QuestionQUESTION: Howard, I am following you on your step by step trouble shooting. Sorry for trying to jump ahead!! I took the three coils to a Radio Shack with my ohm meter. My ohm meter, while new,does not work well. I tested against resistors from Radio Shack stock and the readings were intermittent. I used their digital meter and the readings I got were as follows:
The old coil: 1.5 Ohms
The new coil that requires a resistor: 1.5 Ohms
The new coil that does not require a resistor: 3.7 Ohms
Now that I know what a coil resistor looks like and how it hooks up, the car NEVER had a resistor.
Let me know the next step.
Why don't you write a book?
Have you seen that e-mail about the barn in Portugal with the cars? If interested let me know your e-mail and I will send to you. It is quite amazing!!
Thanks for patience, I know dealing with knuckle heads like me can be challenging!!
ANSWER: OK Robert, The ohm test of the primary circuit of the coil is just to correctly ID the coil. What year and model MG is this? some MGs had a resistor wire in the wiring harness and thus require the 1.5 Ohm coil. If it does not have the resistor wire you need to use the 3.7 coil. Next we need to know what kind of distributor do you have? Is this pointed or electronic? (you may have said in a previous e-mail but I don't keep these in any file so you have to remind me on each e-mail)
You can do a rough preliminary test of the coil without a scope by powering the (+) side of the coil. Put a coil wire in the tower and put a good spark plug on the coil wire and lay the plug on the case of the coil. Then take a test lead and connect it to the (-) side of the coil and scratch it across the case of the coil. You should see a spark and it should be thick (pensile lead thick) and it should be blue in color. If it is thin like a hair and yellow or orange in color you need to add a condenser to the (-) side and ground it to the case of the coil and repeat the test. If you then still get a thin yellow spark, that coil is bad. (Do this in a garage as sun light will sometimes look like a bad spark when it is good)
I have the photos of the barn in Portugal and I even run some of the photos through a photo editing program to brighten up some that were dark so I could try to ID some of the cars. Car collectors dream about things like that.
We have a car museum here in Nashville and the owner travels all over Europe buying up cars like that. He has cars that I never heard of.
Thought about a book but I do have a website up that has tech tips and stuff you may find of interest. http://mg-tri-jag.net
Give me the year and model of your MG and lets get back to work.
Howard
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QUESTION: Howard, it is a 1975 MGB with a pointed distributor. The model is the 45D4.
I tried to do that test on two distributors but could not get a spark. I scraped the paint off of the coil to make sure I had a good connection between the sparkplug and the case of the coil. I had 12 volts to positive. Jumper from neg to the bare metal of the coil case. A coil wire from the center tower of the coil to a good spark plug secured to the bare metal of the coil.
The coil was not in the car. I had it laying on a work bench.
If it is not jumping the trouble shooting process I would just as soon use a new coil as the old one is the original to the car.
Is there a way to test if the car has a resistor wire so we can put one fo the new coils in and try the next step?
Regarding the O-Ring on the distributor, there isn't a speck of old O-ring on the disgtributor and I can't ell where it goes. All of the manuals show the O-ring but I can't figure where it would go. There are thre places that look like an O-Ring would fit. Your original note said at the bottom. The space at the bottom would be in in purpetual motion when the car is running. The second location would be over the trust washer which means that half the O-Ring would be touching a stationary part of the distributor and the other would be on a revolving part of the distributor.
The third is just under where the base of the distributor rests on the engine block. From there it would be on a non-moving part of the distributor.
I looked around the web to see if I could get a good picture bit no luck.
Thanks in advance!!
ANSWER: I thought I answered this one once but it may not have went through.
You can do the test on the bench just be sure to connect the battery (+) to the + on the coil and battery(-) to the coil base. Then connect a jumper to the coil (-) and leave the other end away from any contact. Also connect a condenser to the coil (-) and ground the condenser case to the case of the coil. Install a coil wire in the tower and a spark plug to the wire and lay the plug on the coil case. Now take the jumper wire that you attached to the (-) coil and scratch it on the case of the coil. The plug should spark and the spark should be as thick as a pensile lead and blue in color. If it is yellow or orange and thin like a hair the spark is weak.
The 75 "B" does have a resistor wire in the system and you need to use the 1.5 ohm coil (unless the car has been changed)
The "O" ring should be in a groove just under the mounting flange.
Let me know,
Howard
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QUESTION: Howard, I have been traveling and not able to do the test on the coil until
tonight. This is the 1975 MGB with the car that stalls because of the
overheated coil.
The reason the test on the coil did not work when I tried it the last time was
because I was not grounding the coil body to the battery ground.
The old coil tested fine. It had a good strong blue spark. I compared to the
new coils I bought and they all had the same spark.
So, we are off to the next step in the trouble shooting process.
As a reminder, my car will not crank unless I jiggle the starter relay wires.
Looking forward to hearing from you.
Thanks!
AnswerRobert, you lost me. what was the question?
If it was about the starter relay, if you have to jiggle the wires on the relay to get it to work you need to check to see that the connections are tight and clean. If they are you must have a bad relay.
Howard
