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General Tech Voltage Drop and Starting Problems

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KVH

KVH

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I have 12.5 V at the battery, and 11.5 V at the positive side of the coil. Is that anything of a concern?

I’m having trouble starting, and I am seeing a weak spark at the plugs.

I’m confused what’s going on, as my coil is new, and so are the entire guts of my distributor.

My engine is cranking like I’m out of gas, but I don’t think there’s anything wrong with either my fuel pump or carburetors.

As the saying goes, I think the problem with my carburetors is my ignition. But I can’t put my finger on it.
 
Ground the negative terminal on your coil, then take a reading of your voltage across the positive and negative terminals when you engage the starter and again with the ignition key in the ON position
 
Check all grounding connections.You must have 12.5V at the coil or its trouble.
points will still make spark but pertronix will NOT.
Mad dog
 
Since a Pertronix is involved, if you decide to check the voltage that is feeding the coil by the method I described, you should remove the RED Pertronix wire from the coil during the test.
 
Disconnect the primary lead at the dist. and check voltage at both terminals of the coil and the end of the primary wire that connects to the distributor. No reason for any drop from battery voltage at any of these points. The wires are braided (multistrand) and if some of the strands are broken (as from too much bending where they attach to the terminals) this could account for the drop and failure to start. BTW, has it run with the new dist.? If the problem arose on first try with the new dist., the new dist is where to look (and it might be anyway).
Bob
 
I’m not sure what you mean by the “primary lead“ and the “primary wire.“ Are you referring to the plug/wire from the center of the coil? Or the lead from the negative pole of the coil to the distributor?

The car has been running great for many weeks with this distributor. I truly thought I would have no more starting problems, especially since I also replaced the coil.

However, my “age old“ problems with this car, having intermittent starting and stalling problems has come back yet again.

There is something very obscure going on with this particular vehicle. I have two other Triumphs and have zero problems.
 
Your voltage at the coil depends on whether the points are open or closed. If open, you should see voltage equal to the battery voltage. Once you turn the crank to close the points, you should see no volts on the points side, and very slightly less volts than battery voltage on the side to the ignition switch.

Remember that there has been a rash of bad condensers. A bad condenser is one of the primary reasons for a poorly running car and will lead to burned points.
 
My battery shows 12.9 volts. When my points are closed I have .3 volts at the negative coil side (wire to distributor). When open I have 11.9 volts. At the ignition wire side I have 11.6 volts. Seems all very close. My condenser is new, fwiw.
 
I had a horrible issue years ago. Started when I switched the head lights on - killed the motor. I had 12.9v at the battery but way under 11v at the coil (I want to say ~7.5v). The drop from batt to coil should never be more than 1.0v at most.. 0.25 to 0.50v is normal range.

Turned out to be severly corroded terminals on the ammeter. Pulled the meter. Cleaned the horribly corroded male and female contacts. Reassembled with dielectric grease and new Lucas rubber boots. Worked a treat.

Now I test the voltage drop between the batt and coil every year as a part of my annual maintenance. Drop is always less than 0.50v.

Bob
 
This evening I just about gave up on this car. No matter what I tried, the car wouldn’t start and the spark seemed unusually weak using the old “screwdriver 1/4 inch from ground” method.

I decided to stop in at the local Moss dealer and shop, and I bought a new distributor cap, points and condenser. The engine started right up and runs perfectly now.

This is so frustrating because I put new points and condenser in just a little over a month ago, and I have two old distributor caps that I switched out and none of them made any difference.

I can’t quite even begin to figure out the problem, but I have a few suspicions.

One suspicion is that there are manufacture defects in the distributor caps, and that I finally have one that is correct. Another is that condensers are regularly defective, new or not, but I can’t imagine that a bad condenser would cause me to stall and then also prevent me even from restarting the vehicle. My third suspicion is one I’m actually considering seriously.

It’s this: My Moss Cobalt brand plug wires look great, but fit very tight, and I often have trouble feeling the snap at the back of the spark plug. I’m wondering if this intermittent problem I’m having with my engine stalling, and then not starting, is caused by a plug wire slipping off the spark plug inside the boot.

In any event, as far as I’m concerned, the mystery continues despite my presently perfectly running engine.
 
Congrats on the victory. Ignition problems can be absolutely mind-blowing and hard to solve.

I'm thinking the plug wires aren't the problem. If you got the car running well by replacing cap, points, and condenser, but didn't change the plug wires, then the plug wires weren't the problem. Prior to this, the engine wouldn't fire when cranked; it's pretty unlikely that all four plug wires would fail repeatedly, but fire perfectly with new cap, points, and condenser.

If today's Arizona weather is good (looks like it'll be clear and H O T), then go for a long drive and enjoy the sound of those four cylinders humming as they were built to do.
Tom M.
PS - I'm betting the problem was condenser failure. YouTube has some good videos on testing an ignition condenser.
 
KVH said:
I’m not sure what you mean by the “primary lead“ and the “primary wire.“ Are you referring to the plug/wire from the center of the coil? Or the lead from the negative pole of the coil to the distributor?

The car has been running great for many weeks with this distributor. I truly thought I would have no more starting problems, especially since I also replaced the coil.

However, my “age old“ problems with this car, having intermittent starting and stalling problems has come back yet again.

There is something very obscure going on with this particular vehicle. I have two other Triumphs and have zero problems.
Click to expand...
Glad you fixed the problem--for now.

This experience is typical of a bad connection somewhere. You get good contact, momentarily, and all is well, but later the connection fails again. I suspect you still have one, and in the most recent work you inadvertently "fixed" it for now. I think this would be a good time to go through the entire ignition part of the electrical system and clean and tighten every connection. Also get a reliable ignition capacitor and, if you suspect the plug wiring, just replace it (or, at least, fix the connections so you can trust them).

Electricity really does work when everything is right. But we have a word to describe an electrical system that is 99% working: broken.

And, yes, a bad ignition capacitor could well cause a weak spark and starting/running problems.
 
sp53 said:
could it be the coil? i am sure you must have repalced it
Click to expand...
Well, I watched the YouTubes and tested my two condensers that I’d removed, including the one while the car wouldn’t start. As best I can tell, both condensers passed. And, yes, I replaced the coil.

For the condenser test, I had some problems. First off, my Multimeters, two of them, won’t register anything at the 20K setting. I had to dial it to 200K or to 2M. For volts, I had to dial to “2.” Using the routine on the YouTubes, each condenser held a charge and slowly discharged. Very slowly. Maybe five minutes to reach .1 or less volts. My resistance went up to about .725.

The ease with which my engine now starts is a bit shocking. Half a key turn and I’m running. The mystery continues, though I’m still struck by the Standard Triumph Electrical Fault manual that states, in essence, there is no way to determine a bad condenser other than replacement. Granted that was printed near the time Winston Churchill died.

I still suspect something is wrong somewhere. Three total engine quits in just a matter of a few months and infrequent driving. Zero warning. I once suspected flooded carbs, but no longer. I tested my fuel pump pressure. Fine. I checked the wiring to the distributor. All good. Wiggling wires changed nothing. Likely irrelevant, but with points closed the reading at the neg coil terminal isn’t “0”. It’s more like .03.
 
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