Clamping fuel return line fixes all my problems... what the heck? (1 Viewer)

[Cole]

Long story sorry but kinda necessary... Gentlemen, I've had my 60 for a couple years now and I've driven it from Virginia to Kansas, from Kansas to Florida, from Florida to Texas and from Texas to North Carolina. It did all this on top of being my daily driver and has been running perfect. Next up, North Carolina to California. The trip will be made no matter what since I'm in the Marines. I need my truck fixed and I can't figure it out.

The problem, on my way from Texas to North Carolina the truck stumbled and quit after running for about 6 hours straight that day at 60-65mph. Due to the way it stumbled and quit, I thought my fuel pump went out. After sitting over night and two mechanics stumped, she started right up and ran fine for about 4 hrs the next day to finish my trip. She ran fine but kinda weak the next few days so I put a new fuel pump in. My problems were fixed and she ran more smooth and stronger than ever! Then, she didn't start after about 5 days of driving on the new fuel pump. This was due to the carb being empty.

So, I checked the fuel filter (new OEM btw) and it was fine. With the help of a friend, I observed that pumping the gas pedal did not pump any fuel into the carb. So, we put some fuel in the carb and bam, perfect for a couple more days. We also did some other basic checks and fixes, we looked in the tank by removing the fuel sending unit and everything looked good, I replaced all vacuum lines with silicone hose and we double checked for leaks by spraying carb cleaner everywhere we could get to and as best we could around the intake manifold. No reaction.

The truck was still running weak so I took it to a mechanic to get some measurements with some tools I don't have. Lucky/Unlucky me, the truck quit as I rolled into the mechanic's parking lot after a 45min drive at 55mph. No kidding.

Here's where it gets interesting, all electrical looks perfect, no vacuum can be detected, but overnight without fail the carb will go dry with absolutely no sign of a leak that can be detected by me or a mechanic. Also, while the engine is running at idle, a fuel pressure gauge will show zero psi. BUT if we clamp the fuel return line the fuel pressure jumps up to 5psi and the fuel filter fills up and stays full and the carb doesn't empty out overnight. I now have a clamp zip tied closed on the fuel return line and have driven on that for 4 days without a problem. It starts right up in the morning and runs almost perfect around town and on the highway. Still has an occasional stumble. Thoughts, Opinions, Advice? I have or will provide pictures or video of anything you'd like to see to help me diagnose this problem. Carb was rebuilt by TLC4x4 about 10 years ago.

Thanks in advance.

 

[Slow Left]

With the help of a friend, I observed that pumping the gas pedal did not pump any fuel into the carb.

When you ran this test, was there fuel in the fuel bowl?

If there is fuel coming 1/2 up the sight glass in the front of the fuel bowl, and with the engine off, if you twist the throttle torque rod (or have a buddy press the gas pedal to the floor, you should see gas squirt out of the Pump Jet (#4 in the image below) into the throat of the primary barrel.

Can you rerun that test with fuel coming 1/2 up the sight glass in the fuel bowl and see if gas squirts out of the Pump Jet or not? If not, then the Accelerator Pump (#1) on the carb might be shot or that circuit plugged (note the two ball check valves...if they get gummed up, then the circuit gets plugged).

Also, with the high percentage of ethanol now mixed into US gasoline, it is not uncommon for all the fuel in the fuel bowl to evaporate overnight.

 

[Cole]

When we did the test, No, there was not fuel in the fuel bowl.

Once he put a little fuel in and we got it running we did observe fuel coming out of jet 4 as you've described when I twisted the throttle toque rod and had my buddy press the gas pedal. However, when the engine was not running there was no response from jet 4 from twisting the throttle torque rod or pressing the gas pedal.

Let me make sure I understand what you want me to try:
With a cold engine and a half full carb (as measured through the sight glass), pump the gas pedal and see if fuel comes out of the pump jet?

Further questions:
1.) Ethanol has been in the fuel I've been using since I got the truck. Why this problem now?
2.) Why is clamping the return line helping/fixing my problem whether it's related to the accelerator pump or not?

 

[Slow Left]

Let me make sure I understand what you want me to try:
With a cold engine and a half full carb (as measured through the sight glass), pump the gas pedal and see if fuel comes out of the pump jet?

Yes, with the engine off, if there is fuel in the fuel bowl (coming 1/2 way up the sight glass of the carb) and you twist the throttle torque rod (which is the same as pushing on the gas pedal, because the gas pedal operates the throttle torque rod) you should see gasoline squirting out of the pump jet.

Further questions:
1.) Ethanol has been in the fuel I've been using since I got the truck. Why this problem now?
2.) Why is clamping the return line helping/fixing my problem whether it's related to the accelerator pump or not?

These are good questions.

With respect to Question 1, you are probably right to assume that there is no cause and effect between ethanol in the gas and the problem you are experiencing now. I was just pointing out that it not uncommon for the fuel to evaporate from the fuel bowl overnight. The fuel bowl, should, however, fill up right away under cranking. If not, that points to fuel delivery issues between the tank and the carb (or a clogged inlet on the carb).

With respect to Question 2, I don't see how clamping the return line will change the behavior of the accelerator pump, because the accelerator pump generates it's own pressure to push fuel through it's circuit and out the pump jet. When you twist the throttle torque rod, it pushes the accelerator pump down. A leather tipped plunger in the accelerator pump creates a seal to hole in the carb housing in which it sits, pushing gas past the two check valves in the circuit below and out the pump jet.

In fact, I don't see how the additional pressure from clamping the return line would build additional pressure on any circuit within the carb. The information you provide would indicate that there is a delivery issue to the carb from the tank. When you installed the new fuel pump, did you confirm that the spacer that goes between the side of the engine block and the fuel pump was also reinstalled?

 

[Output Shaft]

If the carburetor cooling fan doesn't run for a least 20 minutes after the engine is shut down, the gas in the float bowl often will be 'boiled away' by the next day.

Ethanol rots the leather seal on the pump plunger WAY faster than normal gasoline used to...and can rot the pump plunger boot lickety split too. If the boot is rotten, as can be seen on the engine side of the carb while it's installed, chances are good that the plunger seal aint doing too good either.

For intermittent go/no-go behavior, when fuel can be seen in the sight glass, I would always suspect there to be a small piece of crap floating around in the float bowl possibly plugging/not plugging the first main jet. A piece of rotten pump plunger boot can easily find it's way in there.

If the carb hasn't' been rebuilt in 10 yrs. Its time.

 

[klinetime574]

What is the condition of the gas cap? OEM?

Also what about the fuel separator (I think thats what it's called) in the passenger side quarter panel?

I'm thinking that clamping the return line could be masking a problem that is further from the carb than we think. And we may as well rule this stuff out just to be sure.

 

[Cole]

Yes, with the engine off, if there is fuel in the fuel bowl (coming 1/2 way up the sight glass of the carb) and you twist the throttle torque rod (which is the same as pushing on the gas pedal, because the gas pedal operates the throttle torque rod) you should see gasoline squirting out of the pump jet.


These are good questions.

With respect to Question 1, you are probably right to assume that there is no cause and effect between ethanol in the gas and the problem you are experiencing now. I was just pointing out that it not uncommon for the fuel to evaporate from the fuel bowl overnight. The fuel bowl, should, however, fill up right away under cranking. If not, that points to fuel delivery issues between the tank and the carb (or a clogged inlet on the carb).

With respect to Question 2, I don't see how clamping the return line will change the behavior of the accelerator pump, because the accelerator pump generates it's own pressure to push fuel through it's circuit and out the pump jet. When you twist the throttle torque rod, it pushes the accelerator pump down. A leather tipped plunger in the accelerator pump creates a seal to hole in the carb housing in which it sits, pushing gas past the two check valves in the circuit below and out the pump jet.

In fact, I don't see how the additional pressure from clamping the return line would build additional pressure on any circuit within the carb. The information you provide would indicate that there is a delivery issue to the carb from the tank. When you installed the new fuel pump, did you confirm that the spacer that goes between the side of the engine block and the fuel pump was also reinstalled?

Thanks, I will test it tomorrow morning.

Unless I have the return line clamped, if the bowl empties over night, cranking does not fill up the bowl. Only putting some fuel in to get it going will accomplish that. If the bowl is empty, twisting the throttle rod does not get fuel squirting from the pump jet. BUT, I have not tried with an empty bowl since I clamped the fuel line because the bowl no longer empties.

I agree that there may be a delivery issue from the tank to the carb but I haven't been able to figure out what it could be. I installed the pump myself so I am very sure that the spacer is there and I got a new spacer and seals. I'm not convinced the fuel pump is perfect but it did run fantastic immediately after installing it and for the next 5 days or so until I had these recent problems. From what I've read, if the fuel pump is installed incorrectly, especially if there's a mistake with the spacer, there will be immediate and potentially catastrophic damage to the engine.

 

[Cole]

If the carburetor cooling fan doesn't run for a least 20 minutes after the engine is shut down, the gas in the float bowl often will be 'boiled away' by the next day.

Ethanol rots the leather seal on the pump plunger WAY faster than normal gasoline used to...and can rot the pump plunger boot lickety split too. If the boot is rotten, as can be seen on the engine side of the carb while it's installed, chances are good that the plunger seal aint doing too good either.

For intermittent go/no-go behavior, when fuel can be seen in the sight glass, I would always suspect there to be a small piece of crap floating around in the float bowl possibly plugging/not plugging the first main jet. A piece of rotten pump plunger boot can easily find it's way in there.

If the carb hasn't' been rebuilt in 10 yrs. Its time.

I did not know all this. I will check it. I agree that the carb is ready for a rebuild.

 

[Cole]

What is the condition of the gas cap? OEM?

Also what about the fuel separator (I think thats what it's called) in the passenger side quarter panel?

I'm thinking that clamping the return line could be masking a problem that is further from the carb than we think. And we may as well rule this stuff out just to be sure.

Gas cap is OEM.

I not sure of the name of what you're referring to being located in the passenger side quarter panel either but I saw that in a couple other threads and I plan to check that tomorrow. I noticed that issues with items located there usually resulted in a strong gas smell inside the cab which I experienced for one day but then went away. I read about those things when reading about the gas smell issue. To be clear though, the gas smell no longer exists.

 

[Elbert]

ever replaced the fuel pump?

 

[Cole]

ever replaced the fuel pump?

Have I ever replaced the fuel pump in this truck? Yes, a couple weeks ago.

Or, did you mean, have I ever replaced a fuel pump before on any vehicle? No, this was my first time replacing a fuel pump.

 

[Elbert]

Have I ever replaced the fuel pump in this truck? Yes, a couple weeks ago.

Or, did you mean, have I ever replaced a fuel pump before on any vehicle? No, this was my first time replacing a fuel pump.

just meant had you ever replaced the fuel pump on the current truck with the problem.... the fuel pressure thing does not make sense to me. Did you use a OEM toyota part. Sometimes #*%$& happens that you can't explain...the logic too or the connection. Just was wondering about that...and did your problems start then or just now (some time after fuel pump replacement).

 

[Cole]

just meant had you ever replaced the fuel pump on the current truck with the problem.... the fuel pressure thing does not make sense to me. Did you use a OEM toyota part. Sometimes #*%$& happens that you can't explain...the logic too or the connection. Just was wondering about that...and did your problems start then or just now (some time after fuel pump replacement).

I did not use OEM as it was 4x the price and I couldn't find any reason it was better on the forum or elsewhere.

My problems started before the new fuel pump which prompted me to replace the pump. Everything ran better than ever for about 5 days with the new pump and then these "new" problems started. Really it's the same problem of stumbling and quitting but a new problem of a dry carb in the morning.

 

[Output Shaft]

cranking does not fill up the bowl

Bad fuel pump or blockage of fuel getting to pump.
(or plugged fuel strainer at needle valve)
OEM fuel pumps are not expensive. Shop around. I would never use a china aftermarket fuel pump.

 

[Cole]

Bad fuel pump or blockage of fuel getting to pump.

How is it possible the fuel pump is bad or there is a blockage if, once she get's started, she runs perfect except the occasional stumble in 3rd gear. Not saying you're wrong, just trying to wrap my head around it.

 

[Cole]

Bad fuel pump or blockage of fuel getting to pump.
(or plugged fuel strainer at needle valve)
OEM fuel pumps are not expensive. Shop around. I would never use a china aftermarket fuel pump.

Also, if this were you're truck what would your action be to identify the exact problem like where the blockage may be? Would you replace the fuel pump if you couldn't find a blockage then? Let me know what you're process would be cause this is what I'm doing this weekend.

 

[Slow Left]

If the bowl is empty, twisting the throttle rod does not get fuel squirting from the pump jet.

Correct...because there is no fuel in the reservoir (aka the fuel bowl) from which the the Accelerator Pump can draw...so the Accelerator Pump is just pumping air.

BUT, I have not tried with an empty 1/2 FULL bowl since I clamped the fuel line because the bowl no longer empties.

If it isn't too much trouble to get the fuel level 1/2 full in the fuel bowl, then confirm tomorrow morning that twisting the torque rod (with the engine off and fuel bowl 1/2 full) results in fuel squirting out the pump jet. This will at least rule out confusion about whether the Accelerator Pump is working correctly.

Unless I have the return line clamped, if the bowl empties over night, cranking does not fill up the bowl.

On a system where the fuel pump is working correctly and there are no issues delivering fuel to the carb, then the level of fuel in the carb fuel bowl is controlled by the float & valve assembly on the air horn of the carb. When the fuel level in the fuel bowl of the carb is below the float setting, the valve is open, allowing additional fuel to be pumped into the fuel bowl. As the fuel level in the bowl rises, the float rises. When the float reaches it setting height (a setting which you can change), it pushes on the needle valve, shutting it and not allowing additional fuel to be pumped into the carb by the fuel pump.
Instead, that fuel gets diverted back to the tank through the return line.

I agree that there may be a delivery issue from the tank to the carb but I haven't been able to figure out what it could be.

I'm wondering if the passageway is clogged between the fuel line inlet at the carb and the needle valve at the base of the float on the air horn. If it is clogged with gunk, it would result in symptoms you are seeing; namely, poor fuel delivery to the fuel bowl.
Then, by clamping the return line to the tank, you are able to build up enough pressure to push fuel past that blockage...enough to deliver fuel to the bowl as long as the return line to the tank remains clamped.

You can remove the metal fuel line at the carb and blow carb spray into it to clean it out. You can also remove the air horn with the carb installed, you just need to be very mindful if you are not familiar with what's underneath...you don't want to loose any of the little bits...it is 75% art and 25% science...
If you have the air horn off, you can remove the need valve assembly (again, there is a spring in there, you don't want bits to go flying) and you can spray carb cleaner through that circuit and it should come out the front of the carb where you removed the fuel inlet line. Blowing carb cleaner back that will will clean any gunk stuck up against the outside of the screen at the inlet.

If you really want to go crazy, you can remove the 4 vac hoses at the base of the carb (be sure to mark which one goes where...it matters) and blow carb cleaner down those ports into the carb, too.

Same with the Idle Mixture screw....if you back that out, spray liberal amounts of carb cleaner down into the carb housing...but then you've got to careful not to bend the tip when you reinstall it by screwing it in too deep (yeah, insert joke here please...)
And then you've got to retune the carb, too.

I installed the pump myself so I am very sure that the spacer is there and I got a new spacer and seals. I'm not convinced the fuel pump is perfect but it did run fantastic immediately after installing it and for the next 5 days or so until I had these recent problems. From what I've read, if the fuel pump is installed incorrectly, especially if there's a mistake with the spacer, there will be immediate and potentially catastrophic damage to the engine.

Sounds like you installed it correctly.

 

[Slow Left]

When you remove the gas cap on the fuel tank, do you hear any prolonged whooshing noise? Is it under pressure or is there a vacuum?

Has the recall on the gas tank been done?

Any leaks on the lines between the fuel pump and gas tank?

 

[Cole]

When you remove the gas cap on the fuel tank, do you hear any prolonged whooshing noise? Is it under pressure or is there a vacuum?

Has the recall on the gas tank been done?

Any leaks on the lines between the fuel pump and gas tank?

When I remove the gas cap, I do not hear any air noise and I know exactly what you're talking about because it did that... before I clamped the return line. Here's where I'm dumb: I never check whether it was positive or negative pressure causing the equalization... i know i know.

I believe the recall has been done... however, the service records for the truck are in storage in California waiting for me. I have not followed the process of giving my VIN to a Toyota dealership to have them check. That will be on my to-do list for tomorrow.

The mechanic could not identify any leaks on the lines between the fuel pump and gas tank and he had it for a few days watching for even weeping fuel. Maybe there is, but it hasn't been found.

 

[Cole]

Correct...because there is no fuel in the reservoir (aka the fuel bowl) from which the the Accelerator Pump can draw...so the Accelerator Pump is just pumping air.


If it isn't too much trouble to get the fuel level 1/2 full in the fuel bowl, then confirm tomorrow morning that twisting the torque rod (with the engine off and fuel bowl 1/2 full) results in fuel squirting out the pump jet. This will at least rule out confusion about whether the Accelerator Pump is working correctly.


On a system where the fuel pump is working correctly and there are no issues delivering fuel to the carb, then the level of fuel in the carb fuel bowl is controlled by the float & valve assembly on the air horn of the carb. When the fuel level in the fuel bowl of the carb is below the float setting, the valve is open, allowing additional fuel to be pumped into the fuel bowl. As the fuel level in the bowl rises, the float rises. When the float reaches it setting height (a setting which you can change), it pushes on the needle valve, shutting it and not allowing additional fuel to be pumped into the carb by the fuel pump.
Instead, that fuel gets diverted back to the tank through the return line.



I'm wondering if the passageway is clogged between the fuel line inlet at the carb and the needle valve at the base of the float on the air horn. If it is clogged with gunk, it would result in symptoms you are seeing; namely, poor fuel delivery to the fuel bowl.
Then, by clamping the return line to the tank, you are able to build up enough pressure to push fuel past that blockage...enough to deliver fuel to the bowl as long as the return line to the tank remains clamped.

You can remove the metal fuel line at the carb and blow carb spray into it to clean it out. You can also remove the air horn with the carb installed, you just need to be very mindful if you are not familiar with what's underneath...you don't want to loose any of the little bits...it is 75% art and 25% science...
If you have the air horn off, you can remove the need valve assembly (again, there is a spring in there, you don't want bits to go flying) and you can spray carb cleaner through that circuit and it should come out the front of the carb where you removed the fuel inlet line. Blowing carb cleaner back that will will clean any gunk stuck up against the outside of the screen at the inlet.

View attachment 1063111

If you really want to go crazy, you can remove the 4 vac hoses at the base of the carb (be sure to mark which one goes where...it matters) and blow carb cleaner down those ports into the carb, too.
View attachment 1063103

Same with the Idle Mixture screw....if you back that out, spray liberal amounts of carb cleaner down into the carb housing...but then you've got to careful not to bend the tip when you reinstall it by screwing it in too deep (yeah, insert joke here please...)
And then you've got to retune the carb, too.



Sounds like you installed it correctly.

Thank you for all the information! It seems that you would be a proponent of rebuilding the carb?