brown7373

I have been dealing with an ongoing problem with my 72 350 4bbl engine. Recently, I suspected a bad Pertronix module, so I replaced the whole distributor with a brand new rebuilt points distributor from NAPA that I had on my shelf. I ran fine for a couple days with no issues. Then it started bucking and missing, became almost impossible to start and keep running. But if I got it started, it would smooth out and idle fine, but even slight acceleration caused it to buck and miss, then stop running and would fire intermittently but not start.


Here is my issue. When I swapped distributors, hooked up the wires, including the full time 12 volts that was added for the Pertronix. Would the full time 12 volts fry my points or condenser and cause my problem?

Fun71

Yes, full 12 Volts will cause pitting of the points. You can install an inline resistor to drop the voltage to the correct level. Your local auto parts store should have one:

Ballast Resistor

Another one


And yet another

You might be able to dress the points with some 400-600 grit sandpaper to smooth the contact surfaces and get them going again instead of buying a new set. Back in the day folks had a points file in their tune up kit along with feeler gauges and dwell meter. Kind of a lost art these days.

Hawghead

On a points distributor the only thing going to the distributor should be the a wire from the negative side of the coil. If you have a constant 12VDC at the positive side of the coil, then yes, it can ruin the coil.

Scott

oldcutlass

Also check and make sure that there was not an over abundance of grease on the wear strip for the points that may have migrated into the points. The others pretty much covered the voltage requirements on the pos side of the coil.

Oldsmaniac

Maybe check to see that no wires are getting grounded on the plate that holds the points inside the distributer. Is not the original wiring there that was original to the car with the resistor wire?

brown7373

It was a total oversight on my part. I have run Pertronix for years, and swapped distributor as a trouble shooting test, and just reconnected all the wires.

rustyroger

You should only have an ignition live to the distributor, maybe two with one routed through a ballast resistor.
Apart from anything else a permanent live will drain the battery if the engine stops with the points closed.


Roger.

MDchanic

Okay, I have the impression that your car had a running problem (which you didn't specify), you swapped distributors to see it that fixed the problem, it did fix the problem, but then within a few days, the car developed a new and different problem, which involves crappy running and hard starting.

First: What was the initial problem that you solved by swapping the distributor?

Second: Have you rechecked the dwell and timing?
All of your current problems can be caused by the dwell being off.

As for running a full 12V to points and a stock coil: Yes, it will eventually lead to problems, but I doubt it would lead to problems this quickly. The primary problem would be overheating the coil, but pitting the points is also possible.
It's easy enough to check the points: Just connect your Tach/Dwell meter and read the "Points" scale, following the meter's instructions - it will tell you whether the points are bad.

While filing the points will "get you down the road," it is not recommended on point sets after the '40s or '50s, because they have a thin plating designed to increase durability and decrease pitting. If you file through that, they will burn up much more quickly.
Sanding points is one of those "universal no-nos" that all manuals warn about, because it changes the contour of the points and will really do them in.
Have I done it? Yes.
Am I proud of that? No.
Would I recommend it? No, unless it's a real emergency or it's a flat-out experiment, like starting a junkyard motor.

- Eric

garys 68&72

Yeah, you probably cooked the coil. Replace that first. Add a ballast resistor to your switched ignition source.
In addition, if you eliminated the ballast resistor bypass wire (yellow?) with the pertronix, the one from the starter solenoid to the + post of the coil, you'll want to hook that up too. It will make starting much easier.

brown7373

Okay. I changed the points and condenser and the car started perfectly when I turned the key. It was on fast idle, kicked down and then ran perfectly and is still running perfectly.


The original problem was the cruise was abruptly shutting off, like I stabbed the brake, only more abrupt. I thought I had a cruise problem. But it got worse and started doing the same with cruise not engaged. It was a sharp, abrupt miss. It continued to get worse, and I suspected the module in the Pertronix. Since I had a new rebuilt points distributor on the shelf in my garage, it was an easy way to replace and see if that fixed it. But I guess I wasn't thinking, because I just hooked up all the wires, including the full time 12 volt. I KNOW points don't get that, but I had a brain fart. But the car ran perfectly again so I thought the module had gone bad. But after a couple days, it started missing again, but this time it got so bad that I couldn't get it to get up to 35 or 40 mph. And it shut off 1/4 mile from my house and wouldn't start. It was like it was firing out of order, or something was shorted. I tried to start it the next day, and it acted like it was flooded and firing out of order. I did manage to get it started, it smoothed out and then idled fine. But when I went to test drive, even very light pressure on the accelerator pedal caused the bucking and missing, so I managed to get it home.



Today, after this thread confirming my suspicions that I fried the points or condenser. The replacement points and condenser solved the problem. Hopefully it won't start doing this again in a day or two.


Before someone suggests that maybe the firing order is wrong or the distributor not installed correctly, the wired haven't been changed in a few years and lots of miles, and the distributor and rotor were installed exactly the same as the one that came out. And it is currently running perfectly, like it always has, except for the past week or so. I did put a new coil on a few months back, but not since the 12 volt fiasco, but it seems fine.

Fun71

So is 12 Volts still running to the coil, or did you install a ballast resistor?
With no resistor you are risking the same thing happening again. Remember, the factory used a resistor (wire) for a reason - to prolong points life!

grampy

This is where aftermarket has the cure.go to a point to electronic conversion. It worth it! A point set up needs 20 to 30 thousand mile replacement back in the day.a hall effect devices are more consistant.if not over heated they last almost for ever.just keep a good cap rotor and wires on it.

Fun71

Wow, you must have missed the second sentence of the first post where he said he suspected an issue with his Pertronix so he put in the points distributor for troubleshooting the issue.

grampy

My bad the unit he is using aftermarket or was using one. I go lost when he said he changed the points and condenser. I thought he was useing a msd like spark unit with points.I have only used crane replacements because they have them for oddball engines.

brown7373

When I bought this car in 2007, it already had the Pertronix installed and it seemed to run fine. I have put many thousands of miles on it. The previous owner had installed the additional 12 volt wire to the unit. I have never done that with the half dozen or so cars I have owned with Pertronix units.


My car has the original wiring to the distributor. From the engine harness, a black & pink stripe resistor wire and a yellow wire that are together on one connector. The mistake I made when I put in the points distributor was to hook the 12 volt wire that had been added for the Pertronix. That, apparently destroyed the points or condenser. Now, after a new set of points and condenser, and disconnecting the 12 volt wire, the car runs great again.