bought a new truck its a 1995 freightliner fl80 and it has a b 5.9 cummins and its lazy and it was starting hard i have another one and thats how i know its lazy no comparison in power tried swaping the lift pumps made no difference anyone have any suggestions on what to check when i bought it drove it 650 km home never missed a click ran like a dream but was lazy no power when you put the pedal to the medal

 

also already changed filter and checked return and seems to have good flow and when i had it out for a drive it came out of it one time and hauled *** like the other one does but only the once

 

check the boost pressure could have a leak somewhere and if the turbo is wastgated make sure its closing.

 

When you press it to the floor any black smoke??..Also whats your max boost??

I had a similar problem where the startup solenoid would not pull fully in the run position..

 

ok no smoke when driving it not sure on max boost pressure have not checked it

 

If no smoke when you punch it...Check and make sure that startup solenoid is pulled all the way up..If its half ways it will stop the rack travel and you will not get full power...

 

will check tonight and get back in about 4 hours

 

Also check your AFC...Check if the tamper proof screw was removed...If it has..Take your AFC housing off and move your plate full forward.Screw the star screw forward and push the AFC hosing full forward..

 

ok checked the fuel shut off pulling up fine

 

If it has a P7100 pump, then it is time to get a fuel pressure gauge on that puppy, let us know idle and 2500 rpm pressures.

 

so check pressure between lift pump and injection pump is that with the return line open?

 

YeS

 

i have already swapped the lift pump with a known good one and it made no difference so the fuel pressure test would only rule out if the overflow valve was faulty correct???

 

Yes or a possible supply problem to the lift pump.

To me it sounds like you have a boost leak somewhere. Either the tube to the AFC housing or a boot leaking to the intercooler.

 

Yep, but the overflow is a more likely culprit than a lift pump, the only real way to discern is with a pressure gauge and then clamp off the rubber portion of the return to see if the pressure rises.

Dog is pretty sharp on these things, do you also have a boost gauge?