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TR2/3/3A Testing spark plug wires.....

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K

karls59tr

Obi Wan
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when testing the wires what sort of ohm readings should I get ie. 5,000 to 6,000 per foot or 10,000 to 12,000 per foot? I'm trying to track down a misfire.
 
I tried testing a new wire 12 inches long and could not get a stable reading. If you have a misfire I would start with the cap first look for a white line near the contact stud. If all four wires read the same + or - and the coil lead is good it may be a bad plug. Depending how bad remove the wires one at a time and the wire that makes no change is most likely your problem most times it is not the wire but the plug or corrosion in the cap. Also clean power leads to coil DC does not like poor connections. Madflyer
 
It's probably closer to 5000 ohms/ft, but it doesn't really matter. If you have continuity, the wire is almost certainly OK. There is no mechanism by which the resistance would double, and even then, it probably wouldn't cause a misfire. Better to try flexing the ends where the connections are made and see if the cable open-circuits. Also, take a good look at the connections to the cap and plugs and make sure they fit tightly and solidly. I'd look for the usual, banal causes: cracked cap or rotor, fouled plugs, that kind of thing.

Are you sure the problem is in the ignition, and not carbs, fuel delivery or some such thing?
 
If all the above has been looked at and seems right. Here a few other ideas. Bad bussing in Distributor, timing off, bad fuel if it has been sitting a while. Question; does it ever smooth out say at temp or change at different RPM's. FUEL AIR SPARK that all you got. Madflyer
 
The miss is only noticeable at idle. The plugs are good. I'm going to check the cap and rotor but I believe they are fairly new. The optimal timing setting is supposed to be 3/8" BTDC correct?
 
The owner's manual actually tells you to set the timing statically and adjust the advance at the knurled nut of the distributor. Back in the 1960s, that was the only method I used, and it worked fine. I think it is equivalent to about 5 degrees. But the timing would have to be pretty far off to cause a miss at idle, and with the difference in fuels, the original value doesn't mean much anyway. It's hard for me to imagine an electrical problem that would cause a miss at idle but not at speed. Are you sure it isn't carbs or something like that?
 
Sarastro said:
The owner's manual actually tells you to set the timing statically and adjust the advance at the knurled nut of the distributor. Back in the 1960s, that was the only method I used, and it worked fine. I think it is equivalent to about 5 degrees. But the timing would have to be pretty far off to cause a miss at idle, and with the difference in fuels, the original value doesn't mean much anyway. It's hard for me to imagine an electrical problem that would cause a miss at idle but not at speed. Are you sure it isn't carbs or something like that?
Click to expand...
My apologies. I should not have said "miss" as that would indicate a plug issue. The issue is more of an "uneven ,irregular or lumpy idle". You can hear it on muscle cars that have a modified cam shaft only on my TR3 it's not as pronounced as that but similar. I am using a mild street cam but I don't think that would cause the affect? I am also using a TR4A long manifold and an exhaust header if that matters? It very well could be a carb adjustment issue? As soon as the Covid issue gets better I'm going to visit a friend that has a newly rebuilt TR4 that ticks over nicely and see what he thinks.
 
Might be valve problem...Have you done a compression test to help with the diagnosis ?
 
Me, I don;t know, I use a feeler gauge, Karl.
Valve burned or sticking usually is more evident at low rpms...it should show up by low compression on the cylinder that's not holding pressure.
 
The feeler gauge is the norm. We may not be sure as to dial gauge you noted you may be think of lead and lag timing to the valve cam. As for feeler gauge some do it with motor running others do set them with cold motor and rotate motor by hand so as not to splash oil around. A Dial indicator tell you when vales open and close not gap on valves. Madflyer
 
dial gauge will indicate the gap better than a feeler if the surfaces arent flat.The gauge stem is positioned inline with valve stem,touching the rocker and moving the rocker up and down by hand you get the most accurate reading.
But its a pian and i dont think its worth the trouble.A feeler gauage cold is easiest.
Tom
 
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