Stalling out-- help troubleshoot please

[BoulderBronco22]

I am having issues with my 69 Bronco stalling out. I had been having some issues with what I thought had been vapor lock -- it was shutting off at very high temps and would not start for a good 15 minutes or so. I have done a number of improvements/changes to try to get this thing running right again.
Here is a list of things that have been done:

New Carter P4070 Electric Fuel Pump
New fuel filter
New 23 gallon TBP tank
New fuel lines
New dizzy cap and rotor
Rewired ignition wiring
Replaced the ignition module
Rebuilt carb
All new spark plugs
Set timing with timing gun and adjust the carb
Rerouted the exhaust from dual to just one exiting far away from fuel lines



SO-- here is what is NOW happening. I seem to be able to drive it normal for about 2 miles and then I start to stumble, its jerky when I give it gas, and then it ultimately just stalls and the vehicle shuts off. There has been some backfiring. When I pull over, I can start the Bronco right back up no problem, but I have to drive at very slow speeds to keep it running. The second I try to give it more gas or take it to higher RPM's, or drive it above 20mph, it just starts to stumble and then die again. I tested the battery with the engine on, and I am getting around 13.8 volts.

Any ideas?

 

[70_Steve]

Any ideas?

Eve with what sounds like a completely new fuel system, it sounds like you're running out of fuel.

What carb, and who rebuilt it? Could be something in the float valve restricting fuel flow into the carb.

 

[BoulderBronco22]

It feels like it would when running out of fuel. Definitely not running out of gas though. It's a Holley 2-barrel carb and was rebuilt by a buddy's dad.

 

[BoulderBronco22]

Nobody has any ideas what's causing this?

 

[broncnaz]

Have you replaced your gas caps? The vents may not be working correctly and your fuel systems is under a vaccum.
You could also have a vacuum leak.

 

[BoulderBronco22]

I have put a new vented gas cap on. I also tried today to run it without the cap on to see if that would help (it didn't).

 

[broncnaz]

Well check that off the list. Just making sure. Once it dies on you I would consider checking the float level. Just to be sure its not to low.

 

[BoulderBronco22]

Things to consider-- check the carb float level when it starts to stall out to see if it is sticking and not getting enough fuel.

I am also sort of wondering if it is still somehow creating a vacuum. I am not sure how the vented cap is suppose to work, but I noticed that when this starts to happen, I pop the cap off and there is a lot of fumes that come out (I would have thought that the vented cap would release a good portion of this on its own?) Also, when I was pulling the fuel filter yesterday to swap it out, there was less than 3 gallons or so of gas in the tank and as soon as I pulled the filter, gas started a steady poor until I scrambled out from under the truck and pulled the gas cap. As soon as I released the pressure, the gas immediately stopped flowing. I will say I had not driven the Bronco for about a week at that point, so that pressure had been in the entire time.

Is there an easy way to check that vacuum pressure?

The last thing I can think of is that their is still a large amount of sludge in the tank itself and it is somehow getting sucked into the tube randomly when driving and then it clogs up the line. This would mean dropping the tank-- which I would prefer to not have to do-- so this is my last resort.

 

[70_Steve]

Is there an easy way to check that vacuum pressure?

WTF!?:?

The vented gas caps have a check valve built in. Lets air in, but doesn't let gas fumes out. So, it's normal for it to build pressure.

Yeah, check the carb float level, but also still consider the possibility of something sticking or clogging the needle valve in the fuel bowl. With all the new stuff, it's common to have a little crap in the line initially.

 

[BoulderBronco22]

I just drove it without a gas cap and was able to replicate the same thing happening. I am not really sure how to tinker and check the float levels with the carb. Do I need to completely remove it and open it up?

It is strange. The engine will sometimes not die out until I push the clutch in and then it is suppose to go back to idle but will just die. As soon as I start it back up and give it a couple pumps of fuel, it will idle fine. Also, the fuel pressure guage was climbing up to 4-5psi this morning when I started it up fresh. When I checked the pressure after the first time it stalled-- it was at 0psi. Clearly there is a problem there but I can't tell what...

 

[SHX669]

Not familiar with that particular Carter fuel pump - but some have to be mounted lower than the gas tank and as close to the gas tank as possible ?
With the new TBPs tank i wouldn't think you'd have sludge or debris in the tank . Could be in the fuel lines - are they "rubber" ?
Did the new tank come with new pickup tube and "sock' filter ? The " sock" filter on the end of the pickup tube can deterioate and plug things up - i assume you've checked the fuel filter.
Holley carb is easy to check float level - remove plug from side of fuel bowl and look.
SHX
SHX

 

[70_Steve]

It feels like it would when running out of fuel. Definitely not running out of gas though. It's a Holley 2-barrel carb and was rebuilt by a buddy's dad.

Well check that off the list. Just making sure. Once it dies on you I would consider checking the float level. Just to be sure its not to low.

I just drove it without a gas cap and was able to replicate the same thing happening. I am not really sure how to tinker and check the float levels with the carb. Do I need to completely remove it and open it up?

Google is your friend. There is a cover with a screwdriver slot on the side of the fuel bowl. That hole is there to facilitate setting the float level (done wtih the screw and locknut on the top of the fuel bowl). The proper fuel level in the fuel bowl will be right at the bottom of that hole.

It is strange. The engine will sometimes not die out until I push the clutch in and then it is suppose to go back to idle but will just die. As soon as I start it back up and give it a couple pumps of fuel, it will idle fine. Also, the fuel pressure guage was climbing up to 4-5psi this morning when I started it up fresh. When I checked the pressure after the first time it stalled-- it was at 0psi. Clearly there is a problem there but I can't tell what...

You told us what's new in the fuel system. Now tell us what's old/original/you didn't change in the fuel system.

 

[BoulderBronco22]

I'm pretty sure I've replaced everything in the fuel system. The coil and distributor are not new. Starter solenoid, alternator, and any other starter parts not mentioned are old.

I did notice that the carb is clean except this screw has some oily funk on it.

 

[BoulderBronco22]

So I checked the float levels and they seem to be where they should be. I am still wondering why I am getting so much fluctuation in the fuel pressure. It will jump up to 6psi and down to 0psi.

 

[70_Steve]

So I checked the float levels and they seem to be where they should be. I am still wondering why I am getting so much fluctuation in the fuel pressure. It will jump up to 6psi and down to 0psi.

Where is the fuel pressure gauge?

When you checked the float level, was the engine running normally? You would want to check it when it's screwing up.

Take it for a drive. When it screws up, turn off the key immediately, then pull over, and check the fuel level in the fuel bowl.

 

[BoulderBronco22]

Yah- I checked it when it idled normally. I'll have to check it again as you suggested.

The gauge is on the frame before the lines head into the engine bay.

 

[Gidge768]

MY 69 was doing something like this a month ago, Im only saying this cause I saw you mention backfire. If that was through the exhaust mine did the exact thing so we knew it was getting fuel. After it wouldnt start we figured out it wasent getting spark. It turned out to be the module in the HEI distributor.

 

[BoulderBronco22]

MY 69 was doing something like this a month ago, Im only saying this cause I saw you mention backfire. If that was through the exhaust mine did the exact thing so we knew it was getting fuel. After it wouldnt start we figured out it wasent getting spark. It turned out to be the module in the HEI distributor.

I was having starting issues a month ago and we were able to put on a different duraspark module and that seemed to fix it. It has to be somehow fuel related. After it sits and completely cools down, I can start it up and drive it no issues for a short period. As soon as I have been driving it for a couple miles, I start to see the same stalling issue.

It does look like other people have had the same thing going on, but it doesn't seem to be just one diagnosis.

 

[Gidge768]

Boulder,

Got ya, I also went through a stage where If I drive the bronco on the highway about an hour in it will start to sputter and loose power so that it cant even climb a mild hill. I pulled over and let it sit and sure enough it started back up and ran fine the rest of my trip which was only about another 15 min. I orignally just thought something was in the fuel lines or something. On the way home it did the same exact thing around the same 1hr mark. Pulled over and let it sit. Fired it up like 10 min later and made it all the way home with no issue. I was also thinking maybe the heat made it Vapor lock. Ive since rebuild the carb and changed my fuel line that came up the driver side of the motor behind the power steering pump. It was a hard fuel line bent up the side of the motor and around to the back then back up the passenger side and up the carb. I have no idea if that was stuck or not. Ive since removed all that hard line and just crossed over the front behind the Distrubitor through a filter past a fuel gauge to be able to check fuel pressure then into my carb. I cant tell you if that corrected the issue since I havent driven the Bronco that far since that day for kind of being afraid...lol Just another idea.

 

[BoulderBronco22]

I think I'm going to drop the tank and see if I can drain it and clean it out. I never had these issues before swapping for the bigger tank. I'm just hoping that there may be some sludge that is clogging flow. At the least I can eliminate that.