Engine tries to stall out during long trips!

[jzak]

I took my CJ5 to the beach which is a 3-4 hour drive from where I live. By the time I got there it started lurching forward like it was about to stall out. If I very slowly put on the gas, it would go away, but it kept getting worse and worse. I was thinking that I was running out of gas, so I filled up. The tank was maybe half empty, but it magically solved the problem, and I never had another issue during the whole trip.

That was, until I drove back home. Same situation. The engine kept on dying on me, and the only way I fixed it was refilling the tank, which again was only half empty.

Its been a week since I got back home, and I haven't had any problem. The CJ is my daily driver, and I take her out for maybe a hour or two. I've also driven plenty of times with less then half a tank of gas, and never had any issue like this.

Just for good measure I replaced the full filter, and pump, but I honestly don't think that's the problem, because it drives like a champ normally, except for this one trip.

Any feedback is appreciated. Thanks!

 

[Captainlance]

Possibly a small hole in the pickup tube I the tank, allowing air to be sucked in when the gas level is below it.

I took my CJ5 to the beach which is a 3-4 hour drive from where I live. By the time I got there it started lurching forward like it was about to stall out. If I very slowly put on the gas, it would go away, but it kept getting worse and worse. I was thinking that I was running out of gas, so I filled up. The tank was maybe half empty, but it magically solved the problem, and I never had another issue during the whole trip.

That was, until I drove back home. Same situation. The engine kept on dying on me, and the only way I fixed it was refilling the tank, which again was only half empty.

Its been a week since I got back home, and I haven't had any problem. The CJ is my daily driver, and I take her out for maybe a hour or two. I've also driven plenty of times with less then half a tank of gas, and never had any issue like this.

Just for good measure I replaced the full filter, and pump, but I honestly don't think that's the problem, because it drives like a champ normally, except for this one trip.

Any feedback is appreciated. Thanks!

 

[twistedskipper]

So, the problem never occurs around town even with a low fuel tank level?

Perhaps a fuel tank venting issue? One test would be to remove the fuel cap when the problem occurs and see if the problem goes away without adding fuel to the tank.

Could also be low fuel flow for some reason, which might only cause a problem at steady cruising RPM and not around town due to more idling, lower RPMs, etc. This could be a clogged fuel filter or weak fuel pump.

 

[Hedgehog]

A possibility .....
Years ago my Harley Davidson would run perfectly, then would do as you describe your CJ doing. I was convinced it was fuel, every time I cleaned the carb. the trouble would go away. Then I realized that it always happened at or near the 100 mile mark on trips. ... Something's getting hot and breaking down.

In the end it was a failing ignition module. A coil breaking down is also a possibility. Stopping for fuel might be allowing electrical components to cool enough to start working properly again.

 

[jzak]

Thanks for the feedback guys! Yes the problem never happens around town, or on a low tank. That said, the engine generally tends to run a bit smother on a full tank.

I'm also thinking it could be a venting issue. To go from puttering into the gas station on half tank, to everything being fine after the fill up, reinforces that. Maybe just the act of unscrewing the gas cap is enough. If so then that's an easy fix.

I don't know if its relevant, but I've always had issues filling the gas tank. The fuel nozzle has to be in just the right position, or it will trip the handle cut off switch.

 

[Lumpy Grits]

Make sure ALL fuel line connections from the tank to the carb are 'TITE'.
I too would say it's a venting issue as the tank is pull'n a vacuum. I say this as you stated the issue went away after fill'n the tank.
One other thing to think about-Are you SURE the tank's pickup line is sit'n on or near the bottom of the tank?
LG

 

[Hedgehog]

If venting is an issue ...... get a new gas cap.

 

[coldair]

My dads yj had the same problem ended up being the steel fuel line where getting hot boiling the fuel. We put rubber hoses from the tank to the throttle body. It helped but still would do it on really hot days on long trips. Installed a 20 gallon tank with a fuel pump fixed the problem completely.