• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Coil Voltage Needed?

Ed Martin

Ed Martin

Well-Known Member
Local time
8:14 AM
Joined
Dec 22, 2014
Messages
115
Reaction score
7
Location
NC
My 68 Roadrunner will not fire up at all for 8 months (but cranks good). In that time I replaced the carburetor, coil, battery, cap, rotor, ignition switch, plugs, ballast resistor and ECU module and checked ECU ground. Now I think it's a voltage problem so have done lots of voltage and resistance checks and checked reluctor gap. With battery at 12.7 V, I measure 11.5 V at +coil with key in start without cranking and 10.2 V at +coil when cranking. Also, get 11 V at starter relay battery connection when cranking -- in case I want to try to run a wire from there to the coil (but haven't tried that yet). Shouldn't 10.2 V at +coil be enough to fire it up? I get sparks from the coil secondary wire (disconnected from distributor) to ground when cranking, but seems weak, but this is with ignition switch in run with 8 V at +coil (using remote starter), not in start where voltage is greater at 10.2 V (using key to crank). Isn't it normal to get a couple volts less than battery at coil (12.7 - 10.2) when cranking or is that too much drop? Does battery itself (if I ran a wire from it to coil) stay at full voltage when the starter is operated?

Thanks for any help.
 
That should be enough. If you get spark it should fire. Are you sure the timing is correct? If you put it on TDC on the balancer (assuming it has not slipped on the rubber) is the rotor pointed at #1 plug?
 
All the voltage readings seem plausible.
Yes, the voltage definitely drops when cranking.
Plug wires?
Pick-up coil?
Maybe the chain jumped? (but it ran when parked I assume)
Agree with Jim, check your timing.
You can pull the plugs and put a timing light on it.
 
Ed Martin said:
My 68 Roadrunner will not fire up at all for 8 months (but cranks good). In that time I replaced the carburetor, coil, battery, cap, rotor, ignition switch, plugs, ballast resistor and ECU module and checked ECU ground. Now I think it's a voltage problem so have done lots of voltage and resistance checks and checked reluctor gap. With battery at 12.7 V, I measure 11.5 V at +coil with key in start without cranking and 10.2 V at +coil when cranking. Also, get 11 V at starter relay battery connection when cranking -- in case I want to try to run a wire from there to the coil (but haven't tried that yet). Shouldn't 10.2 V at +coil be enough to fire it up? I get sparks from the coil secondary wire (disconnected from distributor) to ground when cranking, but seems weak, but this is with ignition switch in run with 8 V at +coil (using remote starter), not in start where voltage is greater at 10.2 V (using key to crank). Isn't it normal to get a couple volts less than battery at coil (12.7 - 10.2) when cranking or is that too much drop? Does battery itself (if I ran a wire from it to coil) stay at full voltage when the starter is operated?

Thanks for any help.
Click to expand...

68413217_2542586785806931_5018865187424305152_n.jpg
What have you done with the Charging system?
READ:
Early Charging System modified for use with a 70 style VR

There are a number of reasons one might want to upgrade a per-1970 system to a transistorized voltage regulator. The list of reason include

  • Chrysler recommends you switch to a transistorized VR if you upgrade to an electronic ignition from a points style ignition.

http://www.imperialclub.com/Repair/Electrical/charging.htm
 
Of all the things you mentioned, you didn't say whether you have verified spark at the plugs.

You also didn't mention fuel, other than replacing the carb. Have you looked down the carb while operating the throttle to verify raw fuel squirting down the bores? Could be a bad pump or clogged filter.
 
Ranger16 said:
Of all the things you mentioned, you didn't say whether you have verified spark at the plugs.

You also didn't mention fuel, other than replacing the carb. Have you looked down the carb while operating the throttle to verify raw fuel squirting down the bores? Could be a bad pump or clogged filter.
Click to expand...

I had been checking to see that it was squirting good all along. This weekend I started thinking about the age of the fuel in my tank and looked back to see it was 19 months old! I don't put many miles on it so it's not unusual to go a year without burning a full tank and have never had fuel go bad before. I looked back to see that the last time I was able to start it was last July and it had been hard to start for about several months even before that. It was ethanol-free gas, don't know if that makes a difference on how long it should last before going flat. With a couple-second spray of starting fluid, it started right up and was able to run (roughly) enough to heat the engine and continue to run on the bad gas and let me drive it. After making all those electrical changes! … am I dumb or what? THANKS for your help!
 
For what it's worth, I run 10% ethanol because I have no choice. The car sits from Oct. to Apr. and I never have a problem starting it. That said, I always prime the float bowls before starting it after a long winters nap. Before I started doing that, the first start would take a lot of cranking.
 
Had this issue with a 70 GTX once, turned out to be the fusible link and/or corrosion on the connection IF you are not getting spark.
 
Ranger16 said:
For what it's worth, I run 10% ethanol because I have no choice. The car sits from Oct. to Apr. and I never have a problem starting it. That said, I always prime the float bowls before starting it after a long winters nap. Before I started doing that, the first start would take a lot of cranking.
Click to expand...
So you don't have ethanol-free available? I only started using it two tanks ago. I don't know of any problems it has caused me in the years before that since ethanol started being added. I noticed right after my last fill-up in July 2018, I started having starting problems (and thought it was electrical) and could not start it at all since July 2019. Now I wonder if the gas was stale when I first got it and maybe (I'm just guessing) there may not be a big demand for ethanol-free and it might just sit at the station for a long time. I don't think I'm going to worry about using ethanol-free any more.

That's interesting about letting your car sit from Oct to Apr. I always, in the past before I replaced my carburetor, had to drive mine every 3-4 weeks to keep the bowls in my old from going dry (leaking down or evaporating) and would have to prime it (even after that short of time). Do you have any other problems from letting it sit for that long other than I guess your bowls go dry? I guess there would be no difference to the engine from letting it sit for 3-4 weeks and Oct to Apr?
 
My cars sit for 5-6 months as well.
I try and drive them a good 1/2 hour before storing them and get gas shortly before putting them to bed.
Cap off the exhaust and carb opening. I used to close off the fuel line and flood them with 2 cycle mixed with gas but it's a pain to remove all the plugs each spring. My Plymouth still has a Carter on it and it doesn't take real long to start even after sitting so long.
 
Don Frelier said:
My cars sit for 5-6 months as well.
I try and drive them a good 1/2 hour before storing them and get gas shortly before putting them to bed.
Cap off the exhaust and carb opening. I used to close off the fuel line and flood them with 2 cycle mixed with gas but it's a pain to remove all the plugs each spring. My Plymouth still has a Carter on it and it doesn't take real long to start even after sitting so long.
Click to expand...

Thanks for this Don. Have you noticed any adverse effects on the engine (cylinders, rings, etc) from letting them sit for that long? Do they start-up ok? Any stale gas problems? You probably drive it more than me. I only drive it about 10 miles at a time and it takes months to use up one tank. But never had stale gas problems for years and years when going about a year or more between fill-ups until now. I don't know if stale gas would be more of a problem with ethanol-free or not?
 
If you think it's bad gas, squirt new done carb throat,
If it starts either bad gas in tank or no supply
 
Ethanol free should last longer, Stabil is a good idea.
No never had any stale gas problems, I do drive them both.
In the spring I will run it near empty before the first refill.
The Charger gets driven more than the Satellite maybe 1,500 -2,500 miles per year, still my favorite.
My Charger engine has been in for 22 years and around 35,000 miles.
No issues maybe not quite as snappy as when it was new.
Note too that the choke needs to be set properly to help it start quickly.
I had an instance this past summer where the choke didn't close on the Plymouth, wouldn't start.
But I knew how long it normally took to crank and fire something was wrong, so I took a look and sure enough the choke was still open.
Fixed it and it started immediately.
 
Ed Martin said:
So you don't have ethanol-free available?
Click to expand...
Not in my neck of the woods.

Ed Martin said:
That's interesting about letting your car sit from Oct to Apr. I always, in the past before I replaced my carburetor, had to drive mine every 3-4 weeks to keep the bowls in my old from going dry (leaking down or evaporating) and would have to prime it (even after that short of time). Do you have any other problems from letting it sit for that long other than I guess your bowls go dry?
Click to expand...
Nope, she fires and runs like I shut her down yesterday. I don't think your problem is gas. I've started a generator with about 8 year old gas (10% ethanol) and it only took about 5 pulls.
 
Last edited:
Don Frelier said:
Ethanol free should last longer, Stabil is a good idea.
No never had any stale gas problems, I do drive them both.
In the spring I will run it near empty before the first refill.
The Charger gets driven more than the Satellite maybe 1,500 -2,500 miles per year, still my favorite.
My Charger engine has been in for 22 years and around 35,000 miles.
No issues maybe not quite as snappy as when it was new.
Note too that the choke needs to be set properly to help it start quickly.
I had an instance this past summer where the choke didn't close on the Plymouth, wouldn't start.
But I knew how long it normally took to crank and fire something was wrong, so I took a look and sure enough the choke was still open.
Fixed it and it started immediately.
Click to expand...

Thanks Don. I'm pretty sure the choke is set right cause it looks like it is whenever I've been checking to see that the accelerator pump I spraying. I will see what happens when I put some new gas in it and see if it fires up without using starting fluid like I had to the other day to fire it. If it's not stale gas, I'm at a loss.
 
What type of plug wires?
How old?
I've seen these cause starting problems.
 
Don Frelier said:
What type of plug wires?
How old?
I've seen these cause starting problems.
Click to expand...
The wires are several years old but are good quality Moroso. But now (last weekend) I did get it to start (using starting fluid) and run (normally), I think the wires are ok.

I think I will try stabil as you suggest from now on because I routinely go more than a year on a tank of gas. Do you know of any side-effects or have you used it?
 
I've used Sta-Bil in snowmobiles that sat for a year and in the above mentioned generator, and in my Road Runner (when I remember). No side effects........that I am aware of.
 
You must log in or register to reply here.

Similar threads

Tony 69
Low voltage to coil
Replies
14
Views
471
RJRENTON
RJRENTON
blue69runner
No fire at spark plugs.
Replies
11
Views
716
blue69runner
blue69runner
mrmolding
No crank, no start, no accessories but headlights work.
2
Replies
25
Views
2K
mrmolding
mrmolding
XS22J8R
Coil Voltage question
2
Replies
26
Views
3K
Mbrew
M
Don67Satellite
A Progression Ignition Question
Replies
9
Views
1K
Don67Satellite
Don67Satellite
Auto Transport Service
Back
Top