Fuel System Troubleshooting and final resolution (IT WAS THE SOCK)

[98G]

I am just not sure why so many resist removing that plate, it is only two small screws and then you do not have to stand on your head, hold your tongue just right and worry about getting the rod out of the way, seems like a no brainer every time I do it, but whatever gets the job done

I fear inducing an oil leak

 

[Retiredwarhorses]

If this is truly a lifter problem, you need to replace it immediately before Diesel fuel gets beyond the diaphragm and thins out the oil and you score your cylinders and bearings or even seize the engine.

That’s impossible, the vent on an m998 before the mods were done would contaminate the closest geared hub and maybe the front diff.
After the mods to the vent system, the excess fuel is sent back to the fuel tank filler neck in an isolated vent line dedicated the fuel pump vent.

 

[Mogman]

I fear inducing an oil leak

That makes no sense if you use a new gasket, but as I said whatever gets the job done, as long as you are aware of the issue.

 

[98G]

Since this thread is now something of a repository of fuel system info, above is the video showing lift pump replacement including the plate.

The two fuel pump bolts are 7/16. The threaded fuel hose nut is 5/8.

I'm an idiot and left the switch on so it's stranded where I left it and I'm working on it in direct sun

Lift pump is out. The plate is still in place. Any difficulties and I'll just pull the plate as well.

Hopefully I'll be updating this with further progress later this evening.

 

[marchplumber]

Since this thread is now something of a repository of fuel system info, above is the video showing lift pump replacement including the plate.

The two fuel pump bolts are 7/16. The threaded fuel hose nut is 5/8.

I'm an idiot and left the switch on so it's stranded where I left it and I'm working on it in direct sun

Lift pump is out. The plate is still in place. Any difficulties and I'll just pull the plate as well.

Hopefully I'll be updating this with further progress later this evening.

Don't ya HATE when ya do something, THEN realize you could've done it different/better? UGH! I feel for ya, in plumbing, that can be quite often. Looking forward to the update!!

 

[98G]

New pump is not exactly like the old pump. No breather (presumably not needed) and the fuel inlet is facing the wrong way.

Pump is mounted. Hard line is connected. Contemplating ways to make a 180* turn to connect the soft line.

The drive rod from the cam is truly cursed. Getting it up and out of the way is an exercise in patience. I kept it out of the way with a piece of fuel line that I pulled once i got both fuel pump bolts started. It's probably less trouble to pull the plate.

 

[Mogman]

New pump is not exactly like the old pump. No breather (presumably not needed) and the fuel inlet is facing the wrong way.

Pump is mounted. Hard line is connected. Contemplating ways to make a 180* turn to connect the soft line.

The drive rod from the cam is truly cursed. Getting it up and out of the way is an exercise in patience. I kept it out of the way with a piece of fuel line that I pulled once i got both fuel pump bolts started. It's probably less trouble to pull the plate.

Sounds like you got the wrong pump.

 

[98G]

Sounds like you got the wrong pump.

Three different part numbers are given as being equivalent. This was the one with 0030 in it (memory).

Wrong pump was my first thought. But the hard outlet line lined up perfectly. The soft line wouldn't be an issue other than it isn't where it was and there's insufficient slack to make the change.

Breather seems trivial.

I suspect that minor details have been revised multiple times since 1986.

We'll find out.

Correct any misconceptions I have...

 

[TOBASH]

New pump is not exactly like the old pump. No breather (presumably not needed) and the fuel inlet is facing the wrong way.

Pump is mounted. Hard line is connected. Contemplating ways to make a 180* turn to connect the soft line.

The drive rod from the cam is truly cursed. Getting it up and out of the way is an exercise in patience. I kept it out of the way with a piece of fuel line that I pulled once i got both fuel pump bolts started. It's probably less trouble to pull the plate.

Sounds like wrong pump AND use grease or Vaseline to keep pushrod up in place. It harmlessly washes out once you start the engine.

 

[Castle Bravo]

I could never get grease to hold up the rod, so I used a hacksaw blade with a bend in it that allows enough clearance to get the bolts started. A longer piece of feeler stock might work as well.

 

[Mogman]

I could never get grease to hold up the rod, so I used a hacksaw blade with a bend in it that allows enough clearance to get the bolts started. A longer piece of feeler stock might work as well.

Did you remove the rod and grease it or try to stick some grease on it without removing the rod?
I have never had any issue when removing the rod and greasing it including the rod end where it contacts the cam.

 

[98G]

I could never get grease to hold up the rod, so I used a hacksaw blade with a bend in it that allows enough clearance to get the bolts started. A longer piece of feeler stock might work as well.

The fuel line worked pretty well.

A hacksaw blade was what the paperwork that came with the pump recommended.

 

[Castle Bravo]

Did you remove the rod and grease it or try to stick some grease on it without removing the rod?
I have never had any issue when removing the rod and greasing it including the rod end where it contacts the cam.

It's been a decade since last I did it, but I don't think I've ever removed the rod.

 

[Milcommoguy]

I can bet more rods have been snapped off / busted... if the story was told. Hacksaw blade sounds like it would be in the way. LOL

Always grease your rod first, CAMO

 

[98G]

I can bet more rods have been snapped off / busted... if the story was told. Hacksaw blade sounds like it would be in the way. LOL

Always grease your rod first, CAMO

You sir are OBSCENE!

LOL

 

[Milcommoguy]

You sir are OBSCENE!

LOL

At least it's not a 1000 bottles of baby oil.

That's a slippery subject, CAMO

 

[98G]

I replaced the soft line from the last hard line on the frame rail to the fuel pump inlet.

I took the genset and a set of slave cables over to it.

It's running!

Tomorrow in daylight I'll police up around it real well and make sure i got all the tools picked up and drive it the 7 miles to the co-op and fill it up. We'll have a definitive answer as to the cause. (Or it'll be back on the Strap for the Tow of Shame.)

 

[marchplumber]

I replaced the soft line from the last hard line on the frame rail to the fuel pump inlet.

I took the genset and a set of slave cables over to it.

It's running!

Tomorrow in daylight I'll police up around it real well and make sure i got all the tools picked up and drive it the 7 miles to the co-op and fill it up. We'll have a definitive answer as to the cause. (Or it'll be back on the Strap for the Tow of Shame.)

Appendages crossed!! Eagerly awaiting the "outcome"....ya know what they say, "One day at a time!".......hopefully your mech adventure has come to a successful conclusion.....

 

[98G]

Picture of the box with the part number of the pump I'm using.

There's no vent on the top of it, and the inlet is facing 180* off. These are the two differences compared to the pump I removed.

I ordered this one. Had I put eyes on it, I would have bought one that was an exact match.

 

[dengroff]

I have had similar issues with both gas and diesel engines over the years and it almost always is the pick up sock. As the engine runs and return fuel agitates the fuel in the tank, crap from the bottom gets sucked up to the screen. Eventually enough gets on it to restrict flow to the point of stalling. When the engine stalls and the pump stops creating suction the junk falls off and you can start the process again. If you have an old fuel system vacuum gauge you can plumb it into the suction side of the lift pump and tape it to the windshield, drive the truck if vacuum drops during power loss there is a restriction before the gauge or the previously mentioned clogged vent. If the vacuum goes up there is a restriction after the lift pump. If there is no change you're looking at a high pressure side problem.
Hope this helps