PcWilliams
Member
Hi all. Seems i'm not getting full voltage to the coil. I'm getting about 5 volts when i think i should be getting about 8 (?). Any ideas?
Low voltage to coil
- Thread starter PcWilliams
- Start date
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5V with engine running or not?
PcWilliams
Member
I believe running. It was my mechanic's and he said it was only getting about 5 volts. I assume he meant running. It runs like it's weak.
Measure the voltage on the other side (feed side) of ballast resistor. It should be about 12 v. If it is, your coil or ballast resistor could be bad. I am assuming you have a ballast resistor.
If it is a stock ignition ballast resistors and coils are pretty cheap. I would shotgun both.
If voltage is not near 12 v, more troubleshooting of supply circuit will be needed.
If it is a stock ignition ballast resistors and coils are pretty cheap. I would shotgun both.
If voltage is not near 12 v, more troubleshooting of supply circuit will be needed.
PcWilliams
Member
67Dart273
Well-Known Member
This may or may not be a good strategy
1....You want to find out that there is or is not (should not be) voltage drop between the ballast resistor ignition switch feed, through the harness, switch, bulkhead, all the way back to the battery
2.....Ballast voltage will vary A LOT depending on whether idling slow or engine off, etc, the type of coil you are running, and just plain variations over the years
So........
To check for voltage drop, with engine off, turn key to "run." Measure voltage between battery POS post and the keyswitch side of the ballast. You should have a VERY low reading, the lower the better. More than about .3V (3/10 of one volt) means there is voltage drop in there
2....Check coil+ voltage both with key on / engine stopped. and engine running at low idle.
Check again, rev engine up to simulate "medium cruise" RPM IE as if you were cruising down the street at 40-45 mph
Here, battery should read nominally 14V (13.8---14.2 if warmed up) and coil will read 10--12V +/- again, depending on the coil
Yeah, agreed on the troubleshooting 67Dart. Just thought that for a non electronic guy replacing the two obvious parts might be a cheap first shot. Everything else gets a lot harder.
PcWilliams
Member
Wow. I will give this my best shot. Thank you.
67Dart273
Well-Known Member
...........And I'd agree that this is a variable that can be subjective. Frankly, if the supply voltage TO the ballast is OK, and the ballast is not cutting out/ intermittent etc, then it itself is likely OK. The other issue of course, with replacement...............is the Chineseoationized "quality" of today's parts.
Yeah, the Chinese parts have been an issue for me a lot of times, particularly electrical parts. They are even in the name brand stuff now. I had to buy a coil for mine for a “side of the road” repair. All they had was the house brand. It lasted about a month. I ordered a Borg Warner one thinking it would be higher quality- it was the same exact crap coil. I wound up buying a Mr Gasket (I think) nice Chrome one. It has been fine.
In the past, it seems like I have had a little more money than time and patience. Often times if I couldn’t isolate a problem quickly, I would buy the “cheap and easy” stuff to try and reduce the number of variables. My theory was that if the parts were very old,it wasn’t a bad idea to replace them anyway & it kept the car in more reliable condition. However, if the parts you are putting in are questionable, then my strategy falls apart. Instead of narrowing down the issue, it could be adding to it. Very frustrating.
In the past, it seems like I have had a little more money than time and patience. Often times if I couldn’t isolate a problem quickly, I would buy the “cheap and easy” stuff to try and reduce the number of variables. My theory was that if the parts were very old,it wasn’t a bad idea to replace them anyway & it kept the car in more reliable condition. However, if the parts you are putting in are questionable, then my strategy falls apart. Instead of narrowing down the issue, it could be adding to it. Very frustrating.
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