Starting problem

ok the story starts in the spring. I go out to the hanger where our cars are to get my father's Jaguar pictured above. The batteries were dead. I thought no problem I have my jump box. would not start. I did not have time to mess with it so I left it.

Well a couple of weeks ago when I got the 47 willys. I tried again, same thing turns over no start. I thought the points must have rusted or something. so I pulled a plug wire to put in a test plug, and it fired right up. put plug wire back on and I ran great. I figured I fixed even though I had not done anything.

I went out this morning to pick it up as I wanted it for the back to bricks car cruise in the Flint Mi. area. would not start, turns over no fire. so for E36M3 and giggles I pull the plug wire and it fires right up. What is going on.

Which plug wire? How do the grounds look?

I have had similar caused by a bad dist cap and another time by a bad ground.

The grounds look good, but I was thinking the bad battery might have not transmitted to the ground well? I took out the 2 6v batteries and put in a large 12v and it seems better so far.

I got nothing for ya … but dang … that's a beautiful car

Try new plugs.

I was thinking that you might have been making another ground when you used the spark tester. Getting an engine started takes a lot more juice than keeping it running.

Just a guess obviously since I'm not there.

Low voltage from the dead batteries could cause funny behavior when cranking. Try running a lead from the starter side of the solenoid to the coil to see if it fires better.

I don't know how the Jag ignition is wired, but I would expect something similar to this since all points ignitions would need to deal with the same issues.

GMs used to have two leads to the coil, one from the solenoid and one tied to the rest of the keyed 12v leads. The one from the solenoid was a plain copper wire and provided power to the coil only when cranking.

The other wire that was powered when the key was in the on position. This wire either had a resistor in line or was a special resistance wire to reduce voltage to the coil at idle. If the resistance was missing on the lead to the coil during normal running, the coil could overheat at idle due to the longer dwell. The resistor would heat up at idle and increase resistance to reduce voltage to the coil to avoid overheating the coil, at higher rpm the coil would cool off and the resistance would drop increasing the voltage seen by the coil.

If the lead from the solenoid was missing it could produce a hard start condition that may only show up if there is a low voltage condition.

Is the car still positive ground? Does it still have the varnished cloth insulation?

Positive ground had a valid use back in the day, but as you know those cars require maintenance(or at least a visual check) of just about every system all the time.

In reply to Ojala: It is still positive ground. the harness was replaced 25 years ago or so when the car was put back together. I just think it is odd.

In reply to jstand:

I think the low voltage has something to do with it. I took the 2 6v batteries out and put a big 12v in and it seems fine.

Thanks