just replaced fuel filter after noticing it was taking a tad longer to start (went a long time, like 20K miles before changing). started once but now won't. turns over but just won't start. Am I looking at a lift pump issue? Is that and the sending unit one and the same (that canister looking thing that sits on top of the fuel tank where I need to either drop the tank or lift the bed)? Is this different than the injection pump? Thx guys

 

no lift pump on these trucks. the fuel pump (CP3) lifts fuel all the way from the tank to the engine. the pump sits in the valley of the engine near the front. the fuel filter is in between the tank and CP3.

have you tried pumping the primer bulb till hard, crank and pump again? sometimes it takes a few times to get the air out.

if there is any kind of leak or hole that allows air to get in then it will make it hard to start.

the filter is under a vacuum being on the suction side of the CP3. this is the most common area where air gets into the lines. check the bleeder screw on the top of the filter housing for cracks or bad seal. this is the easiest one to fix and one of the most common problems. sometimes the seals around the primmer bulb wear out and leak. there is rebuild kits that have all of the parts to fix this.

there are others but i would start with these first

 

thanks for the info on the CP3. I didn't know that. Yes, I have pumped the primer a lot on top of the fuel filter. I did the fuel filter housing rebuild thing on another LB7 so I am familiar with that...maybe this one needs it too.

 

you can always replace the hose on the output of the filter housing with a clear one to see if there are air bubbles in the fuel

 

got it started...had to pump at the same time while another was turning the key. I ran some errands making 3 stops and it started successfully each time. However, it takes slightly longer (no much but just a little) to turn over before it starts. Also I noticed a tad more black smoke than it should be blowing. I do have a PPE programmer but it has and is still set to stock for a while now. 248,000 miles on it.
Sounds like a potentially failing CP3?

 

not so fast, you should rule out an air leak and bad injectors. LB7 or much for know for there injector problems then bad CP3s

 

all 8 injectors have been replaced at 190,000, then 2 more 6 months ago.

 

if it's the original cp3 then it is probably getting a little weak. they blow more smoke because the injectors aren't getting the needed pressure to properly atomize the fuel. Mine got to the point where it wouldn't spin over 2,000 rpms and had lost a lot of power.

 

.. What kind of prssure should one see from a good CP3 ? and how does one test this pressure reading ? ... been looking at a few D-max trucks latley

 

you would need a good scan tool or tuner to read the pressure if the truck dosent have after fuel rail pressure gauge with a scan tool and some tunners you can command Max pressure on a lb7 it's 23,000 psi it should be withen 3,000 psi of desiered pressure