LT-1 Transistor Ignition Dwell

[Ted K.]

Re: LT-1 Transistor Ignition Dwell

Great info. What is a 1-3 candle power lamp equal to in watts or volts?
No o-scope available. Wish there was an old Sun Engine Analyzer around.
Is there a spec. for the gap between the magnetic coil pickup and the distributor lobe?
Ted

[Jack H.]

Re: LT-1 Transistor Ignition Dwell

I cited the advice in candle power because both your copy of the car's owners manual and the shop manual list the various lamps used by lamp number and candlepower.

Want to convert to watts? Well, in general you can't because candlepower is the light output profile of the lamp and filament efficiency (heating power in to light output) varies from lamp to lamp.

But, if you run a Google search on "candlepower to watt", you'll find articles that quote a 'reasonable' way to get the job done.

On specs for the air gap, I'm sure there were/are some, but I can't quote them. What I was saying is this.

For there to be a SIGNIFICANT pulse height difference, you'd expect a significant air gap variance (the TI amplifier has a fixed gain). So, go look for something obvious like a broken magnetic coil finger...

Old Sun Engine Analyzers ARE around and pop up quite frequently at various swap meets. Good luck getting one calibrated and running if it needs parts though!

So, want answers to these questions? Go crack a book or do a web search. The info is out there. But, your copy of the service/shop manual also lists the primary side winding resistance of various ignition coils and you can save yourself the conversion exercise. Remember, you're simply trying to attach a dummy load to the TI amp that mirrors/mimics the ignition coil you're replacing.

The key points about using a lamp are:

(1) You MUST provide a load for the TI amplifier to work through. It's transistor based, of VERY early design and is essentially a current NOT VOLTAGE amplifier. Therefore, you have to give it a load to run with...

(2) A lamp is something most of us have on hand and many have filament resistance profile that just happen to be in the ballpark of the ignition coil's primary winding resistance.

(3) Because a lamp illuminates, you get visible feedback vs. having to use a meter or scope.

[Ken A.]

Re: LT-1 Transistor Ignition Dwell

Great info. What is a 1-3 candle power lamp equal to in watts or volts?
No o-scope available. Wish there was an old Sun Engine Analyzer around.
Is there a spec. for the gap between the magnetic coil pickup and the distributor lobe?
Ted

You do not need any of the whiz-bang tools or light bulbs to test the PU coil. All you need is an AC voltmeter. Disconnect the white connector from the PU coil and connect the probe leads to the 2 terminals from the PU coil, either side works. Crank engine and observe volts. Should be a minimum 1.4 volts to trigger the amplifier. You may also check the resistance of the PU coil-should be a min of 580 ohms up to 700 ohms. The clearance between the stator and pole piece should be equidistant the thickness of a thin business card-while you're doing this, also check for a cracked magnet. Crack=low gauss=low volts.
In addition, you may be experiencing a break in the coil windings which tests ok when cold but when it gets hot & expands-the break shows up.

[Duke W.]

Re: LT-1 Transistor Ignition Dwell

This is a fresh motor with 10 miles on it. New plugs, wires, distributor cap, old rotor. I'll check out them all out tomorrow.
Thanks,
Ted

Now you tell us...

You also need to have a correct coil for the TI, which has difference resistance/inductance than typical coils for the single point ignition.

Duke

[Ted K.]

Re: LT-1 Transistor Ignition Dwell

Wow! I see now why so many of factory equipped TI cars have been converted to standard distributor, (points).
I will pursue some of the suggestions. My problem is a slight miss throughout the RPM range, not one specific cylinder. The reason I believe it to be an ignition problem is I can see occasional flickering in my timing light on most all cylinders which seems to correspond with the miss.
Ted

[Jack H.]

Re: LT-1 Transistor Ignition Dwell

Please re-read...

My 'wiz bang' advice wasn't focused at the magnetic pickup coil. It was intended to be helpful for one trying to ascertain the SYSTEM level operation of his TI. That's distributor + wiring + TI amplifier up to the coil primary side.

If I remember correctly, the thread began with complaints of sporadic mis-fire at various RPM points and a general question about how to assess the proper operation of a TI ignition system. Heck, the problem(s) could be as simple as spark plug wires...

[Jack H.]

Re: LT-1 Transistor Ignition Dwell

Then I'd say go put it on an engine analyzer and monitor/document the spark profile...

[Terry M.]

Re: LT-1 Transistor Ignition Dwell

Jack,
I was not suggesting your advice was using wiz-bang technology -- quite the contrary. Your suggestions were functional using commonly available items.

It was I who equated the oscilloscope with the current day lab scope. I do think the chances of Ted finding a shop with a lab scope are greater than the chances of finding an oscilloscope. Both these scopes are the wiz-bang technology I was referring to.

It would be prudent to eliminate, or at least test the simple things (spark plug wires and spark plugs, or distributor cap or rotor) before delving into the more complex area of the TI system itself. New does not necessarily mean that the part is good. One needs to test (measure the resistance of the wires, be sure the rotor is not too short to properly conduct the high voltage to the cap terminal) the part and verify it is good.

[Ted K.]

Re: LT-1 Transistor Ignition Dwell

Appreciate all the info. There are parts of each post that will be helpful to me as I try to figure out my problem. When solved I'll respond.
Thanks,
Ted