So i have 86 6.9 with 366kms on it and it runs okay but it has its problems.

after running for a bit it hunts(revs up and down)
I will be driving it with my foot to the floor it looses all power and dies on the road, is hard to start after that. last time I drove it it died 5 times driving only 30kms.

I think its a fuel problem but I am no expert.

I have replaced the return lines, o rings and caps, replaced the fuel filter, replaced the lift pump, I have glow plugs on a manual button, I have replaced all the battery cables with quality cables, new rear fuel tank.

could it be my injecton pump? injectors?

 

How much fuel in the tank ?
Has it sat for a while ?
Are you able to test the fuel pressure before the injection pump ?
What is known about the injection pump , age ?

 

Its almost full. I had this problem when I was driving it daily. I can test the pressure just need to get a gauge. I don't know details on the pump. Doubt its been replaced for a while if ever.

 

I'd say the injection pump is on its way out .
But before you condemn it test the fuel pressure developed by the lift pump .

 

Check fuel volume as well at the shrader valve. (1/3 pint in 10 seconds cranking IIRC) You may have a pinhole in the line between the lift pump and tank, sucking air. Look for fuel seeping or damp lines.

 

how do i check fuel volume?

 

I believe you could take out the valve in the schrader valve and crank it over while collecting the fuel that comes out. Should be able to use a stop watch or something and see if 1/3 of a pint or so comes out in ten seconds.

Kind of a crude way to do it I guess but it should get you reasonable results.

If it still hunts while revving it at idle and not under any load you could hook up a hose directly to your fuel pump and put it in a bucket of diesel. See if it still hunts while not using the tank or fuel lines going back to them. There by taking them out of the equation and putting more emphasis on how the IP is working.

Just some ideas.

 

Did you replace the seal at the filer housing and the one at the injector pump?

There could be a slight air leak. A1 Cardone makes the seal kit available at any parts store, but they'll have to order it. I would try that first.

 

so i plugged in a fuel pressure guage to the shredder vavle, and started up the truck, the truck was running but the guage showed no presssure building up, I tried reving it up, still no pressure.

so after I pulled the shreader vavle off and turned it over 10-15 seconds at a time, barley any fuel came out which i thought was weird so i pulled the line going from the lift pump to filter housing and had good flow coming out when i turned it over. so then i pulled the line off leaving the fuel filter and there was good flow leaving the filter.

any thoughts would be great. not sure where to go from now

 

If you have good flow coming out of the filter head, I don't know why you wouldn't have it coming out of the shrader valve. I'd say you have verified the lift pump is working, now try the suction side in a can of fuel to see if it runs ok.

 

It is possible that the schrader valve is screwed up .
Try to remove the valve - just like you would on a tire valve stem .
I'm thinking you may indeed have a rusty or otherwise deteriorated fuel feed line on the chassis .