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?

 

[tonytony9]

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?

Are you able to tell from my photo if this is a two way cap? I have a lot of pressure build up when I pop the cap off.

I might have to add a canister or some sort of system to take care of the smell.

I do have the oval punch out, drivers side! I was wondering what that was. It has a rubber gasket of some sort, similar to the drain plugs in the floor pans of Jeeps.

In terms of vent tubes, the only one I remember seeing is what I identified in the picture above of the fill cap. I will take a closer look next time I am working on her.

Since I have a new tank, would you recommend its time to install the new tank, replace fuel lines and replace with new pick up/pump? I am not sure where I should start with trouble shooting.

Ah, thats a great point. I am still running points. The distributer is from the PO and I have no way of knowing how old it is.

 

[Bronco-Brian]

Hoping I understand your question correctly. If I had to guess most likely cause of poor fuel delivery, It would be either the 3-way selector valve is clogged, or you have a rubber fuel line that has collapsed on itself. When I've had fuel issues, the first thing I try is blow compressed air back thru the line(s) (at the fuel pump supply hose) into tank(s) and check for any restrictions. You can also switch the selector valve and check its function with this method.

 

[tonytony9]

Hoping I understand your question correctly. If I had to guess most likely cause of poor fuel delivery, It would be either the 3-way selector valve is clogged, or you have a rubber fuel line that has collapsed on itself. When I've had fuel issues, the first thing I try is blow compressed air back thru the line(s) (at the fuel pump supply hose) into tank(s) and check for any restrictions. You can also switch the selector valve and check its function with this method.

I am asking for troubleshooting steps...so this was a great tip, thank you.

I have read when blowing air back, you can put a rubber glove on the fill and if it inflates you know you do not have a clog. Or, you listen for air hitting the tank.

 

[DirtDonk]

I only had to listen when doing mine. The sound was obvious, even when I was checking the smaller vent lines.

 

[tonytony9]

I only had to listen when doing mine. The sound was obvious, even when I was checking the smaller vent lines.

Great, thank you.

First thing I am going to do is check the functionality of my coil and points. For the coil, I will set up an apparatus to determine if it is providing interrupted grounds. I will then check the dwell and condition of the points/condenser. Seems a straight forward process. While doing this, I will make sure timing is right.

With vacuum advance disconnected, how many degrees above TDC should I be?

I am interested in moving to an electronic ignition system, such as a Petronix Ignitor 3 with their coil, although, I think this is a bigger project as I would need to go through all my grounds, potentially adding some additional block to frame grounds, to ensure I am getting a proper 12v. I would wire to an open fuse that is ignition controlled and not a resisted line such as the positive on the coil. I believe that would be the correct setup.

 

[DirtDonk]

Are you able to tell from my photo if this is a two way cap? I have a lot of pressure build up when I pop the cap off.

I’m sure someone can, but I can’t.

I might have to add a canister or some sort of system to take care of the smell.

Lots of discussions about that here on the forums.

I do have the oval punch out, drivers side! I was wondering what that was. It has a rubber gasket of some sort, similar to the drain plugs in the floor pans of Jeeps.

Yep. Sounds like the body stamping had already started to plan for the transition.

In terms of vent tubes, the only one I remember seeing is what I identified in the picture above of the fill cap.

My guess is that you would not find any. But then again, maybe the tank manufacturing had already started the transition as well.
Be interested to hear what you find.

Since I have a new tank, would you recommend its time to install the new tank, replace fuel lines and replace with new pick up/pump?

Yes. If you have the time, you already have the parts. Might as well.

Ah, thats a great point. I am still running points. The distributer is from the PO and I have no way of knowing how old it is.

Don’t have to know how old. Just what condition it’s in now.
Start checking…

 

[tonytony9]

I’m sure someone can, but I can’t.

Lots of discussions about that here on the forums.

Yep. Sounds like the body stamping had already started to plan for the transition.

My guess is that you would not find any. But then again, maybe the tank manufacturing had already started the transition as well.
Be interested to hear what you find.

Yes. If you have the time, you already have the parts. Might as well.


Don’t have to know how old. Just what condition it’s in now.
Start checking…

I changed out the points and we are back in business! Lesson learned, my first time working with points. Easy and fun process to learn. Thank you for your help...fuel system either way is higher on the priority list to upgrade.

 

[DirtDonk]

As the good Doctor used to say "90% of fuel problems are ignition related. And 90% of ignition problems are fuel related." or words to that effect. I think he used "carburetor" rather than "fuel" now that I think about it.
You just found one instance. Felt/seemed like fuel, but was really the ignition.

And just because it's fixed for now, does not necessarily mean that you can ignore it the next time something flares up. Modern parts are a shadow of their former selves in many cases it seems, so if a similar problem crops up in the future, check your points again.
The condensers are a known failure prone part nowadays. Many are bad right out of the box. And that's the problem, because when you change something for new, you figure you've eliminated that as an issue. Only to find out after much head scratching and hair pulling, that the new part is what is giving you the fits!
It's an almost never ending circle now.

Paul

 

[oldiron]

Ah, thats a great point. I am still running points. The distributer is from the PO and I have no way of knowing how old it is.

This is where your problem will most likely be.