Vapor Lock

Hey Everybody,
So happy to find this site.
I have a stock and original Cj5 that my father bought new in 1969. Dauntless V6. I have a new fuel pump with the return line. Heat shield.
I looked at the forums but didn't find my particular case and I don't remember this happening when I was young and we wheeled a lot at altitude here in Colorado.
What happens is, the jeep runs great until we hit around 11,000 feet and then it vapor locks. I have poured water on the pump when we stop and it runs great for awhile then starts again. This will then keep even at low altitude once it starts but when we get on the highway it goes away.
Does gas today vapor lock easier? Is the old engine running hotter? Any thoughts on more shielding, insulating, remedies?
TIA

Brian Rowland, Mar 25, 2019Report

 

I would maybe start by looking at where the fuel lines come from the tank to the fuel pump underneath the driver's side. Pretty tight in there and they pass fairly close to the exhaust. If the fuel lines are original, they are poly lines. Likely time to replace as I bumped one once in a 69 ever so slightly and it just broke. Another test might be to get some non-ethanol fuel, you can usually find a place that sells it. Workman's Truck Stops and Conoco stations here have it.

It could be something else as well, perhaps some of the high-altitude guys will chime in with ideas.

 

Yes.
Is your return line hooked up?

 

Mine used to lock all the time with the return line disconnected. Hooked it up never happened again

 

Yes, return line hooked up.

 

They aren't routed that way on a 69

 

Antique car guys will go to an in-tank fuel pump, or mount an external one below the tank level, so as it "pushes" fuel rather than pulling it. Any suction increases vapor formation.

 

My 70 has the stock fuel system and I regularly go Jeeping at high elevation. I've never had a vapor lock.
I would check the fuel pump pressure, make sure it's putting out what it's supposed to. Also, if you can find a gas station with ethanol free gas, that's worth a try as well...my Jeep runs better on real gas.

 

Here's the list of ethanol-free stations in CO.

Ethanol-free gas stations in the U.S. and Canada

 

Wow, thanks. There are a couple close actually. There has been so much snow here this winter it will be July before I can go up high but will try this for sure.

 

Interesting. Thanks.

 

Hi everybody, just a quick update, new pump, filter, wrapped exhaust, good gas, thanks for all the tips. They helped a lot! here is a pic from this summer at about 11,500 feet and we went even higher with no problems. Thanks.

 

Great pictures! Where is that?

 

Kingston Peak near Idaho Springs Colorado

 

I gotta move to Colorado!

 

Yes, it is pretty amazing.

 

This! If you have a pump that isn't up to spec and/or a partial restriction in the line to the tank they will enhance the prospects of vapor lock. Those would be addition to excess fuel heating.

I never had a problem with my CJ 5 at high elevation either.

 

Re: Restriction in line...had something happen recently that I'm still shaking my head over...

Went out to use the Jeep a few weeks ago and it wouldn't start. It was fine when I parked it a couple days earlier. But that day no amount of cranking would work and normally it starts instantly now with one hit of the key and no cranking. I figure it's either spark or fuel.

So, I looked at everything and it all looked fine; lines tight, no leaks, all looked OK. So I put a bit of gas into the carb and it started instantly then died. So I figure it's either the new electric fuel pump or a blockage. Pump was chattering away like normal so I'm thinking blockage.

I took the hose off the input to the carb. Carb inlet was clear. So I set it up so I could run the fuel pump from the engine compartment. I took a glass cup I keep out there and ran the pump. Good fuel flow, nothing wrong there, and I'm just about to shut it off when...BLOOP. WHAT the heck was THAT? There's something floating in the gas. At first I thought it was big piece of rust or a flake of paint. I looked at it close up and it's a freaking cockroach, just the size of the fuel line ID. I stood there staring at it for literally 10-15 seconds in pure disbelief. So I fished him out, reconnected everything and it started instantly and ran fine as before.

Of course I'm wondering how the heck he/she/it got in there. There's a fuel filter after the fuel pump and if it came from the tank I'd expect it would have been stopped there. My guess is it was in the fuel regulator which I needed for the new electric fuel pump. That regulator was essentially new but had been stored in a box for years before I took 2 days of tearing the garage apart to find it. It never occurred to me to look inside it for bugs.

I'm just glad that a) it was easy to find and fix, and b) my diagnostic process seemed to work (this time!).

 

Mud daubers usually get me.