Fuel Issue

[Jroch]

Greetings,

I have a 1985 CJ with a 343ci with a Holley Carb, I am not getting fuel to the carb consitantly, I have dropped the tank checked the pickup unit, ran new fuel line from pick up to carb, installed a new 9psig electric fuel pump, fuel pmp was orginally mounted on fender in the engine comparment moved to frame rail just behind the drivers seat, fuel line is aprox 4" from exhaust on the frame rail, tank has fuel in it, this is a single line fuel system not return to tank. I don't think it's a vapor lock issue but not 100% sure, I can run around the block with it and then run into the issue if I remove the fuel line from the carb I can pump fuel via the fuel pump with out issue.

Any and all assistance would be greatly appreciated as I am truely stumped on this

Thanks

Justin

 

[mylittlecj5]

when you run around the block, what are the symptoms when you start having problems?
will it idle, stumble, surge, just shut off...? does it re-start right away, or does it take a while?
when it dies, can you see fuel pump from the float bowl into the carb throat by pumping the throttle?
What kind of ignition are you running?
Have you tried loosening the fuel cap and see if the problem goes away?

 

[CJ]

can you see fuel pump from the float bowl into the carb throat by pumping the throttle?

That is the question I am most interested in...

 

[Jroch]

when you run around the block, what are the symptoms when you start having problems?
will it idle, stumble, surge, just shut off...? does it re-start right away, or does it take a while?
when it dies, can you see fuel pump from the float bowl into the carb throat by pumping the throttle?
What kind of ignition are you running?
Have you tried loosening the fuel cap and see if the problem goes away?

Thank you for your response and interest in my question/problem. When I first start it up it's fine I put a clear fuel filter on it and can see fuel. I run around the block with it and it will run like a champ and then sputter and die like a car running out of gas. As soon as this happens I pull over and check the fuel filter and it will be bone dry, I will let it sit for 5-10 min with the pump running and it will fire back up but will die within a minute or so. I have been able duplicate the problem in the driveway once by holding the engine at higher revs for a period of time, what I saw when I did this, fuel level in the fuel filter would slowly go down until dry, fuel entering the pump was sparatic meaning I would see squirts of fuel followed by air or bubble's I have not looked into the carb when pumping to see if fuel is squirting in made the assumption if there was no fuel at filter it was dry at the carb I will check that today. I have tried running it without the fuel cap and still had the same issue I also ensured the vent lines were clear when I dropped the tank to check the pickup unit. On the ignition I am not sure what kind it is, it's a coil with distributer setup older style. when I have fuel the motor runs great, someone suggested I run the fuel lines on the outside of the frame rail going to try that today just out of pure desperation
A little more detail on the Jeep may help 1985 CJ 343ci from a AMX very mild cam in it, Holley Carb four barrel not sure on the cfm, regular exhaust manifolds, straight pipes duel with mufflers, 20 gal plastic fuel tank,

I bought the jeep about a month ago in that time I have put new floor boards in,installed new rear deck pan, Rhino lined the interior replaced the suspension rebuilt the roll bar, cleaned the mess of wiring out from under the hood, got it running as it did not run when I got, and now i have run into this issue which is really trying my paitence as I am just stumped on it.

Thank you again for your interest and assistance with this issue

Justin

 

[Old Dog]

Makes me wonder if the pump is getting hot and vapor locking.

Or maybe you just need a return line.

Any way it sounds like vapor lock to me.

 

[mylittlecj5]

some electric fuel pumps are designed to push fuel, not pull.
meaning that with your fuel pump located mid-ship under the driver's seat, it might not be happy in either case.
I'd re-locate the fuel pump to as near the lowest point of the gas tank as possible before I'd move a factory fuel line.
Since you don't have headers, there should be plenty of clearance between the manifold and the frame mounted lines to avoid vapor lock.
Another place to look is the fuel line from the frame rail to the carb. Is it the stock metal line, or a replacement rubber line? the heat from the engine can heat the metal line enough to cause vapor lock, also.

BTW, when my mild built 360 is running, there is very little fuel in the clear fuel filter also. but I don't have the problem you have. So that might be a little mis-leading as to a symptom.

 

[Jroch]

Makes me wonder if the pump is getting hot and vapor locking.

Or maybe you just need a return line.

Any way it sounds like vapor lock to me.

Thank you for your response, I was wondering that myself? the pump does get warm, but if I remove the line from the carb it will pump? my understanding "and I am by no means a auto mechanic I do supermarket refrigeration" is if it is/was a vapor lock the pump would not pump even with the line removed as the fuel would turn to vapor from the heat? is that correct?

Agian thank you for your time and interest in this issue

Justin

 

[Jroch]

some electric fuel pumps are designed to push fuel, not pull.
meaning that with your fuel pump located mid-ship under the driver's seat, it might not be happy in either case.
I'd re-locate the fuel pump to as near the lowest point of the gas tank as possible before I'd move a factory fuel line.
Since you don't have headers, there should be plenty of clearance between the manifold and the frame mounted lines to avoid vapor lock.
Another place to look is the fuel line from the frame rail to the carb. Is it the stock metal line, or a replacement rubber line? the heat from the engine can heat the metal line enough to cause vapor lock, also.

BTW, when my mild built 360 is running, there is very little fuel in the clear fuel filter also. but I don't have the problem you have. So that might be a little mis-leading as to a symptom.

Thank you for your response and interest in my issue, all help, advice and comments are GREATLY APRECIATED!!! The pump is located at what I would say is the lowest point closest to the tank as possible if I go back any futher with it I will be on the up swing of the frame by the rear tire. The fuel line is brand new rubber line "I replaced it" from the tank all the way to the Carb the only breaks in the line are at the fuel pump and at the fuel filter the rest is solid one piece line the only thing I did different was run the fuel line along the drivers side frame rail versus the passenger side where the factory line was, I did this so I wouldn't have to cross the motor to feed the carb, the inlet is on the drivers side. I did put a guage on the line and the pump is hitting 9.2psig. The level on my fuel filter starting out can get to about 3/4 full then will drop I don't think I have ever seen one that is full all the time? , I don't think I have a line size issue. At this time I am down to two courses of action, try running fuel line on the outside of the frame rail "which I really don't want to do" also thinking of dropping the tank again and pressure test the fuel line from the carb back to the base of the pick up unit to see if there is a hole/leak i didn't see?

Very frustrating issue, one of the reasons I bought this jeep was I liked the fact that it had an AMC motor in it which I haven't seen a lot of, most of the time you see the 305/350 conversions, unfortunately what I am finding is the 343 was/is not a real popular motor so parts have been an issue on it and any type of techincial advice had been even harder to find.

Again thank you for your time and assitance with this

Justin

 

[mylittlecj5]

You've got a rubber line running from the tank all the way to the carb?

anyways, check to see that is not pinched anywhere. Its beginning to sound like a restricted delivery problem, not vapor lock.

 

[IOPort51]

I would run a hose from a gas can to the fuel pump and maybe even from the pump back into gas can. of course that would keep the pump cool with unrestricted fuel flow, you may want to dead head the pump and get it warmed up?? was this a problem before the fuel pump?? Is the fuel pump new??

 

[Jroch]

WOW What a day!!!! Well I got the fuel issue fixed I think? rerouted the fuel line again, I also moved the pump a little lower on the frame rail, now the fuel filter is full of fuel, ran it around the block a couple of times and no issue still a little gun shy to take it on a main road LOL.

So after I got the fuel issue figured I was just kinda tinkering cleaning some wires up zip tieing things in place and I notice water dripping on the ground, so I start checking hoses and clamps getting looking at the motor and see it seaping out of the block, so I do what any person would do and start scraping away the old oil and grime to investigate the the source doing it very gently and my screw drive suddenly disappears half way into the block coolent pouring out of course not think I stick my finger over the hole to stop the flow until I can get a bucket under it, it didn't take long to realize the motor was still a little warm. LOL Well that lead to having to replace 4 casting plugs today not a lot of fun to do with the motor in, I couldn't get the steel ones I had to use the rubber plugs for now, I am planning on pulling the motor down the road and doing a rebuild will install the proper one's then.

Any way thank you guys very much for all the advice and assistance on the fuel issue

Justin

 

[mylittlecj5]

WOW! when it rians it pours!

You can pull the fenders off to help make it easier to get the freeze plugs replaced...

 

[Jroch]

WOW! when it rians it pours!

You can pull the fenders off to help make it easier to get the freeze plugs replaced...

No Kidding LOL I figured I was through the rough stuff with the floor boards and the suspension lift, although it's been extremely frustrating a couple of times, I have really enjoyed tinkering with it. Thank god I don't need it to be a daily driver LOL

 

[Jroch]

Son of a gun, I thought I had it all straightend out and it did it again tonight!!! Same exact thing runs for a bit and then dies, I am more cinvinced now then ever that it's a Vapor lock issue, but I don't know how to correct it. fuel line and pump are located outside the frame rail away from any heat source. I have googled the issue and found plenty of the same post's I have about the issue but not one post on the corrective action. I may try switching to a mechanical pump, wondering if the electric pump isn't causing the issue? but on the flip side there are countless others out there running electric pumps without the issue?

Very frustrating I have done everything I can think of and them some

 

[IOPort51]

Do you have a return line on the fuel line?? I'm thinking the lack of flow is making a warm pump which gives you a lack of flow. This is sounding like some kind of Zen thing. any way is the pump cooled by the fuel flow?? I know an in the tank pump is and the biggest cause of failure is running low on gas consistently, the pump over heats and fails.

 

[IOPort51]

oh yea and about the freez plugs, you have to be a bit parinoid about the ones under the bell housing. does it look like they rotted from the outside or the inside??

 

[Jroch]

oh yea and about the freez plugs, you have to be a bit parinoid about the ones under the bell housing. does it look like they rotted from the outside or the inside??

Under the Bell housing??? Are you seriose! Hard to tell which way they rotted from, but my guess is the inside out. now what to do? If i am going to go through the trouble of dropping the Tranny and Transfer Case I might as well pop the radiator cap and park a 350 under it LOL I had no idea there was pugs at the back of the motor also, I have been trying to find a blue print of the 343 but no luck so far.

 

[IOPort51]

Oh yea they are there. You can bet lunch on it. I would look very closely at the ones you can see, I can't think of any good reason for them to rot from the inside and several things that may have rotted them from the outside. Clean them off very carefully and see if the they are rusted on the outside. If they rotted because of salt or chemicals of some kind on the outside than the ones behind the bell housing will be just like new. If someone was a bit overzealous with the radiator flush chemicals every year they may have rotted from the inside and they will all be rotted. A little work with the de greaser and a soft brush could save you a lot of work.

can't wait to hear what you find