Engine Am I experiencing Vapor Lock? (AMC 360)

[ColoradoDerek]

Hello again!
Long time no talk!

My jeep is doing well, however it still has one problem that I think I know what it is, but want your guys expert opinions to confirm/deny what I think.

What I think it is, is, Vapor lock.
What I think I can do, is, replace the metal line with a rubber fuel line. I'm looking for opinions on if this is the recommended fix also!

Symptoms:
Jeep fires up and idles just fine in my car port. I've let it idle for at least 15 mins before but maybe longer. It WILL occasionally, for no reason, kind of lose the RPM's (idle) and then like, shut off. It sounds like it would sound if it was running out of gas. I just assume its an older engine (AMC 360, unsure of the year) and that's why it does that, but maybe that is a symptom I'm not giving enough credit to. I can just turn the key, push the gas pedal and it will fire back up and idle again, usually not shutting off again but honestly, I've not let it sit idle for that long so unsure if it would happen again.

So, I start driving it. It drives fine. I mean, its rough compared to a newer vehicle right? supposed to be? I think so, but none the less, it runs fine. Idles at stop lights, etc. 5-10 minutes later, it will start to do what I call "mini-backfire". It sort of backfires, but usually its while I'm pulling out (so higher revs) and then while I'm shifting gears (like say I went into 2nd too slow) it will kind of "mini-backfire" for a few seconds then starts running again. Also, 5-10 minutes in, it starts to not idle so well at stop lights. it WILL idle, but it struggles and I kind of have to keep reving it up to keep it alive. sometimes it just shuts off when I engage the clutch in preparation to stop at a light. it will fire back up at this point but takes a few turns of the key and pushing of the gas pedal to get it to do it.

After a few minutes of it acting like that, it will then shut off at a stop sign or red light and then not turn back on. I can keep trying until the battery dies. Nothing. it just makes that sound you hear until the battery dies. unsure how to type that out. "rurh rurh rurh" ?? anyway....

Let it sit for 15 to 20 minutes, then it will fire back up. doesn't need jumped unless I run the battery down trying to start it which I don't do anymore LOL.
The fuel line coming out of the fuel pump is metal and it bends 180 degrees and goes RIGHT UP between the fuel pump and the engine block literally less than 1/2 an inch from the block. Once it gets to the top, it bends again, goes about 6 more inches then turns into a rubber fuel line which goes to the filter then to the carb.

What would you think the issue is with those symptoms?

 

[j6824]

If that's not what it is, it missed a good opportunity to be

That's where I'd start...try to get it as far from the block as you can with a loom, etc.

I'd wrap it with some of that insulative foil tubing, too

 

[ColoradoDerek]

Thank you for the reply.
Do you think I should swap the metal line to a rubber line and also add a loom or would a loom possibly be sufficient enough on the metal line?


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[CJ]

There are quit a few threads on this, might be something that matches your situation exactly here -->> https://jeep-cj.com/community/search/35941/?q=Vapor+Lock&o=relevance

 

[ColoradoDerek]

Thanks.

I looked through some and most give me dread that my problem won’t be fixed easily.

Not good!!

Let’s hope I’m a lucky one and some thermal wrapping helps because I am not interested in FI or electric fuel pumps as a solution.

Plus, none of those talk about if it’s okay to replace the metal gas line with a rubber one.

Also, if the problem occurs before the fuel line, meaning, where the pump connects to the block, it seems unfixable.

I’m just gonna hope for an easy fix.

I’m already leaning towards ripping this thing out and putting in a LS. That’s why I’m not going to do expensive stuff to this engine.


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[sparkzaflyin]

I had the same issue with my 1972 CJ5. I installed a two outlet fuel filter and ran a return line back to the tank. Problem solved for me, if you choose to do this, the smaller filter outlet hole is on the top, connect to the tank return line.

 

[ColoradoDerek]

I had the same issue with my 1972 CJ5. I installed a two outlet fuel filter and ran a return line back to the tank. Problem solved for me, if you choose to do this, the smaller filter outlet hole is on the top, connect to the tank return line.

I’m unsure where a return line might be but I will look into this. Thanks!


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[sparkzaflyin]

I physically ran a return line to the tank with steel brake line. There should be an unused port or two on top of the gas tank you can tie into. Doing that way is probably not recommended by todays standards as far as rollover shutoff, etc. We die like real men! No airbags either!

 

[Patrick]

If you were not experiencing this issue before, then it might be a sign that your fuel pump is going bad.

 

[Lumpy Grits]

Loosen your gas tank cap and see what happens

 

[ColoradoDerek]

Hello.

I just saw the message about loosening the gas cap, I'll try that (when it starts up again ! lol) but replacing the fuel filter and wrapping the steel fuel line (from the Fuel Pump to the rubber line that goes to the carb) with a heat resistant sleeve didn't resolve this issue. I will have to say though, it seemed to run a lot better while it was running so I'm happy I did the fuel filter.

Is there anything else that can have these symptoms? Again, it ran great for 2 blocks (about 10 minutes) then it just shuts off as soon as you try to let it idle (basically when I come to a stop) and won't turn back on for a few hours. Is there something in the carb that could cause this? Is there something in the air filter that could cause this? Is there something in the spark plugs that could cause this? I can't really think of anything else that might affect it or that I can try (aside from the running a return fuel line which I've not taken off the table yet just will probably be my last resort). I'm looking for further suggestions, or possibly, other things I can test for to try to narrow it down.

The engine did sit for a while back before I got it and I did replace all the lines with new rubber, but if maybe I missed something or if something might be dirty or anything like that, don't assume I know anything or have checked something that might seem obvious. What I've replaced so far is the fuel pump, the fuel filter, the rubber hoses and added that heat shield. As soon as it starts up again, I'll loosen the gas cap and see if that makes any difference also.

Thanks guys!

 

[ColoradoDerek]

I had the same issue with my 1972 CJ5. I installed a two outlet fuel filter and ran a return line back to the tank. Problem solved for me, if you choose to do this, the smaller filter outlet hole is on the top, connect to the tank return line.

This is what my fuel lines look like. Can I assume these things: In the photo of the fuel tank, the left one is the fuel line (with the bigger adapter) and the one to the right of that is maybe a return line?

Related to a return line: the other image shows my fuel line (heading to the fuel pump , the black tube in the middle leftish) and beside that to the right is what I think goes to that fuel tank mentioned above. Again , the question is, is that a return line? Do you think it would still work or should be hooked up anyway? Wonder how I would clear it out ? If all I need to do is run a line off a fuel filter to that connection, that could be more possible than I anticipated.

Thank you!


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[ColoradoDerek]

Hello.
I have been researching this more and it sounds like a possible solution is to add an electric fuel pump between the tank and the mechanical pump to kind of "feed" the mechanical pump. Some folks have said this resolved the vapor lock issue. Some say to just remove the mechanical pump all together and just use the electric pump. It looks relatively easy to add an electrical pump and they aren't very expensive so I might go this route. Any thoughts?

Thanks!

 

[Armyvet25]

Hello.
I have been researching this more and it sounds like a possible solution is to add an electric fuel pump between the tank and the mechanical pump to kind of "feed" the mechanical pump. Some folks have said this resolved the vapor lock issue. Some say to just remove the mechanical pump all together and just use the electric pump. It looks relatively easy to add an electrical pump and they aren't very expensive so I might go this route. Any thoughts?

Thanks!

not really solving the issue, but forcing it to feed, not sure it's good to force fuel pressure to the mechanical diaphragm, vapor lock only occurs in low or no pressure metal fuel lines, gasoline would "boil" when it got to the HOT metal area of the fuel line, this would block the flow of fuel to the pump, vapor lock happens when fuel in the fuel line becomes too hot and turns to vapor before entering the carburetor float bowl, easiest and cheapest solutions are re-routing fuel lines away from manifold/exhaust pipes and engine block, add shields, exhaust wraps to direct heat away, I always run a quality rubber line from the mechanical pump to the carb.