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1986 Bronco
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Discussion Starter · #1 ·
I am having issues with my Bronco project. I replaced the carb, mechanical fuel pump, tank, tank vent valve, fuel sending unit and made sure the fuel lines were clear. When I attempt to fill the tank it struggles to get fuel into the tank and when you put the cap on it builds pressure in the tank to the point it will spew on you when you open the cap, within 15-20 minutes of just sitting there, not running.

That's one issue. The other is I cannot get fuel to the carb for some reason, so I assume the pressure issue in the tank is related. Can this be related to the SMOG system and that the AC and smog pump belt is not attached? I cannot figure out why the tank doesn't vent properly even with cleared lines and why I cannot get fuel to the carb.

Please help with any ideas or experiences. Thanks in advance.

Chris
 

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If you cannot get fuel to the carb, it will not run, and the ac and smog belt are irrevelant.
For fuel not reaching the carb, is the fuel filter clogged?
Venting is seperate, is the vent clogged?
 

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1986 Bronco
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Discussion Starter · #3 ·
The fuel filter is clear. The vent is new with a new rubber seal as well and it also moves air as it should. I am at a total loss with this one, never run into this before.
 

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I am having issues with my Bronco project. I replaced the carb, mechanical fuel pump, tank, tank vent valve, fuel sending unit and made sure the fuel lines were clear. When I attempt to fill the tank it struggles to get fuel into the tank and when you put the cap on it builds pressure in the tank to the point it will spew on you when you open the cap, within 15-20 minutes of just sitting there, not running.

That's one issue. The other is I cannot get fuel to the carb for some reason, so I assume the pressure issue in the tank is related. Can this be related to the SMOG system and that the AC and smog pump belt is not attached? I cannot figure out why the tank doesn't vent properly even with cleared lines and why I cannot get fuel to the carb.

Please help with any ideas or experiences. Thanks in advance.

Chris
Your tank isn’t venting properly… there are several causes… first that comes to mind is a plugged fuel vent line (you replaced the vent valve, but did you blow out the line?). Second thing that comes to mind is a bad fuel cap, but this is less likely due to the fact you have problems filling the tank as well. Thirdly, your tank fuel filler neck has a clog some how. Try removing the rubber fuel fill hose and stat the bronco.
 

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I would suggest replacing your fuel filler neck with an 87+ filler neck. The design is vastly improved for venting. The older ones have this skinny, soft plastic tube that is very easy to kink.
The newer one uses the entire tube to vent, and a hardened line inside it for the fuel.

The older style can be extremely troublesome unless you install it perfectly. If the tank can't vent, then the pressure/vacuum difference in the tank can become too great for the mechanical pump to pull fuel from it.

Wind instrument Line Automotive exhaust Bicycle fork Pipe
 

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1981 Bronco, 4.9L, ZF5, NP208, Detroit Truetracs, 3.55 gears, 31" Wranglers front and rear
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2,472 Posts
I am having issues with my Bronco project. I replaced the carb, mechanical fuel pump, tank, tank vent valve, fuel sending unit and made sure the fuel lines were clear. When I attempt to fill the tank it struggles to get fuel into the tank and when you put the cap on it builds pressure in the tank to the point it will spew on you when you open the cap, within 15-20 minutes of just sitting there, not running.

That's one issue. The other is I cannot get fuel to the carb for some reason, so I assume the pressure issue in the tank is related. Can this be related to the SMOG system and that the AC and smog pump belt is not attached? I cannot figure out why the tank doesn't vent properly even with cleared lines and why I cannot get fuel to the carb.

Please help with any ideas or experiences. Thanks in advance.

Chris
I put a new fuel pump on mine and still had issues getting fuel to the carb. I put a Carter fuel pump on it and issue solved. You said you made sure the fuel lines were clear, but I would replace the rubber lines and check the metal lines over real good for pinholes. Also, it may help to prime the fuel lines for the first start.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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17,889 Posts
Issues filling are usually from a venting issue. The vent lines are metal and run along the passenger frame rail. They run up to a small black box between battery and radiator. This captures fuel vapors and releases them into the engine. My superduty had an issue with that system and i could barely get a gallon of fuel in before the pump shut off.

The 87+ fuel filler neck mentioned above is also a good idea. I need to do that myself.

But building of pressure in the tank should not cause fuel to not move to the carb. Building of vacuum would. Did you get the fuel pump arm installed correctly on the eccentric lobe? Is the mechanical pump identical to the old one? Is the fuel filter on backwards? Are the fuel input and output lines on the pump reversed?

For instance, i replaced the mechanical pump on my 1985 300 with one for a 390 with a bit more flow. The old pump had the line connections on the top, whereas the new one had them on the bottom. If i would have orientated the same as the old one, the pump arm would not have any movement.
 
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