1978 Jeep CJ5 Ignition Problems

Tiny
AMBERIC74
  • MEMBER
  • 1978 JEEP CJ5
  • 4.2L
  • 6 CYL
  • 4WD
  • MANUAL
I have a 258 4.2L '78 CJ5. Engine cranks but will not fire. Carburetor squirts fuel. I have replaced the entire wiring harness with a direct replacement from Painless wiring. The engine started and ran no problem before I replaced the wiring. The old wiring did not include the external resistor but the new kit did, so I installed it. I cannot find any part numbers on the coil, so I do not know what I have. I measured 12 volts to the coil. I measured the resistance of the coil between the two posts and got 1.2 ohms. I took off the center wire from the distributor and placed it within 1/8" of some exposed metal on the valve cover, but I did not see any spark. I am suspecting a bad coil. I also noticed that when I left the key in the "on" position for 15 -20 minutes, the ignition module became very hot. If I can get a decent wiring diagram with voltage and resistance values that would be very helpful! I have attached photos to show you what I have.
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Friday, December 4th, 2015 AT 9:59 PM

9 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Perform the tests in pics to see why ignition system doesn't spark. Then recheck your work with new wiring as something may be wrong with way it was hooked up.
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Saturday, December 5th, 2015 AT 6:43 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
NO SPARK?

PIC 1) WHAT IS THE VALUE HERE AT POSITIVE COIL, WITH THE KEY ON?

PIC 2 AND 3) WHAT HAPPENS IF YOU CONNECT POS BATTERY TO POS COIL AND ATTEMPT A START?

PIC 4) THE TESTER FOR THE IGNITION MODULE AT ADVANCE AUTO PARTS, TEST IT AT LEAST 5 TIMES IN A ROW. IF IT'S BAD, TEST YOUR NEW ONE BEFORE YOU LEAVE THE STORE. I'VE SEEN MULTIPLES IN A ROW, RIGHT OFF OF THE SHELF BEING DEFECTIVE! OTHER STORES HAVE TESTERS TOO!

I HAVE MANY MORE PICS TO AID WITH

HAVE YOU HAD THE DISTRIBUTOR OUT? (I CAN RUN YOU THRU PUTTING IT IN CORRECTLY)

'78 WAS SORTA WHEN THEY WERE TRANSITIONING FROM PRESTOLITE IGN TO MOTORCRAFT. IN YOUR PICS, YOURS IS DEFINITELY MOTORCRAFT. IF YOU THINK YOUR COIL IS WRONG, ASK FOR A COIL FOR A 1979-1986 CJ-7 (THEY QUIT MAKING THE CJ-5s IN 1983) THE COIL YOU WOULD NEED REQUIRES EXTERNAL RESISTANCE. THE ORIGINAL HARNESS HAS A "RESISTANCE WIRE", I'M GUESSING THAT THE BALLAST RESISTOR IS TAKING THE PLACE OF THAT (OTHERWISE YOU WOULD HAVE BOTH, WIRE AND BALLAST, PIC 1 SHOULD TELL THAT STORY)

LET'S KEEP THE COMMO GOING TILL YOU GET HIM FIXED! I'M HERE MOSTLY AFTER 6 PM EASTERN EVERY EVENING

TEST RESULTS/ ANSWERS TO QUESTIONS?

THE MEDIC
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Saturday, December 5th, 2015 AT 9:11 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
ANOTHER DAY WITH YOU JEEP NOT ON THE ROAD IS ALMOST SACRILEGIOUS,

ANY SORTA UPDATE ON WHAT'S GOING ON?

THE MEDIC
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Sunday, December 6th, 2015 AT 5:39 PM
Tiny
AMBERIC74
  • MEMBER
  • 4 POSTS
My apologies for the slow response. Its been hectic between work, family, church, and the holidays. I am getting 12V DC to the coil in the key on position. I tested the ballast resistor and I am getting.6 ohms. I also ohmed out the primary and secondary coils and I am within spec. I attempted to remove the ignition module and found the bolts are completely seized. As soon as I get the bolts removed I will take it in to have it tested. I accidently turned the ignition ground into a hot so I wonder if I fried my ignition module. I will find out soon enough. I also re-verified that my wiring is correct according to the wiring diagram. I haven't attempted to run power straight from the battery to the coil.
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Sunday, December 6th, 2015 AT 9:06 PM
Tiny
AMBERIC74
  • MEMBER
  • 4 POSTS
I have not had the distributor out. The jeep ran with no problem back in August after I adjusted the timing. Several weeks after adjusting the timing I decided to replace the 30+ year old wiring that was full of splices. Now there is no spark.
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Sunday, December 6th, 2015 AT 9:11 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
With key on you should not have 12 volts t coil it shold be like 9 you only get 12 volts when you hit start on ignition. Recheck your wiring that you have done i'd bet there is a problem there or resistor is burnt up. Also making the ground wire hot did something. I sent instructions on how to check module on very first reply. Check ballast resistor by volts shold be 12 on one side and lower on other. Like 9 or so maybe even 6 but it shold be about 9
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Monday, December 7th, 2015 AT 7:03 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
THIS MAY SOUND A BIT UNSCRUPULOUS

MOST PEOPLE FINALLY TAKE A SMALL SCREWDRIVER AND TRY TO TAKE THE IGN MODULE LOOSE- THIS USUALLY RESULTS IN BREAKING THE LOCKING TABS OFF :-(

THE MANUAL SAYS TO GRASP THE WIRES ON EITHER SIDE OF THE CONNECTOR AND PULL.

YEP, IT WORKS!

LIKE Hmac300 SAID, YOU SHOULD BE GETTING REDUCED VOLTAGE AFTER THE CURRENT PASSES THRU THE BALLAST RESISTOR W/ KEY "ON"

MAYBE YOU HAVE VOLTAGE COMING TO THE COIL FROM THE "I" WIRE FROM THE SOLENOID ("I" SHOULD ONLY BE "HOT" [FULL BATTERY VOLTAGE] ONLY WHILE CRANKING) JUST REMEMBER "I" WIRE WILL HAVE THE REDUCED VOLTAGE WHEN NOT CRANKING. AS IT "TEEs" ONTO THE IGN WIRE AND WHATEVER VOLTAGE IT IS, IT WILL ALSO BE! (SOUNDS CORNY, DIFFICULT TO EXPLAIN)

'NUTHER WORDS MAYBE THAT END IS WIRED WRONG

I'M GIVING YOU A DIAGRAM AS TO HOW THIS ALL WORKS, PAY ATTENTION TO THE "TEE" AT THE COIL) "I" IS SORTA JUST A "BOOST" TO THE COIL DURING START UP

I HAVE A 2 PAGE COLORED WIRE DIAGRAM FOR A '79 IN "MY PICTURES" (WHICH SHOULD BE REALLY CLOSE) I BLEW IT UP AND HAVE IT HANGING ON MY WALL. LET ME KNOW IF YOU NEED IT

KEEP US POSTED

THE MEDIC
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Monday, December 7th, 2015 AT 3:20 PM
Tiny
AMBERIC74
  • MEMBER
  • 4 POSTS
The jeep is up and running now. I had a bad ignition ground and when I hooked up a ground to a hot I fried the ignition module. Thank you for your assistance.
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Sunday, December 13th, 2015 AT 7:28 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
YOU ARE GONNA SEND US A PIC OF YOUR BABY AREN'T YOU?

THE MEDIC
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Sunday, December 13th, 2015 AT 3:56 PM

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