Huge jerk, help!

Joined
Apr 3, 2004
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64
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Flagstaff, Arizona 7,000 feet
I've noticed that my 83 fj60 has started (intermitantly) hestiating occasionally when taking off from a stop light. Usually its after you sit at a light for awhile and doesnt occur at speed. Its really such a jolt that you feel like you hit a wall and then it goes again without loosing a beat. I replaced the fuel filter and thought it fixed it but within a week it was doing it again. Any ideas?

thanks

Mark
 
Joined
Mar 27, 2003
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6,169
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Georgia Tech
timing (this fixed my 40 which was doing the same thing)
accelerator pump

a billion other preventative maintenence things.

What is the condition of the truck?
 
Joined
Apr 3, 2004
Messages
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Location
Flagstaff, Arizona 7,000 feet
do you mean timming or accelerator pump. Why would the timing do this intermitantly and what would the accelerator pump have to do with it? Maybe if it was sticking? The engine was rebuilt about 10k ago and runs fairly well. thanks
 
Joined
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Georgia Tech
Just reread your post. Sounds like it could be a weak fuel pump- when engine is idling, the pump has trouble keeping enough fuel in the bowl for accleration. It would make sense that replacing the fuel filter would seem to relieve the problem, but only temporarily.

an accelerator pump thats not pumping won't provide the extra shot of fuel necessary when accelerating from idle. pull aircleaner, look down barrel and depress lever. Should see a strong stream of gas. (while engine is shut off of course)
^ may be a result of not enough fuel in the bowl, leading me back to a weak fuel pump.

My timing was too retarded, would almost always stumble upon acceleration. Probably isn't excusively timing, but in conjunction with other things that are not constants, this stumble results.

You could plumb in an electric fuel pump from napa and bypass the stock pump. See if that fixes the problem. If so I would suggest a new mechanical for the long term. Also you could use a vac/fuel pressure guage and check fuel pump pressure at idle.

Hope this helps
 

iron_giant

SILVER Star
 
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Jun 28, 2003
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Here again...
I just went through the same thing and it was indeed the fuel pump. The truck started to buck violently and I got very worried. But with the help of some of our MUD friends I was able to determine it was the fuel pump. Good luck.
 

gifu

 
Joined
Nov 12, 2003
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1,114
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SF Bay Area, CA
might also investigate the EGR valve. Try disconnecting the EGR actuator and plugging it. The EGR is meant to open very slowly and close slowly. When they wear, the slam shut, causing an intermittant vacuum leak.
 
Joined
Apr 3, 2004
Messages
64
Location
Flagstaff, Arizona 7,000 feet
checked to see if I saw a squirt of fuel when I manually moved the accelerator pump. Is it far down in the throat of the carb? I could hear it but not see it. I started to hook up a pressure guage but decided to head out and get the right size fittings before I blow myself up. I did notice that at idle the vehicle surges quite a bit. It acts like its going to die and then the revs come up. Would this be more indicative of a bad fuel pump or the accelerator pump? It doesnt seem to surge on the highway although sometimes it seems that maybe its not so smooth, that quite possibly could be the same thing, just less noticeable correct?

thanks

mark
 
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