67 427/435 stall.

[Richard S.]

Thanks for the previous assistance with this problem. This morning I tried to perform a distributor pickup coil test with my ohmmeter. With the ohmmeter connected across the distributor pickup coil leads the resistance should be between 500-700 ohms. With the ignition off and battery diconnected I get 001 on my ohmmeter. If I measure the the connector which is part of the engine wiring harness that the distributor pickup coil leads plug in to....I get 087.
The pickup coil test instructions say: Resistance infinite = coil open.
Resistance low = coil shorted. Then it says: ohmmeter connected to either coil lead to ground = ohmmeter should read infinite. When I connect to ground I get 1 on the ohmmeter. Not being experienced enough to know what I'm seeing can someone please help me out here. I don't even know if my small handheld ohmmeter is suited to diagnosing this problem or if it is even working properly. Thanks for the help......

[Joe R.]

Re: 67 427/435 stall.

Rick,

To check the pickup coil it must be completely disconected from the circuit. Same with the ignition coil. You should also double check your reading with another ohm-meter.

JR

[Craig S.]

Re: 67 427/435 stall.

Rick - as JR says make sure you disconnect the pickup coil leads (connector at dist with two wires, white, and white/green stripe). Also, if you don't have another meter handy, pick up a resistor at an electronic supply house or just walk in and they would be happy to verify your meter is reading correctly with a resistor in hand. Then you will know you are testing correctly.....Craig

[Richard S.]

Re: 67 427/435 stall.

Thanks...I had the connector apart when I did the test.

[Duke W.]

Re: 67 427/435 stall.

Checking each lead to ground is testing for a short to ground. The pickup coil must be electrically isolated. If the pickup coil is shorted to ground its signal is shorted out and the amp will not see the proper timing wave form, and the ignition system quits.

The basic test is to unplug the connector on the pickup coil pigtail and check for the specified resistance between the two leads, which should be the 500-700 you quoted from the CSM.

Then you check each lead to ground to verify that the pickup coil is not shorted to ground. Resistance should be essentially infinite. It looks like your pickup coil is shorted to ground.

Also I suggest you wiggle the pigtail vigorously while testing along with rotating the distributor base plate to simulate vacuum advance action. Your short to ground is probably intermittent based on the engine quitting and then firing up again.

Once you've verified a short to ground the next step is to remove and carefully disassemble the dist. doing tests and careful visual inspections along the way to determine, if possible, the actual physical cause of the fault.

I hate replacing parts without knowing the exact failure mechanism, or it might happen again.

IIRC your pickup coil is relatively new. It could be a case of infant mortality due to a flaw in the coil, or it could be an improper installation that lead to a premature short to ground.

Duke

[Richard S.]

Re: 67 427/435 stall.

Thanks for the help....the pickup coil is the original. It has not been replaced yet. Is there anything I can check or modify to eliminate the short to ground or is the only fix a distributor rebuild...which I could not do and would have to send out. The pig tail seems to be intact and not worn anywhere and no change in ohms when moved around.

[Duke W.]

Re: 67 427/435 stall.

Assuming the pickup coil is intermittently shorted to ground (or open), finding the actual physical fault can be very difficult because the coil consists of numerous windings of fine wire.

You mentioned wiggling the pigtail. Did you also excercise the vacuum advance as I suggested? I would continue to "stress test" the pickup coil until you find a reading fault. It may be that the problem only occurs when everything is at operating temperature, so take your ohmmeter with you, and if the ignition quits, immediately run the pickup coil tests while everything is still hot.

On the other hand, if the pickup coil is original, its age/operating time alone makes it suspect, so you could just go ahead and replace it, which will require removing and disassembling the distributor, which is not a complicated job, however, I would continue testing under all possible conditions and try to verify the short to ground or other electrical fault. Also carefully inspect/check all other connectors including ground paths.

I believe I mentioned the pickup coil failure on my Cosworth Vega's HEI, which is basically the same as in the TI distributor. The failure actually occured at Riverside while I was running an event. The engine momentarily quit and let out a huge backfire on the short chute between Turns 6 and 7 (My passenger thought the engine blew.) and then picked up again, but shortly after exiting Turn 7A the engine quit on the straight, and I was able to coast into the pits using the backstraight emergency entrance.

The first thing I checked was pickup coil resistance and it measured infinite, so within seconds I had identified the problem.

Intermittents are much harder to isolate, so unless you are willing to put up with the intermittent temporary failures until it fails hard, there is always a certain amount of guesswork identifying the faulty component, so you have to use system knowledge and any test results and go with the most likely possibility.

BTW the CV pickup coil failure was a broken wire right at the end of the coil wire where it becomes the external pigtail that connects to the switching module. The module also failed a few years later and earlier the external harness to the coil failed. All these failures were exacerbated by the severe vibration environment of a low mass high revving inline four. A V-8 vibration environment is much more benign, but it can still cause failures in the long run.

I now carry a spare HEI distributor and a 9/16" wrench in the spare tire drop center, so if it ever quits again I can swap the dist. in a few minute. The spare HEI dist. is even the same date code as the original!

These type of problems with electronic systems is why I will NEVER replace the breaker points on my SWC with any kind of electronic switching module.

Duke