi-spark coils designed for solid state ignition systems will kill a points system usually knocking out both the points and condensor in very few miles.

I had a points equipped 383 Mopar several years ago with exactly the same problem, the previous owner thought he was helping things by fitting a hi-spark coil. Swapping the coil for a standard unit specced for points fixed the problem.

My vote is also for the condensor. The build quality on condensors these days aren’t that good. An old-timer mechanic showed me a trick one time to greatly extend the life of points. He would get a handful of condensors and every time he filled up, he’d pop the distributor cap off and look at the points. If there was any build-up or burning at all, he’d clean 'em off and change the condensor. He’d repeat this process until he found a condensor that left the points clean. I did this on my '64 LeSabre about 5 years ago and I’m still on the same set of points with very little dwell wander. What was amazing to me is that one condensor would cause burning and pitting, but another one from the same manufacturer that was supposedly the exact same part would work great.

I’d suggest trying different brands of condensors and seeing if that helps your problem.

Is it possible that oil is working its way up the distributor shaft and somehow getting past the bushings and on the points? It is a remote possibility, but it might cause the problem you are having. I can’t believe with your total engine rebuilt that you would have excess crankshaft pressure that would force oil past the distributor bushing.

I am still thinking it is a condenser problem. I would put an ohm meter from the shell of the condenser to a good ground on the engine and make certain that the ohm meter reads zero resistance.

I agree with Triedaq. Make sure the condenser case is getting a good ground too discharge to. To see how much voltage is getting to the coil you need to check the voltage with key ON and the meter lead tied to the plus side of the coil, the meter common lead referenced to ground, and with the points shorted together (for a brief period only).

Whenever I have an odd ignition problem I look for other condensers like maybe one mounted on the coil or on the outside of the distributor. I don’t think you’ll find one but I have had good luck on Chryslers and Fords whenever I cut one off and the car runs a lot better. One thing that gets left off the engine is the ground wire from engine to firewall. It gets left off because it connects to the rocker cover.After that doesn’t work, I’m out of ideas.

Measure coil resistance cold and then hot (after the engine has run for a while) with the ohmmeter portion of a digital multimeter (DMM). Measure from one of the coil’s wire terminals to the other with one wire disconnected. Compare the resistance to a new, stock coil. Alternately you can measure the coil current with the engine off, ignition on and points closed. Short the ballast resistor out with a cliplead. Compare to a new coil. As the coil heats, the current should drop a little.

Otherwise, just buy a new stock coil and try that.

These meaurements are something to try if you find no other solution to the problem.

GO! HEI. please, this is getting OLD!

thanks!
maico

Someone has to be overlooking the obvious on that car. It can’t be that complicated.

thank you! door locks on a mitsubishi montero entail more than this OLD SCHOOL IGN SYS.please make the hurt stop. I beg OF YOU.you have had way more than enough answers.

maico

First, the suggestion to upgrade to HEI is a simple, effective and cheap solution. If determined to keep the points, an experienced mechanic with a scope should be able to find the problem. The voltages stated are well within spec. I will add this, if the ignition is ON and the engine not running with the points closed, they will soon become toast.

Try this site for replacing the points. www.pertronix.com Click on “ignition”, then choose either “Ignitor” or “Ignitor plus”. These are a very simple and dependable electronic system that uses your existing distributor. These systems work on a Hall-effect-type principle. I have had one in my '71 Chevy L-6/ 250 c.i. engine since 9/4/98. Not a single issue! Starts quicker, no burned points, no nothing except that it flat-out works! On your existing situation, I highly suspect 1.) an intermittently defective ballast resistor wire, 2.) are the coil wires hooked up correctly? I replaced my ballast resistor wire with a Chrysler-type ceramic ballast resistor that mounts to the firewall with a single, large sheet metal screw. End of burned-up points. But I got sick and tired of having to re-adjust the points every 10K miles so I swapped that system out for a Pertronix system.