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Unread 06-05-2013, 08:48 PM   #1
gurlcj
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Join Date: May 2013
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Cj 7 cranking but won't start

My 1986 Cj7 cranks but will not start. I have, I think, narrowed it down to a spark issue. I hooked a timing light to the coil wire as I tried to start it and no spark UNTIL I let of the key. When I let offthe key it sparks once. What does this mean?

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Unread 06-05-2013, 10:45 PM   #2
LumpyGrits
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Run a lead from the POS(+)side of the battery to the POS(+)side of your coil.
If it starts now, you have ing switch issue would be my bet.
LG
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Unread 06-06-2013, 12:43 AM   #3
BagusJeep
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It seems like it sparks once because the coil is denergising.

In whic case you have a fundamantal problem on the low voltage side, it is not getting a signal from the ICM on the light green wire on the coil -ve side. That wire should be grounding in time with the engine to denergise the coil to give you a regular spark. It is not, it energises once and then denergises when you let off the key.

It could also be a broken ballast resistor or a missing connection to the I tab on the solenoid but you can check that.

It is a 1986 with the computer? I would check the IGNLPS fuse in the fuse box as a first and easy step. The computer is powered from this fuse and interferees with the sensor going to the ICM from the distributor, no power means no sensor means no signal means no activity on the light green wire.

If the fuse is intact you can investigate that module and coil.

Best tool is a 12V test bulb with long leads, mine cost $5.

First step is to confirm no signal on the light green wire, unhook it from the coil. Hook one lead to the battery positive, other lead to the light green wire. The bulb should blink on and off in time with the engine turning, if not the ICM is not working for some reason.

Hook one end to the battery negative and go looking for voltage. Take off the coil red with tracer wire and hook it to the other lead, you shoud find a Bright bulb in Start and a dim bulb in Run. If you do not have a Bright bulb in Start you are missing the connection to the I tab on the solenoid, see attached diagram.

Now undo the 2 way plug to the module. Probing the harness side you should see a Bright bulb on the red wire in Run and Start and in Start only a bright bulb on the whie wire. If that all works out the ICM and coil are powered.

Now take apart that 4 way plug. The black wire is the ground which is wired back through the base of the distributor. It is notorious for failing. Hook on elead to the battery positive and probe this wire with the other lead. You should get a Bright bulb.

There are then two sensor wires. As you see from the diagram they are iterefered with by the computer. You should get about 600 ohm across these wires if they were connected directly to the sensor.

You know you have it all working if you can get the light green wire to give a signal.

If the computer is suspect you can wire the sensor directly to the distributor, the Nutter bypass.

I attach some fuse box diagrams, a nice sketch of the ignition without the computer and a diagram of your 1986 layout with the CEC computer.
84-86_fuseblock.jpg   84-86fuseboxsch-copy-2-.jpg   durasparkii.jpg   schematic-ignition-layout.png  
__________________
BagusJeep lives in Bali, the Land of Temples.
With a Jeep every prayer counts.

1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1995 Cherokee 4.0 - CHEROKEE
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Unread 06-06-2013, 04:28 PM   #4
gurlcj
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Quote:
Originally Posted by BagusJeep View Post
It seems like it sparks once because the coil is denergising.

In whic case you have a fundamantal problem on the low voltage side, it is not getting a signal from the ICM on the light green wire on the coil -ve side. That wire should be grounding in time with the engine to denergise the coil to give you a regular spark. It is not, it energises once and then denergises when you let off the key.

It could also be a broken ballast resistor or a missing connection to the I tab on the solenoid but you can check that.

It is a 1986 with the computer? I would check the IGNLPS fuse in the fuse box as a first and easy step. The computer is powered from this fuse and interferees with the sensor going to the ICM from the distributor, no power means no sensor means no signal means no activity on the light green wire.

If the fuse is intact you can investigate that module and coil.

Best tool is a 12V test bulb with long leads, mine cost $5.

First step is to confirm no signal on the light green wire, unhook it from the coil. Hook one lead to the battery positive, other lead to the light green wire. The bulb should blink on and off in time with the engine turning, if not the ICM is not working for some reason.

Hook one end to the battery negative and go looking for voltage. Take off the coil red with tracer wire and hook it to the other lead, you shoud find a Bright bulb in Start and a dim bulb in Run. If you do not have a Bright bulb in Start you are missing the connection to the I tab on the solenoid, see attached diagram.

Now undo the 2 way plug to the module. Probing the harness side you should see a Bright bulb on the red wire in Run and Start and in Start only a bright bulb on the whie wire. If that all works out the ICM and coil are powered.

Now take apart that 4 way plug. The black wire is the ground which is wired back through the base of the distributor. It is notorious for failing. Hook on elead to the battery positive and probe this wire with the other lead. You should get a Bright bulb.

There are then two sensor wires. As you see from the diagram they are iterefered with by the computer. You should get about 600 ohm across these wires if they were connected directly to the sensor.

You know you have it all working if you can get the light green wire to give a signal.

If the computer is suspect you can wire the sensor directly to the distributor, the Nutter bypass.

I attach some fuse box diagrams, a nice sketch of the ignition without the computer and a diagram of your 1986 layout with the CEC computer.
Well I went out to work on the darn thing, and I had a completely dead battery. I know there is a short in the system somewhere. I forgot to mention that to you in my first post. Will that make a difference in diagnosing this problem or should I do the same. I also noticed that it looks like there might be wire missing from the solenoid. Hmm. I came online to look at the pictures you posted. That's why I'm updating this post. Could you possibly send those pics to my email? I will pm you with the address. Thanks
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Unread 06-06-2013, 04:42 PM   #5
gurlcj
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Ok, never mind about resending. The android app I was using was the problem. I've got them. :-)
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Unread 06-06-2013, 04:55 PM   #6
LumpyGrits
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The late CJ's didn't use a 'ballast-resistor' It was a 'resistor-wire'.
If the OP does the jumper wire liked I said and it starts. My bet is ign. switch issues as in internal contacts gone bad, BTDT.
Charge the battery and then disconnect your ALT.
LG
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Unread 06-09-2013, 07:51 PM   #7
BagusJeep
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Quote:
Originally Posted by LumpyGrits View Post
The late CJ's didn't use a 'ballast-resistor' It was a 'resistor-wire'.
LG
Is that a fine hair you are splitting?

It is a resistor that ballasts the ignition. As shown in the diagram it is achieved as stock by a piece of wire in the harness that has a higher resistance.

If you have one break or corrode etc then most owners fit a ceramic resistor block and screw it to to the bulkhead and wire through it.
__________________
BagusJeep lives in Bali, the Land of Temples.
With a Jeep every prayer counts.

1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1995 Cherokee 4.0 - CHEROKEE
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Unread 06-10-2013, 08:03 AM   #8
LumpyGrits
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Location: The Mojave Desert Palmdale Ca. U.S.A.
Posts: 4,486
Quote:
Originally Posted by BagusJeep View Post
Is that a fine hair you are splitting?

It is a resistor that ballasts the ignition. As shown in the diagram it is achieved as stock by a piece of wire in the harness that has a higher resistance.

If you have one break or corrode etc then most owners fit a ceramic resistor block and screw it to to the bulkhead and wire through it.
NO hair splitting at all-Just fact
Look, when somebody sez 'ballast resistor', 99% of folk will be looking for something hang'n on the side of the coil.
They will not think about the wire in the main wiring loom run'n across the firewall.
LG
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