Turbine Doc
Just Another Diesel Guy
Okay fuel delivery basics for the 6.5
On the 6.5 you have a fairly simple fuel delivery system.
Starts at the tank, a suction strainer, to lift pump, to filter manager, to IP shut off solenoid, to IP, flow is controlled to IP via PCM demand to PMD/FSD.
Depending on vintage power to the lift is either from OPS (OBD-I/92-95) or OPS/PCM (OBD-II 96+ years)
Healthy IP is capable of pulling it's own fuel past a dead or weak lift provided it is GM flow on fail type lift pump, performance can suffer at higher rpm "fish biting" is common sign of dead lift or bad ops in OBD-I truck, "f-b" same feel one gets when fish 1st hits your line, jerking/tugging you feel in truck sort of similar to "miss" in gasser truck. In OBD-IIs lift power is from 2 places PCM & OPS you have to lose both for total no power to lift.
Lift is supposed to supply 15 gph, a check is capture & measure output from filter mgr drain 1/2 pt in 15 sec should be good lift delivery at idle, yet I've seen "healthy" pumps purr perfectly, and pump meeting idle demand still be bad, so my preference is to load test the lift.
At the filter manager drain snake into your cab on long hose a test gauge, make positive to not pinch off the hose and dead/static head the reading, at idle with good stock pump 5-6 psi is normal, go for drive, at hiway cruise speed 70 mph 3-4 psi is strong lift pump, 2-3 psi is good lift pump but has some weakness, if lift will not sustain 1.5 psi or better, get a new one.
Then do an acceleration test on hard acceleration it is preferable to maintain > 1 psi, it may dip below that but once at desired settled out speed, lift needs to recover quickly to 1.5 psi or better, if it remains less than 1.5 or takes more than about 5 second to recover to cruise psi observed before accelerating, either lift is bad or tank sock is dirty.
Pic of simple vac/press gauge about $20 at part store or less on sale from Harbor Freight a must have piece of 6.5 test gear :
FYI post will close periodically until I finish with it
On the 6.5 you have a fairly simple fuel delivery system.
Starts at the tank, a suction strainer, to lift pump, to filter manager, to IP shut off solenoid, to IP, flow is controlled to IP via PCM demand to PMD/FSD.
Depending on vintage power to the lift is either from OPS (OBD-I/92-95) or OPS/PCM (OBD-II 96+ years)
Healthy IP is capable of pulling it's own fuel past a dead or weak lift provided it is GM flow on fail type lift pump, performance can suffer at higher rpm "fish biting" is common sign of dead lift or bad ops in OBD-I truck, "f-b" same feel one gets when fish 1st hits your line, jerking/tugging you feel in truck sort of similar to "miss" in gasser truck. In OBD-IIs lift power is from 2 places PCM & OPS you have to lose both for total no power to lift.
Lift is supposed to supply 15 gph, a check is capture & measure output from filter mgr drain 1/2 pt in 15 sec should be good lift delivery at idle, yet I've seen "healthy" pumps purr perfectly, and pump meeting idle demand still be bad, so my preference is to load test the lift.
At the filter manager drain snake into your cab on long hose a test gauge, make positive to not pinch off the hose and dead/static head the reading, at idle with good stock pump 5-6 psi is normal, go for drive, at hiway cruise speed 70 mph 3-4 psi is strong lift pump, 2-3 psi is good lift pump but has some weakness, if lift will not sustain 1.5 psi or better, get a new one.
Then do an acceleration test on hard acceleration it is preferable to maintain > 1 psi, it may dip below that but once at desired settled out speed, lift needs to recover quickly to 1.5 psi or better, if it remains less than 1.5 or takes more than about 5 second to recover to cruise psi observed before accelerating, either lift is bad or tank sock is dirty.
Pic of simple vac/press gauge about $20 at part store or less on sale from Harbor Freight a must have piece of 6.5 test gear :
FYI post will close periodically until I finish with it
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