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Dr. Hamman
Dr. Hamman, Automotive Engineer
Category: Car
Satisfied Customers: 5764
Experience:  30 years experience, Repairing, building, & designing, automobiles.
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Am General DJ5M: 1984 Jeep DJ5 Dispatcher. 2.5 4-cyl carbureted.

Resolved Question:

1984 Jeep DJ5 Dispatcher. 2.5 4-cyl carbureted. This car had has the computer removed, along with the harness and runs on a "Nutter Bypass". Starts well, runs well for about five miles (at night) and quits. This is in steady speed driving. It quits at exactly the same mileage every time. Daylight operation without lights extends the range to 15 miles. When the engine loses power, if put immediately into neutral, the engine will continue to run at idle somewhat roughly. If left in gear, it quits. Pull over, shut everything off, wait a minute, start right back up an good for a mile or two. Replaced plugs, wires cap & rotor, coil and ignition module with no change. Running out of suspects!
Submitted: 8 months ago.
Category: Car
Expert:  Dr. Hamman replied 8 months ago.

Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time.



"Nutter Bypass", that sounds like uncharted territory, Lets see if we can figure it out.

Have you checked the spark, and fuel pressure to see if you can determine what is failing. It sounds like an electrical problem, still the basic ignition, and fuel pressure tests are the place to start.

Customer: replied 8 months ago.

Hi Dr.


 


I am no professional, but have done my own work (within reason) for years.


 


Spark is good. Starts and runs fine. Rebuilt Carter carb. new mechanical pump, bypass fuel filter with return line to tank.


 


When the engine loses power, it does not cough or buck. If put into neutral immediately, the engine will idle and not quit. Turn everything off, count to ten, start it back up and off we go for a few miles and then it repeats. Distance traveled until this first happens from a cold start never varies by more than 100 yards.


 


Ignition control module (blue grommet Motorcraft) not warm, nor is coil.


 


Apparently, this was an early pollution control band-aid design that used multiple solenoids on the carb (gone) lots of relays, vacuum switches, etc. All removed before it came to me. "Nutter Bypass" routes the orange and purple distributor wires directly to the Ignition Control Module, not the computer (long gone). I have read this was a common modification when repair parts were no longer available. I have a factory manual and it looked like quite a rat's nest!


 


The fact that it happens so predictably leads me to believe it's thermal in nature. Next time I will let it sit and warm up good to see if that affects when it dies on me.


 


 


 

Expert:  Dr. Hamman replied 7 months ago.

Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time.




With a problem like this sometimes the fault can be pretty elusive. Odds are the fuel pressure, or the spark are going away to cause the problem. I am thinking the ignition might be flaking out, the coil and ign box don’t have to be hot for them to have a problem, although them being cool is a plus. There is an easy out if the ignition is acting up. There is an HEI ignition system with everything including the coil built into the distributor. You just run one hot wire to the distributor, power it up, and the ignition is on, and turn the power off and the ignition is off, it is a great setup.

Beyond that if you look at the fuel system, which could be loosing it's ability to deliver enough fuel, and causing the problem, should be looked at. It is possible the pump is delivering enough fuel, but the carb float could be sticking, and limiting the fuel available to the engine. I really suspect a limited fuel volume problem, might be at the root of this problem. Fuel systems can vapor lock, or you can have a crack in a suction line where it starts sucking air, and cant deliver enough fuel under certain situations. I would start off by installing a fuel pressure test gauge, and watch the fuel pressure as the engine acts up. This will allow you to confirm whether the fuel delivery to the carb is your problem.
Go over all of this and if you have any more questions at all, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer.


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Dr. Hamman, Automotive Engineer
Category: Car
Satisfied Customers: 5764
Experience: 30 years experience, Repairing, building, & designing, automobiles.
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