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TR2/3/3A Lost Spark

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mgedit

mgedit

Jedi Knight
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I've been enjoying my 56 TR3 this summer and it has been running quite well, other than an occasional hesitation. Last week I took it to my weekly golf game and when leaving the golf course it took 4-5 seconds to start, which is very unusual. It normally starts right away. Thought I best check that out. Couple of days passed and I decided to start it up and investigate. Would not start, no attempt to fire at all. Today I started trying to sort out what was wrong. Far as I can tell, I'm not getting any spark. The spade terminal on the nylon slide in connector on side of distributor was loose (turned easily from side to side), so I thought that might be source of poor contact. Had a new one in my parts stash so swapped that out. No improvement. Next changed points and condenser and re-set gap. Still no spark. Getting 12V at both sides of coil (small connectors) and 12V at wire going to points. Coil is measuring 3 ohms across small terminals (primary circuit) and 8900 ohms (secondary circuit) between centre and both small terminals. Don't have another coil handy to try swapping out coil. Am I missing something? What else should I measure/try to identify the fault? Has me stumped. Cheers, Mike
 
Turn the engine until the points are closed, and recheck the voltages on the coil pins. You should still have 12v on the wire to the harness, but close to 0.0 volts on the wire to the points.

If that looks OK, check for spark right at the top of the coil (with the high tension lead to the distributor disconnected). Sometimes rotors can fail invisibly and short the spark to ground.
 
Thanks Randall. With points closed, 12V on both small terminals on coil, and at nylon connector, but 0V at points pin/arm where condenser wire and wire from nylon connector join. No spark from top of coil to ground when cranked. When I was replacing parts earlier replaced rotor with new red one (same as what was there before). Cheers, Mike
 
With points open, do you have power at the moving points contact arm? You might start suspecting the wire from coil to points. When the points are closed and things are normal, that wire is in dead ground and the juice would prefer that circuit to fighting the little resistance in your meter. Thus the near zero reading Randall mentioned.
Bob
 
mgedit said:
Thanks Randall. With points closed, 12V on both small terminals on coil, and at nylon connector, but 0V at points pin/arm where condenser wire and wire from nylon connector join.
Click to expand...
Bingo! The wire from the nylon connector to the points is bad.

Its a special extra-flexible wire, because it has to flex whenever the vacuum advance moves. They do often fail by going open circuit with no external indication.

Might well be the cause of your hesitation, too. Vacuum advance moves when you step on the throttle, and could position that wire just so.
 
Will swap it out again, but it is brand new. Will check again for voltage to be sure. I think I have a couple more new ones in my distributer parts box. Thank you Bob and Randall.
 
Just measured voltages again before doing any swapping. So it was zero on the nut holding the wires to points assembly. At end of wire from nylon connector was 0.15V and also 0.15V on spring wire going to contacts. These measurements with points closed. Cheers, Mike
 
OK one more update. Triumph friend dropped in to say hello tonight. Told him what was happening, wondering if he might has some ideas. We checked wiring and voltages (all as I last reported) and put all back together and car fired up right away. Now I don't have any idea what solved the issue I was having. Glad it sorted itself out, but would have preferred to find and fix a specific problem. Will go for a run tomorrow and make sure things have remained fixed. Cheers, Mike
 
Oh, I hate when it fixes itself without knowing what you did ....I'm with you, I'd of preferred to find the culprit and rectified it...I would be on the edge of my seat for the first few drives...cell phone fully charged and the caa card at the ready :cool:

Cheers
Tush
 
mgedit said:
Thanks Randall. With points closed, 12V on both small terminals on coil, and at nylon connector, but 0V at points pin/arm where condenser wire and wire from nylon connector join. No spark from top of coil to ground when cranked. When I was replacing parts earlier replaced rotor with new red one (same as what was there before). Cheers, Mike
Click to expand...

I just re-read this, and maybe I made a bad assumption. At the point where the two wires connect to the points, the post and nut are supposed to always be grounded. That is why you put the little "top hat" insulator under the point spring, and another one on top of the two wires with the crown pointing down through the wire terminals and again into the point spring.

So when testing for power at this point, check on the wire terminals, or the point spring (which is also a current conductor).

A very common mistake is to put the wires on top of the upper top hat, instead of under it. Won't run that way ...
 
Insulator and wires are in correct positions. Will wiggle wires a bit today and check dwell now that car seems to want to run. Cheers, Mike
 
Well the plot thickens. Went out this morning and car started right away and ran for about 2 seconds. Then back to no spark. More investigation to follow. Cheers, Mike
 
Well, if you were checking voltage before at the wire terminal, rather than the nut; I'd still say it's a bad (intermittent) wire. I've also seen the ground lead (from the moving plate to the distributor body) go bad and be even harder to find. In both cases, what usually shows it up is removing one end and then checking for continuity while gently tugging on the wire.
 
Thanks Randall ... will try to find time tomorrow to identify the culprit. Cheers, Mike
 
Last time I had an intermittent spark I found the nut holding the hot wire to the ignition switch had loosened. So once you clear the distributor, you might want to follow all the connections out from there.
 
Take a good look at the low tension lead between coil and distributor- the wire can break but it still will look intact with the insulation. Happened to a friend of mine and gave similar symptoms.
 
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