Fuel Pressure from tank to fuel filter

[musicman72]

Hi everyone. This is my first post and I'm at a bit of a loss. I just purchased a project CJ7 . It's a 1983 but has a 1979 AMC 258 i6 / 4.2l 6cylinder in it. My problem is that the previous owner went to a lot of trouble to do a lot of upgrades and mods but he ran into a problem which he thought might be the carburetor. He said he dropped the tank and cleaned all the lines and had someone work on the the Weber carburetor. I'm thinking maybe he mis-diagnosed the the problem as I noticed that the there is a clear fuel filter between the tank and the fuel pump. The filter won't hold prime. I replaced the fuel pump, thinking it may be bad, but that didn't change anything. The PO removed all emissions equipment so here is the current setup: Fuel tank --> fuel filter --> fuel pump -->another fuel filter --> Fuel Regulator --> carb. There are no other return lines, vent lines, etc. Some sites say that the fuel line isn't pressurized from the tank to the pump, while other sites say it is. How does the first fuel filter keep primed if their is no pressure on the system? Should I assume there is a leak between the tank and the first fuel filter? I'm going to drop the tank and see if the line holds pressure.

For what it's worth, I have tried priming the carb, running engine but it won't pull fuel from the tank. I've also physically poured gas into the first fuel right next to fuel pump hoping for something good to happen..It looked great...and then suddenly...it totally drained back into the tank.

So...? I'm a newb and would really be open to any ideas or suggestions.

Thanks!

Scott

 

[johnnyreb]

First: no the line is not pressurized from the tank to the pump. It relieves on suction. I would disconnect the fuel line just behind the pump and run it into a gas can and see if it draws fuel.
Second: why the fuel pressure regulator? Is it a high pressure pump?
I would loose the fuel filter between the pump and tank, all it takes is a pin hole to allow the pump to loose prime, if it sits long. IMHO

 

[musicman72]

You and I had the same idea. (Admittedly I saw it on the internet, but....)
I ran gas line from a gas can to the fuel filter. And guess what? It runs great. Two questions that time will tell. Will the fuel pump/filter lose prime after a few minutes or will i be able to crank it up in an hour, or a day, and it still work correctly. (still from a can..not the gas tank)

As far as the fuel regulator, I wish I knew why he has it. maybe the pressure going into the Weber carb was too high? And having two filters? i see no reason for that either. I'll take a pic and let you see what I'm' talking about. Lots of sections of lines...Lots of places where a leak could develop. Pic in a minute....brb.

 

[musicman72]

Fuel System pics.

The red line in pic of the fuel pump is from a gas can next to the jeep.

Oh..and yes....the fuel filter already has lost prime....I cranked it, on and off, for about a minute and it finally caught back up and primed itself. By tomorrow I imagine it will have lost prime completely.

 

[johnnyreb]

sounds like we found the area of concentration. I would look into replacing the lines from the fuel tank to the fuel pump. Eliminate any potential problems. Ideally it may loose some prime, but as long as the line remains submerged it should draw if you let it set, you' may have to crank a minute or so.

 

[musicman72]

Thanks for your help. I'm ordering a replacement line right now. Do you have any thoughts on the current setup? I'm a bit concerned about there not being a line that goes back to the tank. Is that something I need to be concerned with?

 

[johnnyreb]

that maybe why the regulator, so the pump doen't over load the carb float. The return line was an epa thing. My fords from the 60's never had one. You just adjusted the carb accordly.

 

[Kane]

The weber requires a regulator to run correctly. Fuel return lines exist to keep cool gas at the engine and reduce the chance of vapor lock on hot days and reduces the work load on the stock diaphragm fuel pumps. I would take out the filter before the pump as it is a waste and another source of headache.

 

[BusaDave9]

take out the filter before the pump as it is a waste and another source of headache.

Yes, you don't want that filter there. You're trying to suck fuel through a filter. You should only have one filter after the pump.

 

[rr41mag]

I had a similar problem. The hose from the tank to the steel line wasn't tight enough. It's a 5/16 hose and I put 3/8 fuel lie and couldn't tighten the clamp up good enough. I blew air in the fuel line at the pump, thats how I found it.

 

[johnnyreb]

Thanks for clarifing that Kane. Webers are not my forte', i'm more of a motorcraft man.

 

[Torxhead]

Musicman, a possibility to lose fuel from that fuel filter/gas line would be that it is getting sucked back to the fuel tank. If there is no vent to the fuel tank, a vacumn is created as the tank uses up fuel. This can be checked by removing the gas cap after a drive and there should be no sound of air rushing in as you remove the cap. I would think having a fuel filter prior to the pump would protect it from the that comes out of a many years old fuel tank or whatever comes out from a dirty gas station pump. On my fuel injected '86 w/AMC 258 i6 / 4.2l , I have a hi-flow fuel filter to protect the expensive electric fuel pump. Make sure all the rubber lines are good from the tank to the carb by checking for leaks and cracks.

 

[johnnyreb]

the evap system should prevent that unless the PO removed that when he "upgraded" it

 

[musicman72]

Thanks for the suggestions. I just finished dropping the tank and am about to check the lines for leaks. Here is the fuel flow starting from the tank:

Fuel tank --> fuel filter-->fuel pump -->fuel filter (with second nipple that would go back to tank or whereever....plugged up) -->fuel regulator -->carb.

I have another question, though.... From the fuel tank i traced two lines back to the engine bay. One goes back to the carb. The second one goes to a canister that is in the engine compartment, immediately next to the firewall, on the driver side. Nothing comes out of there, although there are plenty of places to attach lines. What is this canister and what is it's purpose? The canister I'm referring to is basically UNDER the windshield wiper fluid tank.

There is another "can" type thing next to the battery tray. It is just rusting away with nothing plugged into it at all. Replace it? Fix it? Ignore it? What is it?

 

[Torxhead]

That is the evaporation cannister used for fuel tank ventalation, providing it is hooked up correctly. The "Can" type thing next to the battery tray is a vacumn cannister used for the complex emmissions system in the later CJs. It is all listed in a repair manual. While you have that tank out, cleaning it out would be a good idea and checking the condition of the fuel pick up sock in the fuel inlet line. You can also adjust the fuel gauge by bending the float arm.

 

[johnnyreb]

well if the evap is still hooked up and not blocked then there shouldn't be any vaccuum created to suck the fuel back into the bank. That plugged end on the fuel filter is for your return line to your tank.

 

[Flex BT]

Remove the fuel filter that comes before the pump and run the fuel return line from the other fuel filter as intended would be my recommendation. Even if you just un-plug it and run it to a gas can. Think of what's going on with the fuel pump if it's hauling *** at 6+ psi while your fuel pressure regulator is set to 3.5 psi with no place for the excess fuel to go.

 

[musicman72]

Hi. I isolated the leak (at least ...the first one so far) and have ordered a replacement fuel line. Once I get that taken care of I'll try to get the other lines repaired/replaced/reconnected to where they need to go.

 

[johnnyreb]

Excellent. Keep us updated on your progress. Everyone is very helpful here.

 

[musicman72]

I finally got a little time to tinker some more and troubleshoot my leaking fuel line. I ordered a new metal fuel line only to find out two things. One, you cant get the original fuel line out without taking off a bracket that is between the tub and the chassis. Two, the old fuel line wasn't the problem anyway. I had run the new one along the same route as the old one and tried using each of them to see if one showed as the problem. No difference at all. Next, I started replacing the rubber fuel hoses which looked worse for the wear and tear. When I got off the fuel line that goes from the tank to the the steel line I noticed the rubber line felt "wrong." Upon closer examination it had been flattened in several places, most likely by being caught by the fuel tank when the PO installed it. I replaced the line, and what-do-ya-know? Fuel pressure problem seems to have disappeared. I'll test it a little more tomorrow, and if all goes well, I can put everything back together.

....i might even get to try to drive her down the street for the first time! (But really slow...as only the front brakes work....and that leads to the next project....)