What is a capacitor jumper

[thistle3585]

My Jeep starts but doesn't run. It started doing this after having sat outside in a hard rain, so I'm thinking my leaky windshield let some water in and it shorted something under the dash. So, I'm going through my ignition setup and saw on the diagram a capacitor jumper that comes off the red wire between the solenoid and the coil. What is this? I recently got rid of the resistor wire to the original coil and swapped in a coil with an internal resistor. I wondered if that jumper was still needed.

 

[IOPort51]

with the ignition in the run position do you have 12V to the positive coil wire?

 

[Torxhead]

Thistle, that capacitor is to handle spikes in the ignition that can also affect radio reception as I recall. I think most guys don't bother replacing them after they go bad.
I would say you have an issue with the run circuit. IO Port has a good starting point.

 

[Lumpy Grits]

The only time you should see 12vdc to the OEM coil is in 'start'. After starting, and the key is in 'run' position. Voltage should be 6vdc or so, because of a built in resistor wire in the loom in the run circuit.
LG

 

[thistle3585]

I put a test light on the negative side of battery and positive lug of coil. I'm not getting anything at the coil when the switch is in the run position but it lights when in start position while cranking.

 

[Torxhead]

I hope you can fix this issue there thistle, there is a resistance wire going to the icm and coil which is not a soldered but clamped connection that could be a cause.
Edit: Oh yeah, and Lumpy is correct the coil and icm get get 6 volts after the resistance wires that run from the #1 terminal at the alternator to the coil and the ignition switch to the icm.

 

[graycj7]

Could someone post a photo of the coil and solenoid connections for 1985 CJ7 AMC 258 i6 / 4.2l . Im having starting troubles. Thanks.

 

[Torxhead]

Gray what you are asking for would be on a wiring diagram for the '85-'86 CJ, this could be tough to put on a computer screen. There are a lot of issues that can cause a hard starting situation. You should probably start your own post and go into more detail.

 

[thistle3585]

I had mentioned in my first post that I had removed the resistor wire and put a coil in with an internal resistor. I actually did that because a wire in the bundle had overheated and melted several wires and I was unable to find a new resistor wire. Not sure if the resistor wire was the cause of that or another one. Since I replaced the resistor wire, I assume the load at the coil is full voltage.

Anyhow, I read elsewhere about the same problem being tach related, so I was messing about under the dash and fiddled with the tach wires and it now runs. I'm still a bit concerned about some of the connections behind the dash, so I am going to go through and check them and clean them up. I might look at replacing some of the old connectors.

 

[Torxhead]

Thanks for the update, for what its worth NAPA sells a resistor wire p/n ICR22, that is about 4' long. I did shorten my resistor wire from the alternator and it now puts 9 volts to the coil with no issues.

 

[Lumpy Grits]

The 'no-run' issue can also be inside the ign switch. Mine was-
OP-Run a 'jumper' wire from the POS(+)of the battery to the POS(+)of the coil.
Will it now start?
If it does-don't run it for more than a couple of minutes as your kill'n the coil with the full 12+VDC.
LG

 

[TeamRush]

What is a capacitor jumper?

It's a guy with burns on his hand and is trying to ring electrons out of his arm.

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Seriously,
*IF* we are talking the '79 you list,
Try this for an explanation...

You have a SPLIT ignition system.
'Crank' or 'Start' is on a different circuit in the ignition module than the 'Run' circuit.

One circuit CAN & DOES fail from time to time, leaving the second still working.
Some guys can get it to fire but won't continue running when the key switch drops back to 'Run',

Other times the vehicle will crank, but not fire, until you let the key switch drop back to 'Run'.

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[thistle3585]

Thanks. That helps a lot. Where does the tach fall in that system and why does it affect whether it runs or not?