Early Ford V-8 Club Forum

EFV-8 Club Forum / General Ford Discussion / Correct voltage from resistor to coil on 34 ford 6

Reply to Discussion | New Discussion << previous || next >>

Posted By Discussion Topic: Correct voltage from resistor to coil on 34 ford 6 -- page: 1 2     supereal 02-19-2014 @ 12:50 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 The best test for a charging system is to check the voltage across the battery. As mentioned, when the engine is running fast enough to close the cutoff relay, you should see about 7.5 volts. In 1940, Ford did use a voltmeter in the dash instead of an ammeter. I don't know why they stopped, because it was a better method of viewing the system. If the charging rate drops off,and the car is running on the battery alone, eventually the coil will be starved to the point where the engine falters and stops. After it sits for a while, the battery will regain some power, and the car will start. I have always suspected that this was the reason that "vapor lock" was invented. deluxe40 02-17-2014 @ 7:08 PM reply profile send p.m. Member Posts: 413 Joined: Oct 2009 Alan, Yes, I need to go over all of the previous readings with the new meter and then take indicated actions. The switch body was replaced with a new (reproduction) one in July, but I'm not convinced it works well. At one point I thought I caught it "leaking". (Old meter showed .2 volts when switch was off). I routinely take a battery cable off when the car is put away, so it won't show up except when parked at an event. Also need to look at the charging system. I have an ammeter, so I know it charges, but maybe not enough. GD ford38v8 02-17-2014 @ 5:16 PM reply profile send p.m. Senior Posts: 2780 Joined: Oct 2009 deluxe40, Now those numbers look good! I would like to direct your attention to the poor reading at the switch, though. The switch is a chronic issue, but is replaceable with NOS, and is also repairable if you can't find NOS. If you'd like to tackle that, the carbon plate can be cleaned up or replaced, and the brass contacts tension adjusted. Alan deluxe40 02-17-2014 @ 4:10 PM reply profile send p.m. Member Posts: 413 Joined: Oct 2009 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 supereal 02-17-2014 @ 2:59 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 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. deluxe40 02-17-2014 @ 1:39 PM reply profile send p.m. Member Posts: 413 Joined: Oct 2009 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. ford38v8 02-16-2014 @ 8:45 PM reply profile send p.m. Senior Posts: 2780 Joined: Oct 2009 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 alanwoodieman 02-16-2014 @ 8:42 PM reply profile send p.m. Senior Posts: 868 Joined: Oct 2009 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 deluxe40 02-16-2014 @ 7:17 PM reply profile send p.m. Member Posts: 413 Joined: Oct 2009 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? supereal 02-16-2014 @ 12:56 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 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.

<< previous || next >>

PAGE: 1 2

NOTE: YOU MUST BE A REGISTERED USER AND BE LOGGED IN TO POST (and reply to) messages in this forum. If you are a first time user, please click the CREATE A NEW ACCOUNT in the masthead above to register and Log In. After that, all you do is LOG IN to enjoy using this site.

DISCLAIMER: The V-8 Club does no independent testing of any of the opinions, thoughts or suggestions presented in the website on the Forum, in the Tech Tips section, or any section. A reader should consider the website to be a forum wherein differing solutions to a particular set of circumstances may be discussed. Ultimately, the selection of an item for an individual's vehicle must be based upon the independent study of the vehicle owner in consultation with people in the hobby and restoration experts.

EFV-8 Club Forum Home | Back to Home Page | Contact the Webmaster

Copyright © 2009 - EFV-8.org
Powered by < CF FORUM > v.2.1