spin on fuel filter

[GentleGiant]

Hello troops,

1984 M1008 CUCV Started easily, ran 5 seconds, and died. Now she cranks fast but won't start. No smoke. No fuel coming out bleeder on stock fuel filter when cranking for 10-15 seconds.

I guess we're having fuel delivery problems here...think its time to do the spin-on fuel filter upgrade.

I've read a bunch of threads but have yet to find the authoritative "best method".

A few questions:

1. is there a best base to use for the spin-on? I see some with both lines off the air-cleaner side and some with a line off each side.
2. is there a best filter / best micron rating for the filter
3. is a fuel heater needed up North (I live in Canada)
4. any authoritative opinion on water drain and primer bulb ideas I've read about?

Any other information on the best setup would be appreciated.

Thanks much,

GentleGiant

 

[cucvrus]

Could be the injection pump throttle shaft seals. Any leak in the fuel system can do that. The spin on is not a fix all. Do as you wish. This is heavily covered on this site. Many scenarios can cause the same issue.

 

[Skinny]

Pull the feed line to the IP and see if you have fuel coming out while cranking. Sounds like you are not getting any fuel to the injectors.

The spin on is a good upgrade but not the cure to your problem. Figure out what the cause is and then tackle the upgrades. Stanadyne has a good FM series of products with many options including primer handles, electric pumps, heaters, etc.

 

[corelokt]

Rotted lines, bad pump, lots of causes. Check your oil, make sure fuel hasn't caused it to rise.

 

[GentleGiant]

Thank you to you all.

So, if I get it... a thorough examination of lines and then more complex things like injector pumps and fuel pumps. Any small leak will let air in and that will allow the fuel to drain back to the lowest point: the tank.

The ultimate solution might be to replace all rubber hoses and then do the spin-on mod. If it still doesn't work... it would probably be a leak in the injector pump.

Does that sound on target?

Thanks,
GentleGiant

 

[GentleGiant]

Mmmm...

The oil level is not higher, corelokt.

I went ahead and changed the filter, because I had a new one handy. I cannot get fuel to come out the bleeder on the filter housing. Drained the batteries trying. Charged them. Tried again for some time. No fuel coming out.

The fuel pump is new a couple years ago because it was cracked and leaking slightly. The new one still looks good (no leaks).

Thoughts?

Thanks,
GentleGiant

 

[gimpyrobb]

I still have a few FM100 filters left. PM sent.

 

[cucvrus]

The new one still looks good (no leaks).

Good looks don't count. Loosen the fuel line and see if fuel is pump out of the flare nut connection. Then proceed to bleed filter if fuel is present on outer fuel feed past pump. But changing the filter base with no fuel being pumped will accomplish nothing. After the fuel pump is changed then bleed filter and you may be good to go. No further work needed. But first things first. But do as you wish. If you go electric put an inertia switch in place so if involved in a accident it is not pumping fuel onto the highway and present more problems. But do as you wish. I am trying to give you a hand.

 

[corelokt]

You can take a jug of fuel and put the pump inlet direct to that and see if it works. A cheap vacuum/fuelpressure tester would not hurt to have. Just a gauge and rubber hose really. They give a good indication of fuel pump health.

 

[snowtrac nome]

look at the rubber hose between the frame and pump I have seen those flex and kink shut once some one replaced the factory hose with a cheep gates fuel hose the factory hose is molded I have used at cooler line successfully as it doesn't get soft.

 

[cucvrus]

Yes and also the motor mounts can be worn out and let the rubber fuel feed get pinched and then it has a small slice in it and will not allow it to pump fuel. I had that happen to me. So the list is long and deep. You have a conundrum here. Check everything fuel line and pump related. Up to and including the fuel lines above the tank and the strainer in the tank. Good Luck. These are all great ideas.

 

[GentleGiant]

Gold Star for snowtrac nome. That hose was replaced when the pump was replaced, and it is indeed kinked flat... very little fuel could possibly get through it. I'll work on it tomorrow or the next day, but I bet that's the problem. Thank you very very much.

Thanks to all others who contributed as well. I'll give a final report after the kinked hose repair is done.

snowtrac nome: "cooler line" can you explain exactly what you mean by that term? do you mean a piece of a transmission cooler line hose?

 

[Ferroequinologist]

Sounds like you probably found your problem. If it still continues and the fuel pump and other lines appear ok, it is probably the sock on the pickup tube plugged up. Drove me crazy on mine till I changed it.

 

[GentleGiant]

Hmmm.... I made up a 3/8" id elbow and put it in the spot which was kinked in the hose to the fuel pump. Seemed like a solid fix.

Still can't get the filter to prime. Drained batteries a couple times trying. Also tried with suction (from shop vac) on bleeder hose... no fuel.

Took the inlet line off the filter... can see diesel about 1" down that hose. put a clear extension on that line and cranked engine 10 seconds twice. No fuel coming out that line.

Have yet to try putting the fuel pump inlet line in a jug of fuel to see if the pump will pull from there.

Can the pump be air-locked? In the TMs it says that after changing the pump just bleed the system as normal. After changing the pump, I'd expect the pump and nearby lines to be full of air...so the pump can move that air and pull fuel from the tank, right????

My assessment is narrowing on the pump or the sock in the tank, or an obstruction in the line. There's no puddle of fuel under the truck, and there is fuel (1/2 full) in the tank.

Thoughts?

Thanks,
GentleGiant

 

[cucvrus]

Did you check if the fuel up is pumping fuel at the flare nut side? Disconnect the feed hose and apply suction to that line and see if you can get fuel. If not try blowing air back into the tank and then try suction again. Do you have a fuel line that is worn thru? Under the cab on the rear cab cross member of M1008. You must get fuel up to fuel pump to get fuel to filter. Report back.

 

[GentleGiant]

Hi all,
thanks for responding so quickly, cucvrus.

I have done a visual inspection of lines from tank to fuel pump... all look good. I disconnected the rubber hose which connects the fuel pump to the steel line coming from the tank and applied suction to the steel line. Got a good stream of clean diesel. So the sock in the tank appears not to be the problem.

I disconnected the rubber hose at the inlet of the fuel pump itself and a little diesel came out. I want to replace all the rubber in that line, even though its only a couple years old (pump was replaced recently). I noticed a small wad of gritty metal stuff on the cardboard under the truck afterwards, along with the diesel spatter..... sort of like drill shavings....could have just been resting on the frame and the diesel washed it off... or could have come from inside the pump. Hmmm...

I disconnected the rubber hose which connects the steel line to the fuel filter and applied air... could not force air down that line backwards through the pump. I wonder if the pump has a built-in check valve?

I applied air into the inlet of the fuel pump and blew clear diesel out the line which would have gone into the filter (I had disconnected it). So that line is clean and open, and fuel will flow through the pump in the correct direction. Or, at least air will flow and push fuel out of the line above.

Thus we have a clear line from tank to fuel pump and a clear line from pump to filter.

I re-connected the line from the tank to the pump with all new fuel hose and a brass elbow to prevent kinks. I applied suction at the hose which leads into the fuel filter and got clear diesel to come up to the filter. It was a much slower flow than the fuel coming just from the tank (because it comes through the pump and also has to climb higher, I assume.) I re-connected that hose to the fuel filter, noting that the hose was full to the top.

So now we have diesel all the way from the tank to the filter. I tried to get fuel to come out of the bleeder by turning the engine over for 10 seconds. No fuel. Then I applied suction to the bleeder line... still no fuel. I have a new filter on there. (well, it has been sitting in its original plastic wrap behind the seat for 10 years, but it has never been installed.) Could there be a blockage in the filter housing?

Then I unhooked the hose into the filter again and put an extension on it and ran that into a jar. I cranked the engine for 10 seconds. No fuel.

If the pump can't pump fuel up a series of clean lines, I assume the pump is not working. I don't know why I can not get fuel to come out the bleeder by using suction, but it still seems like I need a new pump.

Thoughts?

Thanks,
GentleGiant

 

[richingalveston]

I think your pump is bad. They will move fuel when there is no pressure but wont pressure up. so when you remove the line coming out it pumps and looks to be good but as soon as it needs to push pressure it quits.

go ahead and get new filter cheap insurance.

todays mechanical pumps made in china can go out a week after installing or a year or run forever. no real rhyme or reason. Just poor quality.

Rich

 

[GentleGiant]

Thanks Rich,

Sounds right to me.. a new fuel pump. I read the TM on that job. Fairly straightforward except in an awkward spot.

Is there a need to remove the push rod?
Is this a stock Chevy fuel pump for the 6.2 liter diesel, or something special for military trucks? (Can I just get the stock pump from Napa, or is it a special military spec pump?)
Is the gasket which comes with the pump sufficient, or is it better to add some gasket-making goo as well?

Thanks,
GentleGiant

 

[richingalveston]

stock pump and gasket it comes with is what you need nothing special for military.

The push rod will probably fall out. put some wheel bearing grease on it, just enough to make it stick in there and it will help in getting the new one installed.

consider the electric fuel pump install if you wish. I like it for many reasons, makes priming system easy on filter changes. They are not expensive so I can carry a spare and change in 10 minutes on the road if it does go out because they mount on the frame rail and it is easy to get to.

The mechanical pump it is hard to change without turbo and nearly impossible with.

If you have the time and want it to be easy just more steps, remove inner fender, put jack under passenger side of motor, I actually had a small scissor jack I put between frame and exhaust manifold.

remove bolts in motor mount and jack the motor up so the fuel pump can be reached on top of the frame rail.

good luck
Rich

 

[cucvrus]

I can change one in about a 1/2 hour. Just dis connect batteries and remove the right alternator. Everything is right there. The wires on the alternator are long enough to stay connected. The only thing I go down on the bottom side to do is A remove the rubber line if need be. B re-tighten the 2 M6 bolts on the cover plate. No need to remove an inner fender and jack the motor up. The frame cross member will still be there only now the fuel pump is higher. Do as you wish. Good Luck and report back if you wish. Happy Holidays.