[Olin18]

I have been having a real head scratching problem for a while, and I was hoping that maybe I could get some insight on it.
Here are the stats. 1984 CJ-8 With a 1986 Chebby 305 The motor is mostly stock, with a stock Carb. And Stock mec fuel pump. The Jeep has a "New" after market 25Gal Fuel cell.
Here is my problem.... (that I just don't get)
When I fill the Jeep with Gas it runs Great!! The carb is in good tune, and the jeep never misses a beat. BUT.. After I drive around for a while the Jeep starts to run like Junk. The idel is a little off. The accel is down, And it will actually cut out under high load, like the motor is running out of gas. It acts as though the fuel filter is clogged. (it is not because I thought of that and replaced the filter about 500 miles ago). When it starts doing this I head right to the gas station. (MY fuel gauge doen't work) And I fill it up. It always takes about 13.5 Gal. And after the tank is full. The Jeep runs great again... I don't get it. Any help would be great.

 

[ecamp55]

Re: Interesting fuel problem

I'd look at the gas cap and any tank vents (charcoal canister etc)....sounds like it's not venting properly and you're drawing a vacuum.

 

[Jim_Lou]

Re: Interesting fuel problem

Does the fuel cell have the proper pickup? A stock pickup might only reach 2/3 of the way to the bottom. (About 14 gallons is all I can get out of my stock 15 gallon tank.)

Does the pickup have a clean filter screen on it?

Is the fuel cell foam filled? Could some foam have broken loose and be clogging the pickup screen?

Could someone have thrown something into the tank that's restricting the screen? Sawdust might cause it to behave that way. Irritate anyone lately?

How old is the fuel pump? The spring can get weak. It can also break but still have enough effective length to work somewhat.

Could there be a spot in the hard line that got smashed against a rock?

Anything that reduces the efficiency of the fuel supply system could cause your problem. The reduced effectiveness added to the lower level in the tank could put the system right at the point where it can no longer supply the needed fuel.

If you haven't found the problem by the time you've run through that list, it might be best to put a fuel pressure gauge on it to make sure that lack of gasoline is really your problem.

 

[CJ7Taz]

Re: Interesting fuel problem

Are you sure the pickup tube goes deep enough in the new tank?

Some pumps have a problem pulling fuel if the level is only a few inches below the level of the pump. I assume the bottom of the new tank is lower than it was before.

 

[Olin18]

Re: Interesting fuel problem

Hummm, not vented. I had not even thought of that. And I am pretty sure that the gas cap that I have is not stock. I bet that it isn't a vented cap.
One thing that I did not mention in the orig post was that I do have a small leak in the fuel system at the fuel pump. The problem is that I have a rubber flex hose that attaches to the pump, and due to the frame the flex makes a tight bend. I think there is just a little fuel coming out of ether the supply or return. But like I said with a full tank the Jeep runs great. So I don't think the leak plays a factor, because if it did I would think that it would have an ill effect all the time.

 

[CJ7Taz]

Re: Interesting fuel problem

In reply to:

So I don't think the leak plays a factor, because if it did I would think that it would have an ill effect all the time.

[/ QUOTE ]

I'd say that's it.

In my second statement, "Some pumps have a problem pulling fuel if the level is only a few inches below the level of the pump. I assume the bottom of the new tank is lower than it was before." I almost added that the condition would be caused with only a pin hole in the pump diaphragm or a suction line too. I didn't because you didn't mention a leak. If the fuel level is higher than the leak, it will gravity feed (siphon). Once the level gets low enough, the fuel has to be pulled by the pump and part of the suction is lost through the leak hole.

 

[Olin18]

Re: Interesting fuel problem

CJ7Taz. What you are saying makes perfect sence to me. It is a possible problem that I was thinking about. But it was kind of on the back burner. However the way to put it really makes it clear.
I guess I should fix the leak.
I have replaced the flex hose and hose clamps twice already, and that doen't seem to be doing the trick. Like I said I think the bend in the tube is just too much.

What I need are some Fuel fittings. But I am having a hard time finding them. I have looked at in the summit catalog, but can't find what I need.
Does anyone have a good online source for barb fuel fittings. Or any brass barb fittings for that matter. (I have looked at home depo. they don't have what I need ether) What I need is a few 90Deg bends, a few 45's and maybe a 30 or two.
I think I could fix the leak with the correct fittings. unless of course the leak is in the pump... I guess I will fix the line, and if it still won't work I will replace the pump.

Thanks again for the insight Taz.

 

[Caver Dave]

Re: Interesting fuel problem

In reply to:

Does anyone have a good online source for barb fuel fittings. Or any brass barb fittings for that matter.

[/ QUOTE ]

Have yot tried:
McMaster-Carr? or
MSC? or
WW Grainger?

 

[WILL]

Re: Interesting fuel problem

Next time it does it, keep the engine running and remove the gas cap.

I have a similar problem. The cap is not vented. The engine pulls a vacuum on the tank through the vapor purge system. After a while, the pump can't pull fuel out anymore and the engine won't run. Something to try.

 

[027]

Re: Interesting fuel problem

In reply to:

It always takes about 13.5 Gal. And after the tank is full. The Jeep runs great again... I don't get it

[/ QUOTE ]

I would say the pickup tube is not long enough or positioned wrong. If it takes the same amount to fill the tank each time

When you fill it and alls well. Did this pickup come with the tank or was it purchased separately or is it the original from the old tank?

 

[CJ7Taz]

Re: Interesting fuel problem

Virtually any auto parts/hardware store (or any virtual auto parts/hardware store) should have a selection of barb fittings although the 30° may be a little harder to find.

 

[Olin18]

Re: Interesting fuel problem

I do know that the pick up in the tank is long enough. I have run the jeep with very little fuel in it. I do recall once putting 23 gallons in it. Like I said the Jeep will run with low fuel. It just doesn't run well.

As far as the fittings go. I thought they would be pretty easy to find also. But it turns out they really are not. I did look in Granger, Napa on line. and a bunch of other places. I can not for the life of me find a 5/16 barb to barb 90 Deg elbow.

 

[2293]

Re: Interesting fuel problem

Could be vapor lock...Cold fuel keeps the Jeep running until everything gets warm then you have problems....

 

[CJDave]

Re: Interesting fuel problem

This sounds like a vent problem to me. A buddy bought a used Sheevie Caprice Sta wagon that had the diesel engine in it and NO fuel tank cap. He bought a cap and zoomed off into the night, happy with his first-ever dieselcar. The Caprice ran for about 30 miles and then began losing power. It seemed to be the fuel filters and when he called me I thought:"Algae (how DO you spell al-geeee?) growing in the fuel tank from sitting around too much". When I got there to rescue him I could NOT get any fuel up front with my rescue-diesel-electric-pump-setup. I went around and removed the cap and WHOOSH....the air rushed into the tank. His cap was for the GAS model Caprice and was not vented.

In your case, when the vacuum begins to build in the tank the fuel pump sniffs air through the tiny pinholes in those hoses and that also helps to vapor lock the fuel system.

 

[Olin18]

Re: Interesting fuel problem

WELL.... I have an update about this little problem....
I probably should have left the sleeping dog lie, Because when I left work on Wed (chritsmas eve) to head home to (about an hour) My Poor Jeep left me stranded on the side of the road.
I am preaty sure that I had total fuel pump failure. Or total fuel line failure. What ever it was it was a bummer, I had to wait for an hour for a tow truck, and my one hour trip home ended up taking about 4 hours

Now I will be forced to fix the problem.
I thought it was pretty funny that my jeep has been doing this for months, and I have just been dealing with it. I brought it up here, and not three hours later I was stranded.
I think that is one of the reasons I love Jeeps so much. Because they always keep you guessing.

 

[elusive]

Re: Interesting fuel problem

your poor jeep has been trying to tell you for months!!... it has been holding on, geting you back and forth... finally, in a slow cruel death, you starved it.
now, pull the line off at the carb, have a buddy crank it and see what happens....

 

[Dirt Dog]

Re: Interesting fuel problem

Chris is exactly right.

Try the same thing with a wife........

And it won't take too long to be single.