steve4570

What should the voltage be across my coil when ignition is on with engine not running. I checked my voltage across the coil and it is 3.6 volts, is this too low, I have a 1970 454 which only revs to 4,300rpm. I have replaced coil, points, condenser and leads.

MelWff

not sure what you mean by across the coil, the positive terminal should have at least 9 volts with key in run position engine off.

steve4570

Yes that's what I mean, measuring the voltage at the negative and positive terminals of the coil. I get 3.6 volts with ignition on while engine not running. Is this too low and could it cause the engine to not rev past 4,200 rpm.

DUB

I personally have only been concerned about the amount of voltage going into the coil. I am curious if someone gives you an answer. I have never seen anyone ever check for that...and I have been around some serious mechanics over the years when points were still be serviced on a regular basis....and have never seen this one.

I do use my Kilo-volt tester when the engine is running so I can see how 'hot' the current is going to the plugs.

DUB

LB66383

If you are measuring across the terminals of the coil, you are measuring the voltage drop across the coil, not the input voltage. The voltage drop will vary, depending on the resistance of the primary windings in the coil. A 1.5 ohm coil will have a different reading than a 0.6 ohm coil, for example. You need to disconnect the wire from the + side of the coil and then measure the voltage on the wire with the ignition ON.

DUB

I feel that there is another issue going on that does not have to to with what is being asked.

Is the timing mark on the harmonic balancer still in the correct position and has not spun.

Is the distributor allowing the timing to advance and not froze up...and the vacuum advance control correct and working.

Plug wires correctly separated and not all 'zip' tied together....and on any heat source.

I have other ideas also...but without seeing the car and seeing what is going on...it is all just speculation...One being...about 20 years ago..I had the same exact year model and engine in a Corvette at my shop...and it ran rich as heck and backfired quite often. And it was not until I popped the hood and left it popped up...it would not run right due to the aftermarket air cleaner that was on it. The hood was so close to the air cleaner is suffocated the engine when the hood was shut.

DUB

MelWff

To start with make sure the coil terminal wires are not reversed. The + terminal of the coil should have a dual wire connection and the - terminal should have a single wire going to the distributor. If it is set up this way and you take the red lead of your voltmeter and clip it to the + terminal and clip the black lead of your volt meter to a good metal ground you should have way more than 3.6 volts which if that is what you have will cause the engine to run very poorly.