70 Bronco 302 - Fuel System Trouble Shooting

[tonytony9]

Hi Everyone,

I bought my Bronco back in March of this year and am diving in as the second owner. She is an East Coast survivor, all original, and I have adopted the philosophy of fixing/replacing only if it is broken or beyond refurbishment. As a result, I have not touched the fuel system. This past week, as the weather in New Jersey is getting increasingly cold, I have noticed some horrible performance arising (consistently below 35 degrees).

A few days ago, Bronco seemed to be bogging or skipping along at consistent speeds above 50 mph. A day later, consistently above 40mph. Now, it is pretty much at any speed above 15mph. She is not driving smoothly, on acceleration or cruising speeds, she feels like she wants to buck or skip. She is starting up with no issues and idling perfectly, starts up high, and then I can either tap accelator to step her down to the 600-650 rpm or she will gradually step down as she reaches operating temperature (I have a 195 Robert T Shaw 330 Thermostat which is working correctly).

Before these issues arrived, Bronco was running very very well. In the past month, I had the Carb rebuilt by Steve's Carbs in North Jersey (he did a really excellent job and I would highly recommend), I replaced the SparkPlugs with AutoLite ASP 45 from Napa, the Plug Wires with MPW 2801 from Napa and replaced my in-line fuel filter with a metal WIX filter. I have put about 200-300 miles on it since.

I created this diagram to help visual my current fuel system:

1970 Ford Bronco 302, 303 Manual, August 1969 build - Michigan plant, New York DSO, U152 HD Package

Media:

1. Fuel Pick Up - Main Tank

2. Selector Valve (Aux/Main Tank) to Wix Fuel Filter to Line that runs to Mechanical Fuel Pump

3. Gale 304 Aux Tank Fill Cap

4. Fill Neck & Main Tank Breather Tube that runs into the Fill Neck (I do not see a vapor canister or charcoal canister anywhere)

5. Additional Photo of Fill Neck/Breather Tube

6. Fuel Pump

7. Carb Fuel Filter

8. Gas Cap - Duralast 6023 Fuel Cap

There is old, spoiled fuel in the Aux Tank. The inside looks very clean. I have not used the tank. There is no external fill neck, it is only under the seat. I would like to keep this Aux tank and use it in the future. The wetness you see in the photo of the main tank is from a dripping oil crush washer, transmission & tcase seal leak. Next on the list.

I am not sure where to start. I have a brand new Main Gas tank free from the previous owner. Only the tank and strap. No pick-up. The lines look to be rubber or a hard plastic. Kind of a casserole of tubes and clamps. I am honestly considering replacing everything including the pump back. And, while I have the tanks off, addressing any rust and treating with POR-15.

Should I attempt to first replace pick-up and fuel pump? I am thinking of sticking with a mechanical fuel pump. Not sure which brand to go with for pump or pick-up and what type of lines to use. I noticed that, when I go to the fill up and take the Fuel Cap off, there is a ton of pressure released when I pop off the cap. I assume that the main tank is not releasing any pressure out with this cap. The Bronco has a strong fuel smell when sitting in the garage. And people have mentioned it smells like it is running rich, or just a very strong exhaust smell.

Thank you everyone very much in advance!

 

[Broncobowsher]

Ideally there is a pickup filter inside the tank. It is just a coarse filter to keep the big stuff from getting through. By now most of those have fallen apart and you just have an open tube in the tank. Which is more than likely why someone put the inline filter just after the selector valve. Personally I prefer that filter before the selector valve for the purpose of when you have and issue like you are having now you can switch to the other tank and other filter. I realize that is a bit of a mute point right now as the aux tank is bad fuel in it as you mentioned.

To really know what is going on takes testing. A vacuum pressure gauge comes in handy as you can either see fuel pressure drop off after the pump, or vacuum being created before the pump.

I also have to comment on that aux filler. Seen a lot of stuff over the years. That is a first. And that is from someone who has run a BBQ grill propane tank with the valve removed and a loose fitting cap installed as a gas tank.

 

[tonytony9]

Ideally there is a pickup filter inside the tank. It is just a coarse filter to keep the big stuff from getting through. By now most of those have fallen apart and you just have an open tube in the tank. Which is more than likely why someone put the inline filter just after the selector valve. Personally I prefer that filter before the selector valve for the purpose of when you have and issue like you are having now you can switch to the other tank and other filter. I realize that is a bit of a mute point right now as the aux tank is bad fuel in it as you mentioned.

To really know what is going on takes testing. A vacuum pressure gauge comes in handy as you can either see fuel pressure drop off after the pump, or vacuum being created before the pump.

I also have to comment on that aux filler. Seen a lot of stuff over the years. That is a first. And that is from someone who has run a BBQ grill propane tank with the valve removed and a loose fitting cap installed as a gas tank.

Your recommend filter location makes sense to me with a tweak, one before the T valve from the main and one before the T Valve from the aux tank this way all fuel moving up the chain to the pump gets filtered. I was thinking the same thing, having the aux tank is a great back-up.

If the pressure drops after the pump, does that indicate a faulty pump? If the pump is not pulling about 6lbs before the pump, then I assume also faulty? What is the point of testing both sides, apologies might be missing something.

Yeah, its pretty crazy they did not add a fill neck. And god, it would be inconvenient and a potential disaster to fill from under the seat. Do you think this is a crash safety hazard?

 

[Broncobowsher]

Just because you are not getting 6LBS before the bump does not condem the pump, but would confirm there is a fuel delivery issue before the carb.

 

[tonytony9]

Just because you are not getting 6LBS before the bump does not condem the pump, but would confirm there is a fuel delivery issue before the carb.

got it makes sense thank you

 

[tonytony9]

Just because you are not getting 6LBS before the bump does not condem the pump, but would confirm there is a fuel delivery issue before the carb.

Should I be using a two-way vented gas cap since I do not have a charcoal canister system?

 

[DirtDonk]

That’s the only type of cap that will fit on your main tank. Unless it was modified to accept the later cap that is. But it doesn’t really look like it at this point.
August is a very early 70 build. Would not have had a charcoal canister from the factory.
Sometime during that year’s production is when they added it.
Made a big difference in fuel smell in the garage. With the charcoal canister system intact, any fuel you smelled was indicative of a leak somewhere. Or an open element air filter on the carburetor having replaced the original.

I wonder if yours already has the removable panel, or the oval punch-out on the driver side just behind the B pillar?
Right about where your left shoulder would be there was a recovery tank mounted on systems that had the charcoal canister.
Just wondering if your pre-EVAP truck started to some get that.
Wondering also if your rear main tank had any vent tubes (maybe capped off) in front of the main fill tube.

Ford did use a mixture of rubber and flexible plastic. Very durable stuff.
But your rubber hose does look pretty old. Wouldn’t really hurt to replace at least the rubber sections and any filters. Even though the rear one looks new too.
It’s very possible that they are clogging up from old fuel and debris in the back.

It’s also possible that it could be an ignition issue. Maybe an old ignition coil is getting old before it’s time. What kind of ignition do you have?
Still points in the distributor? Or electronic?