Erratic spark in distributor

[Barber31]

What would cause erratic spark? Thanks to my recently acquired clear cap I can see the spark from the rotor is clearly all over the place. From good bright sparks to barely seen weak ones and not always in the same places. My first thought would be coil but maybe something inside the dist. could cause that as well?

[Barber31]

I forgot to add all four are firing just not very well.

[Mike V. Florida]

Poor repro distributor body and/or cap. Un equal gaps at the points in the body. Dirty points, bad condenser, bad grounds, bad spring on the rotor..

[1931 flamingo]

Basically what Mike said.
Paul in CT

[Greg Jones]

Do you have the Ford V8 "modern" points? I had similar problems with them, particularly the brass bus bar that makes contact with the lower plate. I would recommend using the original points plate with the point block.

[Barber31]

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I think I have the modern ones. Ill clean the points and replace condenser. See what happens. Thanks.

[BILL WILLIAMSON]

A check for poor point contact due to oxidation/pitting/etc:
With distributor body, cap, rotor off, plugs out, battery fully charged, & coil wire grounded to a head bolt.
In the DARK, if possible, observe the flash at the points, while a helper gives it a LOOOOOONG crank.
The flash at the points should be a consistant, barely discernable, BLUISH/WHITE flash. If it is inconsistant or occasionally flashes out YELLOWISH/ORANGE, the points need cleaning or replacing. After this test, remove the coil wire from the coil, spin it over again & see if the spark jumps THROUGH the coil tower to the primary terminals, like the tower "may" be cracked or have carbon tracks.
If you gotta' REAL HOT coil, like Purdy runs, spark MAY JUMP out of the tower hole & down the side of the tower to a primary terminal, THIS IS NORMAL, FOR A REAL HOT COIL, SOMETIMES!!
This may sound like a LOOOOOONG test, BUT it just takes a few minutes, in reality.
Bill W.
(Question: Original points have a LARGE contact on the point arm & a small contact on the adjustable part, does this help the problem of the points developing a PEAK & a POTHOLE?)

[Barber31]

Just checked and cleaned the contact points. They were dirty. Ill get back on it and crank it over tomorrow. Don't wanna wake the wife and kids up.

[Tom Wesenberg]

Also make sure the plugs are clean and evenly gapped. I never use coil wire covers on the ends of the wire, as they can trap moisture and cause problems. I've seen it happen, and the original didn't use covers.

I would NOT use the wireless top plate. They are a problem from the start, or a problem waiting to happen on the road.

[gweilbaker]

Also clean the inside of the distributor body as well, could be some carbon dirt playing havoc too.

[johnbuckley]

add to the possible causes micro- crack in body, micro- crack in rotor

[MikeK]

I blame the clear dizzy cap. You certainly didn't see any misfiring with the original cap in place.

Terrible aftermarket part! Ruins the 'Don't do any maintenance 'til broken.' scheme on which many A's are operated.

Original cap: HAPPY. Aftermarket clear cap: WORRIED. Seems simple.

[Mitch//pa]

i rather just use this inline spark tester, can be driven with it on shows spark intensity and int spark problems..i also have 2 long ignition wires so i can drive the vehicle with hood down and the spark tester below the w/shield.

agree with MikeK on above post garbage and you cant see it while driving which is very important in diagnosis

[Mitch//pa]

barber as mentioned if your using one of these wireless plates in your dist get rid of it. if it is not the problem now, one day it will be

[newshirt]

Worn distributor bushing?

Prepare to adjust the points by removing the distributor cap, body, and rotor. Grasp the distributor cam with your thumb and forefinger, and attempt to rock or move the shaft back and forth. There should be no discernible movement laterally. Any movement indicates worn bushings and/or shaft. The distributor will still function, but the point gap will vary by a corresponding amount. Keep in mind the recommended point gap is .018"-.022", not .013"-.027"!

Try taking points readings on all four cam lobes. They should be nearly identical.

Full article courtesy of Marco Tahtaras:
http://www.abarnyard.com/workshop/timing.htm

[ltdann]

Try tightening the armored ignition cable to distributor interface. Excessive engine vibration caused mine to back out of the distributor and cause intermittent spark