fueltank and/or evap problems

[keefer]

ok. its been a year trying to get this truck to work. its starts and runs fine for several minuets and shuts down. the fuel system is definitly the problem. the fuel system has been replaced from the injector pump all the way back to the sending unit. nothing is original between those two parts. the fuel pickup filter is new and the tank has been drained and cleaned out.
heres the deal.....if i take the fuel supply line off of the sending unit and put it in a jerry can, the truck runs great. i drove it several hundred miles like that. as soon as it goes back onto the sending unit, i get the same problems. i tried driving it with the gas cap off incase something isnt venting properly, with no luck.
could my fuel cap be bad? i dont see any evap canister so im assuming cucv's dont have them. i talked to an experienced mechanic and he said it woulnt likely be the sending unit itself. what could it be? please help! i dont want to ride my motorcycle in the snow again this coming winter. I need my truck!

 

[Warthog]

The sending unit is just a pickup tube. No pumping from it.

I have seen the internal portion of the tube corrode but not collapse.

From your testing it does appear that the sending unit is the problem.

What type of truck do you have?

The originals have 4 outlets and the new ones that are available have 3. Not a problem as you have a vent line, pickup and return. The forth line is an extra for draining of the tank.

You may want to pull the sender and check the tubes. The pickup tube may be plugged

 

[Keith_J]

Have you pulled the sending unit? The fuel pickup is a sock made of Nylon, it can plug/break/collapse. Dropping the tank is the only way to tell.

 

[keefer]

@warthog, i have had the sending unit off. its good to go. could the vent tube itself be corroded possibly? i was thinking of taking it to my buddies shop and blowing some compressed air through it to see what kind of air flow im getting.
@keith J, the fuel pickup sock has been replaced.
anyone think it could still be the fill cap?

 

[keefer]

oh and @warthog, its an M1009

 

[mistaken1]

What do you do with the return when running from the jerry can?

 

[keefer]

i ran another line back into the jerry can for the return. thank you for bringing that up, it reminds me of another question. the return system was also bypassed when the jerry can method is used. could my return line going to the fuel tank have a problem causing the injector pump to back up?

 

[gungearz]

I would blow air thru it to see if there's a clog and possibly clear any debris in the line. Worst comes to worst, I would guess to change out the lines.

 

[Warthog]

i ran another line back into the jerry can for the return. thank you for bringing that up, it reminds me of another question. the return system was also bypassed when the jerry can method is used. could my return line going to the fuel tank have a problem causing the injector pump to back up?

The return line DOES play a big roll in the fuel system. If it is plugged then the the pump will quit. This is also what happens when the return line check valve on top of the IP gets plugged up.

Since there is noting on the end of the line, you can easily blow the line out. Just don't use alot of preasure.

 

[kassim503]

If you choose to blow any lines out, please remove the fuel cap so diesel won't spray out of another line, etc & make a huge mess.

 

[wallew]

ok. its been a year trying to get this truck to work. its starts and runs fine for several minuets and shuts down. the fuel system is definitly the problem. the fuel system has been replaced from the injector pump all the way back to the sending unit. nothing is original between those two parts. the fuel pickup filter is new and the tank has been drained and cleaned out.
heres the deal.....if i take the fuel supply line off of the sending unit and put it in a jerry can, the truck runs great. i drove it several hundred miles like that. as soon as it goes back onto the sending unit, i get the same problems. i tried driving it with the gas cap off incase something isnt venting properly, with no luck.
could my fuel cap be bad? i dont see any evap canister so im assuming cucv's dont have them. i talked to an experienced mechanic and he said it woulnt likely be the sending unit itself. what could it be? please help! i dont want to ride my motorcycle in the snow again this coming winter. I need my truck!

OK, I gotta ask one stupid question.

And it will seem that way. DID YOU REPLACE THE FUEL FILTER HOLDER?

they are KNOWN to develop air leaks over time. it's one of the first things I ALWAYS do to my CUCV's when I get them.

Also, your mechanical pump may not be up to the task. An electric fuel pump (mounted up under the frame rail on the passenger side) will give you a steady 5 - 6 psi of fuel.

It sounds like you 'bypassed' the fuel filter in your test. The filter itself could be the culprit OR the plate you mount the filter to could be leaking air.

 

[keefer]

@wallew, the fuel filter was not bypassed in my test.its not the original crappy one either, i converted to a spin on. its not really even a test, its how i drive it. the fuel pump has been replaced.
i ran it yesterday using the trucks original fuel tank but put my return into a jerry can. this bypasses the fuel return line. no joy. so its probably not the return line but im going to a buddys today to blow air through the line anyway. im also going to blow air through the fuel tank vent tube to see whats going on with it because i noticed that the last time i put fuel in the tank, the fuel was wanting to hang out in the filler neck, draining down to the tank slowly.
the only other thing that i havnt done is fill the tank all the way to full. i know its a long shot but maybe that will alleviate any vent issues. worth a shot i guess.
anyone have anythoughts?

 

[gungearz]

In my opinion and for a peace of mind. I would take the entire fuel system apart, clean everything and perform a function check on everything. It sounds like you have a air lock somewhere. Has to be a clog in the line somewhere. Make sure you check the overflow vent tube on your filler neck. Its possible if that's cloggeg you can get a evap lock.

 

[keefer]

@gungearz, i have already done everything that you mentioned. there are no original lines. the evap/vent tube appears to be clear.


@everyone....... yesterday i ran the truck off of the fuel tank with the return going to a jerry can and i got no joy. this eliminated the possibility of the fuel return being clogged.
i also pulled to the sending unit and checked for pinholes, it has none. i checked the flow of the tubes on the sending unit with compressed air, it was a little weak so i cleaned it. couldnt get what seemed to be perfect airflow so i cut most of the bottom of the fuel pickup off. i attached a 3/8 fuel line to the sending unit instead. the line still has the filter sock on it too. everything fit perfectly. this didnt improve anything on the test drive.



can anyone think of anything else? please keep in mind that everything is new from the injector pump all the way to the sending unit. the sending unit is original but modified so that there isnt anyway it wont work and the filter sock is new.
the only fuel system components that arent new are the sending unit, fuel cap, injector lines and the fuel return lines. everything else is brand new.

 

[gungearz]

Keefer, in sorry but I'm stumped. I wish I lived closer to you. I would like to help out.

 

[Warthog]

What tyype of truck do you have?

I may have a spare sending unit that you can test out.

 

[keefer]

@warthog, its an m1009. i should have eliminated the possibility of the sending unit being the problem. i took it off completly and ran one fuel line all the way back to the tank and dropped it in just like i did when i ran the fuel line into the jerry can. just a reminder, i can drive it all day long with the fuel supply line in the jerry can. what i cant figure out is how an open fuel tank (no sending unit) is any different than a jerry can. i think im gonna try an auxilary electric pump to see what happens. there isnt anything left to replace.

 

[gungearz]

Ypu have to drop the tank to get to the sending unit. Its on top of it against the floor.

 

[gungearz]

If you have a fuel gauge.... You have a sending unit.

 

[trukhead]

On an M1008 I'm tinkering on, there is a sending unit feed line, a return line and a third short line I presume to be a vent line.
Does your m1009 have the same setup and could the vent line be plugged?
On my m1008 they had rubber lines, inline filters and electric pump installed and it had a serious vacuum in the tank as the engine pulled fuel that I had to leave the cap on loose. The filter base had been bypassed as well.
I reinstalled a new lift pump and went back to the original base and the starting and running improved dramatically. I have decided to do a cab swap from a cherry residue truck and will be replacing all the additional rigged lines and going to all original lines and the short vent hose. Of course all lines will be purged prior to installation. I think you may have a crossed line some where between your vent line and return line.