'79 FJ40 gasping for fuel (1 Viewer)

[uwum15]

Recently my '79 FJ40 started leaking fuel from the fuel pump so I got a new pump and spacer and replaced it myself. I drove it around town for a few days without problem then had a reliable mechanic just do some brake work and general maintenance for me. When I got it back from the mechanic and was on the interstate going about 60mph it started jerking and felt like it was gasping for fuel. I was losing power and rpms and I downshifted when I could because I was afraid of it dying on the highway. I limped home at about 35mph (with normal rpms) and really didn't have any issues in 3rd gear but trying to accelerate or go up a hill caused the same issues. The week before my fuel pump went out I had a weekend trip on the interstate doing 70-75mph the whole time without any issues and I've never had this happen in the few years I've had my FJ.
Any help on why it might be acting up when I am giving it throttle? There are two lines coming from the gas tank to the pump and the pump has an arm labeled "in" so I have the line with the fuel filter going to that and the other line to the remaining arm. There aren't any leaks from the spacer or the pump and driving it today it was fine about 90% of the day but I had one spell of the same jerking or lugging as I was accelerating. Any help is appreciated, thanks.

 

[Solace in Solitude]

Is your new pump OEM?

Have you tested pressure into and out if the pump? Or, at a minimum, disconnect the fuel feed, at the carb. Put it in a soda bottle or something. Have someone crank the ignition for 15 seconds. It should pump about a half cup of fuel.

If your pump has three ports, the two you mentioned sound right... The 'in' is the fuel feed. The 'out' goes to the carb. The third is the return back to the tank.

When under load: foot buried in accelerator or climbing an incline, the secondary kicks in and sucks a lot more fuel.

Check the solenoid on your carb, should 'click' when you turn the key.

Check the fuel pressure, as I described above.

Check your feed line, from tank to fuel pump... Any very small pin hole or crack of loose clamp or faulty filter will allow the fuel pump to suck air, when under load. I had a fuel filter that wasn't sealed... Same problem...

You should be able to confirm your 'fuel starvation' suspicion, by recreating the failure. When it happens, met it die, flip the ignition off and safely exit the highway. Pull the air cleaner (if you can't already see the sight glass on the carb).mcheck the sight glass. If it's empty, your suspicion us correct. By immediately turning the ignition off, you leave the carb in the exact same state as when it died.

Good luck!

 

[JohnnyC]

What " general maintenance" did he do ?

 

[Curt]

Did you disturb something in your fuel lines? Assuming your setup is stock. Take the air cleaner off and look into the carb, push the accelerator pump down see how much fuel shoots into the carb.

 

[edwjmcgrath]

If I read you correctly, you changed your fuel pump and drove around town at low speed, but didn't try it at high speed until after the "maintenance".
So you don't know if it's what you did, the mechanic did, or just coincidence.
The first thing I would check is the fuel filter. Unless it's clear, you can't tell whether it is clogged and it can clog up very quickly.
The second thing is to double check that you got the correct fuel pump and spacer. There are several versions and if you had the wrong one or wrong spacer, it could 'work' but not pump enough fuel to run at high speed.
Check the fuel lines for possible air leak.
Then I'd ask exactly what the mechanic did and whether that could cause your symptom.

 

[John Smith]

What you are describing sounds exactly like a fuel restriction. I've had the same thing happen twice due to rust particles clogging the fuel supply. Truck runs fine at low speeds but starts to stumble when you accelerate, and won't go higher than a certain speed. You should see rust particles in your fuel filter. If any of these have migrated to the carb, you will now have greater issues. And it is not easy dropping the tank from under a 79+ FJ40 to clean it out.

 

[uwum15]

What " general maintenance" did he do ?

He just checked for vacuum leaks and got the brakes and a few oil leaks taken care of. I had the same thought if he had messed with a lot of hoses or emissions but he said he didn't and he works on FJ's enough to know what he's doing I think.

 

[uwum15]

Is your new pump OEM?

Have you tested pressure into and out if the pump? Or, at a minimum, disconnect the fuel feed, at the carb. Put it in a soda bottle or something. Have someone crank the ignition for 15 seconds. It should pump about a half cup of fuel.

If your pump has three ports, the two you mentioned sound right... The 'in' is the fuel feed. The 'out' goes to the carb. The third is the return back to the tank.

When under load: foot buried in accelerator or climbing an incline, the secondary kicks in and sucks a lot more fuel.

Check the solenoid on your carb, should 'click' when you turn the key.

Check the fuel pressure, as I described above.

Check your feed line, from tank to fuel pump... Any very small pin hole or crack of loose clamp or faulty filter will allow the fuel pump to suck air, when under load. I had a fuel filter that wasn't sealed... Same problem...

You should be able to confirm your 'fuel starvation' suspicion, by recreating the failure. When it happens, met it die, flip the ignition off and safely exit the highway. Pull the air cleaner (if you can't already see the sight glass on the carb).mcheck the sight glass. If it's empty, your suspicion us correct. By immediately turning the ignition off, you leave the carb in the exact same state as when it died.

Good luck!

Thank you, I'll try out a few of these ideas this weekend.

 

[uwum15]

If I read you correctly, you changed your fuel pump and drove around town at low speed, but didn't try it at high speed until after the "maintenance".
So you don't know if it's what you did, the mechanic did, or just coincidence.
The first thing I would check is the fuel filter. Unless it's clear, you can't tell whether it is clogged and it can clog up very quickly.
The second thing is to double check that you got the correct fuel pump and spacer. There are several versions and if you had the wrong one or wrong spacer, it could 'work' but not pump enough fuel to run at high speed.
Check the fuel lines for possible air leak.
Then I'd ask exactly what the mechanic did and whether that could cause your symptom.

Great ideas, thank you. I didn't know enough to check it at high speeds so that is a problem now. I'll start with the simple stuff and go from there, thanks again.

 

[Solace in Solitude]

What you are describing sounds exactly like a fuel restriction. I've had the same thing happen twice due to rust particles clogging the fuel supply. Truck runs fine at low speeds but starts to stumble when you accelerate, and won't go higher than a certain speed. You should see rust particles in your fuel filter. If any of these have migrated to the carb, you will now have greater issues. And it is not easy dropping the tank from under a 79+ FJ40 to clean it out.

If you have to drop the tank, be sure to clean your hard lines while you are at it.

 

[JohnnyC]

Just a thought... (This is a common cruiser problem)

Did it feel as if somebody was applying the brake?

Were any of the wheels exceptionally hot?

 

[uwum15]

And it continues...my mechanic said the 1st fuel pump was missing a diagram or valve so there was no way for the pump to create pressure. It was reading a 0-1 with his pressure gauge. I called CCOT where I got it and it must be a common problem because they didn't ask any questions but mailed me a new one free of charge and didn't ask for the other one back-thank you! I put in a new fuel filter and it looks clean.

We put the new pump in and it registered about 2-5 on the pressure gauge. I assumed it was ready and took off. It ran fine for a few days but then at about 60 mph it started lugging and bucking again. It has happened a few times in the past 2 weeks but never in the lower gears. It does feel slightly underpowered shifting through the gears but I was okay with that until it started lugging again. I haven't tried anything new yet but now it loses all fuel in the carburetor just sitting for a few days in the garage... I'm assuming that is related to the problem, any help is greatly appreciated.

 

[Tigerstripe40]

Replace the fuel filters if you haven't already.
Next, check the timing.

 

[edwjmcgrath]

Losing fuel from the carburetor slowly is a common problem. This is unrelated to the bogging.
If you search here you'll find many theories, but I'm not sure there's a proven fix.

Buying after market stuff (from CCOT or others) that doesn't fit or doesn't quite work is also a common problem.

 

[Blacksunshyne]

Losing fuel from the carburetor slowly is a common problem. This is unrelated to the bogging.
If you search here you'll find many theories, but I'm not sure there's a proven fix.

Buying after market stuff (from CCOT or others) that doesn't fit or doesn't quite work is also a common problem.

I had the EXACT same symptoms with my 1979 FJ40 after putting on the aftermarket pump from CCOT, and as stated above... I switched it back to the OEM pump and it has worked great ever since.

 

[edwjmcgrath]

Sad story, told too often on here.
"I saved $100 on a part but my mechanic has (or I have) been struggling for 2 weeks to get it working right on my truck."

 

[honk]

Sad story, told too often on here.
"I saved $100 on a part but my mechanic has (or I have) been struggling for 2 weeks to get it working right on my truck."

+1 and it seems most often told on here when mechanical parts from CCOT are involved.