Hi Everyone,

Hoping for some advice. I have a 72 coupe that is still new to me with unknown history and corresponding glitches. It has always started and run strongly until today. Here is specifically what happened. I started car with no issues and warmed it up a bit. Depressed clutch and shifted into reverse. The car immediately stalled. Went back into the neutral position and tried to restart. The car cranks strongly but no ignition. At this time I'm thinking a problem with the clutch safety switch so I got under the dash and pulled the plug off the switch to inspect it and reseated the plug. Tried the ignition again and now the car is completely dead, turning the ignition has no effect other than a tiny movement of the speedo. The only area I have been messing in since it last ran is under the driver dash; installed a new hood cable and rubber clutch bumper. Its possible I've dislodged something but I haven't a clue what. Any ideas what it might be?

 

Check to make sure you have fuel in the carb, look and smell after removing the air cleaner. Next remove a spark plug wire and in a dark garage look for a spark, while someone is turning the ignition switch. How old is your battery? Charge it or replace the battery. The clutch safety switch needs to be Jumped with a short piece of wire to complete the circuit, unplugged opens the circuit. Two alligator clips with a short piece of wire will work temporarily. Let us know how you are progressing.

 

Thank you for the reply. The latest is that I have what I believe is called a no crank no start situation. With the ignition On accessories power up and indicator / brake lights work but the car will not crank. Battery is new and fully charged. I tried bridging the clutch safety but made no difference. Carb looks good and fuel is flowing. Will check the plug wire but I'm assuming without it cranking I won't see a spark?

 

Throwing ideas out there. Starter issue or ground issue, if you have HEI Dizzy, maybe wire that feeds from battery to dizzy. You say it is standard, maybe try pushing it and popping the clutch.

 

72 shouldn't be HEI. perhaps transistorised ignition, perhaps breaker points and condenser. Perhaps just about anything if it's not factory stock.
So, with key in run position. Take a test light and check for power to the coil.
Does it have a separate coil?
If you have power to the coil what happens if you jump the starter S terminal to the battery cable terminal?
Check battery cables. In particular the ground cable under the battery box on the frame.

 

Put the ignition to the side for a moment, until you cure the no crank situation.

if you have power everywhere else, it’s not the fusible link by the starter.
Could be a bad or stuck starter solenoid. But I suspect it is related to your clutch safety switch. You said you jumped it, and don’t take this the wrong way, but you jumped the wires in the harness, right? Not the terminals on the switch! Jumping the switch with the harness disconnected does nothing.

 

Thanks for this. I have cured the "no crank" problem. There is a flat brown connector under the dash with two flat pins (looks like a large blade fuse), one wire is purple and the other purple with a white stripe. I have no idea where this plug goes but the previous owner had put a flimsy jumper across both pins which had become disconnected. When I replaced that jumper the car now cranks again but will not start. I believe the sequence of events is this...
1. Car works fine
2. Replace the rubber clutch bumper (potentially damaging the clutch safety switch)
3. Car starts Ok but stalls when attempting to enter into reverse (is there a reverse safety switch also?)
4. Car now cranks but won't start
5. Inspect the clutch switch and accidentally dislodge the temporary jumper on the nearby purple / purple-white plug - car no longer cranks
7. Repair temporary jumper on purple / purple-white plug and car now cranks but won't start
8. Jump the connector leading to the clutch switch - no change in condition, car cranks but won't start

To ensure I understand your point on jumping the clutch safety... I removed the plug from the switch attached to the pedal. Switch is male and plug is female. I jumped the the two female connectors in the plug (presumably) simulating the switch in a closed state.

I'm thinking my next step is to see if there is 12v at the coil and to inspect all the fuses?

 

I've repaired the clutch safety switch and works perfectly. No crank if the clutch is not depressed and cranks with the clutch depressed however still no ignition. I believe the clue is that the engine died and refused to restart exactly when I put it into reverse. This makes me think it is something electrical related to the gear shift. Could the reversing light switch have created a short circuit that has impacted the ignition?

 

No power at the ignition pin in the fuse box with the ignition in the on position. Is that a clue or does it suggest a diagnostic route? Are there any fuses in play before this pin?

 

Do you have 12 volts on the IGN terminal and if not is the fuse on the left side of the IGN terminal good?

 

The fuse was NOT good. I replaced it and now have 12v on the ignition pin on the fuse box but the car still does not start. My next step is to test the coil / spark plug. Its weird that the engine died exactly as I shifted into reverse.

 

Check if that fuse blew again. Maybe you have a short somewhere that is blowing that fuse immediately.

 

If you still have the stock coil and points ignition, the wire to the coil should have ~12 volts when cranking and drop to ~9 volts via the resistor after it is running.
Maybe you aren’t getting that 12 volts boost when cranking.

 

Feeling totally flummoxed at this point. I have a well charged, new battery and 12.4V at the "BAT" terminal of the HEI ignition module with the ignition on. I used a cheap plug tester inline between the distributor cap and the #1 plug lead and can see a flickering glow in the test tool when cranking the engine but still no start. Plenty of fuel flow (I can see it pump and smell it) and the high performance starter is cranking the engine strongly (enough to see movement on the Tach). Not sure where to go from here??. Is it possible the output from the HEI is present but weak? What else can prevent the engine starting? This is a relatively fresh motor that has always started easily and run strongly.

 

Try spraying some engine starter in the carb while cranking the engine to see if you get at least a plug to fire. That will tell you if the spark is ok.

 

Thanks for the suggestion. What does this technique help to establish or eliminate as a potential problem?

 

With a wire of 12 to 14 gauge, connect one end of the wire to the positive side of the battery and connect the other end of the wire to the positive side of the coil. Use an alligator clip. Try to start the car. If it starts, you have a problem with your ignition switch or wiring. Do not leave the connection on after testing. Jerry

 

If you hear the spark plugs fire and ignite the spray, then it may be a fuel delivery problem. You have not made any mention of your carburetor, as the brand, model, age, etc. pictures are always helpful when posting on the Forum.

 

Hi Jerry, thanks for the idea. I've established with high confidence that I have a reliable 12V to the input of the coil. Upon testing the output of the coil with a plug tester inline between distributor and plug I see a weak orange flicker in the tool which suggests to me I have a weak spark. I'm now leaning towards believing I have a faulty coil or a fault in the HEI module. Its the timing of the fault that has me concerned. The engine quit exactly as I entered reverse which is making me wonder if there is a short (perhaps in the reverse switch) that triggered the failure of the HEI module. The concern being that if I install a new HEI unit without finding the root cause I may destroy the new one. Reverse lights don't work on this car now (and not sure they ever did) but I can not locate a short in that circuit so I don't really know. Perhaps the timing of the failure was just pure coincidence?

 

The car has a Holly 4 barrel carb with aluminum intake and Flotek heads. Its a fresh rebuild with new parts (except HEI distributor which looks older) based on a 74 donor motor. With the air cleaner removed I see the butterflies moving correctly and can observe fuel pumping in through the jets on both sides of the carb. After prolonged attempts to start the car I got a kind of backfire up through the carb. Not loud, more of a sharp "phut" sound but with a lot of grey smoke and a strong smell of gas. I'm assuming this was due to flooding the engine and getting a small, mistimed ignition event. I'm leaning towards a weak spark being the cause of the no start. Agree on the pics - will post some more shortly. Below is the HEI module I referred to,