i mistakenly posted a thread in PERFORMANCE about a stalling at stop light problem that suddenly apppeared after an AT==> tremec 5 speed changeout here :

http://www.chevelles.com/forums/showthread.php?p=2491349#post2491349

i am still trying to chase this down.
just considered that wires to starter solenoid may have been damaged in removing and reinstalling headers.
frow what is visible they appear intact.

but i took voltage readings at the coil positive primary terminal.
am getting 11.3 volts at idle but it drops to 7.25v at 1500 RPM.

on the negative side i am getting 10.4v at idle dropping to 4v at 1500.

anyone know what the correct voltages on both sides of the coil primary should be?

also what is the purpose of the yellow lead from the positive coil primary to the outer terminal on the solenoid.
its been 40 years since i had a solenoid apart and dont remember the operational details!

The yellow wire from starter to coil provides 12v to the coil while cranking the engine. Once the engine is running the coil gets power from the other wire on the + terminal. This is a resistance wire, some cars used a ballast resistor. Either way voltage to the coil is reduced once the car is started, no voltage from yellow wire. The lower voltage keeps the points from burning up quickly.

Measuring the voltage at the coil while the cars is running is difficult. The points are constantly opening and closing so the voltage is going up and down. Looks more like an AC voltage than a DC one. What you see all depends on how your meter averages this fluctuating voltage and it will change with RPM. Voltage should be around 9v from resistance wire. You can turn the key to on without starting the car, if the points are open you should read about 9v.

The yellow wire from starter to coil provides 12v to the coil while cranking the engine. Once the engine is running the coil gets power from the other wire on the + terminal. This is a resistance wire, some cars used a ballast resistor. Either way voltage to the coil is reduced once the car is started, no voltage from yellow wire. The lower voltage keeps the points from burning up quickly.

Measuring the voltage at the coil while the cars is running is difficult. The points are constantly opening and closing so the voltage is going up and down. Looks more like an AC voltage than a DC one. What you see all depends on how your meter averages this fluctuating voltage and it will change with RPM. Voltage should be around 9v from resistance wire. You can turn the key to on without starting the car, if the points are open you should read about 9v.

If the points are open, you should read the full battery voltage. If the points are closed, you should read a voltage proportional to the ratio of the ballast resistance versus the coil resistance.

sorry guys but i failed to mention it is a GM HEI with an outboard blaster II coil ...

does this chage the voltages i should see at the coil?

sorry guys but i failed to mention it is a GM HEI with an outboard blaster II coil ...

does this chage the voltages i should see at the coil?

Yes, it does. It may be that the resistance wire is in series with your coil and that is where you are have the issue. You might need to bypass the resistance.

What Balster coil is it? Was it designed for HEI?

Ron

If the points are open, you should read the full battery voltage. If the points are closed, you should read a voltage proportional to the ratio of the ballast resistance versus the coil resistance.

Sorry for that, should have said closed. Open and you get full bat voltage.

Years ago, a member who went by “ ignitionman” recommended removing the coil from the HEI distributor and mounting and external BLASTER II coil. I had a module failure and at that time the discussion was that the heat from the coil was hard on the modules and many of us did this way back when.
that was the hot lick ignition update of the day.

The system has been fine for years.
I just had a tremec installed and upon picking the car up (after 2 months) I had this problem that it would die at stop lights.
I never had this issue before as this engine has a very mild cam and a very stable idle.

Now that this has come up, I can only get reliability by cranking the idle up to 1000 in neutral instead of the old 650 in gear with the auto tranny.

I cant seem to identify a fuel issue so I started to check out the ignition and really have not yet found anything.
Checked timing, cleaned all coil and module connector connections.

then I checked the coil votages while running and they seemed low.

When the wiring was done we did not add a ballast resistor, and as i recall i was told there is a resistor wire link in the line that feeds the coil (original points distributor wiring). I did not bypass that with a direct 12 volt line and used the factory line.
If that recollection is correct & there is a resistor link in the line, then the Positive coil terminal should not read 12 -13.8 when running but something less.

I just dont know that value should be . so I am asking so i can know if the blaster II is being fed proper supply current or if it too low.

I thought this could be a soure of unrelible idle tho as state the voltage seems lower at 1500 than at idle.
I realize this is a pulsating DC signal but i expected the values read to be higher.

You guys know if the HEI module is supposed to run on 12V with out a "voltage dropping" ballast resistor?

What about the "MSD Blaster II" coil?? 12 v or resitor fed?

Make sure they didn't crack your distributor cap while changing the trans. Especially easy to do with the bigger HEI cap. Good luck, Jim

I hope this is not a silly reply but since you had a significant amount of work done it is probably something simple. I have been learning that the hard way after doing a frame off on my car...all problems have been caused by something real basic.

Since you did an auto to manual swap I assume that you no longer needed a vacuum line to the tranny. Was that vacuum port plugged or is the plug leaking? The idling issues sounds like a potential vacuum problem to me.

FWIW

i eliminated the blade connectors that i still had in the primary/ module wiring and ran +12 volts to the coil primary and problem is completely resolved.

those blade connectors must ahve been doing something funky at idle only.