1981 Jeep J10

Tiny
DUSTYCOTTEN
  • MEMBER
  • 1981 JEEP J10
  • 4.2L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 117,000 MILES
After my J10 reaches full operating temperature it begins to skip. At first start up it doesn't do this. Only after riding in it for a couple of hours does it begin. It will start to skip so badly through the entire RPM range that the engine will stall. I've already replaced the fuel pump as well as the fuel filter. It has a new carburetor on it that has been on it since I purchased it.
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Saturday, February 1st, 2014 AT 9:16 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
Problems with the fuel system are going to affect all cylinders equally. You'll have a stalling or a hesitation problem. A single cylinder misfire is caused by a spark or compression problem, and when it's intermittent, you can rule out a compression problem. The most likely cause of a misfire when warm is a weak ignition coil. As it breaks down it can arc internally and fail to develop enough spark voltage. At first that will just affect the spark plug that needs the highest voltage to fire. As the problem gets worse it will affect more cylinders and may result in a no-start condition.

I never like to throw random parts at a problem, but in this case I'd suspect the ignition coil first, but also look at how long it has been since the spark plugs and wires were replaced.
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Saturday, February 1st, 2014 AT 9:50 PM
Tiny
DUSTYCOTTEN
  • MEMBER
I'm going to replace the coil today. If it doesn't work I'll let you know. It shouldn't take long to know because if it starts doing it, it's like you're driving and it skips a second and then completely stalls.
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Sunday, February 2nd, 2014 AT 7:30 AM
Tiny
CJ MEDEVAC
  • EXPERT
SEE THIS TOO!

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I GOT LOTS MORE 258 STUFF!

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THE MEDIC
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Sunday, February 2nd, 2014 AT 2:12 PM
Tiny
DUSTYCOTTEN
  • MEMBER
Any other suggestions? I replaced the coil, and it didn't help. It's not necessarily right at operating temperature, it's after I've been driving it a while at operating temperature. When it does it, it like completely dies until you let of and pat the gas; sometime you have to turn the switch off and crank it again
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Tuesday, February 4th, 2014 AT 11:55 AM
Tiny
CARADIODOC
  • EXPERT
Once it starts doing this, how does it idle in "park"? If you have the misfire there, and it's constant and steady, pull off one spark plug wire at a time to see if you can identify one that causes no change in how the engine is running. If you find one, suspect the spark plug or wire, or even the rotor and distributor cap. Also consider a wobbling shaft in the distributor that is allowing the air gap to change for the pickup coil. You can find that by using an inductive-pickup timing light with the probe on the coil wire instead of a spark plug wire. You'll see the light flashes cut out intermittently.

If the periods of cutting out are more random and last longer than a single misfire, fuel is the likely issue. It's rather time-consuming but you may want to tee in a fuel pressure gauge. I've been running with one clipped to my radio antenna for over a year since I was chasing an intermittent problem. I just left it there to watch. You're going to need an older gauge that reads pressures typical of a carburetor system. That's up to five pounds of pressure. Newer fuel injection systems commonly run over 50 pounds. Those gauges won't even move at five pounds of pressure. If fuel pressure starts dropping when the problem occurs, the main suspect is the sock on the end of the pickup tube in the gas tank. The clue here is restarting the engine. Stopping the engine and fuel pump gives the screen time to stretch back out and open up. The engine will run fine again, but each time the problem will occur after less and less time.
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Tuesday, February 4th, 2014 AT 2:16 PM

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