She runs till she warms up, then nothing.

I am totally confused.

So, I observed a voltage drop of 2.4v...should be zero or near to zero.

I don't understand what that means.

Regards,
Tim

 

It has to be the ignition switch.

If the ignition wire is "hot" when in "run", it's providing a voltage, albeit low (7.7-5.3v) to the starter solenoid. That is not supposed to be right, it's only supposed to provide a voltage in the "start" position.

The wires from the ignition switch to the ballast are always hot in "run" and "start", but due to the incorrect voltage in the switch they are also the wrong voltage, creating a weak spark.

However, for some reason, the spark is just strong enough to work when the engine is cold, but once the engine warms up it's no longer strong enough to sustain ignition.

Is this correct thinking?

Regards,
Tim

 

I've already got a new ballast on the way. The switch is this one.

Regards,
Tim

 

Get yourself a wall switch (30 to 50 amp), a momentary push button switch (for starting) and some wire.

Disconnect the wire from the coil side of the ballast resister, hook that to one side of the wall switch.
Connect a wire to that same terminal and run to the push button and another from the opposite side of the push button to the terminal on the starter.
Connect another to what will be the battery side of the wall switch and run that to the big terminal on the starter or + side of battery.

test the coil output by flipping on the wall switch and punching the starter button and see how strong a spark you have. Bright, heavy spark? Replace the coil lead into the center of the distributor and start the engine.

Weak spark? replace the coil and try again.


Let her get good and warm, shut her off and restart. If she starts right up, you should be ready for "Lets run around and see what happens!". But stay close to home.
Just in case.

Personally, to me, it sounds like the coil is failing.

 

I've ordered the switch as well. I'll replace one thing at a time, but I'm pretty confident now the switch is failed and a problem. The ballast could be indicating a failure, but it may be symptomatic of the switch problem given there seems to be bleed through of voltage where it shouldn't be.

Regards,
Tim

 

Robert, who helped when stranded the other day, did just that with my help. Spark was weak but his opinion was the ballast was a likely cause with another issue somewhere (like a ground) given how hot it got so quickly, but not the coil.

Ill fix fix the switch and / or ballast first, then if my problem still exists I'll swap the coil out. One thing at a time...

Regards,
Tim

 

Just a though. When I first got my cj5 running after it has set for more than 20 years after an engine replacement, it would start and run when cold, but noticed that the clutch pedal would spark (clutch depressed, and hitting the body). Investigating further, when the engine was swapped, the mechanic didn't re-install the ground strap from the engine to frame ground.

You should check your strap grounds from engine to frame.

Where are you placing the - (negative) lead when you made your measurements? 1. - (negative) battery terminal 2. - (negative) battery terminal 3 Body ground bolt or 4. engine ground. When making the measurements above, did you check the voltage drop from - (negative) battery terminal to engine block?

 

One check was battery to engine block continuity. I checked the strap as well as measured, it was zero ohms.

A few weeks ago I installed a common grounding lug on the firewall and then connected that to the battery neg terminal. Battery neg is also connected to the starter mounting bolt. There is a strap between engine block and frame; at the firewall lug I have a common ground point for each engine compartment system (only starting & charging system is grounded so far). It's connected to a similar point on the cockpit side and this is where all instruments and internal switches are grounded. Picture:


The neg lead is going to one side of the voltage check for each step. Not a physical grounding point in all cases; most are a hot-hot check.

Regards,
Tim

 

Well, I replaced the ignition switch yesterday and started the same voltage checks (FSM section H-4). Got about half way through and the check basically said "clean connections at solenoid". Did that and the start wire was a bit loose. Rebuilt the connector and cleaned the connections. Started over, voltages better but still not right so I decided to replace the ballast.

At this point, the entire circuit is new. So instead of running checks I turned the key and she started cold very quickly. No touch to the throttle at all. Idles a bit high at 1000 rpm, but that's an easy fix. Before I drive her I'm going to let her get fully warmed up, but I can't think of a reason she won't go. Local only of course.

Root cause? My gut tells me I had multiple things coming together at once, the good news is these old Jeeps run even when things are not perfect (unlike today's cars) but when everything gives up the ghost, then she stops.

Now I can return to driving and fixing small stuff, like backup lights.

Regards, and thanks for all the help.
Tim

 

Alright!!
:tea:

 

Glad it's getting better and look what your learning in the process.

 

That what happened to my Jeep when I bought it : all was good but after a week all went bad, it was mutliple problems adding together.
All was chenged ... slowly... and then, perfect.

Good luck.