Help? Last 4 gallons, trouble starting B4V

Has anyone dealt with a problem starting their B4V or B4 when they get down to the last 4 or 5 gallons in the tank?

My '96 Passat TDI was leaking fuel at the injector pump and I took it to Old Poopie. That, unfortunately, was not the cause of this problem.

Jim

no,but i did have a check valve on the inlet side (right by the tank outlet,trunk) over time get clogged up w/ crap.one day while driving it stopped running.i'd start there.

Inside the tank?

Several of my customers have discovered cracks in the fuel lines back by the tank. Something to check.

Our wagon appears to run out of fuel around the top of the red on the gauge. I pulled the fuel sender out, expecting to find a crack there but could not.

Where is the check valve?

tdijim, do you notice bubbles hanging out in the fuel lines between the filter and IP before starting? Talking with a friend the other day we suspected that the level in the tank could cause the fuel to drain back out of the IP through the return line. Pure speculation at this point

Let us know what you find out, though.

I would do what 87turboquattro suggested. My 98 Jetta did the same thing when it went lower than half full. After several filters and cutting the last one open (clean ) I pulled the whole sending unit out. The bottom pick up was cloged up with crap. Clean it all out and no more problem. Getting down to the last 4-5 gal would indicate this.

Yup...got bubbles. I, too, am trying to understand if the check valve is outside the tank or inside. Go ahead and laugh, I am no mechanic!

when you lift the inspection cover,mine was on the output line.right on top of the tank.i had 2,1 on the out and 1 on the return.output 1 was black,think return was white.
while your in there,inspect the bottom of the tank,mine had some stuff in there.

Check valves prevent reverse-flow. They do not prevent draining. Fuel can't drain out of the pump unless something else (air) is allowed to drain INTO the pump.
If there is air in the fuel system it has been sucked in.
Because this happens at low fuel levels I suspect that the air is getting in through the pick-up in the tank.

There's a joint connection half way down on the pick up. This might be where the air ls getting in when low on fuel. You can pop the bottom out with a small flat head screw driver. Clean and if you decide, you try to replace to o ring or glug the shaft together. I just cleaned and put back together and worked fine.

Can anyone explain how to check the check valve? It's the white knurled white piece on the inlet (in to fuel sender) piece, yes?

kooyajerms said:

Can anyone explain how to check the check valve? It's the white knurled white piece on the inlet (in to fuel sender) piece, yes?

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Take the check valve out. Pressurize it in one direction it should seal, reverse the direction it should flow. You can use pressurized air but probably better with pressurized fuel

My goal is to see if it's clogged in any way. But the car is running absolutely fine, fuel was flowing out of both lines when I pulled the fuel sender.

I believe it's the outlet that I'm supposed to check on... to see if it's causing my inline pump some flow issues.

Please let us know what you find. I am having the same problem and have just been refueling at 700 miles per tank.

kooyajerms said:

My goal is to see if it's clogged in any way. But the car is running absolutely fine, fuel was flowing out of both lines when I pulled the fuel sender.

I believe it's the outlet that I'm supposed to check on... to see if it's causing my inline pump some flow issues.

Click to expand...

bite the bullet,buy 4 small clamps and remove them to inspect.i put barbs back in to replace them.car runs great.

mine we're clogged up w/ crap.this caused my hard start to then dying on the highway.
i kept the old check valve for show and tell but finally ditched it.it would have made a nice pic.

kooyajerms said:

Can anyone explain how to check the check valve? It's the white knurled white piece on the inlet (in to fuel sender) piece, yes?

Click to expand...

both are check valves.supply one is the one that clogs.

Thanks Bill, so ditching the check valve is the way to go.

It's only diesel I'm not concerned about it spilling =)

kooyajerms said:

Thanks Bill, so ditching the check valve is the way to go.

It's only diesel I'm not concerned about it spilling =)

Click to expand...

yes

i'll try to take a pic of it tonote.i need to check for a leak any way.

My check valve died either from crap or biodiesel. I simply removed it. No ill effects so far.

I found this problem because a pump attached to my fuel supply line at the motor wasn't able to pump much fuel. Barely a dribble. After pulling out the check valve I had a nice, clear, thick stream.

If you have good flow to the motor the issue is not likely to be the check valve.

heres my set up.i kept the valve on the return,for now.

Using brass for the barbs is bad choice for diesel yeah? Can't seem to find anything other than that at the Home Depots n Ace Hardwares.

kooyajerms said:

Using brass for the barbs is bad choice for diesel yeah? Can't seem to find anything other than that at the Home Depots n Ace Hardwares.

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You don't need a barbed fitting in place of the check valve. Use a piece of 5/16 pipe, steel or aluminum. The barbs are not necessary since there is no pressure there and just makes removal more PITA!

yeah,i used some stainless tubing i had at the shop.

I think I replaced the entire rubber line with new non-rubber lines, no butt connector needed.

Finally got to this. Stainless tubing is expensive when you only want a small bit. Stainless steel barb menders are even harder to find locally.

Brewing equipment stores (Kegworks), online shops have them though! If anyone wants a set, I'll send it over to you, I had to buy from two different shops to get the 1/4" and 3/16" size.

This is the size if you use a barb mender. 1/4" for the thicker feed line, and 3/16" for the return line. I ended up not using the 5/16 barb because it's hard as hell to shove it into a rubber line that wants to creep behind the tank. Just do a good job with the hose clamps



check valvectomy

You could have gotten the tubing from an old TV telescoping antenna, telescoping mag pick up tool, telescoping inspection mirror etc. There are 4 or 5 sizes to choose from and one of them will fit 5/16 hose (actually it's 8 mm). It's made of nickel plated brass which is fine for diesel or bio. A tubing cutter works perfect on it. No barbs makes future removal a cinch.

I actually had that. The issue was, I was not sure about the nickle plated brass, or if that plating was the same on the inside.

kooyajerms said:

I actually had that. The issue was, I was not sure about the nickle plated brass, or if that plating was the same on the inside.

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The nickel plate is mostly on the outside of the antenna, and is even better than brass as far as corrosion and compatibility to diesel fuel. Did you ever see corrosion on a car antenna? Nickel plating is good stuff!

As far as brass and compatibilty to diesel here's a pre-filter used on Mercedes diesels. You can clearly see a brass insert/ support in the plastic inlet/outlets. Notice there are no barbs? That filter is on the inlet side of the lift pump and is under vacuum. Barbs are not needed when under vacuum.

Finally got around to removing both check valves and pulling the sender for inspection. The sender was clean, no black coating or crud on the perforated pickup base. I didn't take apart the sender to vacuum test it since it is 2 pieces of bent steel lines in good condition. I just can't see them having any kind of a leak. I tested both check valves with a Mityvac and they held vac (25" HG) in one direction, which means they are working just fine, and they looked clean inside with no gunk. I replaced both check valves with 5/16 and 1/4 o.d clear hard nylon lines with antenna insert/ support (so they won't slowly collapse) and used spring clamps on them. The air bubbles I was seeing with a low tank is no more! I suppose the check valves presents a small restriction and is enough to cause air bubbles when the tank is low.

With clear lines for both supply and return at the sender and in the engine compartment, I will be able to pinpoint any (future) air leak problems easily by just looking at the clear lines.

I used to see occasional small bubbles even with a full tank. Just filled up the tank and noticed that the occasional bubbles are gone!