Quote:
Originally Posted by GhostBS  I have a 1976 cj5 with the 304v8. I've replaced the starter, solenoid, ignition coil, plug wires, plug, distributor and cap, and the tank has gas in it. The engine turns over, gas is sprayed into the carb but the plugs aren't firing. I get power from the battery to the coil, but not from the coil to the plugs. It's a 12v coil with an internal resistor, i was told it would work. Whats the deal? can anyone help me? |
ONE THING JUMPS RIGHT OUT!
'76 is a Prestolite ignition system,
And Prestolite NEVER used an internally resisted ignition coil...
(or external ignition resistors. It's a full 12 volt system all the way through, NO RESISTORS FROM THE FACTORY...
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Throwing parts at it usually doesn't fix the problem...
SO!
*IF*... YOU STILL HAVE THE FACTORY PRESTOLITE IGNITION!
Try this...
Use a $6 test light from one of the discount autoparts stores, Get the kind that has a BULB, not LED Lights.
Or make one from a light bulb socket, bulb and some wire.
Connect the test light to the battery NEGATIVE terminal.
Probe the battery POSITIVE terminal.
This tests the light, and lets you know what a 'BRIGHT' light should look like.
NOW,
Remove the 'RED' wire(s) from the POSITIVE side of the ignition coil.
Have someone help you,
Probe the 'RED WIRES' while your helper turns the key switch to the 'RUN' position.
You should get a 'BRIGHT' light.
Now, probe the 'RED WIRES' while your helper turns the key switch to the 'CRANK' or 'START' position.
BE READY FOR THE ENGINE TO CRANK!
You should get a 'Bright' light.
IF YOU DO NOT GET A BRIGHT LIGHT
When the key switch is in the 'Run' or 'Crank/Start' positions,
The problem is with the wiring from the coil/ignition module back to the ignition switch...
Could be fuse, ignition switch, Factory tach if you have one, wiring between ignitions switch and the coil with all this stuff in it.
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This diagram should help you track your wiring at the ignition end of things...
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IF YOU DO GET A 'BRIGHT LIGHT',
Then you should put the 'Red Wires' back on the coil Positive side where you got them....
Move the wire from the battery NEGATIVE TERMINAL,
To the battery POSITIVE TERMINAL.
PROBE the battery NEGATIVE TERMINAL to make sure you get a 'BRIGHT LIGHT'.
..........
Take the 'GREEN WIRE' off the NEGATIVE side of the coil.
Probe the 'Green Wire' while your helper turns the key switch to 'Crank/Start' position.
Your test light should FLASH ON & OFF WITH AN EVEN RHYTHM as the engine cranks over.
*IF IT DOES FLASH...*
REATTACH THE GREEN WIRE TO THE IGNITION COIL NEGATIVE TERMINAL.
Then you need to build a
TEST PLUG.
Take an old spark plug,
Strip about 3" of wire, and wrap it SECURELY around the plug threads,
Move the other end of the 'Ground' wire to the NEGATIVE BATTERY TERMINAL,
And strip about 3" of that end, and SECURELY attach the 'Ground' wire for your test plug to the battery NEGATIVE TERMINAL.
Once this is done,
Pull off one of your plug wires,
(doesn't matter which one, but normally I use a short one)
Connect the spark plug end of that plug wire to the test plug,
NOW,
Pull the coil high voltage wire out of the coil,
And insert the distributor cap end of the spark plug wire into the ignition coil.
NOW,
Have your 'Helper' crank the engine while you observe the 'Test Plug' you just made...
You should see 4 firings in the plug gap every engine revolution.
IF YOU DO NOT see spark,
The ignition coil is probably bad, or you don't have your engine heads grounded properly anymore.
IF YOU DO GET SPARK AT THE 'TEST PLUG',
You have a bad coil wire, distributor cap or rotor.
(no chance for all 8 plug wires to be bad at the same time!
OR,
The heads are no longer sufficiently electrically grounded.
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Now, if you test the coil 'Green' wire, and you DO NOT get any flashing,
The problem is with...
1. Ignition Module.
2. Distributor Trigger.
3. Wiring between module, distributor and/or coil.
To figure out which one,
First make sure the black wire from the module is getting a good electrical ground.
The ONLY WAY TO DO THIS IS TO RUN A DEDICATED GROUND WIRE FROM BATTERY NEGATIVE OR PRIMARY GROUND LUG TO THE MODULE 'BLACK' WIRE!
Next, move your 'Test Light' back to NEGATIVE BATTERY TERMINAL,
Pull the 4 wire plug apart that services the ignition module,
And probe the HARNESS SIDE power feed to the module.
(Probably 'Red' With Color 'Trace' Stripe, or 'Red w/Trace')
Test this connector terminal both when the key switch is in the 'Run' and 'Crank' positions to make sure it's getting power when you are trying to start, and when the key switch settles back into the 'Run' position.
*IF*...
You get power in both 'Crank' and 'Run' (bright light)
The 9 chances out of 10 power is getting through to the module...
*IF*...
You DO NOT get power to the module in 'Start' and 'Run' positions, then you have a bad wire/connector between the ignition coil and the module connector.
...................
Now,
Take the 'Green' wire OFF the ignition coil,
And use a piece of extra wire to ground that green wire DIRECTLY to the battery NEGATIVE (Jumper Wire).
Connect your 'Test Light' to the battery POSTIVE terminal,
And probe the 'Green' wire at the HARNESS side of the module connector.
*IF*...
You get a 'Bright' light,
Then the 'NEGATIVE' or 'GROUND' wire for the ignition coil is working...
*IF*...
You DO NOT get a 'Bright' light, or no light at all,
Then the green wire has a break in it between coil and module connector.
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The only thing left is the two distributor wires...
'BLUE' & 'WHITE' wires on the '76 if it's correctly wired...
DO NOT APPLY POWER TO THESE WIRES WITH THE DISTRIBUTOR PLUGGED IN!
Unplug the distributor,
Ground each wire with your 'Jumper Wire',
And test for 'Bright Light' at the module connector.
Both should give you a 'Bright Light'...
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That will only leave the distributor 'Hall Effect' trigger,
And the module it's self...
The module can be tested at any of the parts stores,
And the distributor can be tested with a common Ohm meter...
Between the two distributor trigger terminals at the plug, 1.6 to 2.4 Ohms.
Then test between each terminal and the distributor housing... (Shorted trigger test).
Both BLUE and WHITE wire to housing should show an OPEN circuit (usually 'OL' or 'Over Limit' on digital meters)
starting problems! 
Linear Mode
