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Discussion Topic:
Correct voltage from resistor to coil on 34 ford 6
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Peaches |
02-15-2014 @ 6:27 PM
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Member
Posts: 19
Joined: Sep 2013
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Can someone provide me what the correct voltage should be for the resistor to the coil on a 6 volt system for 34 ford V8,
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ford38v8 |
02-15-2014 @ 7:43 PM
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Senior
Posts: 2780
Joined: Oct 2009
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Peaches, your resistor is actually variable, and will drop the available voltage to your coil by about 2 volts. Your coil wants to see about 3-4 volts.
Alan
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Peaches |
02-16-2014 @ 5:18 AM
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Member
Posts: 19
Joined: Sep 2013
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Alan, thanks for the info, will check today. Gary
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supereal |
02-16-2014 @ 12:56 PM
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Senior
Posts: 6819
Joined: Oct 2009
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To check the voltage at the coil, either the points have to be closed, or the terminal to the distributor must be grounded. Otherwise, you will see battery voltage. Check with the engine off, but the ignition switch on. Voltage at the coil with the engine running will be inaccurate, as the action of the points creates a pulse thru the coil. As said above, correct voltage should be between 3 and 4 volts.
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deluxe40 |
02-16-2014 @ 7:17 PM
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Posts: 413
Joined: Oct 2009
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By coincidence I did a set of tests on my '40 today. Here are the results: Across battery 6.75v At switch input 6.45v At switch output 6.35v At resister input 6.36v At at resister output 6.35v At disconnected coil wire 6.35v At connected coil wire (engine off) 2.29v (points must have been closed) At coil terminal (cold - fast idle) 4.50v At coil terminal (warm - slow idle) 3.50v* At coil terminal (warm - 45mph) 6.00v* Across battery after 20 mile trip 6.45v Notes: * Two measurements on road were with an old analogue gauge corrected for error (reads 1.0v high). All measurements taken with inexpensive Radio Shack digital voltmeter except two noted above. Stock '40 Batt gauge needle rested on line between orange and green at 45 mph. Car ran almost perfectly, although not as smoothly as another car with new engine. I'm chasing a condition that causes the car to start missing after it runs for an hour or so and is then shut off for a while. I just installed a new Haney coil and am now testing it. Battery is an eight month old Optima. Is my ignition resistor over or under resisting?
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alanwoodieman |
02-16-2014 @ 8:42 PM
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Senior
Posts: 868
Joined: Oct 2009
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2.29 is very low-would cause a misfire or studder upon acceleration, also would cause the coil to heat up. first battery voltage 6.75-running or engine off? last battery voltage 6.45-running or off--if running generator or voltage reg needs adjusting
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ford38v8 |
02-16-2014 @ 8:45 PM
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Senior
Posts: 2780
Joined: Oct 2009
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deluxe40, from reading your observations, I have some of my own: I find it interesting that after a 20 mile trip, your battery was not fully charged. A trip of half that distance should charge a battery that was used only to start the engine. My only explanation for that is that you had your battery charger on while doing your static tests, and your voltage regulator prevented the battery from returning to that highest charge state. Not a problem other than the inability to have confidence in the readings obtained. Your readings obtained with the engine running must be ignored as unreliable in any case. The reading obtained at the disconnected coil input is notable in that this reading is the same as at the switch output. This, after three wire terminals and about 5 ft of wire is admirable, but should be checked again. The reading with the points closed is far too low. This reading should also be rechecked. An input that low would make for hard starting, and would indicate a problem to look into. I would take these readings over again after your battery has normalized rather than while hooked to the charger or immediatley afterward. Also worth noting, a good alligator clip will provide a better connection than a probe.
Alan
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deluxe40 |
02-17-2014 @ 1:39 PM
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Posts: 413
Joined: Oct 2009
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Retest on 2/17/2014 - after car sat all night with battery cable removed. Note: I cut the probes off of the volt meter and soldered on some alligator clips (using the vice as a heat sink). Engine not turned yet today. Across Battery (cold) 6.40 Across Battery w/ charger attached 8.20 (I don't think it was on yesterday) Across Battery after 5 min charge (@2 amps) 6.76 At switch input 6.36 At switch output with switch on & coil connected 5.35 (?) At coil (wire on, engine not running) 2.20 At coil wire (disconnected) 6.29 At coil (wire on again) 2.26 At this point I made a new hot wire from neg battery terminal to an alligator clip. Then I installed an old resister directly to the coil terminal. At alligator clip on end of hot wire 6.37 At coil terminal with hot wire on resistor input 2.58 Now I am trying to decide whether to go buy a new meter or to pull the condenser and clean up the ground bolt. I tested the condenser a few days ago when I installed the new coil. The condenser (from C&G) was new in July. The points and rotor are also new and the distributor was set up on a machine in July.
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supereal |
02-17-2014 @ 2:59 PM
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Senior
Posts: 6819
Joined: Oct 2009
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I agree with my friend Alan that your charging system seems to be deficient. Voltage across the battery poles with the engine running at a fast idle should be close to 7.5 volts. That said, a couple of years ago, my '47 developed a miss on hard pulls after reaching common operating temperature. All ignition parts checked out. Finally, i turned to fuel delivery and found it to be low and inconsistant. The fuel pump was fine. The inlline filter was new. Finally, I decided to check the only part of the system that hadn't been considered: the fuel line between the tank and the firewall. We removed it, straightened it out, and tried to push a wire thru it with no luck. It was mostly blocked with rust and dirt. A replacement returned the car to full operation with no missing or bucking. The quarter inch line is just sufficient to do the job, and any blockage will produce the symptoms mentioned here. You have covered the ignition, and it is likely time to consider other causes.
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deluxe40 |
02-17-2014 @ 4:10 PM
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Member
Posts: 413
Joined: Oct 2009
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I cleaned up the condenser/timing cover bolt and made a ground wire to go from there to a manifold bolt just to be sure. I even soldered the connectors. Still 2.34 volts at coil on my old digital meter. I put new batteries in my old analogue meter and measured across the battery - 5.8 volts (wrong). So I went out and bought a new analogue meter. It reads 6.5 volts across the battery and 3.8 volts at the coil. Now I have a good baseline on the ignition and two old meters in the recycle box. The car still feels like it has a very occasional miss when pulling. I think Super is right - time to look at something else. We installed a new fuel line, new flex line, new fuel pump and rebuilt carb (Daytona kit) a year ago so I'm not sure where to go next. I would say, "don't let the perfect be the enemy of the good", except that this car has run fine around town several times before and then started missing on a day-long tours. Thanks to all for your helpful comments. GD
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