Tach help
- Thread starter dickyeb
- Start date
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KitCarlson
Well-Known Member
Where is the tach getting 12V? If from the coil +, it is fed from the ballast and lowering the coil supply voltage. That will starve the coil of current when the dwell is short at high RPM.
Measure coil +, if less than 7V, there may be too much voltage drop in ignition wiring. Things like bulkhead connectors.
Measure coil +, if less than 7V, there may be too much voltage drop in ignition wiring. Things like bulkhead connectors.
KitCarlson
Well-Known Member
Did you measure the coil + with engine running?
I think the ignition is weak to begin with due to other problems. A conventional tach slightly loads the coil -. The coil -, has a transient peak that can be 300 to 500 volts for ignition event. A scope is used to observe problem there.
I think the ignition is weak to begin with due to other problems. A conventional tach slightly loads the coil -. The coil -, has a transient peak that can be 300 to 500 volts for ignition event. A scope is used to observe problem there.
TrailBeast
AKA Mopars4us on Youtube
What I was asking earlier was, does the timing change when you hook up the tach?
Just a thought
Just a thought
Ooohhh. Gotcha. No haven't check the timming. Didn't think of doin that. I will check timming. Could it be that I have a stock box from auto zone. Also this is the orignal harness that has been made into electronic igntion. Plus removed te amp meter using the mad eletrical way. I'm not going to be able to touch it till tommorrow .i will let Y'all know what my readings are. Thanks so much.
67Dart273
Well-Known Member
15V is too high. You need to start by making some tests.
1--First and foremost, unbolt the regulator and notice whether the bolts are stripped or can be made tight. Scrape the firewall around the bolts, as well as the regulator mount. Use star washers.
2--Check the ground. Run the car at a good fast idle, and run check 2 and 3 first with all accessories off, and again with lights, heater, etc running. Stab one meter probe directly into the top of the battery neg. post. Stab the other directly onto the regulator mounting flange. You are hoping for a very small reading, the less the better, and zero would be perfect. Over .2V means you have a ground problem between battery NEG and the regulator case
3--Check the hot side of the ignition harness. Turn the engine off, but switch the key to "run." Stab one probe into the top of the battery POS post. Hook the other probe to the ignition "run" buss. Either at the "key" side of the ballast, or at the blue field wire on the alternator. Again, you are hoping for a very low reading. More than .3V (three tenths of one volt) means you have a voltage drop problem in the path ---------
from the battery -- fuse link --- bulkhead connector -- ammeter -- in harness splice -- ignition switch connector -- through the switch -- back out the switch connector (on dark blue "ignition run") back out the bulkhead connector -- and to components under the hood, ignition system, alternator blue field wire, regulator, etc.
Your top most suspects are, the bulkhead connector, the ignition switch connector, the switch, ammeter connections or the ammeter itself, and in rare cases (but it does happen!!) a failed "in harness splice."
1--First and foremost, unbolt the regulator and notice whether the bolts are stripped or can be made tight. Scrape the firewall around the bolts, as well as the regulator mount. Use star washers.
2--Check the ground. Run the car at a good fast idle, and run check 2 and 3 first with all accessories off, and again with lights, heater, etc running. Stab one meter probe directly into the top of the battery neg. post. Stab the other directly onto the regulator mounting flange. You are hoping for a very small reading, the less the better, and zero would be perfect. Over .2V means you have a ground problem between battery NEG and the regulator case
3--Check the hot side of the ignition harness. Turn the engine off, but switch the key to "run." Stab one probe into the top of the battery POS post. Hook the other probe to the ignition "run" buss. Either at the "key" side of the ballast, or at the blue field wire on the alternator. Again, you are hoping for a very low reading. More than .3V (three tenths of one volt) means you have a voltage drop problem in the path ---------
from the battery -- fuse link --- bulkhead connector -- ammeter -- in harness splice -- ignition switch connector -- through the switch -- back out the switch connector (on dark blue "ignition run") back out the bulkhead connector -- and to components under the hood, ignition system, alternator blue field wire, regulator, etc.
Your top most suspects are, the bulkhead connector, the ignition switch connector, the switch, ammeter connections or the ammeter itself, and in rare cases (but it does happen!!) a failed "in harness splice."
67Dart273
Well-Known Member
That varies with RPM and battery voltage. Once you get the overcharge fixed, IE the system should be close to 14V, the coil + voltage varies from around 6-8 (not running or low idle) to as much as 12.
Now, you don't have any accessories hooked to that do you?
Now, you don't have any accessories hooked to that do you?
KitCarlson
Well-Known Member
As 67Dart273 suggests the wiring needs help because the 15V, at battery. The 7V at coil is in typical range, however it should be there at high RPM. I would check for a blue spark, if red or orange, it could be coil. Also check that the mopar box, has clean and tight ground connection.
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