Just got around to checking again, I'm an idiot; pump is 35 gph, only 4-7 psi

 

The transmission has been my theory for awhile now, we had it flushed a couple months ago, did get a little bit of burned fluid when this all started.

The only thing that seems odd is that there aren't any other symptoms than the power loss, it shifts and drives fine.

 

i would think the trans would be slipping causing hi rpm with no forward momentum.

 

That's what I've been thinking too, but wouldn't I be able to feel that?

 

Yeah, good point.

It's a head scratcher. Do you have a Catalytic Converter?

 

Ethanol fuel related maybe? It killed the last fuel pump I put on my 78 in only 3 years. No telling what the inside of carb looks like. Or pickup in tank.

 

how about the fuel filter. you might want to check fuel volume. if its running lean it would cause this.
how clean were the plugs.

 

Alright, let me throw out another thought, tell me what you think about this. I didn't think it was related, but it could be.

The Bronco also builds up really excessive pressure in the gas tank: my test uphill a couple nights ago involved getting gas on the way home, and when I popped the cap, it let out a lot of vapor. It's been doing this for a while, sometimes it's hard to fill. But that being said, could that excess pressure be limiting the fuel at speed uphill?

 

Both fuel filters have been replaced, along with the pump. Plugs were clean, as mentioned above.

 

plugs should be a tan color i would think. if they are white you are probably running to lean.

have you tried to advance your timing more? perhaps its to retarded. advance it till you max out the vacuum.

 

If the tank is not getting air it could cause problems. But I would think it would die and not be doggy.

On my 1986, someone disconnected the fuel vent line from the canister. It had dirt on the end of the hose.

I would make sure the vent line is not clogged.

I used a vacuum pump so I would (hopefully) not get any dirt in the tank.

 

That's what I thought too, but I'm convinced this issue is going to be something stupid, so why not this.

I checked into the vent lines; PO removed the cannister, and capped the vent line. Which means the vent isn't doing anything, but it ran fine like that prior to this issue. I'll fix that anyway, just so we can fill the tank all the way.

​​​​​​What he did for the return line is odd though, the inline filter before the carb has two outputs; one to the carb, and the other to the return line. The input comes from the pump. I replaced that filter with the same model some weeks ago, and looked into it, apparently that's suggested in the Edelbrock documentation, to prevent vaporlock.

The weird thing is that he left the air pump system in place, but removed the cannister. Again, not sure how it could cause power loss, and it obviously worked before, but it's interesting nonetheless.

So no real progress there, but it does feel like it's being limited somehow under heavy load. Once you hit 45 uphill, it will not go faster, throttle has almost no effect from 50% on. I could see fuel delivery being the issue, but I would think it would sputter once it's starved. It runs totally smooth throughout the range, just won't pick up speed.

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I was just thinking, your gas cap should let air in. Should say vacuum on the cap I believe.

Have you tried driving it with the cap off or loose?

Also with the line capped by the PO, maybe the PO put on a vented gas cap.

 

Doh! If it was a vented cap, you wouldn't have a build up!

 

i think at this point i would look at the carb. make sure the float/s are working right and set right. see what jets are in it. if the plugs are clean then like the other poster said it might be lean and you have to find out why.