74' No Start Troubleshooting Help Needed

[Robert S.]

Background: 1974, L48, manual, conventional points ignition, uniset point set new installed today as part of troubleshooting. Last used about 3 weeks ago and started and ran normally. No start today. Battery and starter strong. Car has a history of consuming points in a few hundred miles which is why the new point set was installed. Never have found the cause for this but did change out the starter solenoid a year or so ago so see if that would help the point issue.

Troubleshooting done today: Tried starting ether - no response, measured full battery voltage at plus side of coil when ignition switch turned to on ( not sure this is correct?) , continuity of black wire from minus side of coil to points checked ok, verified that new points are opening and closing via a VOM continuity check while turning over on the starter, cap and wires appear like new (don't know the age but not many miles), pulled number 1 plug and put on a spare spark plug - wife said she saw little to no spark when I cranked the engine - not sure what to make of that.
I am beginning to suspect the coil may be bad as I think it is original to the car.

Looking for ideas of where to go next?

[Tom B.]

Re: 74' No Start Troubleshooting Help Needed

Here is an easy to follow coil check proceedure.

http://www.secondchancegarage.com/public/coil-troubleshooting.cfm

I think I see why you would only get 300 miles or so from a set of points. you should not have 12v to the + coil terminal with the swtich in the on position; only in the start position. This is burning them up. Is your resistor in place on the 12v lead to the coil? I'm not sure if a '74 had a ballast resistor or a resistor wire. I'm thinking wire. You should only have 12v to the + coil with the starter activated on a points system. The rest of the time, with the ignition switch in the on position, voltage should be less. One source I read says 9.6v. If you have a full 12v to the coil all the time that would cause the coil to run hot and also cause the points to burn up prematurely.

Someone might have removed the resistor in the past if they had an electronic igniition in the car. Electronic ignition require a full time 12v power source.

Test the coil as outlined in the link above and check for 12v at the + coil terminal with the key in the on position.

If the coil checks bad replace it with a proper coil.
If you have 12v at the coil + in the on position check for a missing resistor wire and replace it.

Tom

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

Thanks for the link - I will use this to check out the coil. The car is 100% original as far as I can tell (not the first owner) and the positive side of the coil has the ganged two wire end clip which has both the resistance wire and a non-resistance wire together on the same end clip. Also on this terminal is the capacitor. I think this is the way it was built in the factory.

[Jim T.]

Re: 74' No Start Troubleshooting Help Needed

From what I know about my 1968 a resistor wire is connected from the block of taped wires that is coming from inside the car. The resister wire reduces the 12 volts from the block outlet to the ignition coil and continues to reduce voltage to the coil with key on when driving the car. My 1970 has this same type of resistor wire from the same block located below the brake master cylinder to the coil.
The resistor wire is located the taped wiring coming from the block. Inside the car this is the block with all the fuses for the wiring on the firewall side.

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

Yesterday I disconnected the coil wires and ran the suggested resistance checks and the coil appears to be good. I pulled all the plug wires one at a time off the cap and looked for corrosion and they all looked ok except for some minor stuff on one that I cleaned. I put the wires back on the coil minus the capacitor wire and it started right up. Shut down and installed the capacitor wire and it started right up.
Not where I want to be. Checked a dozen things, basically found nothing wrong other than slight corrosion on one spark plug cap tower and it is back working with no explanation. The only thing changed out was the points but it would not start after the point change and after I had verified that the new points were opening and closing using a VOM. I did not touch the points again from that time until it started.

As for checking for "ignition on" voltage at the plus side of the coil I have read that the reading you get will vary depending on whether the points are open or closed when making this check. Can someone verify if this is correct? If so then would it be appropriate to disconnect the wire from the coil to make this "ignition on" voltage check?

[Mark E.]

Re: 74' No Start Troubleshooting Help Needed

Robert,

An intermittent problem can be challenging. Some thoughts-

- Make sure all primary connections are clean, dry, and tight. This includes the coil, points and its condenser. There's a short wire hidden under the breaker plate that sometimes becomes damaged or loose which can cause this symptom. It grounds the breaker plate to the distributor housing. Check for good ground while wiggling it around.

- Full voltage to the + coil connection will burn points, so it's important to check for proper voltage. To help ensure a good spark while cranking, the coil and points are designed to operate on less than full voltage while the engine is running. The resistance wire (or ballast resistor on some cars) provides this reduced voltage. While cranking, the resistance wire (or ballast) is bypassed to provide more voltage and spark. This design aids starting by providing maximum available voltage to the ignition when the battery load is high (from cranking) and available voltage is reduced. I don't remember the exact voltage drop (3 to 4v? ...the spec is in the CSM), but if working properly voltage at the + coil lead should be a few volts less than voltage measured at the battery. Remember that battery voltage is higher with the engine running. With the ignition switch "on" and the engine not running, I've checked this with the wire either connected and disconnected... it doesn't matter. It can also be checked with the engine running and realizing battery voltage is greater.

- The capacitor mounted on the coil bracket and connected to the + terminal is for radio noise suppression. The ignition will perform without it, so remove it during diagnosis. It can develop an intermittent short.

Keep us posted what you find.

[Joel A.]

Re: 74' No Start Troubleshooting Help Needed

Did you actually adjust the new point set when you installed it? From what I've read here, it appears it would start and run before you put the new point set in. I would suspect the points are not set properly. If you have a helper, adjust the points while someone cranks the engine over and see if it won't fire up. If it does, then you'll need to either set the points with a feeler gauge, or a dwell meter.(everyone still has one of those, right?)
Just checking to see if the points will open and close with an ohm meter will NOT assure they are properly adjusted.

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

After I got it running I put a dwell meter on it and it was off a few degrees but not much and set it to 30 degrees. I used the VOM during troubleshooting just to make sure the points were opening and closing which they were. Clearly if they were staying shut then it would not start and I wanted to be sure that I was not making my troubleshooting any more confusing.

[Mark E.]

Re: 74' No Start Troubleshooting Help Needed

Robert,

Have you determined the root cause of the "no start" condition?

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

I have not found the root cause of the no start condition nor have I determined why I am getting such short point life. Right now the car is starting ok. I don't think the points I replaced is the root cause since it would not start just after point replacement ( after I verified that the points were opening and closing with the VOM) but the points were the only thing I changed out.
As for the short point life I am pretty sure all the electrical wiring is as it came from the factory. I cannot imagine the resistor wire not providing the required resistance as I assume it would either work as intended or provide no voltage ( i.e. a broken wire) when the key is released from the starting position and hence the engine would die (which it does not do). Perhaps the voltage regulator is not regulating the voltage correctly ( i.e. too high) but I am just widely guessing at this point. Very frustrating to me. The point ignition system is relatively straightforward and it would seem to me that I should be able to find the root cause.

[Mark E.]

Re: 74' No Start Troubleshooting Help Needed

From your first post: "No start today. Battery and starter strong... did change out the starter solenoid a year or so ago so see if that would help the point issue. Troubleshooting done today: Tried starting ether - no response..."

Clarifying question: Is the engine not cranking (starter not turning over the engine)? Or is it cranking but will not start/run?

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

Starter is turning the engine over with gusto but it would not start. I suspected an ignition issue but I first tried starting ether as it is easy to do and I wanted to see if the engine would at least pop. It did not and I could see that the accelerator pump was working in the carb. so I focused on ignition issues.

[Mark E.]

Re: 74' No Start Troubleshooting Help Needed

When it cranked but did not start, what was the voltage at the coil's + terminal?

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

I did not measure the voltage when cranking only when the ignition switch was "on". As I recall, as it was two weeks ago, the reading was quite high on one reading - I vaguely recall about 14 volts but maybe I am remembering wrong, and I recall measuring it another time and it was around 7-8 volts but again maybe I am remembering wrong. I subsequently read that the voltage you read depends on whether the points are open or closed when you measure the voltage. Sorry I can not be more definitive.

[Mark E.]

Re: 74' No Start Troubleshooting Help Needed

The next time it cranks but doesn't start, check voltage of + coil terminal while cranking engine. It should be equal to or close to full battery voltage (realize battery voltage drops while cranking).

If ok ==> ignition getting input power but not working, or ignition is ok and problem is another system (like fuel). Check rest of ignition first- secondary then primary. Let us know if you're going down this path and we can share more about troubleshooting this.

If coil has zero or low voltage, check voltage at R terminal of starter solenoid (yellow wire I believe) while cranking. If zero or low ==> probably a bad solenoid. If ok ==> open yellow wire (goes from solenoid to coil).

This is an intermittent problem, so treat the next no start as an opportunity to troubleshoot.

Report back what you find.