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Old 03-24-2014, 11:22 PM   #1
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Question Need help desperate for solution

I have an 87 yj with a 78 AMC v8 360 in it. I am loosing my mind trying to figure out what makes it randomly cut off while I'm driving. It starts after a few turns and drives fine, after a few miles it will randomly cut off, the last time I got it to start back up and it cut off again a 1/4 mile down the road, it took several tries to crank back up, but did the same thing. The confusing thing is that sometimes I can drive 80 miles to the farm and back with no issues then the next outing I can't make it 5 miles. I have replaced the ignition module, ignition coil, new holly two barrel carb, all the spark plugs, and put a new battery in it. The last time I drove it I noticed that fuel was pulsing into the carb after I had cut it off. That is the first time I've noticed this, but it's been cutting off for a while now, so I am not sure if there is any correlation with the two. I do not know much about working on vehicles so any advice would be greatly appreciated. I bought this jeep as a big toy, but have not been able to fully enjoy it due to being nervous every time I drive it wondering if or when it's going to randomly cut off while I'm driving it.

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Old 03-24-2014, 11:26 PM   #2
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I don't know if this helps, but I had a stalling gremlin on my TJ.
I would be driving down the highway and the Jeep would suddenly die.
If I left it for 10 minutes, it would start up and run like normal for a long time.
I eventually replaced the PCM and everything is great now.
My theory was that the PCM would get hot and something in it would stop working.

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Old 03-25-2014, 01:29 AM   #3
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I'd see if the fuel pump might be clogged. It's a cheap replacement.
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Old 03-25-2014, 04:45 AM   #4
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Sorry. Filter. Not pump. Fuel filter.
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Old 03-25-2014, 05:37 AM   #5
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Check the all the vacumm connections.
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Old 03-25-2014, 07:11 AM   #6
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It shouldn't be too hard to figure out since you are carbed. Its either spark or gas. First, figure out if you are losing spark or fuel, then go from there.

Fuel:

When you pump the throttle after it dies, does it spray gas into the carb as it should? (or is the carb dry?)

Filter, as suggested above

Can you rig up a fuel pressure gauge into the cab, so you can monitor the fuel pressure while you are driving? And while you are cranking after it dies.

Is the gas fresh? Try new gas (but it sounds like this has been happening a while)

Is your tank dirty/full of crap? Fuel pump inlet is clogged?

Float in carb sticking? (probably not in two different carbs)

Do you have a mechanical fuel pump or electrical? Bad electrical connection to the pump? Rig up a 12V light to the pump and run it into the cab. So you'll know if the power to the pump is being interrupted.

Ignition:
Are you getting spark when you try to start it after it dies?

You could rig up an inductive multimeter to one of the plug wires or coil wire and check for spark while you are driving/cranking. Harbor Freight has a cheap one that would work fine for this. Put it in tach mode.
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Old 03-25-2014, 11:36 AM   #7
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Quote:
The last time I drove it I noticed that fuel was pulsing into the carb after I had cut it off.
Fuel pulsing into the carb? That's interesting. That would indicate too much pressure in the fuel line, or a stuck open needle valve. Typically you have a float in your fuel bowl that will close the needle valve when the bowl is full. If that float is saturated or leaking it will lose bouyancy, or if you have too much fuel pressure, your valve won't close. Flooding will certainly stall an engine if it's bad enough, and will also make restarting difficult.

How did the old plugs look when you pulled them?
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Old 03-25-2014, 12:39 PM   #8
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I had a similar problem with my 87, it was the ignition switch. when it happened I would loose elec power to the gauges.
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Old 05-21-2014, 01:00 PM   #9
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X2

What 9T4YJ said!

If your plugs were fouled that would be an indication it is flooding constantly.

What jets are you running are they two big?
Did you rebuild the carb or take it to someone?

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Old 05-21-2014, 11:24 PM   #10
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Check the plug where the harness goes through the firewall. If it is loose that could cause the issue you describe.
Good Luck, L.M.
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Old 05-23-2014, 11:12 AM   #11
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All the answers above are good ones and its possible that your problem is one of them.

I had a CJ with a 304V8 in it and experienced the same problem that you are currently going through. It ended up being the fuel was vaporizing in the line from the pump to the carb, because the motor ran warm. It would run fine, until it got up to temp and then randomly cut out. On cool days it would run for ever, and never had a problem in the winter.

I took a section of 5/8" heater hose and sleeved the fuel line from the pump to the filter to insulate it from the heat of the motor. Never had the problem again.

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