Engine stumbles under load... - JeepForum.com
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post #1 of 6 Old 10-18-2008, 04:34 PM Thread Starter
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1991 FSJ Wagoneer 
Join Date: Mar 2008
Location: Oregon
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Engine stumbles under load...

I having a problem with my 91 360 Grand Wagoneer, it like the engine stumbles under load. The fuel pump its new, new also coil ignition spark plugs and wire, new oil and no leaks.
Like when I drive it on a hill it has very difficult to climb it. But if i stop in the hill, shif in N and give gas, the engine works perfect without problem, but after shift in D or 2, has difficult...
I though also about the transmission...

Any guess???
Thank you!

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post #2 of 6 Old 10-19-2008, 09:27 AM Thread Starter
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1991 FSJ Wagoneer 
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Location: Oregon
Posts: 128
No guess???
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post #3 of 6 Old 10-19-2008, 11:11 AM
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Location: Northwest Oregon
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It could be alot of things...but check for vacuum leaks. If your vacuum lines are old, start replacing them one by one. If you've already done that, I'd ask when was the last tune up? Cap, rotor, ignition wires, etc. A cracked distributor cap will do the same thing...especially when the distributor advances. I can't remember if the new FSJ's use a vacuum advance system or not...but I know the older ones do. Next look at the carb. How long since it's been rebuilt?

Start with the easy stuff first...like the vacuum lines.

It's been awhile since I've worked on a FSJ, but my old 401 was the same design. And being nobody answered, I figured I'd throw that out for ya'.

Hope that helps some.

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post #4 of 6 Old 10-19-2008, 07:15 PM Thread Starter
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1991 FSJ Wagoneer 
Join Date: Mar 2008
Location: Oregon
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The engine does not have leaks, 15 days ago I changed the oil pan. ANd tune up it, with new spark plugs, wire. I also checked the fuel line and its work.
Now I will look a the transmission...
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post #5 of 6 Old 10-25-2008, 05:36 PM
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1978 FSJ Wagoneer 
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Location: Oregon
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I had the same trouble with a 74 Cherokee. Ran great - had been driving it for two hours on a road trip. Then it started to stumble. I pulled over, jeep idled and revved fine. Took back off and it fell all over itself. I started f*ing around with the distributor thinking that it had slipped. As it turned out (after I towed it another hour into town) the fuel supply line into the carb was loose.

A very experienced mechanic from a local shop helped me find it. I spun theories of timing and the like and he immediately focused in on fuel supply. In his opinion (which was spot on) there is nothing that will fail under load vs. revving EXCEPT fuel supply. Maybe a single plug or wire but not all in entirety.

Double check fuel filters, and line leaks. If the fuel pump is delivering well I would assume the problem is further down line (like at the carb).

Hope that helps.

78 Wagoneer
63 CJ
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post #6 of 6 Old 10-26-2008, 12:39 AM
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1984 J-Series Truck 
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Vacuum advance on the dist gone bad will affect it. Cracked vacuum hoses won't lose fluid, but they will make it run weird.
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