• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Time for a new coil?

Share this page

Morris

Morris

Yoda
Offline
Does anyone have any good tips for determining if it's time to replace the coil?

Morris
 
Since coils seldom partially fail, the time to replace it is when it fails, or when you just don't feel comfortable with it's age, condition, or design. Would you feel better with a new coil or a 40 year old coil? If you just want to get the last little bit out of the old coil, carry a new spare with you & be prepared to change it when needed. I personally feel more comfortable with a fairly new coil & skip the spare.
D
 
I don't know when it's time to replace the coil. However, I was having some ignition problems, and most people said it wasn't the coil. So I replaced all the usual stuff, did the normal tuning. Was still having issues. Replaced the coil, and everything worked great. I say replace the coil, they're cheap. I agree with Dave, feel comfortable with a new one.
 
My racer has a coil suitable for a Chevy V-8. I bought it at a discount auto place for $16 and the ballast resistor was about $5 more. For that price, why not?
One test that may be good is to spray water on it at night while it's idling (use a plant sprayer). If you see any sparks jumping, the coil insulation may be shot. Also, the spark should be able to jump an 1/8" gap easily (when cranking).
In conjunction with a Pertronics electronic igniton, mine makes a fierce spark....it never fouls, even with my rich carb setting.
By the way, I run the ballast resistor all the time (during cranking as well as running). Simpler that way and starts fine.
 
When my coil went bad, it gave intemittant ignitions problems. It would be hard starting and would momentarily cut out. A new coil ran me about $25 and resolved the problems.

There are specifications out there somewhere about what the resistances should be. If you are truly concerned, you can always check it.

Also check the wires. Worn out spark plug wires can also cause some weird running problems.
 
Good advice guys. Thanks!

Nial, can you give me more info on your coil? At what store did you pick it up? If I were going to buy one, how would I ask for it?

morris
 
I forget the name where I bought mine.
It was one of the discount auto parts places.

Tell them the year, make and model, in your case '79 MG Midget.

You would need a 12v non ballasted coil. (You have a separate ballast resistor on your car).

This is one instance I would recommend NOT going to Napa.
They show the wrong coil listed (They show a ballasted coil).

When you install it, just be sure the + and - terminals are connected the same way as on your car now.
 
I have heard of some of the most bizarre, confusing and generally exasperating problems eventually being attributed to coil failure.

I guess it could be considered relatively cheap insurance against loosing your mind.
 
My coil is externally ballasted, and it gets HOT! I could fry eggs, or hands and fingers for sure.

Sorry to bother you with another annoying question, Nial, but what is the ballast listed under?

According to the website, my local Autozone carries that very inexpensive coil in stock.

Thanks again for all the great advice, guys!

morris
 
Coil shouldn't get too hot. Warm, but not hot.
I just asked for a "general" ballast resistor. I'm not sure what part number it really was.
But here's one:
0.85 Ohm Ballast Resistor
Part Number 150001
$12.99
I believe this will work with a basic coil, but they say it is made for the 140001 "Super Coil" (whatever that is?).
 
Back
Top