Ignition system

Tiny
MDAVIS72
  • MEMBER
  • 1978 JEEP CJ5
  • 5.0L
  • V8
  • 4WD
  • MANUAL
  • 150,000 MILES
I have, I think, a 78 cj5 with a 304 I just install a fiberglass body and I have everything grounded. It now starts but it only runs with the starter. I have replaced the ignition switch on top the column. The only thing I have tried is jumping the coIL to the battery and it runs like it should. Is this telling me the resistor wire is bad? If not what do I need to check? I'm pretty new to this. Thanks
Do you
have the same problem?
Yes
No
Monday, February 15th, 2016 AT 4:09 PM

7 Replies

Tiny
CARADIODOC
  • EXPERT
Yup. I'd have to dig up a wiring diagram to know for sure, but there is going to be a ballast resistor, (Chrysler), or resistor wire, (GM) to limit current flow through the ignition coil when you have breaker points. Because battery voltage is drawn down during cranking, average voltage to the ignition coil would be even lower, so the resistor is bypassed to get the spark voltage back up. Many electronic ignition systems don't use a resistor, but some do. When one is used, it too must be bypassed during cranking. Ford did that with a tap on their starter solenoid. There's at least three different designs that all look the same with the two large copper terminals and the two small ones on top. If you have the wrong solenoid, the starter system might work but you won't have the resistor bypass circuit. Your symptom doesn't agree with this.

GM bypassed their resistors with a "resistor" (R) terminal on the starter solenoid on top of the starter. Early Chryslers did this with a separate extra contact in the ignition switch. By the mid '70s they used an extra contact on their starter relays.

Regardless which system you have, if there's a break or defect in the resistor part of the circuit, the engine can't run due to no spark, but that defect gets bypassed during cranking. By running a hot wire from the battery positive post, you're proving there's a break in the circuit, but that won't tell you where.
Was this
answer
helpful?
Yes
No
Monday, February 15th, 2016 AT 4:27 PM
Tiny
MDAVIS72
  • MEMBER
I have a resistor wire that is 1.35ohms and runs from the fuse block and where it splices for the coIL and starter solenoid. How do I check it or fix it? I can't just cut it out and install new as easy because it is in the fuse block and is more involved then just cutting and slicing. Would rather be able to check or run a temp to test it
Was this
answer
helpful?
Yes
No
Monday, February 15th, 2016 AT 4:47 PM
Tiny
CJ MEDEVAC
  • EXPERT
LET'S TRY "KEY ON" (NOT KEY AT "START")AND THIS TEST BELOW (SEE MY 1st PIC AT THE BOTTOM) YOUR RESULTS MAY VARY.

ON YOUR VIN, STARTS OUT "J" THEN A NUMERAL. MY 1977 CJ-5 STARTS OUT "J7" MEANING IT'S A '77. IS YOURS "J8"?

DO YOU HAVE PRESTOLITE IGNITION OR OTHER? NOT KNOWING WHAT YOU HAVE OR SHOULD HAVE MIGHT MEAN YOU HAVE SOME OF YOUR IGNITION SYSTEM WRONG.

MY 3RD PIC IS OF A PRESTOLITE DISTRIBUTOR FOR A 304, NOTE THE 2 PROTRUSIONS ON THE FRONT, THEY ARE PLASTIC, ONE SIDE HAS A VACUUM HOSE CONNECTION

IF YOU HAVE A MOTORCRAFT SYSTEM, THERE IS NO PLASTIC FRONT, THE SIDE WITH A VACUUM CONNECTION WILL HAVE A METAL BELL ON IT. IT WILL LOOK SIMILAR TO MY SIX CYLINDER DISTRIBUTOR IN PIC 4

GIMME SOME ANSWERS, WE'LL GET YOUR BABY RUNNING REAL SOON, I'VE GOT MANY MORE "HOW TO" PIC, INCLUDING SOME WIRE DIAGRAMS

IN FACT, IF IT WILL RUN WILL AT "STARTING", I CAN SHOW YOU HOW TO MAKE IT RUN (JUST TO MAKE YOU FEEL GOOD/ TEMPORARY). BUT WE WILL STILL HAVE TO FIX THE PROBLEM TO GET IT RIGHT!

THE MEDIC
Was this
answer
helpful?
Yes
No
+1
Monday, February 15th, 2016 AT 5:07 PM
Tiny
MDAVIS72
  • MEMBER
I'll have to do the test tomorrow but I believe I have the MOTORCRAFT system. Vin number won't help its off a 70cj5 so I know it's not right
Was this
answer
helpful?
Yes
No
Monday, February 15th, 2016 AT 5:38 PM
Tiny
MDAVIS72
  • MEMBER
Ok so I did the test in pic 1 and I get no voltage on the + of the coil. What's that tell me?
Was this
answer
helpful?
Yes
No
Tuesday, February 16th, 2016 AT 1:25 PM
Tiny
MDAVIS72
  • MEMBER
Well I did some more checking and I found a wire unplugged under the dash and now it runs fine. Thanks for the help I'm sure I'll need it again
Was this
answer
helpful?
Yes
No
Tuesday, February 16th, 2016 AT 3:06 PM
Tiny
CJ MEDEVAC
  • EXPERT
JUST WHEN I THOUGHT THAT I MIGHT SPEND SOME TIME WITH A CJ!

GLAD YOU GOT IT GOING

ANY OTHER ISSUES, JUST SHOOT!

MY WILLYS HAS A FULL FIBERGLASS BODY, 'CEPT FOR THE '43 WW II GRILL

THE MEDIC
Was this
answer
helpful?
Yes
No
Tuesday, February 16th, 2016 AT 3:18 PM

Please login or register to post a reply.

Recommended Guides