Joined: May 11, 2005 Posts: 52 Location: Tucson, AZ
Posted: Mon Oct 30, 2006 9:09 am Post subject: disconnect your battery cables!!!!
I know this is elementary but in my haste to finish putting my jeep back together after testing my fuel pump install I decided to quickly tighten a nut on my starter that I noticed was a little loose. My wrench made contact with the wire and housing that connects to the bottom of the distributer and POW I now can not get the engine to start. It was late in the afternoon so I did not explore what damage was done to the distributer but it sound like I am not gettting a spark to the plugs. I assume I blew out the coil or welded the points.
Dont feel bad.I did just about the same thing once too except I got the wrench against the block and did the sparks fly. Ended up with a ruined wrench and had to buy a new starter switch. I was probably lucky thats all the damage it did.
I would check the points to be sure you didn't weld them shut. I can see possible damage to the radio filter capacitor in the terminal housing and the condenser on the distributor plate. I don't see any reason for your coil to be damaged. If the points are undamaged then check for spark at them when you open and close them. If none then check the condenser and capacitor. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: May 11, 2005 Posts: 52 Location: Tucson, AZ
Posted: Wed Nov 01, 2006 8:33 pm Post subject: testing
Wes,
What is best way to test radio capacitor? Do you unplug it and use a standard electrical tester while cranking engine?
I also assume to test the points you hook up battery and crank engine and look for spark at points when rocker arm opens and closes as the cap rotates.
If these fail how do you test the coil?
I read the manuals twice but these questions are not really answered.
Thanks,
Dave
"I would check the points to be sure you didn't weld them shut. I can see possible damage to the radio filter capacitor in the terminal housing and the condenser on the distributor plate. I don't see any reason for your coil to be damaged. If the points are undamaged then check for spark at them when you open and close them. If none then check the condenser and capacitor."
It is best you have a very clear understanding of how the ignition distributor produces spark. This writeup by Jerry Adams was posted about 4 years ago and is a very good read.
Quote:
Hi Rob:
You bring up a good point, which deserves an explanation. I did not include a capacitor in the test circuit because I wanted to keep it as simple as possible and still tell if the coil is working. A capacitor is definitely needed for proper operation, which is why I said to repeat the test only once... Here's a little write up I did a while back that tells what the
condenser does:
**************
In a system that uses the breaker point/capacitor/coil method of creating the high voltage necessary to fire the plugs, the required energy to produce a spark is stored in the form of a magnetic field:
Although they *may* be physically connected in a configuration that the electronic
types refer to as a "autotransformer," there are two windings in a spark coil, which interact to create the "spark." Here's what they do:
The primary winding is composed of relatively few turns of relatively heavy wire, and the secondary winding is composed of a relatively great many turns of relatively fine wire. "Relatively" is used to compare the two windings with each other, not necessarily with any other frame of reference. The exact gage and number of turns is determined by the design parameters of the coil.The Primary winding has its ends connected to the two terminals on top of the coil marked "ign" or "+" and "gnd" or "-". The secondary winding has one end connected to the case of the coil and the other end terminates at the high voltage output where the wire that goes to the distributor cap is attached.
The cycle begins when the ignition points *closed*, completing an electrical circuit from the power source (the battery), through the ignition switch, to the coil, to the distributor points, which connect to the grounded motor block, hence back to the battery.
This completed electrical path, or circuit allows current to flow through the "primary" winding of the ignition coil. This in turn creates a magnetic field, with is concentrated by the iron core of the coil. This represents stored energy that can be used to create a high voltage output. The current flows for as long as the points are closed, which is referred to as the "dwell time," or simply the "dwell." It is important that you have the proper dwell. Too short a dwell time, and the core will not have sufficient time to fully charge with magnetic energy, or "flux." Too long a dwell causes unnecessary heat build up in the coil, which can shorten its life expectancy. The proper dwell is designed into the cam lobes in the distributor, but this can change if the lobes become worn down. In an ideal
situation, the lobes will allow the points to remain closed long enough for sufficient flux to build up in the core of the coil at the highest design RPM of the motor, but not so long as to excessively overheat the coil during periods of prolonged idle. This wear on the lobes is one reason why you should replace or rebuild a point equipped distributor periodically. I like to do it about every 60 to 75 thousand miles. Good cam grease can prolong the life of a cam substantially.
It is important to know how the coil and points work to create the high voltage needed to fire the plugs. This happens when the points ****OPEN****. When the points open, the electrical circuit that was supplying current to the primary of the spark coil is interrupted. Without the energy supplied by the current flowing through the primary, the magnetic
field in the core of the coil begins to collapse. I will not go into the physics involved, but suffice it to say that the collapsing magnetic filed induces a voltage in the windings of the coil that is trying to sustain the collapsing magnetic field. This induced voltage will be opposite in polarity to the voltage that sustained the current that created the magnetic
field in the first place.
This induced voltage is called "magnetic kick." The amplitude of the "kick" is dependant on the *rate* at which the field collapses, and the design parameters of the coil itself. Generally speaking, the faster the collapse, the higher the "kick" voltage. The speed of the collapse (and therefore the magnitude of the "kick") is highest if there is a very high resistance between the terminals of the primary winding, and correspondingly is lower as this resistance decreases.
An inductive "kick" is created in both the primary and the secondary windings when the magnetic field collapses. Because there are a lot more turns in the secondary winding, the magnitude of the "kick" is much higher in the secondary than in the primary. It is this voltage that is used to fire the plugs.
However, provision must be made to deal with the primary "kick." If the primary "kick" is allowed to dump itself across the points as they open, the resulting arc will very rapidly destroy the points! The capacitor is used to store the energy from the inductive "kick" in the primary winding.
When the points close, the capacitor stores an electrical charge at the voltage of the system. When the points open, the voltage in the primary begins to rise in response to the collapsing magnetic field. This rising voltage is stored inside the capacitor where it is held until the points close again, shorting out the capacitor. Because the energy is bled out from the capacitor at a higher current and lower voltage, over a relatively long period of time when compared to the time it took the magnetic field to collapse, the arc across the points is reduced, and they are protected.
It is important that the capacitor have the right value to work properly. Too much capacitance, and it will slow down the collapse of the magnetic field, causing a weak spark. Note that both the primary and secondary windings draw the energy for their respective inductive "kicks" from the same source - the collapsing field in the core of the coil. Too little, and it will not be able to store enough of the energy induced in the primary when the field collapses, resulting in poor point life. The exact value of
capacitance needed depends on several factors, including the specific parameters in the particular coil installed (inductance, resistance of the windings, etc). I do not change out a capacitor when doing a tune-up if the points are wearing uniformly, as it is properly balanced to that system. On the other hand, I have been known to buy a half a dozen capacitors and try to find the best one by substitution. Yes, it costs some money, but it gets the best performance from the system.
It is possible that the capacitor, points, etc. are working to specification, but you will still have a weak spark. Inside the coil, a high resistance short anywhere within the primary winding could be syphoning off power that should be going to make a good, hot spark. Also, a partial short to ground anywhere in the high voltage side can rob a lot of power. Other possible sources of "power theft" include: A cracked or delaminated core in the
coil; bad high voltage (plug) wires, including the insulating boots; cracked or moist cap; cracked rotor; or a cracked porcelain on one or more plugs.
**********
I hope this helps... The coil will create a spark without a condenser in the circuit, but it will also create a much higher voltage across the primary winding that it experiences in normal operation. This is a lot of stress on it, which is why I said to do the test only once. I am not sure about your observation that a coil without a condenser makes a weak spark,
unless you are referring to one that is attached to a distributor... The points will burn very rapidly, which will create a high resistance in the primary circuit, which in turn will definitely lead to a weak spark. I once got called by a neighbor to help him. He had done a tune up job himself, and neglected to install the condenser. He got about four blocks before the motor quit and would not start. When I popped the cap on the distributor, the whole inside of the distributor was covered with black soot, and the points were cremated! I had to replace the cap, rotor, and points that he had just installed... He got about a half mile out of them.
Thanks for spotting my omission!!! I'm sending this along to the list in case someone else is wondering about it, and to Bob Hadskey, who has some ignition problems as well...
Always, Jerry Adams Goleta, CA
Do the point test first. If it checks good then you don't need to test the capacitor. You don't need to crank the engine to check the points. Just pull the cover so you can see the points. Rotate engine by hand untill the points close. Then turn master on and manually open and close points. They should emit sparks. Don't leave her turned on too long with the points closed.
The coil can be tested two ways. By disconnecting all wires and checking for primary side resistance which will be about 5.3 to 5.5 ohms and secondary side resistance which should be about about 11K or more. Take these readings with the coil at room temp and then again after you warm it with a heat gun or hair dryer untill it's slightly uncomfortable to hold for a long time.
A more complicated amp test is in the manual as well. With coil at romm temp and connected the primary amp draw with the points closed and the switch on should be 2.7 amps at 24 V and then do a flash test maintaing 24V and the current should be 3.0 amps. This test is tough because you need to control input voltage very accurately to exactly 24 V.
Technically you use a capacitor tester. If you remove the capacitor and the condenser and take them to your local electronics shop they can test them for you. The condenser should test at .18 to .21 MF and the noise capacitor should test at 2.0 MF. But in the field the usual remedy is to substitute a known good unit or bypass the capacitor temporarily. If you are proficient with a digital VOM just check for open between lead and case and for continuity from the inlet pin to the wire terminal using the red/black leads one way then the other. You should get a fixed resistance when you connect the ohm meter +/- leads in one direction then whe you reverse the leads you should get a increasing ohm reading which will suddenly drop.
The condenser is layed out differently since it has one wire and the case. You check with an ohm meter +/- reversing technique as above but at the one wire terminal to the case.
The detailed electrical troubleshooting, overhaul, repair and specifications for your jeep's electrical components are in the Auto-Lite Electrical Compnents Manual TM 9- 1825B dated 1952 or newer (24 volt systems for our jeeps aren't in the earlier versions). _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
You don't need any parts yet. If there's no 24 volts at the wire feed to the distributor then that is why you have no spark. That wire should be #12 and it should run non-stop back to the master switch. Check the master switch's terminal for power at it's end of wire #12. with the switch on. If still no power on #12 leave the switch on and check # 27. If still no power then check #10 or #11 (depends on weather you have early (11) or late (10) wiring. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Wes,
Did the non-electronic auto ignition systems have a resistor of a small value (maybe a couple of ohm's) in the power to the primary winding or maybe built into the coil to lower the current to keep it (the coil) from getting too hot?
ken _________________ Tropical Veteran
35th Inf. Reg. "CACTI" 4th I.D. VN
Amateur Radio K5XOM
They sure did. So did a lot of electronic ignitions. It started over 80 years ago when the industry standard coil was 6 volts which was good up to 8 volts and delivered about 15,000 to 20,000 volts to spark the plugs. This was adequate secondary voltage so why switch. As the industry switched to 12 volt electrical systems from 1930's thru the mid 50's the 6 volt coil remained and a resistor was added to drop the voltage. Eventually more modern coils simply had the resistor built in. The 24 volt M38/M38A1 coils have a built in resistor. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: May 11, 2005 Posts: 52 Location: Tucson, AZ
Posted: Sat Nov 04, 2006 8:17 pm Post subject: problem solved
Well after tracing the ignition wire from the distributer to the switch I located the problem. the wire came apart at the douglas connecter behind my instrument panel. Evidently a bad crimp or something and completely coincidental with the grounded out wrench. GO FIGURE!
Not a total loss - I got a lesson in electrical troubleshooting and didn't need to buy all new distributer parts.
Thanks Wes and others for all of the helpful advice.
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The Jeep started to pop and steam up!
