My 86 crew cab dually has been acting sluggish lately to the point where last time I drove it I didn't think I would make it home. To start with it was just slow to pick up from a dead stop but now it's loosing power on any hill, there is one hill on my way home I hit doing 70 because it is so steep and normally I get to the top still at 50-60 but the last time I got down to 30 which is not normal even with a trailer behind me. I haven't had time to do much diagnosis but I do know I have plenty of good clean fuel in both tanks, there is no abmormal noise or smoke, the turbo is still boosting 5-7 psi depending on the load, oil pressure and coolant temps are normal and oil and coolant are both full, clean and not mixing with one another. I just changed the fuel filter and filled it with liqi moli diesel purge and ran it to allow that into the pump and injectors to clean them as I let it sit overnight so maybe that will help some. The ip and injectors are not that old but were included with the cheap jasper reman engine so they could be the culprits. I did also recently run a compression test because it will not start cold and is hard to start warm unless I activate the glow plugs for a second or two but it has 380-400 psi in every cylinder. I am sure it is a fuel delivery issue but it got so bad so fast I want some advice before I start throwing parts at it. THANKS for any help you can provide

 

What's the smoke look like? You said "abnormal" so did you have some smoke prior to the power loss?

(BTW, It's refreshing to read a post that was thoroughly investigated before it was written. Too many other people just post "running slow... help?" and hope we can figure it out for them. Your post had most of the variables addressed.)

 

Either you're ip is starving for fuel, it in itself is bad, or the return is restricted.

I would start by getting a cheap fuel pressure gauge and hook it where the Schrader valve is on the fuel filter (looks like a valve stem)
Try to look for a couple of pounds at idle, at wot it can go down to zero which is pretty normal

You could pull the top off your ip and make sure it's the linkages for the fuel shut off aren't all sticky, go ahead and test the fuel shut off solenoid while it's off to make sure that when it engages its hard to pull away from itself, just an electro magnet. Use a pair of jumper cables and grab it and ground it back to the battery and then use the factory wire to test it, if weak check for voltage at the wire powering it. (Front one, rear one is timing advance)

Do take some care putting the top back on or you can get a runaway symptom but normally the key will kill it, it'll just be stuck wot while on. I always remove the air cleaner and metal screen when messing with the ip just incase, a scrap piece of 2x6 works excellent screen is 15/16 size

You're injector pump nuts could have come loose and it retarded itself but you will normally be making some form of gray/white smoke.

You can disconnect the return line on the back of the motor where it goes back to the tank and blow compressed air into it.

And last but not least if you have a muffler and it's stock it could be clogged, there is a flange under you're passenger seat that you can unhook to check that but the bolts will be a pain in the you know where, a simple map gas torch works wonders here.

 

I thought about return line restrictions as well, but you'd expect some decent black smoke out the back if that was the case.

 

On a roosamaster/db2/db4/ds4 a return restriction will not let the ip pump fuel so you get a starving effect, most of the time without any smoke, it's like running out of fuel very slowly without the clack and white smoke

EDIT: Clean out your inbox genscripter, its too full for me to send you anything

 

So after sitting overnight with the fuel system cleaner in it there is a definite improvement in performance, I have put about 100 miles on it this morning and it seems to hold speed up hill and will also accelerate uphill. It is still super sluggish off the line so I am still in need of advice but it's doing better. Also I think my pyrometer has stopped working because it seems to be staying on 400 degrees all the time. I thought about advancing the timing a hair and maybe turning the fuel up half a turn since I never get any type of smoke I figure it might just be not getting enough fuel. Thanks

 

check fuel pressure at the filter head. your lift pump may be failing.

 

70 down to 30 towing up any appreciable grade was normal for my 6.9 turbo with well worn pump and injectors. 100cc pump and new injectors and it was only marginally better, but EGT limited rather than HP limited. With your other symptoms I was leaning towards low compression and a plain worn out engine (hard starting being key), but compression seems fine. I suspect the pump and maybe injectors. Verify fuel inlet pressure and flow at the IP first, them pop test injectors. Check timing too. If none of those it's probably the IP.

 

I'd definitely bet on some sort of clog reducing fuel available to get into the IP - likely between the tank and the lift pump.

It could be a clogged fuel filter, too.

I'd do as others said, pull the "vacuum switch" on the outlet of the fuel filter and install a chunk of hose and a 0-15 PSI gauge. I used a cheap set of copper lines and a little mechanical gauge, then zip-tied it to the cowl such that I could see it from inside the cab. That way, I could watch it when driving, but it it leaks, no fuel inside the cab.

Personally, I see about 3-5 PSI to the output of the filter, even with my 110CC IP - 4-5 at idle, 3-ish under heavy acceleration. It doesn't go to zero, and shouldn't.

 

I actually had pieces of my gas tank pickup in my fuel line which significantly reduced the interior size of the hard line.

 

Happened to me too, they were all stuck in an elbow on the sending unit, luckily they never made there way to the fuel tank valve, caused mine to sit there and lope

 

Well I have not had much chance to fool with the truck but I did notice the metal fuel line is leaking at the lift pump, it is tight as it can be but there is some damage to the flare fitting from rust so I guess I have to find a replacement. Something else I noticed is the rubber line between the pump and the chassis is regular gas hose not reinforced fuel hose so I am betting that hose is sucking flat when I hit the throttle. Last, it has a facet duralift electric pump near the selector valve for what reason I don't know and I thought about removing it and just running the mechanical pump which is new. I know I don't need both and that could be the problem. Thoughts?

 

the duralift is a pass through pump.
is it hooked up? i prever the duralift pump over the mechanical pump. the duralift has been on my truck for 15 years and 300k miles now. the best i ever got out of a mechanical pump is around 5 years/100k miles.

 

Yes, it is connected and working, I have tried disabling it and the truck seems to run the same either way. I am currently trying to find my pressure tester so I can see what the pressure actually is

 

my guess is the e pump was put in because the line at the mechanical pump that is now leaking was sucking air.
this leads me to think that you either have a blockage between the lift pump and injector pump, or the injector pump is dead.