1986 4.9l help!!!!!
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Junior User
Joined: Oct 2006
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From: jasper,GA
1986 4.9l help!!!!!
86 f-150 with 300I-6,carb model. idles irradictly and hesitates under part throttle,under full throttle runs smooth. checked all vacuum lines and is good. egr is new, so is oxygen sensor, any ideas possible sensor on carb? which one? any help would be greatly appreciated. also when running a constant speed on highway, it jerks and sputters, almost like fuel is getting cut out and on. thanx guys
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Junior User
Joined: Oct 2006
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From: jasper,GA
changed all that today,gapped plugs .045, motorcraft plugs , checked timing and set at 10 btdc. it idles a little smoother, and does not hesitate when accelerating , but when accelerating has good power till bout 1/2 throttle than no matter how hard u step on it , it doesnt go any faster, almost like its choking .
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Joined: Dec 2006
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Originally Posted by cuztom79
changed all that today,gapped plugs .045, motorcraft plugs , checked timing and set at 10 btdc. it idles a little smoother, and does not hesitate when accelerating , but when accelerating has good power till bout 1/2 throttle than no matter how hard u step on it , it doesnt go any faster, almost like its choking .
Postmaster
Joined: Nov 2003
Posts: 3,568
Likes: 1
From: Middleton, ID
Have you done anything with the carb? My '84 Bronco has the 300-6 and does the same thing till it gets warm. Mine is a total loss and I'm just waiting till I get the cash to swap the intake and carb for an aftermarket setup.
Also, might be in the exhaust i.e catylitic converter.
Also, might be in the exhaust i.e catylitic converter.
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
Check the feedback solenoid. If the feedback solenoid is working erratic, it could cause these problems.
Here is a blowup of a Carter YFA 1B Carb.
The feedback solenoid (AKA: Air/Fuel Ratio Solenoid) is pictured on the left about a 1/4 way down the page.
Here is a blowup of a Carter YFA 1B Carb.
The feedback solenoid (AKA: Air/Fuel Ratio Solenoid) is pictured on the left about a 1/4 way down the page.
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Junior User
Joined: Oct 2006
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From: jasper,GA
thanx guys, i took off the carb and cleaned it, put it back and runs much better now. these damn feedback carbs suck! also do they make a choke that does not require the heat riser tube, its rusted in half
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my prob is similar, runs great...well, ok...GOOD when warmed up. Horrible when cold. Very erratic. May run good, may try to stall whenever you let off the gas to shift. I'm thinking its gotta be electrical and/or carb related.
Senior User
Joined: Jan 2007
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I am not sure how "stock" or Original you want to keep this but may i make a few suggestions.
Kill the computer and the feedback system You can do so by doing the following.
Remove that junk feedback carb. Go to the junkyard, find a Carter YF from a late to mid 70's Ford with the 300 in it. ( no major emissions, and feedback)
Find a DurasparkII Distributor from the 77-80/1/2 range This has the module mounted on fenderwall/wheel housing with the Blue grommet. Switch all that over, you can use your existing coil.
By doing this, you eliminate the feedback system, thus get a better running, more stable truck. You can modify the choke when you buy a different carb, either modify the heat tube set-up or get all electric etc.
Go over to fordsix dot com. those guys have covered this many times and are really willing to help out just like these guys here, infact some members watch both boards. Just my 2 cents, hope I have helped some.
Kill the computer and the feedback system You can do so by doing the following.
Remove that junk feedback carb. Go to the junkyard, find a Carter YF from a late to mid 70's Ford with the 300 in it. ( no major emissions, and feedback)
Find a DurasparkII Distributor from the 77-80/1/2 range This has the module mounted on fenderwall/wheel housing with the Blue grommet. Switch all that over, you can use your existing coil.
By doing this, you eliminate the feedback system, thus get a better running, more stable truck. You can modify the choke when you buy a different carb, either modify the heat tube set-up or get all electric etc.
Go over to fordsix dot com. those guys have covered this many times and are really willing to help out just like these guys here, infact some members watch both boards. Just my 2 cents, hope I have helped some.
Post Fiend
Joined: Jul 2004
Posts: 8,786
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From: Northern California
Just make sure your state will allow you to remove that stuff.
In California for instance it is a big no-no.
If you ever plan on moving out here to california, with the truck, or live in California now, then dont remove any of the smog and make sure it's in proper working order.
Other states are also following California's examples so just be carefull is all I'm saying.
================
As for Carb issues, it sounds like if the original poster would put a Carb rebuild kit into his carb, that would probably fix the problem.
The gaskets fail, the jets plug up, the power valve cracks, the float valve wears out or becomes dirty, as examples. That could throw the computer controls into a fit too.
hope this helps...
In California for instance it is a big no-no.
If you ever plan on moving out here to california, with the truck, or live in California now, then dont remove any of the smog and make sure it's in proper working order.
Other states are also following California's examples so just be carefull is all I'm saying.
================
As for Carb issues, it sounds like if the original poster would put a Carb rebuild kit into his carb, that would probably fix the problem.
The gaskets fail, the jets plug up, the power valve cracks, the float valve wears out or becomes dirty, as examples. That could throw the computer controls into a fit too.
hope this helps...
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Junior User
Joined: Oct 2006
Posts: 63
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From: jasper,GA
thanx guys this all helps. i rebuilt carb sunday, is 85% better., probably need to change the air/fuel solenoid. better yet trash the motor, swap in a 302 with a 4 barrel no emmisions carb!