I had posted in another thread a problem re: car starts when I let go of key when hot. I found that there is fuel and 7 volts at the ballast resistor when cranking and it jumps to 11 volts when I let go of the key. It doesn't seem like the engine is firing at all. Once it does start after letting go of the key it runs fine although I really haven't put my foot in it as its new and I am still doing maiden voyages. I just checked the newish coil resistances (AC Delco E552C) and see that the secondary resistance is 14k ohms. I can't find published specs but seems high. Perhaps its a dud? I have a spare old Delco Remy coil that is 1.7 / 10k ohms which I will try.
Ignition coil secondary resistance is high / hard start when hot
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Secondary readings vary all over the place.
You should have higher voltage at the coil primary WHEN CRANKING, about same as cranking battery, and then lower voltage when running
So what are we working on and what sort of ignition system do you run?
You should have higher voltage at the coil primary WHEN CRANKING, about same as cranking battery, and then lower voltage when running
So what are we working on and what sort of ignition system do you run?
Yeah I got to double check those voltages run vs start. I have std electronic ignition with orange box. Not all coil mfg's seem to list specs but those that do show around 9500 ohms secondary (I haven't looked at the hp coil specs)
You can not compare coil ohms readings over different brands and part no's of coils. Transformer voltage is determined by what is called "turns ratio", meaning that if you have say, 1200 turns on the primary, with 120VAC in, and 120 turns on the secondary, that is a 10:1 ratio, and would give you 12V AC output.
So if a different part no./ brand coil has a larger gauge primary for more current flow, but a different winding turns total, the secondary might be quite different
I would carefull re-measure your voltages and be careful you don't get the key "between" positions, etc. Measure at least 3 times to be sure
So hook your meter to coil plus and ground, and remove and ground the hi tension wire. Crank the engine long enough to get a stable reading, and read, return back to "run" and read.
If the voltage truly is much below battery V during cranking (not 12.6 static, but battery CRANKING V) then either there is voltage drop in the bypass circuit, or something is drawing lots of current.
Bear in mind, as well, that on a Mopar ECU, during cranking, the coil + side of the ballast feeds power BACKWARDS through the resistor to power the ECU box. That is the only source of power during cranking.
So if a different part no./ brand coil has a larger gauge primary for more current flow, but a different winding turns total, the secondary might be quite different
I would carefull re-measure your voltages and be careful you don't get the key "between" positions, etc. Measure at least 3 times to be sure
So hook your meter to coil plus and ground, and remove and ground the hi tension wire. Crank the engine long enough to get a stable reading, and read, return back to "run" and read.
If the voltage truly is much below battery V during cranking (not 12.6 static, but battery CRANKING V) then either there is voltage drop in the bypass circuit, or something is drawing lots of current.
Bear in mind, as well, that on a Mopar ECU, during cranking, the coil + side of the ballast feeds power BACKWARDS through the resistor to power the ECU box. That is the only source of power during cranking.
You will NOT gat an accurate reading of the sec winding when using a digital meter. Old fashioned moving coil meter is ok.
You have two ccts:
- crank
- & run.
Sounds like there is a problem [ most likely wiring, loose connection ] with the crank[ing] cct.
You have two ccts:
- crank
- & run.
Sounds like there is a problem [ most likely wiring, loose connection ] with the crank[ing] cct.
I pulled the coil out and checked resistances again and the coil is fine at around 9300 kohms. I must have it tested incorrectly. The distributor reluctor gap is 0.008". I checked voltages at the resistor wire plugs for start and run and it seems fine too. I'll check this again along with the coil voltage next time the car is warm and won't start.
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I would not at all get hung up on secondary resistance UNLESS you have a hard figure of the exact coil part no. from the manufacturer. Also, LOL, make certain that your fingers are not touching the probes
Sounds like you could have blue and brown wires backward if coil voltage goes down when cranking. The wiring diagram for my 69 barracuda has them reversed.
When the ballast resistor goes bad on a car that is wired correctly, just the opposite happens.
When the ballast resistor goes bad on a car that is wired correctly, just the opposite happens.
I think the whole coil voltage thing was a red herring. I had another hot hard start today (every time I take it out). This time I dumped 5 - 10 ml of gas down the carb and it started on the second or third go. I am leaning towards a fuel vaporization issue now. The carb body is too hot for my liking. I'll see if I have room for at least a 1/2" phenolic spacer of some sort or maybe one of those Edelbrock 9266 heat spacers.
I got a pretty thin phenolic spacer & it worked like magic
That’s good to hear. I just picked up the Edelbrock one. It’s less than 1/2” thick.
Just to close the loop here (I posted this in another thread) I have been running around trying to solve issues with hard hot starting (vaporization or electrical) and unresponsive carb tuning and I believe I have solved one of these at least. I found the brand new Mopar distributor had 0.025" pickup gap. I checked it before but got fooled by the magnetism thinking that the 0.008" feeler was tight. I'm surprised it started at all. My theory is that when I let go of the key the coil fires once and that spins the engine enough to get a decent signal to the ECU to start the engine. Once the engine was started adequate signal was sent to the ECU for it to do its thing. Who knows.
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