I posted a few days ago about some problems I was experiencing with my truck: https://www.dieseltruckresource.com/forums/showthread.php?t=156030

I replaced the gasket in the fuel heater and thought I introduced air in the system. The symptoms were very hard starting, tons of white smoke at startup, teh truck wanted to die at idle and rough acceleration.

Yesterday I decided to bleed the injector lines. After a rough start I got the truck into the entrance of the garage. With the engine running I bled each injector starting at the front. When I got to the third injector the engine stalled and died. It would not restart.

I opened the bleeder screw on the top of the fuel filter housing and pushed the plunger on the lift pump. I got air, lots of air. In fact, after pushing for a few minutes I didn't get fuel.

I removed the fuel heater bowl and saw no fuel under the screen. I held a finger over the fuel exit path in the center of the heater and pushed the plunger. I felt vacuum, although it wasn't really, really strong.

Next I removed the fuel filter housing. There was very little fuel in it. I was getting very concerned that my lift pump was out.

I removed the fuel inlet hose from the firewall. I put my finger over the barb on the engine side and pushed the plunger on the lift pump. I felt vacuum although it was very light.

I removed the fuel tank cap. Next I connected a length of hose to the firewall (fuel tank) side of the line. I tried to blow air into the line and couldn't. I sucked on the line thinking I should get a mouth full of diesel and couldn't. I felt like there was something blocking the line.

I think the next thing I am going to do it siphon some fuel into a 5 gallon bucket and put a hose on the engine fuel inlet, prime the pump and start her up. If it runs I know the fuel system works. I only have 100 miles on this tank of fuel so there is close to 30 gallons in there. I don't want to drop the tank unless I have to.

Does anyone know if there is a check valve that could have malfunctioned somewhere in the sending unit? Anyone else have this problem? Am I barking up the right tree?

Bob Elliott

 

I think you have an air leak, guessing on the steel lines on the bell housing.
You would have to be one heck of a sucker to be able to get any results by mouth.
Try an air compressor but remember to leave the fill cap off.

 

If you need to get into tank , some have undone the bed mounts & tilted the bed to get access , then you can get to fuel lines & put pressure to them & vacuum , to look for leaks , I say pressure & vacuum , because I have had vacuum hoses that would leak with vacuum on one end & not the other .

 

If I had a leak I shoudl be able to blow air in the line, no? I couldn't do it when I blew into the supply line at the firewall.

 

A leak that causes problems can be so small that you would hardly notice when blowing by mouth.

 

That was my point. I cannot blow air into the line. I would think you would be able to blow air into the fuel tank through the supply line with the tank cap off, unless there is a check valve. Is that the case? Why can't I blow air into the tank or draw diesel?

 

Same thing as doing new plumping in a building , put pressure in system [ 100 lbs in house syst. , 30lbs in fuel sys. ] then let sit for a day + with gauge , should read the same over time .

 

Bob, I would highly doubt you could blow hard enough to push the fuel back through the small lines to the tank by mouth. Normal people are hard pressed to get to 3-4 PSI with lung power, and that shouldn't be enough to back feed it.

Try a air hose set at 20 PSI, it should work then, or if you have access to a mityvac you could rig up a glass jar with a stopper and a bung for the vacuum and another to connect to the fuel supply line at the filter housing, pump it up and the fuel should easily flow into the jar.

I don't have my 97 FSM here with me, but I just looked at the 2001 I have on PDF and there is no check valves in line on those, so my money is no check on a 97.