Engine/Transmission (1998.5 - 2002) 2001 fuel bleed problems

[hcole]

I'm going to chime in one more time on this and ask about the banjo bolt that you replaced when you put in the pressure port fitting. Do you suppose it was machined wrong from the factory and won't flow enough fuel? I ask this as you say that was the only thing you touched when you worked on it.

 

[Kalaehina]

I was actually attaching a line to the original banjo bolt, when I removed the stem to do this and installed the line (to put a sending unit at the end of it) is when the problem first occurred. I then put the valve stem back in the Schraeder port and put everything back to how it was before I messed with it and the problem remained. Stumble at 1700-1800 rpm.

 

[JR]

Ouch, not a good scenario to have play out when it's on your dime.....
Honestly like was mentioned earlier your best bet is going to try to find a diesel tech that can connect to your truck and read live data. There is something amiss at this point and its probably going to take some extensive trouble shooting. There just isn't much to a VP powered truck to make it run... . Lift pump, inj. pump, ecm, crank/cam sensor and it will run. Add the APPS and MAP sensor to allow it to come off idle and run proper and that's basically it... . Injectors can cause a similar type of problem but is very unlikely in your case because everything ran fine prior to tearing into the fuel system.
Assuming you have no leaks in your fuel system, and the VP was installed correctly, and no restrictions in the air intake or missing clamps/torn boots, it's likely going to require some deeper troubleshooting. Have you studied Blue Chips Website and followed his diagnostics page? How about battery voltage? Are you running 13+ volts? Low/inconsistant voltage/bad grounds will cause some funky issues as well

 

[Kalaehina]

I just started reading Blue Chip's diagnosis page, I'm going to try a few of his recommendations. What is the best/proper procedure for removing air from the system? Bleed at the schraeder port or the return line banjo bolt?

 

[Sticks]

It all depends on how air locked you are. If the engine is running, you have the air out of the system. If you are severely air locked, I hot wire the transfer pump on, crack open the fuel filter outlet until I have good fuel, then the VP inlet, VP return, then I'll crack open the injectors that I can get to and bump the starter 4 or 5 times to roll the engine over (there will be LP pressure present at 1 injector every time the VP is rotated to that point of injection for that cylinder) and get fuel coming from the injection lines at the head (same procedure I use when I R&R a VP44 - except I hand roll the engine over).

For future reference, when you change the fuel filter, I crack open the fuel inlet side of the VP then bump the starter to cycle the lift pump, when all the air is done rushing and I have good fuel, I close up the VP inlet, then do one more then bump the starter again to make sure. Makes a mess, but the air is out. You learn where to place the oil pan underneath the axle.

 

[Kalaehina]

Ok now I bled the low pressure side, fuel pressure shows 11 and wants to go higher when I bump start. Now here's where it gets weird, it seems that if I start the truck, I get 0 fuel pressure, if I bump start I get up to 11 psi. It's a brand new FASS DRP pump.

 

[JR]

Bad overflow valve on the vp??
I would think you would have gotten an new one when u replaced the VP but maybe not. That could explain the lack of power at higher rpm. Without a working fp gauge before, it would have been tough to diagnose that one. Where did you get your injection pump from?

 

[Kalaehina]

Yup no new overflow valve, but I also noticed my exhaust brake not activating. Could this be related to a throttle issue? Since the lift pump doesn't seem to work at idle and the exhaust brake is not activating?

 

[Kalaehina]

Ok recalibrated the APPS and the exhaust brake works now. So is it possible for the return line to be the culprit? Resulting in lift pump pressure during bump starts and then no pressure when the truck and VP are running? Could fuel be draining or leaking somewhere (which btw I could not find any leaks) any not allowing pressure to build up when the engine starts?

 

[hcole]

Why don't you disconnect the lift pump wire and hook it on the battery and then start and run it down the road and see if it still stumbles, if not then get you a relay that is activated on the ignition switch in run and run the pump like that. It will not hurt it as mine is hooked up that way for a couple years now and I don't draw power off the ecm any more. This is BETTER than the factory design. The lift pump can and will run continuously without harm to anything.

 

[Kalaehina]

Thanks for that suggestion, I am going to power the pump separately to purge the air so I can give this a try as well. Thanks!

 

[JR]

Nothing wrong with running the lift pump that way, all of the high volume aftermarket pumps are wired independent of the ecm. I would suspect if it was an ecm problem your lift pump would not be running when you bump the key. You can try to squeeze the return hose GENTLY with a pair of pliers to see if the overflow valve is passing. The more you squeeze the hose down the more the lp pressure should come up. Dont pinch it off completely, just have someone watch the gauge to see if it moves as you apply pressure. If it is passing bad enough to have zero pressure while idling then you should see an increase in pressure as soon as you start restricting the line. Wrap a rag or something around the return hose so the pliers don't mar the hose.

 

[Kalaehina]

Thanks I'll give that a try as well. Do the hardwire lift pumps have shorter life spans because they're running continuously?

 

[JR]

As long as you wire it with a relay and a fuse you will be fine. Tie into an accessory in the pdc (fuse panel) in the engine compartment that only comes on with the key on to trigger it. Use a piggyback type fuse. I'm not familiar with the amp requirements of your lift pump but make sure you size the fuse and relay properly to avoid any potential problems. FASS probably has both available on their website, at least Air Dog does for their pumps.

 

[hcole]

No, the pump runs continuously even through the ecm and at full voltage regardless of pressure achieved. All that is required is that the engine is running when operating through the ecm. Just hook it up to the battery and try it out and see hoe it performs and change it like I said if it runs good.

 

[Kalaehina]

Hard wired the lift pump and the same thing is happening. No codes, good pressure when I bump start, as soon as engine starts, pressure drops to zero.

 

[hcole]

Kal, look, hook the lift pump up to the battery + terminal and - terminal. It should run ALL the time. Pressure should be high. THEN start the truck and drive it. Pressure should stay high. Now see if the truck runs OK. If it does THEN hook it up to a relay that is powered off of something that only operates in the RUN mode. Then the coil on the relay will be powered by anything that is hot when the ignition switch is in the ON position. Sounds like you have done nothing to change the operation with what you did.

 

[Kalaehina]

Yup hard wired straight to battery, good pressure at bump start, soon as engine starts, pressure drops to zero even with pump continuously on. However stumble is gone at 2000 rpm. Also dash gauge reads pressure at bump start but mechanical gauge does not. Problem at fuel line between filter and pump maybe??

 

[JR]

If you truly have 12 volts constant going to the pump and it drops off as soon as you start it the only other thing that could be causing that that I know of is the overflow valve.

 

[Kalaehina]

Sorry forgot to mention I just replaced that this morning as well.