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Discussion Starter · #1 ·
My cj just dies while driving.I can restart fine then every now and then it does it again.Any ideas on what could cause this?Checked wiring and seems ok.Misc electrical parts underhood have been replaced but still a problem.Any input would be great.

 

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Same thing happened to my CJ last summer. It was a wire that was shorting out under the dash. Somehow as I coasted to a stop, the wire must have moved and then it would start and run fine for a day or even a week until the wire moved and shorted again.
I fixed the wire and it hasn't happened since.


80 CJ7 258 T176
36X12.5 Swampers
Fiberglass body
 
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Discussion Starter · #4 ·
When that happened to me, it was a brittle wire broken inside the insulation, (making it very hard to tell since the wire looked intact) the wire broke right where it attaches to the coil. When mine starting acting up, I could simply "jiggle" some the various ingintion wires and get it going...until it finally quit for good.
It wasn't until I was in the process of swapping out the coil that I found it.
I was told later, that sometimes when a short occurs or for some reason a wire is carrying to much current for its rating, the wire(s) going to get really hot, it may not be enough to fully melt the wire or the insulation, but will heat the wire enough so that loses its tensile strength/flexabilty and over extended time and use, the wire will actually becomes brittle.
Hope you find your problem a lot quicker and easier than I did.

DrummondCJ
 
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Discussion Starter · #5 ·
My '75 CJ-5 did that usually after a small bump on the road. Found out to be ignition module. That thing would cut out and had to turn the key off before I could restart.

Mark Boden, '75 CJ-5, Stock.
 
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Discussion Starter · #6 ·
Most likely it's an ignition module problems. A '75 has the Prestolite ignition system which is affectionately known as prestocrap. Swap in an HEI system and get rid of the problem ridden prestolite.

'75 CJ5,258 w/Howell EFI,T18a,4.27's,33's,On-board air,Warn 8274
 

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Not to discount the electrical/ignition possiblities, but I had a '67 Mustang that did the same thing. Would cut off intermittantly, then fire right back up after a minute or two. Ended up being a clogged fuel filter. It's cheap to replace on most vehicles and eliminates itself as being the "cause" before spending countless hours & $$$$$$ on the "cure". HTH

Caver Dave
'68 Jeepster Wagon
225, 3spd, & road salt A/C
Vintage Jeeps(ters) have Character,
new Jeeps just have payments.
 
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Discussion Starter · #8 ·
I would bet my life that it's the ignition control box. Got the same one on my 76 and it's a piece of crap. Mine did the exact same thing as you are going through right now and after re wiring, replacing the ignition switch, coil, checking the alternator and battery about 100 times, I changed the ignition control box-Presto, fixed the problem immediately. Problem is, I got a lifetime-warranty-made-in-Mexico number from autozone, also crap. It's dying after about two months. Went down yesterday to replace it, and luckily I installed it right there in the parking lot (had to exchange it) and the NEW one was bad. Stupid thing wouldn't even start the jeep. Just kept turning over and over until the battery was almost toast(I know, that's bad). Hooked the old one back up, started right away. Took it back inside and they have to order me a new one. What's the moral of the story? Do the TR ignition upgrade NOW, and if you can afford it, go with the MSD control box. Good Luck!!

--Laugh and the world laughs with you. Cry and the world laughs at you.
 

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had the same problem on my 73. It was the fuel line. The body had settled and pinched the fuel line off partially. I rplaced all the ignition parts before I discovered the fuel line problem, real bummer. My .02.

If your kidneys don't hurt, it's not a real Jeep!
 

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Dunno if it's the same on yours, but on my CJ it was the ignition something-or-other that's mounted under the washer bottle. Kinda sucked when the engine cut out one time when I was turning across 3 lanes of traffic.

Sean

 
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Discussion Starter · #12 ·
I had a 74 CJ-5 with the same problem and I thought initially it was ignition and turned out to be a rubber fuel line. At some point when I shoved it onto a nipple a small flap was cut on the ID and sometimes it would act as a valve a shut the fuel supply off. Drove me nuts for awhile.

 
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Discussion Starter · #13 ·
I had the exact same symptoms on my Scout. It was a dry rotted fuel hose between the sender and the plastic line. Had to drop the tank to get to it. I replaced all of the lines up to the carb with a filter before and after the fuel pump. Never happened again.

 

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Does that thing have big ballast resistor on the firewall? If so, gently take it off, turn it over and see if it's cracked. Classic symptoms of a bad ballast resistor opening under load and killing the ignition (Jeep dies quickly) only to have it work when cold.

 
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Discussion Starter · #15 ·
Please forgive the complete electrical ignorance, but what is a ballast resistor, do I have one and why?

--Laugh and the world laughs with you. Cry and the world laughs at you.
 

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A Ballast resistor does the same thing as a resistor wire in later model Jeeps. When the ignition key is in the Start mode the coil gets 12 volts applied to it... a hoter spark... better starting. Once the engine starts and the ignition key moves to RUN, the ignition switch moves the voltage to the coil from 12 volts to about 8.7 volts (or so). If the coil continued to recieve full voltage then the coil would overheat and die. Most FOMOCO ignition modules of that era work with resistor wire, while MOPAR used Ballast resistors. Both the ballast resistor or the resistor wire do the same thing... that's cut the voltage down.

 
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Discussion Starter · #17 ·
hey leve, ive got the afformentioned problem with a bonus. every time it starts dying the timing changes...to about 12* or so (from the stock 5*). Then when i change the timing back to 5* it runs fine until the symptoms start again. i have found a duct taped wire in the harness going to the coil, but i cant think of how that would affect timing. then again, if timing changes to 12 from 5 it would run rough...but it doesnt, it just dies like you shut off the key. if i cant figure this out i may just buy a 401!

scott

Scott,
76304150202030
 

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Scott, A Bonus is not how I'd describe the problem, you're a much more forgiving man than I am!

If the ignition module were attempting to die... lots of things can happen. As example, the ignition module recieves a pulse generated by the distributor. The pulse is:

1. Recieved.
2. Used to trigger a 2nd pulse to the Coil.
3. This pulse is shaped for:
a. Amplitute (How High)
b. Freguency (How Fast)
c. Duration (How Long)
4. Sent to "Ring" the coil.

The Coil in turn uses the pulse to control the pulse to the plug wire. Notice I said CONTROL... The Coil works on good ol' electrical principles... in electronics you'll see that most stuff in not "Making" something, it really got an ability to run full tilt. But to advoid that catastrophe some other component is inserted to controll it's exuberance.

As example:

The Coil can run full tilt, so the ignition moudule is inserted to control the coil. Then the hall effect switch is inserted to control the ignition module. We've got a series of controls here. If one runs amuck, it mucks up the rest of the system...and understanding the system is the key to repairing it. Just where is the problem introduced. Work backwards, or work forwards, where to start? Well the easiest place to start is in the middle and decide on which side of the middle is problem occuring. Go to that side and divide the remaining circurity in half and decide which half the problem is occuring in and so forth, and so forth. It's a simple binary search and a very FAST way to diagnois ANY problem. You just gotta know what you're doing.

So, as you can see, the ingnition module really is the heart of the ignition system. Like any computer (simple, yes, but the module could be considered a very crude computer) if you get garbage in you get garbage out. In the case of the FOMOCO modules if you get a good pulse in you can still get a garbage out. If the ignition module is recieving a good signal as an input and throwing out a bad output pulse to the coil lots of things can happen... the engine can be attempting to recover but it's stuck in the loop provided by the ignition module pulses and vacuum responds accordingly. You're going to get lots of coughing/sputtering/and dyin'. Now if you've (or the previous owner) jacked up the idle a little in response to the problem another problem has just been introduced. Of if when the engine's a dyin' the distributor actually looses drive and moves BACKWARDS as the engine attempts for a split second to come to a rest position and now:

1. The ignition is still on.
2. The hall effect switch is pulsed because it doesen't car which way the distributor is turning to create a pulse.
3. The pulse is sent to the ignition module and ingnition phase is started anew.
4. The engine's at about 8* BTDC now still attempting to go to rest.
5. The plug fires.
6. The engine now attempts to respond to the plug firing... again...with a weaker plasma charge.

That's gotta be some goofy symptoms that result!

What have you done to diagnois the problem such as replace parts?

I doubt the duct taped wire has anything to do with the problem... but you never know. So here's what I'd do.

Put EVERYTHING you can back to OEM SPEC. Start with the KNOWN to diagnois the UNKNOWN. Then start with the obvious and work your way out of the problems one by one. Fix them ONE BY ONE. Make sure the problem is fixed, not masked. Only then go on to the next problem or you've created a whole sub-set of problems that will bite you in the cedar end later.

1. Trace the wiring back to make sure it's not connected in error.
2. Repair the splice.
3. Recover the harness in either heat srink tape, electrical tape or plastic sheathing.
4. Replace the Ignition Module.
a. See if the symptoms change.
5. Replace the Distributor pulse generator (Hall effect switch/points?).
b. See if the symptoms change.
6. Replace the coil.

Of course don't forget to make sure all you're grounds are nice and shiney and re-installed with some dialetric grease on them when you bolt them all back together. Keep us informed... this one's a real "fun" problem!

 
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Discussion Starter · #19 ·
Wow, thats alot of stuff my non-electrical mind cant comprehend. i did however understand the important stuff. i have the prestocrap system. you mentioned what i had done to fix the problem. what I have done is as follows (none of which fixed the problem) :

1. new ignition switch (on top of column)
2. new coil
3. new control module
4. reman distributor
5. new plugs/wires

and for good measure i tinkered with the fuel system by adding a remaned carb and new fuel filter (but it doesnt have any fuel delivery problems (no sputtering, coughing or rough running). just the electrical cutout/timing change. only thing i havent checked is the timing chain, gears, or cam drive gear (which i might add did not like to fit with the new cam gear on the remaned distributor. so, to wrap things up i cant figure it out...can you help me out? you have much more knowlege of the system than I do, would love some suggestions.

thanks
scott

Scott,
76304150202030
 

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By George Scott, I think you've done almost everything you could be asked to do... except the timing set. Remember how to check the timing gears and chain?

Start by staticly timing the engine.. forget using a timning light!

1. Pull the plugs.
2. Put a plug in the #1 plug wire, ground the plug so you can see the electrode.
3. Put a ratchet on the crank pully bolt.
4. Stick you finger in the #1 plug hole.
5. Manuall turn the engine with the ratchet til you feel pressure building up.
6. Stop at between 6* and 8* BDTC.
7. Loose the distributor hold down bolt.
5. Rotate the distributor to obtain a spark.
6. Narrow down the rotation til you've got it as narrow as possible.
7. Lock down the distributor.

Try the engine! Does it work better? It should.

Now test the timing chain/gears.

1. Pull the distributor cap.
2. Put that ratchet back on the crank pulley bolt.
3. Note the positon of the ratchet handle, start to turn the engine CW.
4. Have a buddy watching the rotor, have him yell when he sees movement.
5. If the handle's moved more than about 5*... replace the gear/chain set.
6. Repeat steps 1 - 5 to reconfirm what you saw in step 5.

If the distributor gear is tight, or worn, that can cause problems but I'd not think it would cause shuch an advance.

 
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