Fuel issues

proffjl · Post by **proffjl** » Sat Jul 31, 2010 10:21 pm

I have been having lots of bubbles going into the the injection pump and almost a foam of bubbles coming out while motor is running. And then when I shut the car off the bubbles run backwards coming out of the pump creating an air gap in the top of the filter and the lines. This happens within a few min of shutting off. This air gap has cause a slight hesitation when starting. First thing I did was replace the fule filter, no change in bubbles.

Today I hooked up a auxiliary tank directly at the filter. When using this it eliminates nearly all of the air going into the pump. Just a few small bubbles. That I believe are coming from the valve, the gasket, or one of the connected hoses to the valve on top of the fuel filter. I tightened the connections there and pushed the valve down snug and stopped the bubbles nearly completely.

The thing that has me confused is what happens when I shut the car off with the aux. tank hooked up. Something is pulling the fuel out of the aux. tank at a fairly rapid rate. Like there is some sort of vacuum pulling it towards the tank. It pulls nearly a liter of fuel down in about 5 min. What could be causing this? I didnt see any huge puddle of fuel on the ground anywhere. So I feel like it is going back to the tank. I'm just really baffled.

82vdub · Post by **82vdub** » Sat Jul 31, 2010 10:35 pm

Is the aux tank elevated above the IP, at the same level as the IP, or sitting on the ground? If you install an aux tank and most of your bubbles disappear, I'd say that the fuel line problem mostly exists between your interception point and the tank. A restriction in the line will let lots of air in the weakest point. The weakest point may be in the filter area, but it could be anywhere along the fuel line. Inlet screen in the tank plugged? They are easy to access.

proffjl · Post by **proffjl** » Sat Jul 31, 2010 11:35 pm

I have the aux. tank elevated above the engine. should it be below or level with the injection pump?

I'm going to check the tank screen tomorrow.

proffjl · Post by **proffjl** » Sat Jul 31, 2010 11:48 pm

hmmmm well it just sort of hit me that with the aux tank elevated above the level in the real fuel tank, the fuel is just draining back to the take via the return line hooked in at the filter. So maybe I dont even have a problem there???

82vdub · Post by **82vdub** » Sun Aug 01, 2010 5:56 pm

proffjl wrote:hmmmm well it just sort of hit me that with the aux tank elevated above the level in the real fuel tank, the fuel is just draining back to the take via the return line hooked in at the filter. So maybe I dont even have a problem there???

That's the theme from the question. Investigate further and post results.

proffjl · Post by **proffjl** » Wed Aug 04, 2010 12:10 am

well I still havent found where the air is coming in, but i'm hopefully narrowing it down. I have pulled the fuel sending unit and cleaned it out, wasn't very dirty. I have also removed the water separator, no change in the amount of air. Next I will be replacing the check valve in the supply line. After that I guess I will start replacing lines and fittings.

But removing the fuel sending unit has created a new issue for me. My fuel gauge only shows 1/2 full when it should show about 3/4 or more. How could I have messed this up? Can the wires I cut on the water separator be causing an issue with the gauge?

82vdub · Post by **82vdub** » Wed Aug 04, 2010 8:54 am

If the gauge reads full when the tank is full and empty when the tank is empty, it's probably functioning normally. The tank is typically not symmetric, meaning that half the distance from the top to the bottom of the tank isn't exactly half it's capacity. And, it's possible that you could have messed up the wrapped wire assembly on the sending unit, causing a slight issue.

Post by **Fatmobile** » Thu Aug 05, 2010 10:17 pm

If the screen in the pickup was clean,
the restriction is probably caused by the check valve.

The check valve is supposed to keep fuel from syphening back to the tank,.. but you see fuel/air heading back to the tank.

Air in the fuel lines is almost always caused by a restriction.

proffjl · Post by **proffjl** » Fri Aug 06, 2010 1:52 am

I have ordered some check valves from McMaster. Along with some tubing that is supposed to be biodiesel rated, incase I want to go that route someday. Hopefully the check valves will work. Here are the two products if anyone is interested. I will hopefully be installing them tomorrow. Also previous problem of only showing half full has fixed itself with some driving and a fresh fill up.

2987K25 Fda-compliant Nylon Check Valve, For 1/4" Tube Id, 1-11/16" End-to-end Length

5549K335 Clear Tygothane Polyurethane Tubing, 1/4" Id, 3/8" Od, 1/16" Wall Thickness

Post by **Fatmobile** » Fri Aug 06, 2010 3:03 am

I think the check valve was for draining the water seperator.
So fuel wouldn't syphen back and let air in.

I don't think it's needed.

I've removed them with no problem.

proffjl · Post by **proffjl** » Thu Aug 12, 2010 1:33 am

Ok. I have installed the tubing. Front to back on the supply line. This has removed all but the smallest bubbles. I think these are coming from the fuel warmer on top of the fuel filter. I'm just going to get a fuel filter without, and hopefully fix that issue. This also cleared up the foamy looking return line.

But I still have the problem where the fuel drains back towards the tank. As soon as I shut the car off the process starts. It hasn't created any huge starting issues yet. But I would like to get this issue resolved. Could a bad fuel cap cause a vacuum in the tank? I'm going to try and drive around with the cap off to see if that helps. If not I guess i need to check the vent valves on the tank. Any pointers on how to start there?

Also for anyone following this post. Do not use the check valves I posted earlier. The restrict the flow and cause more issues.

82vdub · Post by **82vdub** » Thu Aug 12, 2010 8:53 am

proffjl wrote:Ok. I have installed the tubing. Front to back on the supply line. This has removed all but the smallest bubbles. I think these are coming from the fuel warmer on top of the fuel filter. I'm just going to get a fuel filter without, and hopefully fix that issue. This also cleared up the foamy looking return line.

But I still have the problem where the fuel drains back towards the tank. As soon as I shut the car off the process starts. It hasn't created any huge starting issues yet. But I would like to get this issue resolved. Could a bad fuel cap cause a vacuum in the tank? I'm going to try and drive around with the cap off to see if that helps. If not I guess i need to check the vent valves on the tank. Any pointers on how to start there?

Also for anyone following this post. Do not use the check valves I posted earlier. The restrict the flow and cause more issues.

The cap should not be an issue, becuase likely it's a non vented cap. Have you installed a vacuum gauge in the supply fuel line close to the IP? This will tell you if you've got a vacuum situation building up. Could be something with the tank vent or a clogged pickup screen. Great results in the bubbles though.

Post by **Fatmobile** » Thu Aug 12, 2010 12:40 pm

Yep, a vaccum gauge will let you know if there is a restriction in the line.

Is there still a check valve in the line?
Without it fuel can syphen back to the tank,
if one of the small lines between the injectors is leaking or any leak is letting air back in.

Sooo, as soon as you shut it off,
air comes back out of the pump inlet,, heading back to the tank?

It takes awhile for air to make it from an injector return line to the input of the pump,.. sucked all the way through the pump.

If air is coming out immediately after shutdown, the banjo crush washers might be leaking,...
or the main shaft seal is junk.

There is an o-ring on that style fuel filter,
with the recirculator/warmer that can be replaced..
It is a spendy filter to replace,
compared to the spin-on Rabbit filter.

proffjl · Post by **proffjl** » Thu Aug 12, 2010 9:38 pm

Yes, the air starts as soon as I shut the car off. And no I do not have a check valve in the line anymore. where can I get one that works?

I have a clear line running from the tank to the filter and from the filter to the in banjo of injection pump. So I can see that the air works it way back from the injection pump and goes down the line towards the tank about 10 inches below the filter.

I have put brand new hose with braided cloth housing going between all the injectors. So i dont think there is a problem there.

The reason I want to bypass the fuel warmer is that it looks to have some small cracks in the plastic. I have replaced the o-ring with the new filter.

Are the crush washers made of brass? or some other soft material that crushes down?

82vdub · Post by **82vdub** » Thu Aug 12, 2010 11:13 pm

If the air flow starts as soon as the engine is shut off, I tend to think it's pulling a vacuum somewhere.