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By Lanny White - 4 Years Ago
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I must be Dunce of the Day! Is there a simple, on car, test for the coil without special tools?
What I have: 1954 Merc, stock 256, 6 volt, positive ground.
Problem: No power to the distributor (points). There is power to the ignition terminal on the coil with the ignition switch on. The coil to distributor wire is intact and properly connected and just to be sure, I used a by-pass jumper wire to verify.
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By Tedster - 4 Years Ago
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Test for ohms resistance of the primary winding between + and - terminals, and test ohms resistance of the secondary winding between either terminal and the coil output terminal. Typical values might be 1 or 2 ohms and 8k for primary and secondary. Ignition coils do fail though not very often.
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By Lanny White - 4 Years Ago
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Thanks for the reply, Tedster. I am way NOT handy with a multi-meter but I think I figured it out. Is the test conducted with the ignition switch on or off.
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By Hoosier Hurricane - 4 Years Ago
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Lanny, test the ohms with the ignition switch off. Also, disconnect the small wire to the distributor so you won't get a false reading through the points.
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By Lanny White - 4 Years Ago
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Thanks, John. I just came back into the house after testing again. I got a reading of zero across the plus and minus terminals and a 7.8 across the center of the coil to either + or -. However, I am not sure what this tells me.
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By Gene Purser - 4 Years Ago
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A "0" reading across the primary (+/-) terminals would indicate a faulty coil because of a completely open circuit. If the two terminals were connected with a solid wire, you would read a "1" on the ohm meter. A reading of "0" indicates just the opposite, no connection at all.
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By kevink1955 - 4 Years Ago
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Gene Purser (3/15/2020)
A "0" reading across the primary (+/-) terminals would indicate a faulty coil because of a completely open circuit. If the two terminals were connected with a solid wire, you would read a "1" on the ohm meter. A reading of "0" indicates just the opposite, no connection at all.
Not really, A "0" indicates continuity, either a direct short or a resistance so low that the meter cannot resolve it. An open is infinity (infinity symbol is an 8 on it's side) which would be no meter movment at all (same as having the meter leads connected to nothing.
With the small lead going to the distributor disconnected and the key on, tap the empty coil terminal to ground, do you get a spark (this proves power and a coil that at least conducts) , if so with the points open (or a matchbook between then) tap the small distributor wire to the empty terminal, do you get a spark. If so you have a ground in the distributor, could be a shorted condenser.
Passed the above tests then rotate the engine till the points are closed, tap the small distributor wire to the empty coil terminal, you should get a spark, if not you may have a bad wire to the points or the points are so fowled that they are not really closing. 1 other thing to check is the ground strap on the breaker plate, is it intact. A missing strap could (not likely) let the plate become insulated from ground.
All the above tests sound like a lot but they are really simple and no meters required
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By Gene Purser - 4 Years Ago
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You are correct, I checked my meter and I had remembered/posted in reverse of actual. I apologize.
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By kevink1955 - 4 Years Ago
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Gene, Its confusing and almost counter intuitive that "0" is a closed circuit with no resistance, the mind sees it the other way around Lol
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By Lanny White - 4 Years Ago
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Kevink, thanks for the input. I did get a spark with the matchbook in place and now will pull the distributor again to check out ground wire and replace the condenser.
However, I discovered in examining the dist. cap that the rotor has been making contact with the lower faces of the wire towers. I checked the dist. end-play while still installed and found there was none so it seems that the dist. shaft extends a bit too far into the dist. housing causing the rotor to strike the inside of the cap. Not too sure what to think of this but will maybe know a little more upon removing the distributor. Any thoughts?
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By Cliff - 4 Years Ago
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Oil pump drive rod to long.
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By Lanny White - 4 Years Ago
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Thanks, Cliff. Do you know how much end-play there should be between the housing at the collar and the relative distance from the collar to the end of the shaft at the oil pump drive tang?
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By Cliff - 4 Years Ago
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I don't know, however I always check to see when the distributor. gear is resting on the machined surface in the block that there is still some end play in the oil pump drive, I have seen some blocks that were machined to deep (same problem), this can be fixed with a shim, the oil pump drive can be cut down, if it's a rebuilt distributor. the gear maybe located in the wrong place, I know it's a lot to check.
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By kevink1955 - 4 Years Ago
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Lanny, I would be looking at the condenser first, you said previously that you checked the wire so as long as it is not pinched where it enters the distributor the only way I know of that could provide a ground with the points held open would be a shorted condenser or a bad insulator on the points.
Cliff brought up a good point about the oil pump drive being to long (or the wrong length distributor shaft) placing upward pressure on the distributor shaft. Is the distributor original or a rebuilt, there was a problem a while back with the 57 and up distributors being built with the wrong length shaft (they were to short) but who knows what goes on at the re-builders
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By Lanny White - 4 Years Ago
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Thanks again Cliff and Kevink. I remember many years ago finding a brass washer-like shim(?) part with my spare distributors, caps, etc. and maybe I should have installed it. Possibly the block was machined and/or cast a little bit too deep. The dist. is a rebuilt and has been in use for about 3,000 miles.
I pulled the dist. yesterday, pulled the points and condenser, cleaned the plate, checked the coil and ground wires, reinstalled and set the points and condenser as they appear to be in good shape. and then re-installed the dist. I will re-do yesterday's tests today, especially on the condenser.
I will attempt to find the shim to install and maybe file off a tiny bit from the tang to relieve the uplift pressure on the shaft which ostensibly will allow for clearance at the rotor and cap.
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By 57RancheroJim - 4 Years Ago
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The rebuilds that Cardone sold has a 289 type triangular shaped body the Y block has a round body. They drilled and relocated the hole for the gear, how accurate is questionable and it's a critical dimension.. The shaft is also shorter where it engages the pump. If I recall end play should be .022-.030. If the stack of tolerances for the end play, cap, rotor add the wrong way the rotor can be to high in the cap as you are experiencing. I had that happen on one dizzy and just sanded off .015 from the bottom of the rotor, worked fine after that
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By charliemccraney - 4 Years Ago
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A triangular (Motorcraft) body by itself does not indicate any problem with the distributor. I have two, one points, and the other retrofitted duraspark. Both have correct dimensions.
The problem with shafts began in the past few years.
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By ian57tbird - 4 Years Ago
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I would check the drive gear to distributor base measurement first to see if that is correct. Replacement shafts required drilling and it could have been done incorrectly.
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By Lanny White - 4 Years Ago
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Ian57tbird, do you know the measurement?
I reinstalled the distributor yesterday- number one cylinder on compression, rotor on number one cap wire, timing mark at 3 degrees, and did a test-lamp test at number one spark plug. Everything checked out and after the work yesterday inside the distributor I have good spark at the points which have been set correctly.Still I cannot get it to start.
I did not change the condenser, but with good spark at the points I would presume that the condenser is ok, Am I correct? I suppose I could have a weak coil (about 3000 miles on it) but do not know how to check the out-put performance short of grabbing the number one plug wire end. Its been a looong time since I fell for that one!
Once I get it running I can address the dist. shaft or simply buy another rebuilt but I don't want to just start throwing money at guessing what is wrong. I've already just installed a freshly rebuilt ECK from the Hot Rod Reverend.
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By Hoosier Hurricane - 4 Years Ago
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Lanny, one purpose of the condenser is to prevent excessive arcing of the points. Could be a condenser problem. Pull the coil wire from the distributor, hold it close to a ground and crank the engine. You should see a fat spark at the end of the coil wire. No spark could be a bad coil wire, coil, or condenser. A good spark there and no spark at the plugs means a grounded rotor, a distributor cap issue, or bad plug wires.
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By kevink1955 - 4 Years Ago
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I think the condenser assists in the collapse of the magnetic field in the coil when the points open so it is needed to get a good hot spark as well as preventing point burning
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By Lanny White - 4 Years Ago
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Getting really frustrated! I did two more tests this morning - one by pulling the coil wire from the distributor and shorting it toward the exhaust manifold while cranking the engine. It arced across at about one inch but wasn't very impressive, i.e. a big fat spark. I haven't done that test with a six volt coil for over 50 years so I really don't know what to expect. It seemed to fire rhythmically as it should. Then I pulled the number one spark plug, reconnected the plug wire, grounded the plug base, then cranked the engine and got a spark on several revolutions by observing the marked timing dampner.
Still it will not fire when trying to start and now the starter is beginning to drag after so much cranking. Battery is on the charger again and I ordered a new coil today.
Thanks to all who offered help and support! I will be back when the coil comes. . . .
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