Stumbling / stalling after driving for 20-30 minutes (2 Viewers)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Mechanical pumps will typically last much longer than electric pumps, are less prone to heat failure & as designed my Toyota will keep the correct pressure.
I have 2 OEM mechanical pumps that I could rebuild. wouldn’t that only work if you had the original carburetor? I’m running a Weber dgas on an F. Can you adjust the pressure on the mechanical pumps or would you need a fuel pressure regulator to drop it back to the 2.5 to 3.5 psi recommende?
 
I have a 1980 FJ40 that is keeping me on my toes with gremlins lately.

I have recently (4/20) replaced the electric fuel pump and filter after it just died and wouldn't pump any more. I bought the same cheapo looking "autobest" 42S that the PO had in there, and it seemed to do fine riding around locally on short trips to the grocery store and such. I have also replaced the Weber 3236 with a Weber 3838, and I was absolutely shocked at how much of an upgrade that has been.

Recently, on longer drives I've noticed that out of the blue the truck will start bucking and trying to stall and die like it's not getting enough fuel - usually this happens at the higher RPMs in 3rd gear or when I'm pushing it hard in 4th. This only happens after driving for a while, maybe 20-30 minutes into a trip. I can keep it from dying by pushing in the clutch and letting it slow down before putting it back in gear, usually the lower RPMs in 3rd. Then to get home I basically have to just barely accelerate and play with the clutch to get home.

The truck starts up immediately and there's no coaxing needed from the gas pedal or anything like that. Starts and idles like it was fresh off the assembly line. I'm no carb expert but it seems like everything on there is as it should be - I tightened the two idle air screws all the way in, just barely hand snug and then backed them both out 1.5 turns.

I've combed this forum and found a number of things that could be causing my issue, and I have a friend that has suggested I move my fuel pump as far back to the fuel tank as possible (better pusher than sucker is what I'm seeing a lot of). I had also wondered if it was overheating where it's situated (see attached pic) but it seems like there's plenty of open space and airflow where I have it located. It seems like it's going to be an enormous PITA to relocate it next to or near the tank....

I'm going to put on new plugs, wires, cap and rotor today, just because I have no idea when the PO did that last and I'd like to rule that out.

Also, the hose coming out of the fuel pump goes from a rubber fuel line to a hydro line, then back to a rubber hose before going to the carb. Is there anyway that could be causing thruput issues or is that some kind of hack job done to prevent vapor lock? I attached a picture so you can see what I'm referring to.

View attachment 3322622

View attachment 3322623
I have a 1980 FJ40 that is keeping me on my toes with gremlins lately.

I have recently (4/20) replaced the electric fuel pump and filter after it just died and wouldn't pump any more. I bought the same cheapo looking "autobest" 42S that the PO had in there, and it seemed to do fine riding around locally on short trips to the grocery store and such. I have also replaced the Weber 3236 with a Weber 3838, and I was absolutely shocked at how much of an upgrade that has been.

Recently, on longer drives I've noticed that out of the blue the truck will start bucking and trying to stall and die like it's not getting enough fuel - usually this happens at the higher RPMs in 3rd gear or when I'm pushing it hard in 4th. This only happens after driving for a while, maybe 20-30 minutes into a trip. I can keep it from dying by pushing in the clutch and letting it slow down before putting it back in gear, usually the lower RPMs in 3rd. Then to get home I basically have to just barely accelerate and play with the clutch to get home.

The truck starts up immediately and there's no coaxing needed from the gas pedal or anything like that. Starts and idles like it was fresh off the assembly line. I'm no carb expert but it seems like everything on there is as it should be - I tightened the two idle air screws all the way in, just barely hand snug and then backed them both out 1.5 turns.

I've combed this forum and found a number of things that could be causing my issue, and I have a friend that has suggested I move my fuel pump as far back to the fuel tank as possible (better pusher than sucker is what I'm seeing a lot of). I had also wondered if it was overheating where it's situated (see attached pic) but it seems like there's plenty of open space and airflow where I have it located. It seems like it's going to be an enormous PITA to relocate it next to or near the tank....

I'm going to put on new plugs, wires, cap and rotor today, just because I have no idea when the PO did that last and I'd like to rule that out.

Also, the hose coming out of the fuel pump goes from a rubber fuel line to a hydro line, then back to a rubber hose before going to the carb. Is there anyway that could be causing thruput issues or is that some kind of hack job done to prevent vapor lock? I attached a picture so you can see what I'm referring to.

View attachment 3322622

View attachment 3322623
I’m having a similar issue on my 1973 F. I was under the impression that it was flooding that would produce those symptoms. I’m new to this as well so I’ll follow this thread. I’m running a Weber dgas. Specs say a max of 2.5-3.5 psi. Tried a new pump and considering an in-line pressure regulator.
 
I’m having a similar issue on my 1973 F. I was under the impression that it was flooding that would produce those symptoms. I’m new to this as well so I’ll follow this thread. I’m running a Weber dgas. Specs say a max of 2.5-3.5 psi. Tried a new pump and considering an in-line pressure regulator.
I think I may also have a flooding issue to deal with as well. I'm not sure how to tackle that but I do have a new gas tank on order with my mechanic so at least part of the problem is dealt with...
 
I ran an inline fuel pressure gauge with my Weber. Who knows what PSI your pump is putting out and who knows what the pressure drop is through your fuel filter(s).
I also ran the weber fuel pressure regulator, mine ran great set to 2.5 psi with an OEM mechanical pump.
Cool. Was it a Weber dgas or a 38? I want to rebuild the mechanical ones if possible. I never thought about the pressure the filter might absorb. Should the fuel reassure regulator go after the filter just before the carb?
 
I think I may also have a flooding issue to deal with as well. I'm not sure how to tackle that but I do have a new gas tank on order with my mechanic so at least part of the problem is dealt with...
Find out your model of carb. Print out the specs and it will give you exact directions to retune your carb. YouTube has lots of web we carb info. Some is pretty good, some not.
 
I ran an inline fuel pressure gauge with my Weber. Who knows what PSI your pump is putting out and who knows what the pressure drop is through your fuel filter(s).
I also ran the weber fuel pressure regulator, mine ran great set to 2.5 psi with an OEM mechanical pump.
This was a spot on reccomendation. I rented one from o'reilleys and it turns out my "2.5-3 psi" rated pump was putting out closer to 8. Got a Mr. Gasket fuel pressure regulator and dropped it down to 2.5, thing runs great and the flooding stopped.

Now for a bonus question for anyone still reading - my buddy swears up and down that the "pancake" regulator I bought will either fail in under a year or cause the pump sitting behind it to wear out and die before it's time. He said that there is an early 80s Jeep fuel bypass filter that outputs at about 3 psi and then has a outlet to return the overflow back to the tank which keeps the fuel pump from being overstressed. He doesn't have the part number, but I assume people here know about it and/or run it. Would any of you guys know about that and if so, have the part number?
 
I had a similar problem and it was vapor lock on a carbed engine. As soon as the fuel in the lines heated up the pressure spiked and very little liquid made it to the engine.
 
This was a spot on reccomendation. I rented one from o'reilleys and it turns out my "2.5-3 psi" rated pump was putting out closer to 8. Got a Mr. Gasket fuel pressure regulator and dropped it down to 2.5, thing runs great and the flooding stopped.

Now for a bonus question for anyone still reading - my buddy swears up and down that the "pancake" regulator I bought will either fail in under a year or cause the pump sitting behind it to wear out and die before it's time. He said that there is an early 80s Jeep fuel bypass filter that outputs at about 3 psi and then has a outlet to return the overflow back to the tank which keeps the fuel pump from being overstressed. He doesn't have the part number, but I assume people here know about it and/or run it. Would any of you guys know about that and if so, have the part number?
Following
 
Now for a bonus question for anyone still reading - my buddy swears up and down that the "pancake" regulator I bought will either fail in under a year or cause the pump sitting behind it to wear out and die before it's time. He said that there is an early 80s Jeep fuel bypass filter that outputs at about 3 psi and then has a outlet to return the overflow back to the tank which keeps the fuel pump from being overstressed. He doesn't have the part number, but I assume people here know about it and/or run it. Would any of you guys know about that and if so, have the part number?
The OEM setup is a robust design, tried and true. Been running fine in many FJ40s for 50 some odd years now.

If you're going to stick with the carb setup, might as well use what has been proven.

Start putting Jeep parts on it and you might want to check to see if your insurance covers tow trucks!
 
^^^
So true…why try to reinvent the wheel?🙉
 

Users who are viewing this thread

Back
Top Bottom