Noob with a challenge! can you figure this one out?

Noob with a challenge! can you figure this one out?

dadsdream85

Jeeper
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Location
Cedar Falls, IA
Vehicle(s)
'85, CJ 7, 258, T-176, AMC 20, Dana 30, D-300, mainly stock, body by Max-Bilt, Max-Bilt Command Center Console, 31's, black wagon wheels
Calling all really smart Jeepers! CJ starts, won't run
So, My step daughter has just entered the Jeep fray as we have dragged home to IA an 83 CJ 7, 258, T-4, D-300 with swapped in narrow track axles (why did they do that?)
She knows the PO and got a good deal because it was running fine and then one day, poof, it would not start!
Being the really smart Jeeper I am (and wanting hero status) and having restored an 85, how hard could it be?
Very methodically we ran new fuel line rubber, new filter, cleaned out needle and seat and siphoned all the gas out of the tank (stank to high heaven).
Next morning I found the problem!!!! The + battery cable had broken at the solenoid~! Off to AA for new battery cables, solenoid,coil, cap, rotor, wires and plugs. After replacing the cables and solenoid it started! Feeling good! drove around the block 16 x's and pulled to the front curb to wash it so she could start the rattle can paint job! When we were finished I went to move it and it would fire but not run. Put in the plugs, cap, rotor, wires and coil, still no go.
Dragged it back to the garage with the starter and it sat for the night.
tried starting it Sun morning and it did not. Put in the coil, and it fired and purred! drove around near our house for 1/2 hour at city speed, alls fine. Maiden truip to Wal-Mart required 55 mph for a stretch (i was following in my Jeep). AS she accelerated I saw it backfire through the carb and watched her coast to the shoulder. Towed her back, checked connections and tried again after 45 mins or so. Started again! drove at 25 mph for 45 mins, alls well. Was it the acceleration? Took it back out of town, backfired through the exhaust but kept running.....well. Turned around at the lake and 1/2 way back she stopped to tell me it was running great......and it dies!

Read more threads. replaced the starter, ICM, ignition switch, cleaned every available connection with contact cleaner, filed where I could and regreased.
Over the course of the next week it would start and run fine. The next day it would not. I ran dedicated grounds to ICM, distributor ground, starter, alternator and solenoid.

I performed the 12v test light test at the distributor connector ie probe the + connector to neg in run and start and passed that test. Probed the - connector in start and run and passed that test.

I did the nutter bypass test by clipping the orange and purple wires at the ICM and the dist and ran rumpers to take the ICM out of the loop. Did not start! rewired back to stock

I have 600 ohm reading at the distributor stator wire (i'm told it should be between 400-800 ohms and 600 is ideal).

I removed the starter cable from the solenoid and pulled the lt. blue wire. Jumpered from that to + battery, it clicked and I measured 12v at the red wire on the dist. with the key in the off position. Pulled the jumper and with the key in run got 6-7 volts (resistor is working?).

I have read this thread http://www.jeepsunlimited.com/forums...t+stay+running

I have taken my 85's ICM and replaced the "discount" ICM. Still no go.

Took the coil out of my 85 and swapped it in. No difference....but, swapping the new coil from the 83 into the 85, the 85 died. The "studs" on that coil are apparently slightly thinner so the coil connector is loose. It runs now and I will get a new coil connector for the 85.

So, can you help me find hero status? She really wants to drive her Jeep!
 
before we start rewiring, or stuff I want to ask a question and relate a story.
Have you replaced the cap rotor and wires?

I ask this for a reason, I had an 83 toyota hylux. On day I was running down the street and it just backfired and died. Could not get it to start for anything so, Having a spare coil I replaced it and it fired up and ran again, for about 4 miles. I next had to replace the rotor and cap but got about 4 miles out of that,
My roommate at the time told me the spark plug wires were bad, and to replace the cap and rotor with them even if I had just replaced them.
So I did, and it fixed the problem.
it seems our modern Spark plug wires do not have solid core wires anymore and when they go bad they are a bear to deal with as you cannot tell by looking at them.
So, just as a place to start, and because it is part of a tune up anyway, get a set of plugs, cap and rotor and swap them out.
 
Have you checked the fuel pressure? I would hang a fuel pressure gauge on the windshield wiper so you can see what it reads when the jeep acts up. You will have to make a tee fitting in front of the carb to hook the gauge to. You may have a weak pump or a clog in the fuel tank. Be very careful though. Make sure you have tight connections. You don't want the fuel line to come off and spray gas around. You should only be dealing with less than 10 pounds pressure.
 
Hows the timing on that bad boy? sounds kind of like what mine did except mine wasnt the timing chain(which i replaced), the dizzy turned 180 degrees, dont know how just did.
 
I had a mystery like this once on my 84 CJ 7. It was running crappy so I took it to Tunex. After I got it back it was doing stuff like this. Starting and running some of the time and then plain old not starting at all. I kept taking it back and they would tell me it was running fine for them. (of course) Finally a friend of mine came over ( I'm a mechanical idiot, trying to mend that issue ) And we got looking at the carb and discovered a sticky butterfly. That was it! So simple and yet the pros couldn't figure it out!
 
before we start rewiring, or stuff I want to ask a question and relate a story.
Have you replaced the cap rotor and wires?

I ask this for a reason, I had an 83 toyota hylux. On day I was running down the street and it just backfired and died. Could not get it to start for anything so, Having a spare coil I replaced it and it fired up and ran again, for about 4 miles. I next had to replace the rotor and cap but got about 4 miles out of that,
My roommate at the time told me the spark plug wires were bad, and to replace the cap and rotor with them even if I had just replaced them.
So I did, and it fixed the problem.
it seems our modern Spark plug wires do not have solid core wires anymore and when they go bad they are a bear to deal with as you cannot tell by looking at them.
So, just as a place to start, and because it is part of a tune up anyway, get a set of plugs, cap and rotor and swap them out.

new cap, rotor, plugs, wires, coil, ICM, starter, solenoid, battery cables, ignition switch cuz I'd have done it, like you said in getting it roadworthy. Just don't know why it fires in start and dies in run?
 
Have you checked the fuel pressure? I would hang a fuel pressure gauge on the windshield wiper so you can see what it reads when the jeep acts up. You will have to make a tee fitting in front of the carb to hook the gauge to. You may have a weak pump or a clog in the fuel tank. Be very careful though. Make sure you have tight connections. You don't want the fuel line to come off and spray gas around. You should only be dealing with less than 10 pounds pressure.

I can try that. Just asking though....we siphoned the old gas out, added fresh. New rubber in the engine bay. Two new filters, (just making sure), cleaned the needle and seat, pulled the line off to the carb and turned it over and gas shot across the garage. Working the linkage provide strong shots of gas into carb throat. In the start mode it fires but as soon as I let off the key into the run mode it "dies". It has run every other day or so and when it runs it runs great.
 
Hows the timing on that bad boy? sounds kind of like what mine did except mine wasnt the timing chain(which i replaced), the dizzy turned 180 degrees, dont know how just did.

Great thought but when it starts and runs it purrs. If the distributor was 180* off it may run but not smooth at all, right?
 
Which carb is in it? Might throw a kit at it - after rebuilding my YF, my 7 is running better than ever - and getting better mileage.
 
I had a mystery like this once on my 84 CJ 7. It was running crappy so I took it to Tunex. After I got it back it was doing stuff like this. Starting and running some of the time and then plain old not starting at all. I kept taking it back and they would tell me it was running fine for them. (of course) Finally a friend of mine came over ( I'm a mechanical idiot, trying to mend that issue ) And we got looking at the carb and discovered a sticky butterfly. That was it! So simple and yet the pros couldn't figure it out!

Thanks. The electric choke seems to function with the plate closed when cold and opens as it warms. It seems electical as it is combusting on "start" with exhaust and the whole nine yards. Its the second I let off the key into run, it dies. I have replaced the ignition switch and it is set in the right spot. I have 12 v to coil and 6 volts at coil in the run position ( 6 volts cuz the resistor in the run circuit is doing its job?)
 
Which carb is in it? Might throw a kit at it - after rebuilding my YF, my 7 is running better than ever - and getting better mileage.

Great idea! but for now, it wont run. Starts but won't run. It has gas? Steady stream as the linkage is engaged. Dies as soon as the key is let to the run position.
 
I can try that. Just asking though....we siphoned the old gas out, added fresh. New rubber in the engine bay. Two new filters, (just making sure), cleaned the needle and seat, pulled the line off to the carb and turned it over and gas shot across the garage. Working the linkage provide strong shots of gas into carb throat. In the start mode it fires but as soon as I let off the key into the run mode it "dies". It has run every other day or so and when it runs it runs great.
You just said something important in diagnosing this. You said it runs in START but then dies in RUN. The coil gets 12 volts from the starter solenoid in START. The coil gets about 6 volts in RUN mode. This 6 volts starts at the Ignition Module plug as 12 volts and goes thru a resistor. This is pretty common since the coil will burn up if it gets 12 volts all of the time. To verify this, run a jumper wire from the battery pos. post to the coil pos. post. If it runs all of the time, you need to find the break in the RUN circuit. It contains 2 splices and a resistor between the Ignition Module and the Coil. My Haynes wiring diagram says it is a red w/tr wire. Not sure about the color. I have better luck with factory manuals. Try this: There are 2 pigtails coming out of the distributor module, a 4 wire and a 2 wire. Check the red wire in the 2 wire plug. If it has 12 volts in RUN, your problem is in between there and the coil. If you don't have 12 volts coming to that plug, your problem is the other way and could be in the fuse box or ignition switch. I hope you have access to a wiring diagram.
 
in his OP he has troubleshot the ignition voltage going to the coil and it is correct
he is not burning up coils, he is having trouble with the system continuing to run, As he is getting 6 volts that system is good.
So now how long does it run in run?
 
Still sounds like it may be the ignition switch. I got one that was junk right from the parts store. I would pull the switch and check for continuity in all positions before twisting my brain up on alot of other wiring possibilities.
 
You just said something important in diagnosing this. You said it runs in START but then dies in RUN. The coil gets 12 volts from the starter solenoid in START. The coil gets about 6 volts in RUN mode. This 6 volts starts at the Ignition Module plug as 12 volts and goes thru a resistor. This is pretty common since the coil will burn up if it gets 12 volts all of the time. To verify this, run a jumper wire from the battery pos. post to the coil pos. post. If it runs all of the time, you need to find the break in the RUN circuit. It contains 2 splices and a resistor between the Ignition Module and the Coil. My Haynes wiring diagram says it is a red w/tr wire. Not sure about the color. I have better luck with factory manuals. Try this: There are 2 pigtails coming out of the distributor module, a 4 wire and a 2 wire. Check the red wire in the 2 wire plug. If it has 12 volts in RUN, your problem is in between there and the coil. If you don't have 12 volts coming to that plug, your problem is the other way and could be in the fuse box or ignition switch. I hope you have access to a wiring diagram.

Well, well well.............so new deal today! Does not fire in start today! I have 12 v at the coil in "run" and no 12 V at the red wire into the ICM.
I wish I could read/understand wiring diagrams better.......this is getting exasperating. I did recheck the ignition switch and it is installed-set correctly. there is 12v coming into the switch on a heavy red wire.

I cant understand how yesterday I had 12 v at the ICM and now nothing? And 6 v at the coil in run and now 12v? Jeepers.

 
ignition switch is the first...make sure that its in the right position.....check both cjs on the key switch....is it "springing back" from start to run...then check that the rod is not bent leading to the ignition( i have bent 100s in my locksmithing career ) then check position of switch then contacts of switch....maybe totally off but i have seen (some of the symptons ) that once in a old chevy...
 
ignition switch is the first...make sure that its in the right position.....check both cjs on the key switch....is it "springing back" from start to run...then check that the rod is not bent leading to the ignition( i have bent 100s in my locksmithing career ) then check position of switch then contacts of switch....maybe totally off but i have seen (some of the symptons ) that once in a old chevy...

Thanks. Did not know of the condition of the Ignition switch when we bought it. On the first day after messing with connections the jeep started and ran fine. Next day it would fire on start but die on run. Replaced the ignition switch and after several attempts it ran. Next day it did not! It would run on again/off again. Replaced the ignition switch on Sat again just in case ( i cracked a piece of plastic during install). Started then stopped.
Took it out again today to be tripley sure it was set right, installed with the key on the off/ lock position and the slider in the second detent position.
I have power into the switch on a heavy red wire. The actuator rod is perfectly straight and the switch turns on the radio in accy, Off in locked, radio off in off/unlocked and radio on in run and off in start. May not be scientific but seems to operate correctly? it does spring back from start to run.
 
When it's in the "fail to run" mode... pop one of the plug wires off and pop it onto the spark plug you've conveniently carried in your pocket for this purpose, with an extra-large gap so you can see what it's doing. Hold the body of the plug against the block & have somebody crank the engine. Do you get spark across that plug when the Jeep fails to start?

Looking at it the other direction... can you tee a fuel pressure gauge into the fuel line & drive around with it like that? When it dies, is the pump still delivering plenty of fuel pressure (cranking)?
 

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