My truck (1985 5.8 4bbl stock ford/Holley) starts fine drives fine UNTIL it gets warm then the idle picks up and idles high and it starts dumping fuel out of the mechanical pump. I’ve replaced the mechanical pump, the internal fuel filter, the accelerator pump diaphragm, cleaned out the carb but it’s still goes right back to where it was before. I’m at my wits end with it tbh pleeeease someone help 🙂 truck is the base model. No AC.

 

More importantly, I hope you changed the oil and filter. That fuel pump likely dumped gas into the crankcase. Fuel diluted oil just doesn't do very good and you can wipe out your bearings in short order.

What speed is the idle at when it acts up? Sure it isn't hanging up on the fast idle cam?

 

Thanks for replying. Ive replaced oil, filter, cap, rotor, plugs, wires, coil. It’s at about 850 when it’s in gear then it jumps to about 2000 rpm and sits there dumping gas.

 

Didn't it stop dumping gas with the new fuel pump?

 

yes for a while, I took it out for a run and stopped running after about 1/2 mile. It would start, drive a bit then lose power. Idled fine. Then I did all the cap rotor plugs etc and used it for runs to the store and back (2 miles ish) with no problem. Then last week I gave it a gentle 60 mile round trip and that’s when it started pissing gas again. Every time it runs, sits and gets warm that’s when the RPMs pick up and it starts dumping gas.
This does happen when using either the front or rear gas tanks.
hope that helps

 

Did this start just out of the blue? Is it vaccum secondary or mechanical?

 

Still wondering what he means "dumping gas". Is it spilling out on the ground?

 

I noticed when I bought a new fuel pump for my 77 that they had two versions, a 6PSI and an 8 PSI, could yours be the wrong one and pumping too much? I don't know if an 85 would have two versions, but that might be a reason - not sure just throwing it out there.

 

Id say not if its causing it to idle at 2000 rpm.
Is this the carb that has a choke supply line with an electric choke? Whats the voltage at the choke when its idleing this high. Has the floats been check.

 

I cant imagine 2 psi differece would cause this issue. Maybe surge underload but if the psi was to high it would bend the needle and cause a high idle all the time, or low idle stalling issue.