My original Bosch coil is 0.40 ohms.Originally Posted by nkemp
I measure real low resistance by pumping 1.00 amps into the resistance and measuring the voltage over the resistance. Hence I read 0.40 volts when I do that.
Location: Leonardtown, MD
Posts: 9,005
My VIN: 03572
My original Bosch coil is 0.40 ohms.
I measure real low resistance by pumping 1.00 amps into the resistance and measuring the voltage over the resistance. Hence I read 0.40 volts when I do that.
Location: Leonardtown, MD
Posts: 9,005
My VIN: 03572
Bill insists his Ford unit is the best but I tested one and it is pretty much the same as our OEM unit.
The GM module has great dwell change, has current limiting and shuts down when the engine is not running. I put mine on an aluminum plate and mounted that plate in the OEM ignition box.
Posts: 1,244
I know this is an old thread, but I need some info. I understand I can get a different coil and not run a ballast resister. I don?t have a good understanding of our current system, but I like the idea of eliminating the resister. Something that is not there can?t fail. Also, I like the idea of running a coil that is more standard. Easier to find parts on a trip.
Can anybody hold my hand and give me step by step instructions? Starting with exactly what to order.
Location: Leonardtown, MD
Posts: 9,005
My VIN: 03572
The ignition coils normally need about 6 amps of current when running. The use of a resistor was the normal design so when cranking a cold engine you could get that 6 amps when the battery voltage is lower due to the 100 plus amps of starter current.
When engine is running you normally get about 14 volts battery voltage. Using ohms law (I = E/R) the resistance of the primary of the coil would need to be 2.3 ohms with 14 volts to get 6 amps of current. When cranking the engine you expect to have 11 volts of battery voltage which would result in 4.8 amps of coil power with that 2.3 ohms of primary resistance.
Our stock coil has 0.40 ohms of primary resistance. Add the two half ohm resistors and the wiring resistance in the harness and the result is approaching about 2 ohms. So if you use a 1.4 ohm primary coil and no resistors it would result in the same current with engine running. But less current when cranking the engine.
If your running the GM ignition module or most other newer then stock units they have built in current limiting around 6 amps. That current limiting result acts like a variable resistor (produces heat if active). So you could run the OEM coil without resistors but the ignition module would get as hot as the resistors. Using a 1.5 ohm coil will still give you 6 amps cranking and 6 amps running and keep the ignition module pretty cool.
Posts: 1,244
Dave, you are vary smart in this kind of stuff. I am not. I kind of get the basics. I?m looking for something like this.
1. Buy Summit Racing coil #44325
2. Install in normal coil location with same wiring.
3. Unhook all wires at ballast resistor and remove.
4. Join red wire to blue wire and tape off all others.
5. Drive your car.
I don?t know if it can be this simple, but I can dream. Are you saying I need to change the ignition module to change coil?
Location: Leonardtown, MD
Posts: 9,005
My VIN: 03572
The white/yellow goes to the coil. The white wire gets 12 volts with the key on (from AUX relay). So you would connect the white wire to the white/yellow wire and tape off (or remove) all other wires. I don't have the relay bypass wiring diagram so that info is from the car schematic. You can try that now before changing the coil to see if it starts. (I like to change one thing at a time).
Posts: 1,244
Are you saying if I do that and don?t change the coil, it should start, but it will burn up the coil eventually?
Location: Co
Posts: 326
My VIN: 2245
I got a new coil a few years ago, Napa had it in stock. How often does the resistor fail? I don't think very often. If you're worried about not being able to find one, you could just carry a spare.
Location: Leonardtown, MD
Posts: 9,005
My VIN: 03572
Yes. Don't keep running it like that with a 0.40 ohm primary coil.
Posts: 1,244
That would mean caring a spare coil and resister. I think a standard coil is available anywhere and again, the resister can?t fail if you don?t have one. I already carry a spare alternator and starter and belts. I wouldn?t carry them if I knew I could get them at any auto parts store.
The only reason I can see for keeping the current system is to keep it stock. While I like the outside stock, I don?t have any qualms about making utility better. I already have non-stock tires, brakes, shocks, lights and exhaust. And, of course, a bunch of Dave?s relays.
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