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Non-running diagnosis.

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C

Crisis

Jedi Hopeful
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Could anyone tell me, when a coil is about to give up the ghost for good, can it be intermittent? TR6 died on me one beautiful day while cruising. Thought it was the heat-but no it didn't start the next morning either. Then a few days later I thought I would give it a try. It started and ran great so I thought I'd take it to run a few errands...well it just quit at the worst possible time and has not started since? I suspect the coil, but don't know for sure. Don't want to start replacing things just to find out. Any more thoughts?
Thanks.
 
Safest way to check things out is to replace one at a time. My 74 TR6 just died one day, about two weeks after a full tune up. After replacing the rotor, she fired up and has run perfectly since. When she died, felt just like running out of gas. Could be your coil, don't know if their problems can be intermittent. Good luck, Andrew. /ubbthreads/images/graemlins/driving.gif
 
Sometimes, replacing one bit at a time is as good a way to find the problem as any. But first, I'd do some basic checks to determine a: at what point (no pun intended) spark is no longer occuring; and b: if you might (instead or also) have a fuel delivery problem.

Coil is one possibility, given what you describe, but so are either rotor or condensor, not to mention something floating around in the gas tank that occasionally blocks off the feed line.
 
Start with the easiest things to check, which are all the wires that lead to the coil and from the coil to the distributor. These are thin and can be awfully brittle over the years. Also check the main Plug-type wire, because this can sometimes work itself out.

If you pull the distributor cap, there should be some type of evidence of scorching or carbon or such if the problem is there.

You can pull the fuel line at the carbs and run it into a coffee car or jar and bump the starter to see if fuel is coming at enough pressure (or if you had SUs, it's easier to just pull the float bowl tops.)

But my guess is a bad wire, rather than bad coil. Coils just seem to croak, rather than fade in and out (although it can happen.)
 
I've had coils that failed abruptly w/o warning... but have also had a coil that failed only when it was hot. Much easier to diagnose the first case.

Well I think everyone should carry a spare coil so checking this possibility is pretty easy -- no need to even mount the spare coil, just bungee/tiewrap/duct-tape it to the old one and switch over the wires for a test.
 
Step 1: Pull a plug wire and stick an extra plug into the end. Somehow get the metal part of the plug to stay in contact with a bare metal part of the engine (don't hold on to it, that could be bad) And have someone crank the engine. The "dummy plug" should be sparking. If so, the coil and distributor are working. Move on to fuel.
Step 2: If there is no spark in step one, check the ignition parts.
A: With the key on, one of the wires to the coil should have 12V positive. If not, get a wiring diagram and find it's source. Your problem is in that circuit.
B: you have 12V to the coil. The other wore goes to the distributor. It should switch between grounded and open as the engine is being cranked over. If not, pop the dizzy cap off and inspect the points, condenser, and the little grounding wire that goes from the points plate to the dizzy body.
Recheck for spark after each step.
Other common points to look at are
Any wiring connection points. especially at the fuse block and on the coil.
Plug and coil wires, cap, rotor, etc...
Good luck Guv'na
 
Thank you all for the help. Have determined that I get spark at the plugs so will move on to fuel.
Will first check fuel filter and fuel pump and I guess then move on to the fuel tank? I rebuilt the carbs 2 years ago and they have been good for 1000 miles or so, I'll therefore assume they're ok.
Any thoughts?
Thanks
 
Assume nothing.

You might want to disconnect the fuel line just before the carbs, point it into a jar or can, then have someone crank the engine to see if you are getting fuel.

It won't come out like a fire hose, just sort of pulsing squirts is enough to keep the bowls filled and things running.
 
Resistance increases with heat. Electrical component failures can be intermittent. A component that is weak may work OK when it's cool, but fail as the temp increases. Try replacing the condenser. I've seen intermittent problems with them. Also check your ground wire. Grease and corrosion or a loose connection either at the battery or the mount to the actual ground. The heat/resistance thing comes into play with dirty or loose connections.
 
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