CJ5 258 81 Surging, Struggling, Vapor Lock? - JeepForum.com
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post #1 of 13 Old 09-13-2021, 10:55 AM Thread Starter
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Cj CJ5 258 81 Surging, Struggling, Vapor Lock?

Hello there everyone!

I have been working on my cj and have got her rolling pretty good for the most part. Yet I have been having issues with random bits of struggling. I can fire her up in the morning and drive around, after she is parked for a bit she will sometimes stall/choke and struggle. Loosing power, and dropping rpms till she dies. I can crank her over and get her to move, and she will go abit and then do the same thing. I thought it was a fuel filter issue and I have replaced a few, but it feels too consistent. It also seems to happen on a new tank after I fill it up. A buddy of mine thought it might be vapor lock as it has been so hot recently and happens on a warm/hot motor. There has been one time when it did it after a bit of highway driving as well.

What do you all think? Does this sound like vapor lock or something else? If it is vapor lock, what are my options?

Thanks!
Mike

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post #2 of 13 Old 09-13-2021, 11:18 AM
Matt1981CJ7
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If you have a return line from your fuel filter to the fuel tank, and it's oriented in the 12 o-clock position, then vapor lock shouldn't be an issue.

Have you pulled any plugs, especially after is stalls out? They often provide clues to problems, especially fuel-related issues.

Also, is your choke operating properly?

Matt


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post #3 of 13 Old 09-13-2021, 11:48 AM
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How 'bout a pic of your fuel filter?

Even lay the hood back to the windshield and remove your air filter

Pics on the left, right, and overhead of your engine---not close ups---not too far back---the more the merrier!

Maybe we can spot something.

How long before it will fire back up?

How does it act when dying and also before it comes back to life?

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post #4 of 13 Old 09-13-2021, 01:19 PM Thread Starter
TheFlynn01
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Quote:
If you have a return line from your fuel filter to the fuel tank, and it's oriented in the 12 o-clock position, then vapor lock shouldn't be an issue.

Have you pulled any plugs, especially after is stalls out? They often provide clues to problems, especially fuel-related issues.

Also, is your choke operating properly?

Matt
I will check, I have not messed with the return line at all so it should be good. I have not pulled any plugs, what should I be looking for when I do?

I am not sure if it is or is not. I got in the summer and its been warm, so as far as I know it has been fine. I did have to rebuild the carb, did not mess with the choke as it is in a 'tamper proof' case. How could I check if it is working or not?

Quote:
How 'bout a pic of your fuel filter?

Even lay the hood back to the windshield and remove your air filter

Pics on the left, right, and overhead of your engine---not close ups---not too far back---the more the merrier!

Maybe we can spot something.

How long before it will fire back up?

How does it act when dying and also before it comes back to life?
I can get some pics when I get home. I am out and about at the moment and sneaking in some stuff on my down time on my phone.

So as for how it acts and will fire up:

it will fire up right away sometimes after a few cranks, sometimes it will idle for a moment then it will die. Other times it will fire up fine and drive for days before doing it again.

When it is dying it will start to slow down hard, like something is pulling me down. The RPMs will drop and it just sort of slugs to a stop. It does not die outright, its a slow death. Other times it will slow down and slug about and then idle, drive in first for a bit and then start to act up again by the time I try to put it in second gear. Then... it eventually clears right up and will go days with no issue.

I appreciate all the help guys! I will get photos soon.
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post #5 of 13 Old 09-13-2021, 03:58 PM
Matt1981CJ7
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The next time it dies a slow death, pull a few plugs and post pics of them. If they are a whitish color and dry, the fuel mixture was lean when the engine died, which would suggest a air leak in the fuel system. If they are black and wet, the fuel mixture was rich when the engine died, which could be as sticky choke, or other carb-related issue.

Do a search on how an e-choke works. There is ton of info on the subject.

I had similar symptoms once. Out of nowhere the engine would lose RPMs and stall out when it was hot. It turned out to be an easy fix. The hose clamp on the inlet side of my fuel pump was loose. When the engine got hot, the clamp would expand enough to cause an air leak. I put a new clamp on tightly and the problem went away.


Good luck,

Matt


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post #6 of 13 Old 09-13-2021, 07:01 PM Thread Starter
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Just got home and took some pictures. Figured I would let you see what you all think. I took the air filter off and got top right and left pictures. I also took a quick pick of the fuel filter. Looks to be at 12 to me.

The plug was interesting. It did not look too happy, very white and kinda crusty?
Attached Thumbnails
motor right.jpg   motor left.jpg   motor top.jpg   carb top.jpg   plug 2.jpg  

plug.jpg   filter.jpg  
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post #7 of 13 Old 09-14-2021, 07:37 AM
Matt1981CJ7
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Nice looking mostly stock engine.

Are you running any type of fuel additive? If so, that could explain the white ash on the plug.

Personally, I like to see a little more color on my plugs. Yours appear to be a little too hot/lean. Do they all look that way?

I's difficult to see if you have a return line, or not, on your fuel filter. Does it have 2 nipples on the outlet side?



Matt


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post #8 of 13 Old 09-14-2021, 09:14 AM
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Fuel tank not breathing properly maybe?
Try removing the fuel cap next time it happens.
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post #9 of 13 Old 09-14-2021, 09:18 AM
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You can verify quickly if it is a vacuum condition in the fuel tank causing your motor to stall. First you can verify that there is no excessive vacuum pressure in the tank when you open the gas cap. If there is you can try removing the gas cap for a drive and seeing if the problem goes away or no. if it doesnt then I would say you could probably rule that part out. It is also possible that your return line has been clogged with sediment up around the axle location where it is only metal tubing instead of the larger hose. Try taking a compressor and blowing into the return line in the engine compartment and see if it’s going all the way through to the gas tank. A heat based vapor lock typically can occur on the inlet side of the fuel pump where the gas boils due to the vacuum pressure in the tubing causing a gaseous condition that will block fuel flow. Ethenol fuel boils much quicker than regular gas. If that is the case you can try insulating the fuel pump and fuel hose and see if that helps. If it is a heat based vapor lock and you cannot insulate sufficiently to prohibit it, As a last resort or modification, you can also apply an electric in-line pump. That will keep fuel at the fuel line inlet of the fuel pump at all times allowing it to work and overcome the ethanol boiling condition.

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post #10 of 13 Old 09-14-2021, 10:30 AM
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Plugs look like lean conditions. Intermittent problems can be a bear to diagnose. After it dies will it start if you put a little gas in the carb? I am suspect of the fuel pump.
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post #11 of 13 Old 09-14-2021, 12:10 PM Thread Starter
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Quote:
Originally Posted by Matt1981CJ7 View Post
Nice looking mostly stock engine.

Are you running any type of fuel additive? If so, that could explain the white ash on the plug.

Personally, I like to see a little more color on my plugs. Yours appear to be a little too hot/lean. Do they all look that way?

I's difficult to see if you have a return line, or not, on your fuel filter. Does it have 2 nipples on the outlet side?



Matt
I will check today if they all look that way. The filter does have two. I will post a new pick soon. Big one in the middle. Smaller one on top at about 12 o clock position.

So if it is lean how do I fix that?

Quote:
Originally Posted by exheep View Post
Fuel tank not breathing properly maybe?
Try removing the fuel cap next time it happens.
I will try, what would cause that?

Quote:
Originally Posted by CJ5_Fan View Post
You can verify quickly if it is a vacuum condition in the fuel tank causing your motor to stall. First you can verify that there is no excessive vacuum pressure in the tank when you open the gas cap. If there is you can try removing the gas cap for a drive and seeing if the problem goes away or no. if it doesnt then I would say you could probably rule that part out. It is also possible that your return line has been clogged with sediment up around the axle location where it is only metal tubing instead of the larger hose. Try taking a compressor and blowing into the return line in the engine compartment and see if it’s going all the way through to the gas tank. A heat based vapor lock typically can occur on the inlet side of the fuel pump where the gas boils due to the vacuum pressure in the tubing causing a gaseous condition that will block fuel flow. Ethenol fuel boils much quicker than regular gas. If that is the case you can try insulating the fuel pump and fuel hose and see if that helps. If it is a heat based vapor lock and you cannot insulate sufficiently to prohibit it, As a last resort or modification, you can also apply an electric in-line pump. That will keep fuel at the fuel line inlet of the fuel pump at all times allowing it to work and overcome the ethanol boiling condition.

Thank you for the info. I will have to check the return line. I had to put a new tank in it and sending unit. It was doing it before I replaced them and is still doing it. Old tank was rusted and the sending unit was cracked at the bottom of the neck, so it would spill out when full.

Quote:
Originally Posted by mudbfun View Post
Plugs look like lean conditions. Intermittent problems can be a bear to diagnose. After it dies will it start if you put a little gas in the carb? I am suspect of the fuel pump.
It starts just fine runs fine too. When it gets it’s fits it will still fire up and run for a moment or two before dropping rpms like a slow death.

The old pump died. This one is new, two weeks old and I had to replace it.
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post #12 of 13 Old 09-15-2021, 02:34 AM
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Quote:
Originally Posted by TheFlynn01 View Post
The old pump died. This one is new, two weeks old and I had to replace it.

That's not good. I hope you used something other then the same brand that died after 2 weeks. There was a recent thread of another Jeep owner who kept blowing out fuel pumps. (However that works) Im not sure if that issue ever got resolved or not.
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post #13 of 13 Old 09-15-2021, 09:57 AM Thread Starter
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Originally Posted by mudbfun View Post
That's not good. I hope you used something other then the same brand that died after 2 weeks. There was a recent thread of another Jeep owner who kept blowing out fuel pumps. (However that works) Im not sure if that issue ever got resolved or not.
Hopefully I don't get that curse! the new pump seems to be working fine.

UPDATE: I checked all the plugs and they all had that same look, I did notice though that all the plugs were really easy to take out and did not seem to have any uniform torque. As I had some of the 985's with the new Iridium ones and put them all in to factory torque. Then I went though and tightened every clamp to the fuel lines to see if there was any leaks or lose lines like Matt had mentioned earlier. I found the fuel line connection from the tank/sending unit had a bit of sticky dried gas. so I put in a new line and clamp and tightened it down well and good. I then took it for a drive and went several miles, and turned it off. Then turned it on again after waiting for a while and went again several more miles and ran with no issue. It actually seemed smoother with the new plugs as well. Not sure if I found it or if it was just a better day, but... found two things and fixed them so thats always good!
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