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Discussion Starter · #1 ·
Hello all, have a problem with weak spark in a 289. Have replaced the solenoid, coil, cap, rotor, points, condenser, and plug wires and still the spark is weak (using a tester, and the light is dim but there is definitely some spark coming through). Any ideas on what to try next?

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Ugg, these are always fun,

well, like 07redstang mentioned, check the dwell setting which is related to the points gap. You need a dwell meter hopefully ya got one.
I don't exact rem what it was (.017) maybe? But I had better luck with the ol' matchbook cover, I know
on my old 71' coupe/302 auto, the matchbook worked better than what the book said. (the match book maybe was .015)?
AND PLEASE Check these settings I'm goin from memory here. But I think they are all the same points gap or close enough it'd work.

Make sure of the voltage feeding the coil and the points is right, I believe power to the points on my 66' last check was 3.5v thru the resistor wire.
The coil should be getting 12v
I remember that for certain because I was in the mist of converting it to a pertronix ignitor 2, after the first one failed. I realized the installer at the time used the incorrect power supply
as those ignitors need 12v for sure or they will fail over time, and it sure enough killed the first one.

If all the source voltage is good, this one can get you and fool you for sure - a bad ground connection(s).

The Battery to engine, to frame/body ground.

The 71' I had wouldn't even crank over but everything else worked, my brother said check your ground (I said huh? I was 17 at the time). He hooked a jumper cable to the NEG on the battery
and the other end to my bumper [to get a known good ground] and it started! - I was missing the engine to body/frame ground strap.

Not sure how much stuff you've "repainted" but that can affect grounds and cause weirdness.

I wouldn't think the spark plug cables were bad, but it sounds like we just don't have a good circuit for all of this to function. (too much resistance).

Check your source voltage, check/ clean / add a temporary ground strap(s) and see if it helps, it may help you find the culprit or at least provide enough ground to work.

I've had to do this on my 51' pickup to get the extra electronics to function well,
and even having the wrong size battery cables can get you in trouble here.
My 73' Vw and my buddy's 51' pickup (6v pos ground) both were fixed with installing the correct size battery cable and a extra ground strap to get the battery-engine-frame/body circuit working.

Well, Good luck with it and let us know how it goes!


6,575 Posts
I always remember the points gap as 0.017" because that is 1/2 of the spark plug gap of 0.034". Yes, this is related to dwell, but on Fords of this era you simply set point gap when the nylon follower is on the top of a cam lobe. GMs had a method of changing the point gap while the engine was running so were set using a dwell meter.

The points and distributor are in the same circuit so see the same voltage. The points are just a switch that goes on-off several times per second, triggered by the lobes on the distributor cam. When the ignition switch is on the "run" position, the coil gets power through a resistor wire that reduces the battery voltage by about 1/2, or 6 volts. While in the "start" position, the coil gets power from the starter solenoid with no resistor, for a hotter spark and easier starting.

If you have a weak spark, check the voltage at the coil during both start and run cycles. Verify zero resistance between the battery negative and the engine; clean/ repair the ground cable and connectors.

Remove the spark plugs and clean the threads, along with the cylinder head counterparts. A toothbrush and WD-40 works well for this. Hold your shop-vac at the cylinder head openings to prevent any debris from falling into the combustion chambers while cleaning. Anti-seize compound on these can create resistance so use it sparingly if you must. I prefer not using any.

Check for clean and connections at each end of each spark plug wire and the coil wire. They should "click" in snugly. Use a small amount of dielectric grease on each boot to seal out water.
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